Instrumentation Tubing and Their Connections

TECDOC-01SEPTEMBER 2008 TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS Instrumentation Technical Document Series By: Nirbhay Gupta This Page is intentionally kept blank ii PREFACE Instrumentation design and construction is a very interesting proposition. One is supposed to know the electronics and electrical aspects as well as the mechanical aspects too. Instrumentation tubing is one such field where an instrumentation engineer has to don the robes of a mechanical engineer. In NPCIL, for a long time, it was felt that there is no single document that can cater to the needs of budding as well as practicing engineers when they want to search some information on instrumentation tubing and connections. Instrumentation tubing covers both Impulse tubes (sensing lines) as well as pneumatic tubes. Connections include tapping points, root valves and tube fittings. Usually one has to refer to myriad technical documents, codes and standards to s earch for a specific aspect of tubing design or construction. This technical note is an attempt to put all the information at one place. The efforts have been put to expose the reader to all the aspects of tubing and make him aware of all the developments in the world. A comprehensive list of all the reference documents is given at the end and they have been liberally used while preparation of this note was underway. Effort has been made to represent all the relevant information here however, enterprising readers will benefit even more if they peruse the reference documents directly. Attempt has been made to demonstrate analytically that if the design and installation practices are followed as per this note then the sensing line will meet the intent of class -I tubing. Readers may note that the word tube/tubing used here should be inferred as instrumentation tubing only limited to maximum 1” size. It may be noted that various tubing practices have not been discussed in this note. The detailed installation practices for various process measurements will be discussed in respective process measurement/field installation technical notes. However, salient issues common to all installations have been discussed in detail. Author is grateful to a large number of engineers with whom they had an opportunity to work with during their long career in NPCIL and on the way a lot of design aspects were concluded. Nirbhay Gupta 23rd September, 2008 Mumbai iii This Page is intentionally kept blank iv . 6 2.4 4.6. 1 1 2 3 3 5 5 6 13 13 13 13 14 15 18 18 19 19 19 20 23 23 23 24 25 27 27 28 29 34 35 36 38 39 39 v .4 2.2.8 2.10 3.7 2.1 4.0 7.3 4.5 1.1 2.TABLE OF CONTENT Section 1.6 1.3 2.5 2.6.4 1.6.2 4.0 4.7 2.2 2.3 1.1 2.3 2.0 7.9 2.2.6.0 4.1 1.0 1.0 2.1 TITLE INTRODUCTION DIFFERENCE BETWEEN A PIPE AND A TUBE MAJOR ADVANTAGES OF TUBING OVER PIPING SYSTEMS TYPES OF TUBES GUIDELINES FOR SELECTION OF INSTRUMENTATION TUBES DIFFERENT SIZES OF TUBES CRITERIA FOR SELECTING THE SIZE OF A TUBE SELECTION AND DESIGN CRITERIA DESIGN OF TUBING AND TUBING SYSTEMS CLASS-I INSTRUMENTATION TUBING DESIGN REQUIREMENTS OF MATERIAL FOR INSTRUMENT TUBING/PIPING AS PER NB-2000 DESIGN REQUIREMENTS OF INSTRUMENT PIPING/TUBING AS PER SUBSECTION NC (NC 3600) PRESSURE DESIGN (INTERNAL PRESSURE) OF INSTRUMENT TUBING/ PIPING ANALYSIS CRITERION OF TUBING/PIPING SYSTEM ANALYSIS OF SS TUBES USED IN NPCIL WALL THICKNESS AND PRESSURE RATING OF DIFFERENT SIZES OF INSTRUMENT TUBING STRESS ANALYSIS OF TUBING SYSTEMS ANALYSIS FOR SUSTAINED MECHANICAL LOADS ANALYSIS FOR OCCASIONAL LOADS (LEVEL A&B SERVICE LIMITS) ANALYSIS FOR STRESS DUE TO THERMAL EXPANSION AND OTHER SUSTAINED LOADS CONSIDERATION FOR VARIOUS FORCES TUBE BENDING CONSIDERATIONS SPECIAL DESIGN ASPECTS TO MEET THE REQUIREMENTS OF CLASS-I TUBING AND TUBING SYSTEMS CONCLUSION TECHNICAL REQUIREMENTS OF SS TUBES PNEUMATIC TUBING ADVANTAGES OF USING COPPER TUBES DIFFERENT TYPES OF COPPER TUBES RECOMMENDATIONS FOR SELECTION OF A TYPE OF COPPER TUBE TECHNICAL REQUIREMENTS OF COPPER TUBE APPLICABLE INTERNATIONAL STANDARDS FOR COPPER TUBES ASTM TUBING SPECIFICATIONS OUTSIDE DIAMETER/WALL THICKNESS EMBEDDED PENETRATIONS METHODS OF CONNECTION OF INSTRUMENTATION TUBES WELDED JOINTS Page No.2 2.1 2.2 2.2.6.0 6.2 1.5 5. 1 13.0 10. FLARELESS AND COMPRESSION JOINTS THREADED JOINTS GUIDELINES FOR TAKE OFF C ONNECTIONS FOR SENSING LINES LOCATION OF PRESSURE TAPS CONSIDERATIONS FOR PRESSURE TAP DESIGN RECOMMENDATIONS FOR PRESSURE TAP DESIGN GUIDELINES FOR ROOT VALVES INSTALLATION OF INSTRUMENTATION TUBING BEST PRACTICES FOR IMPULSE TUBE INSTALLATION SOME PRACTICAL GUIDELINES FOR TUBE LAYING AND BENDING TUBE BENDING CHECK LIST CHARACTERISTICS OF A WELL-MADE TUBING CIRCUIT COMMON CAUSES OF IMPERFECT BENDS ROUTING OF BENDS GUIDELINES FOR C OPPER TUBE INSTALLATION GUIDELINES FOR C OPPER TUBE BENDING COPPER TUBE JOINTS IMPULSE TUBE/SENSING LINE SUPPORT IMPULSE TUBE INSTALLATION THROUGH EPS TUBE FITTINGS REQUIREMENTS OF A TUBE FITTING CONSTRUCTION OF A TUBE FITTING TYPES OF TUBE FITTINGS FLARED FITTING FLARELESS BITE TYPE TUBE FITTING FLARELESS C OMPRESSION TYPE TUBE FITTING SINGLE FERRULE FLARELESS COMPRESSION TYPE TUBE FITTING TWIN FERRULE FLARELESS COMPRESSION TYPE TUBE FITTING FERRULE AND ITS PURPOSE SWAGING OPERATION OF A TWIN FERRULE TUBE FITTING EFFECT OF TUBE THICKNESS ON SWAGING SAFETY PRECAUTIONS FOR TUBE FITTING INSTALLATION REPEATED ASSEMBLY AND DISASSEMBLY OF TUBE FITTING SPECIFICATION FOR SS TUBE FITTINGS SPECIFICATION FOR BRASS TUBE FITTINGS THREADS USED FOR TUBE FITTINGS EVOLUTION OF THREADS TYPE OF THREADS SIZES TAPER/PARALLEL THREADED JOINTS 39 40 41 41 42 43 44 45 45 48 50 54 55 57 60 60 61 62 64 65 65 67 68 68 69 69 70 71 72 73 74 78 80 82 83 85 87 87 87 88 89 vi .8.8.8.2 13.3 10.3 13.8 10.2 10.0 14.7 10.1 13.3 13.4 FLARED.5 13.2 7.8 13.7 13.8.0 13.3 9.0 10.10 13.5 10.0 8.2 8.0 13.4 13.0 12.6 13.9 13.4 10.4 13.1 8.2 14.3 8.1 10.11 14.3 14.9 11.6 10.2 13.1 14.7.5 13.8. 4.1 15.4.6 15.4.4.9 15.1 15.5 15.10 15.0 15.3 15.11 16.0 DRY SEAL NPTF THREADS WELDING METHODS 300 SERIES STAINLESS STEELS C1018 FITTINGS TIG WELDING ORBITAL TUBE WELDING ORBITAL WELDING EQUIPMENT REASONS FOR USING ORBITAL WELDING EQUIPMENT INDUSTRIAL APPLICATIONS FOR ORBITAL WELDING GENERAL GUIDELINES FOR ORBITAL TUBE WELDING THE PHYSICS OF THE GTAW PROCESS MATERIAL WELDABILITY WELD JOINT FIT-UP SHIELD GAS (ES) TUNGSTEN ELECTRODE WELDING BASICS AND SET-UP WELDING PARAMETER DEVELOPMENT References and Suggested Reading 93 96 96 96 97 98 99 99 100 101 102 102 103 104 105 106 109 116 vii .4.3 15.8 15.4.4.4.2 15.4.2 15.14.4 15.4.4 15.4.5 15.7 15. This Page is intentionally kept blank viii .   inside  diameter.  and  also  for  round  tube.  Therefore. whether for simple household use or for  the  more  exacting  requirements  of  industry. Table 2 and 4. inefficient and costly to  assemble  and  maintain.  Figure 1­1 Tubing provides simplified.  the  nominal  diameter  corresponds  with  the  outside  diameter.  the  use  of  pipe  in  these  systems  has largely been replaced by tubing because of the many advantages it  offers.  Dimensions  and  permissible  variations  (tolerances)  are  specified  in  the  appropriate ASTM or ASME standard specifications. free flow system        Nirbhay Gupta                                                                                                                                  1    .  A  pipe  is  a  tube  with  a  round  cross  section  conforming  to  the  dimensional  requirements for nominal pipe size as tabulated in ANSI B36.  and  are  usually  made  of  tubing/piping.  Pipe versus Tubes  Standard fluid line systems.  L  and M copper tube  (See  section­6  for  details) may also be specified by nominal size and  type  only.  Round  tube  size  may  be  specified  with  respect  to  any  two.19.  For  special  pipe  having  a  diameter  not  listed  in  these  tables.  Generally  tubing  is  specified  by  giving  O.  but  not  all  three.  1.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      1.1 Difference between a pipe and a tube  The  fundamental  difference  between  pipe  and  tube  is  the  dimensional  standard  to  which each is manufactured. valves and tube fittings.  Such  systems  under  high  pressures  were  plagued  with  leakage problems besides being cumbersome.  and  wall  thickness  whereas  pipes  are  specified by giving nominal diameter & wall thickness (NB and Schedule).10.  A tube is a hollow product of round or any other cross section  having a continuous  periphery.  wall  thickness.  were  for  many  years  constructed  from  threaded  pipe  of  assorted  materials  and  were  assembled  with  various  standard  pipe  fitting  shapes.  type  K.  Table  1. and  ANSI  B36.0   Introduction  Impulse  sensing  lines are  the  lines  containing  process  fluid  which  run  between  the  sensing  instruments  and  process  tapping  points.  of  the  following:  Outside  diameter.D.  unions  and  nipples.   is  easy  to  bend.2 Major Advantages of Tubing over Piping Systems  1. Greater Strength ‐ Tubing is stronger as no threads are required for connection.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      Old  Method  ­  Each  connection  is  threaded  ‐  requires  numerous  fittings  –  system  not  flexible or easy to install and service connections not smooth inside ‐ pockets obstruct flow.  Fewer  fittings  mean  fewer   joints.  6. Flexibility  ‐  Tubing  is  less  rigid.      Nirbhay Gupta                                                                                                                                  2    . Fewer  Fittings  ‐  Tubing  bends  substitute  for  elbows.  5.        Figure 1­2: With no threading necessary.    1. Bending  Quality  ‐  Tubing  has  strong  but  relatively  thinner  walls. No  weakened sections from reduction of wall thickness by threading.  has  less  tendency  to  transmit  vibration  from  one  connection to another.  Tube fabrication is simple. tubing does not require extra wall thickness     3. fewer leak paths.    2. Economy  of  Space  and  Weight  ‐  With  its  better  bending  qualities  and  a  smaller  outside  diameter.    4. Less  Turbulence  ‐  Smooth  bends  result  in  streamlined  flow  passage  and  less  pressure drop.  Tube  fittings are smaller and also weigh less.  tubing  saves  space  and  permits  working  in  close  quarters.    Modern  Method  ‐ Bendable tubing needs fewer fittings ‐ no threading required  ‐ system  light and compact ‐ easy to install and service ‐ no internal pockets or obstructions to free  flow.  10mm.  2. carbon steel tubes. 20 mm  etc. 1”  etc. metal chips. PVC Tubes.  10. ½”.   b.        9. Tighter Joints ‐ Quality tube fittings.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008        7. The only exception to this rule is  copper tubing with brass fittings. Better  Appearance  ‐  Tubing  permits  smoother  contours  with  fewer  fittings  for  a  professional look to tubing systems.4 Guidelines for selection of instrumentation tubes  Proper Tubing Selection 1.  11. Categorization based on material of tubes e.  Again  no  threading.  Galvanic Corrosion (Electrochemical)  All metals have a specific relative electrical potential. where dimensions are specified in inch units e.  3. Metric tubes. Categorization based on tube dimensional specifications: Tubes can be classified as  a. Easier Assembly and Disassembly ‐ Every tube connection serves as a union. Tube  connections can be reassembled repeatedly with easy wrench action. a low intensity electric current  flows  from  the  metal  having  the  higher  potential  to  the  metal  having  the  lower  potential. Tubing should be used only with S. Categorization  based  on  method  of  tube  drawing  i. Less  Maintenance  ‐  Advantages  of  tubing  and  tube  fittings  add  up  to  dependable.  1. give better assurance of  leak‐free systems. Mixing materials can cause galvanic corrosion.g. Copper  tubes. (See Galvanic Series Chart)    Nirbhay Gupta                                                                                                                                  3    . Always Match Materials –   S.  The  result  of  this  galvanic  action  is  the  corrosion  of  the  metal  with  the  higher potential (more anodic). Inconel tubes.  trouble‐free installations.  1. foreign particles in system. ¾”. When dissimilar metals come  in contact in the presence of moisture (electrolyte). where dimensions are specified in mm units e. Fractional tubes.S.S.  welded  and  drawn. etc.   1.g. SS tubes.  seamless  etc.e.3 Types of tubes  Tubes can be categorized in different ways.  8. Fittings. correctly assembled. minimum chance of scale. Cleaner  Fabrication  ‐  No  sealing  compounds  on  tube  connections.g. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008        Figure­1­3: Galvanic Series chart      Nirbhay Gupta                                                                                                                                  4    .  10mm. cut  off  any  undesirable  sections.  Proper  surface finish ensures leak‐proof compression joint with fitting. 3/8”. owing to the chance  of blockage after long service. RB 80 recommended..  These  “deep”  scratches  can  cause  leaks  when  attempting  to  seal  low‐density  gases  such  as  argon.  nitrogen. Tubing surface finish –   Always select tubing free of visible draw marks or surface scratches.  or  helium.  1.D.  If condensation is likely to occur or if gas bubbles are likely to be liberated.    1. ½”. 12mm. 20mm and 25mm. ¾” and 1”.  Copper tubes (Fractional): ¼”. ¾” and 1”.5 Different sizes of tubes  Following tube sizes have been used in NPCIL NPPs  SS Tubes (metric): 6 mm. Select proper tubing hardness –   Remember  instrumentation  tube  Fittings  are  designed  to  work  within  specific  hardness ranges. 3/8”. should not be smaller than 10 mm. 10mm. For proper swaging  the hardness of the tube should be less than the hardness of the fitting. Select proper tubing wall thickness –   Proper wall thickness is necessary to accommodate accepted safety factors relative  to desired working pressures.    3. 20mm and 25mm. If possible.  When  long  runs  cannot  be  avoided. 12mm.S.  SS tube (Fractional): ¼”.    4.  the O.  the  internal  diameter  of  impulse  tubing/piping may be selected as per the following table‐1‐1:          Nirbhay Gupta                                                                                                                                  5    .6 Criteria for selecting the size of a tube  The selection criteria for sizing the tube are as follows:  • • • The O. ½”.D.  Copper tubes (metric): 6mm.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      2. of the tubes/impulse tubes should be the same and not smaller than  6 mm even with clean liquids and non corrosive piping. RB 90 maximum for S.   Table  1‐2  lists  common  materials  and  their  associated  general  application.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      TABLE – 1­1  Pressure signal  Inside Dia. should only be used for sensing lines.  installation  and  material  cost.  Properly  designed  tubing/piping  based on service conditions.7 As very long runs of impulse tubing/piping are not expected in our systems  and also process fluid is expected to be clean.  The use of a particular type of tube for a specific usage depends on the application  and  the  process  condition.  The  following  table  briefly  describes  the  application  guidelines for a specific tube material.  Further.  radiation  streaming  considerations.  different  materials  have  different  levels of hardness. in mm of impulse tubing/piping for different process  transmission  fluids  distance  Water/steam  Wet air or gas Oil of low to  Very dirty  (meter)  liquid or gas  Dry air/gas  med.  higher  size  (>10  mm  OD)  tubing  is  not  recommended  for  pressure/∆P measurement in primary/nuclear system in general. Dissimilar materials in contact may  be  susceptible  to  galvanic  corrosion.6 mm has been found to be adequate.  Table  1‐2  also  lists  the  maximum  and  minimum  operating  temperature  for  the  various  tubing  materials.  of 7.  The  practice  of  mixing  materials  should  be  strongly  discouraged.  The  most  important  consideration  in  the  selection  of  suitable  tubing  for  any  application  is  the  compatibility  of  the  tubing  material  with  the  media  to  be  contained.  Based  on  hold  up.  Selection and Design criteria  Following  requirements  should  be  met  for  impulse  tubing  for  sensing  the  pressure/differential pressure signal for all types of process systems including for  safety and safety related systems.  The  only  exception is brass fittings with copper tubing.D. and can adversely affect the fittings ability to seal on the tubing. viscosity  0 ‐ 16  7 to 9 13 13 25 16 ‐ 45  10 13 19 25 45 ‐ 90  13 13 25 38 • 1. 10 mm OD tubing having I.    Nirbhay Gupta                                                                                                                                  6    . for pressure/ ΔP measurement  except  for  some  cases  for  level  measurement  in  tanks/vessels  using  ΔP  principle.  In order to achieve a gas‐ tight  seal.  This  is  accomplished by the ferrules penetrating the surface of the tubing. 2. consideration should be given to media.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      Table­1­2  1.   For operating temperatures above 800 °F (425 °C). 300 Series  Stainless  Steels  are  susceptible  to  carbide  precipitation  which  may  lead  to  intergranular  corrosion  at  elevated temperatures.  ferrules  in  instrument  fittings  must  seal  any  surface  imperfections. Penetration can only be    Nirbhay Gupta                                                                                                                                  7    .  All temperature ratings based on temperatures as per ASME/ANSI B31­3 Chemical Plant and Petroleum  Refinery Piping Code. 1999 Edition.  Gas Service  Special care must be taken when selecting tubing for gas service.   Tables‐1‐3  to  1‐10  below  indicate  the  minimum  acceptable  wall  thickness  for  various  materials  in  gas  service. Heavy walled softer tubing such as  copper  may  be  used  if  chemical  compatibility  exists  with  the  media.  the  higher  strength  of  steel  or  stainless  steel  permits  the  use  of  thinner  tubes  without  reducing  the  ultimate  rating  of  the  system.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      achieved if the tubing provides radial resistance and if the tubing material is softer than the  ferrules.  Thick  walled  tubing  helps  to  provide  resistance.  the  size  of  tubing  to  be  used. better results can be  obtained  by  using  tubing  well  below  this  maximum  hardness.  For  example.  System Pressure  The  system  operating  pressure  is  another  important  factor  in  determining  the  type. Combinations which do not have a pressure rating are  not recommended for use with instrument fittings.  The  following  tables  (1‐3  to  1‐10)  list  by  material  the  maximum  suggested  working  pressure (in psi) of various tubing sizes.  However.  a  desirable  hardness of 80 RB is suitable for stainless steel.  and  more  importantly. Acceptable tubing hardness for general application is listed in Table 1‐12.  In  general.  The  ratings  in  white  indicate  combinations  of  diameter  and  wall  thickness  which  are  suitable  for  gas  service.  These values are the maximum allowed by the ASTM.  tube  fitting  assemblies  should  never  be  pressurized beyond the recommended working pressure.  Table­1­3: Fractional 316 or 304 STAINLESS STEEL (Seamless)          Nirbhay Gupta                                                                                                                                  8    .  high  pressure  installations  require strong materials such as steel or stainless steel.  In  any  event. The maximum allowed by ASTM is 90 RB. For gas service. Acceptable tubing diameters and wall thicknesses  are those for which a rating is listed. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      Table­1­4: Fractional 316 or 304 STAINLESS STEEL (Welded & Drawn)       Table­1­5: Seamless Stainless Steel metric tubing          Nirbhay Gupta                                                                                                                                  9    .  psig   Note: For gas service.10 0.134   0.180                                           0. in. select a tube wall thickness outside of the shaded area.049  0.  1/8   3/16   1/4   5/16   3/8   1/2   5/8   3/4   7/8   1   1  1/4   1  1/2   2   0.   8000   10 200       5100   6 600   9600     3700   4 800   7000   9600     3 700   5500   7500     3 100   4500   6200     2 300   3200   4500     1 800   2600   3500       2100   2900       1800   2400       1500   2100         1600                               5900  4600  5300  3700   4300  3200   3700  2700   3200  2100   2500  1800   2000  1500  510 0   430 0   370 0   290 0   240 0   170 0   4100   3200   3600   4000   4600   5000   2600   2900   3300   3700   4100   5100  1900   2100   2400   2700   3000   3700    Table­1­7: Carbon Steel Metric tubing  Nirbhay Gupta                                                                                                                                   10      .220   Working Pressure.028   0.148   0.035  0.120   5  9  0.   0.065  0.09 0.083  Tube Wall Thickness.165   0.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      Table­1­6: Fractional Carbon Steel (Seamless)  Tube  OD  in. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008          Nirbhay Gupta                                                                                                                                   11      . TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      Table­1­8: ALUMINIUM (SEAMLESS)     Table­1­9: COPPER (SEAMLESS)                       Table­1­10: MONEL 400 (SEAMLESS)     Note:  • • • • All  working  pressures  have  been  calculated  using  the  maximum  allowable  stress  levels  in  accordance  with  ASME/ANSI  B31.3.  All working pressures are at ambient (72°F) temperature.  All calculations are based on maximum outside diameter and minimum wall thickness.  Ratings in gray are not suitable for gas services.  Chemical  Plant  and  Petroleum  Refinery  Piping  or  ASME/ANSI B31.    Nirbhay Gupta                                                                                                                                   12      .1 Power Piping. 79 .78 .73 .00 .80) would apply (see Table 1­11 above) and the “at temperature” system pressure would be  3700 psi x .  Simply  locate  the  correct  factor  in  Table  1‐11  and  multiply this by the appropriate value in Tables 1‐3 to 1‐10 for the elevated temperature  working pressure. Copper  and  aluminum  tubing  are  suitable  for  low  temperature  media.00 .97 .90 .76 .79 .90 .94 .37 304 SS 1.    Table-1-11 Temperature Derating Factors Temperature °F (°C) 100 200 300 400 500 600 700 800 900 1000 1100 1200 (38) (93) (149) (204) (260) (316) (371) (427) (486) (538) (593) (649) Copper Aluminum 1.  Stainless  steel  and  carbon  steel tubing are suitable for higher temperature media.00 1.59 1.76 EXAMPLE: 1/2 inch x .73 .88 .78 .88 .81 .80 .62 . Special alloys such as Alloy 600 are  recommended  for  extremely  high  temperature  (see  Table  1‐2).TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      Systems Temperature  Operating temperature is another factor in determining the proper tubing material.00 .82 .49 .80 .69 .82 .77 .50 1.79 .00 .00 1.82 . If the system were to operate @ 800°F (425°C).80 = 2960 psi        Nirbhay Gupta                                                                                                                                   13      .86 .82 .80 .30 Steel Monel 400 1.85 .00 .00 1.00 . a factor of 80% (or  .77 .00 1.40 316 SS 1.  Table  1‐11  lists  de‐rating  factors  which  should  be  applied  to  the  working  pressures  listed  in  Table  1‐3  to  1‐10  for  elevated  temperature  (see  Table  1‐2).96 .79 .00 1.049 wall seamless stainless steel tubing has a working pressure of 3700  psi @ room temperature.  A‐ 213.  Recommended  Hardness  90 RB Fully Annealed 60 Max. Rockwell  15T  72 RB ASTM‐A‐179 ASTM B‐210 ASTM B‐165 ASTM‐B‐622. 316. J525b Fully Annealed Carbon  1010  Steel      Aluminum  Alloy 6061  Monel™  400  Alloy C‐ C‐276  276  Alloy 600  600  Carpenter  20CB‐3  20™  Titanium  Commercially  Pure Grade 2    Soft Annealed Temper 0  Max. Condition Stainless  Steel  Copper  304.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      Table‐1‐12  Material  Type  ASTM Tubing Spec.  316L  K or L  ASTM‐A‐269. B‐626 T6 Temper Fully Annealed Fully Annealed 56 RB 75 RB 90 RB ASTM B‐167 ASTM B‐468 Fully Annealed Fully Annealed 90 RB 90 RB ASTM B‐338 Fully Annealed 99 RB 200 Brinell  Typical    Nirbhay Gupta                                                                                                                                   14      . A632  ASTM‐B75 B68. A‐249. B88*  (K or L)  SAE‐J524b.     Thus for instrument tubing.19.   Thus design guidelines given for small size of piping is being followed for Class I instrument  tubing  also.1 CLASS­I INSTRUMENTATION TUBING DESIGN  In  ASME  Section  III‐Division‐I  sub‐section  NB  (Class  I  components). Wrought  seamless  and  welded  (without  filler  metal)  pipes  and  tubes  shall  be  examined  and  may  be  repaired  in  accordance  with  the  requirements  of  class‐I  seamless and welded (without filler metal) piping and tubing of SA‐655 (specification  for special requirements for pipe and tubing for nuclear and other applications).    Also  as  the  outside  diameter  of  instrument  tubing  is  being  limited  to  1”  (25  mm).2 REQUIREMENTS OF MATERIAL FOR INSTRUMENT TUBING/PIPING  AS PER NB­2000    a.  c. which have  been  classified  as  class  I  in  design  specification.  may  be  designed  and  analyzed  as  per  subsection NC.    As per NB 3630 (Piping design and analysis criteria) the piping of 1” NB or less.  tubes  and  fittings  need  not  be  examined  by  the  rule  of  NB‐2510  (examination of pressure retaining material).    2. MAXIMUM ALLOWABLE STRESS  For  design/calculating  minimum  wall  thickness  of  instrument  tubing/piping. the material & testing requirements shall be as per subsection  NB whereas the design and analysis will be as per subsection NC.  Nirbhay Gupta                                                                                                                                   15      . so any design concession permitted for lower size piping (<1”) will also be applicable  to instrument tubing.  d.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      2. Impact testing for austenitic stainless steel is not required.  the  maximum  allowable stress for the  material  at design temperature shall be used as  given in ANSI/ASME B36.  b.  Also impact testing is not  required  for  a  pipe/tube  with  a  nominal  pipe  size  less  than  6”. Seamless  pipes.0 DESIGN OF TUBING AND TUBING SYSTEMS  2.  irrespective  of  wall  thickness.  the  design  criterion/design  requirements  for  instrument  tubing  has  not  been  covered  separately.    2. Pressure  retaining  material  should  confirm  to  the  requirements  of  one  of  the  specifications for material given in NB‐2121.3 DESIGN REQUIREMENTS OF INSTRUMENT PIPING/TUBING AS PER  SUBSECTION NC (NC 3600)  i. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008        2. DYNAMIC EFFECTS  Impact forces caused by either external or internal loads shall be considered in the  piping/tubing design.19  shall not be exceeded and piping/tubing product shall not be used at temperature in  excess of those given in ANSI/ASME B36. For pipe/tube with a   ratio less than 6.  PRESSURE DESIGN (INTERNAL PRESSURE) OF INSTRUMENT  TUBING/ PIPNG (Ref.  Y    = a coefficient having a value of 0.  Also the effect of earthquake and non‐seismic vibration shall  be considered in the tubing design. (I) as follows:    tm=P* Do 2 S+PY +A                                                                                            ……. (2) below                              ………. mechanical strength & bending etc.  iii. NC­3640)  Minimum Wall Thickness of straight tube/pipe:  The minimum wall thickness of straight tube/pipe shall not be less than that determined  by eq. the  value of ‘Y’ for ferritic and austenitic steels designed for temperature of 480 oC  and below should be taken as per eq. corrosion  and erosion allowances and allowance for structural strength needed during  erection.    Nirbhay Gupta                                                                                                                                   16      . kPa  A   =    Additional thickness. kPag   DO = Outside diameter of tube/pipe.19 for all the materials of which the tubing  is made. ALLOWANCES  Increased  wall  thickness  of  tubing  shall  be  taken  for  providing  allowances  for  corrosion or erosion.4. mm  S    =   Maximum allowable stress in the material due to internal pressure and joint  efficiency at design temperature. to provide for material removed in threading.4 a) ii.  iv. (1)  tm =  minimum required wall thickness. mm  P    =   Internal design pressure. (2)  Where  d = Inside diameter of tube/pipe.. PRESSURE AND TEMPERATURE RATINGS  The pressure ratings at the corresponding temperature given in ANSI/ASME B36. 06 tm  5  tube/pipe diameter  1.14.    “The  design  of  complete  piping  system  shall  be  analyzed  between  anchors  for  the  effects  of  thermal expansion.           1. unless otherwise justified by the design calculation the ovality of tubing/piping after  bending should not exceed 8% as determined by following eq. weight and other sustained mechanical loads must meet the  requirements of following eq.. actual wall thickness of  tubing/piping is to be increased as per following Table –2‐1 (This is based on NC 3000):    TABLE – 2­1  Minimum thickness recommended Prior to  bending  6  tube/pipe diameter or greater 1.”  The detail requirements/analysis criteria are given in following sub‐sections. (3)    %  100   Where       Do     Dmax    Dmin   2.5 = Nominal outside diameter of tube/pipe  = the maximum outside diameter after bending or forming  = the minimum outside diameter after bending or forming  ANALYSIS CRITERION OF TUBING/PIPING SYSTEM    Analysis requirements for tubing/piping systems as per NC‐3650 are given below.5                                                              …………………… (4)  Nirbhay Gupta                                                                                                                                   17      .TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      b) Wherever bending of tubing/piping is likely to be involved in installations. CONSIDERATION  OF  DESIGN  CONDITIONS  (STRESS  DUE  TO  SUSTAINED  LOADS)(Refer NC 3652)  The effects of pressure.25 tm  1 As per ANSI/ASME B31. (4). the minimum  wall thickness after bending shall not be less than the minimum wall thickness calculated  as per eq.1 this value is 1. (1) above.  To meet this requirement. However NC3000 is more conservative.                                                  ……….  a. weight and other sustained and occasional loads.08 tm  4   tube/pipe diameter  1.             tm    =    minimum wall thickness required as per eq. (3).  Bend Radius    c)   Also.16 tm1  3   tube/pipe diameter  1. (1) for straight tube/pipe.  kPa.2 (b)­1  MA         =   Resultant moment loading on cross section due to weight and other sustained  loads. CONSIDERATION OF LEVEL A AND B  SERVICE LIMITS  (REF. (5). mm     B1.3  Z            =   Sectional modulus of pipe/tube.2)  Nirbhay Gupta                                                                                                                                   18      . other sustained loads and thermal expansion for which level  A and B service limits are designated.       kN‐m.  Sy              =      material  yield  strength  at  temperature  consistent  with  the  loading  under  consideration. kPa    SUSTAINED PLUS THERMAL EXPANSION STRESSES  The effects of pressure.     kPa.  Pmax =  Peak pressure.0  Where    = Sustained plus thermal expansion stresses.8                                 ……….5  Sy  ii. mm  Do  =   Outside diameter of tube/pipe. NC­3653)  i. weight.  Ste  = range of resultant moments due to thermal expansion  MC  = Allowable stress range for expansion stresses. for which level B service limits are designated.g. weight. mm3  Sh               =   Basic material allowable stress at design temperature consistent with loading  under consideration. Where  Mb   =  resultant moment loading on cross section due to non reversing dynamic loads e.  SA  i               = Stress intensification factor (refer NC‐3673.75 i shall not be less than 1. STRESS DUE TO SUSTAINED PLUS OCCASIONAL LOADS  The effect of pressure. kPa  P  =   Internal design pressure. mm      b.75                 ………(6)  0.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008              Ssl  =   Stress due to sustained loads. (6). shall meet the requirements of following eq. B2 =   Primary stress indices for the pipe/tube (As per Figure below) NC 3673. NC 3653.  Sol    =  stress due to occasional loads. must meat the requirements of  following eq.    occasional  loads  such  as  thrust  from  relief  and  safety  valves  loads  from  pressure  and flow transients and earthquake.    2 1 1.   0.  tn               =   Nominal wall thickness. (5)  But not greater than 1. other sustained loads and occasional loads including  earthquake. 2 (e)‐1    TABLE: 2­1A  Number of equivalent full  temperature cycles (N)  7000 and less 7000 to 14000 14000 to 22000 22000 to 45000 45000 to 100000 100000 and over Stress range  reduction factor (f)  1.5   Stress intensification factor ‘i’ can be calculated using following equation (8)               2                     …… (8)  Where   C2 and K2 are stress indices for class‐1 piping products or joints from NB 3681 (a)‐1.8 0. (4)    Allowable stress range for expansion stresses (SA) can be calculated using following equation  S A  = f (1. For  straight pipe/tube the value of C2 and k2 are 1.25 SC + 0.7 0.6 0.    For curved pipe/tube or welded elbows ‘I’ can be computed as per equation (9) below (refer  NB 3681)  .                                                                              …… (9)    …… (10)  where      tn  R  r                                                                                           =  nominal wall thickness of tube/pipe  =  bend radius  =  mean radius of tube/pipe      iii. CONSIDERATION OF LEVEL C SERVICE LIMITS     Nirbhay Gupta                                                                                                                                   19      .TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      = ratio of bending moment producing fatigue in a given number of cycles in a  straight  pipe/tube  with  girth  butt  weld  to  that  producing  failure  in  the  same number of cycles in the fitting or joint under consideration.25 Sh)                                                                          …….  Other terms are same as of eq. (7)  = Basic material allowable stress at minimum (cold) temperature.  Sh  f         = stress range reduction factor for cyclic conditions for total number N of full   temperature  cycles  over  total  number  of  years  during  which  system  is  expected to be in service from table‐2‐1A below NC 3611.9 0.  SC  = Basic material allowable stress at maximum (hot) temperature.0 0. TESTING REQUIREMENTS AS PER SUBSECTION – NB  Requirements  of  material  testing  as  per  subsection  NB  is  briefly  mentioned  above.    In  addition  to  examination/testing  requirements  as  per  SA‐655.  2.25 times the design pressure with minimum holding  time of 10 min.  Thus following equation can be used  tm=P* Do 2 S+PY +A   We can make following assumptions  • There will be no threading on the tubes  • Corrosion.    iv. 304L material at 310oC temp.    Following data may be used  P   = design pressure (= 195 kg/cm2)  S   = maximum allowable stress of S. (1) in the analysis criteria above.  Nirbhay Gupta                                                                                                                                   20      .TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      In  section  II  in  calculating  the  resultant  moment  MB.6.  still  to  be  on  conservative  side.6  ANALYSIS OF SS TUBES USED IN NPCIL  2.   Using eq. thus separate analysis for level C service  limits is not required.  (= 986 kg/cm2)  Y  = 0.  Though the above pressure and temperature may not exist simultaneously in  any  system.  all  the  sizes  of  tubing  will  be  designed  for  above ratings. the minimum wall thickness of straight tubing  can be calculated. erosion is negligible (hence allowance for corrosion and erosion may  be neglected)  • Bend radius is not less than 3Do.  moment  due  to  SEE  conditions  is  proposed to be used which is more conservative.  the  minimum  wall  thickness  for  different  sizes  (Do)  of  straight tubing is tabulated in following Table‐2‐2.  tubing  should  be  hydrostatically tested at not less than 1.4  By  putting  the  above  variables. The actual wall thickness is to be increased as  per Table‐2‐1 above.S.1 WALL THICKNESS AND PRESSURE RATING OF DIFFERENT SIZES OF INSTRUMENT TUBING  The  maximum  design  pressure  and  temperature  are  taken  as  195  kg/cm2  and  310oC  respectively.   the  required  minimum  wall  thickness  for  16mm  OD  tube.8  mm.25  tm )  Specified wall  thickness as per (PB‐ M‐17) in mm  kg/cm2  and  design  temp.  2.83 1.1 ANALYSIS FOR SUSTAINED MECHANICAL LOADS  When  the  tubing  is  installed  in  the  field. should be 1.83 2.  the  effects  of  pressure.83 mm of 16 mm size will be adequate from pressure rating considerations.5 (as per NB – 3680)    .    Similarly.8(See note below) 20  1.    As  maximum pressure and temperature may not be simultaneous so 1.e.69 1.    For  this  application.  including the bending allowance.      < 1.86 3.47 1.5 16  1.  of   310oC)  6  0.  the  minimum  required  wall  thickness  including  the  bending  allowance  for  16mm  OD  tube  should  be  1.D.2 12  1.  in  some  applications  like  F/M  supply  circuit. (4) i.8 mm”.2.29 2.  (Do) mm  Required  minimum  wall  thickness  of  straight  instrument tubing (tm) in  mm  (for  design  pressure  of  195  Minimum  recommended  wall  thickness  (mm)  prior  to  bending  (1. the maximum pressure & temperature in PHT system will be 125 kg/cm2  and 310oC  respectively. 2  /     and      Where   tn = nominal wall thickness of tube    2   Nirbhay Gupta                                                                                                                                   21      .92 1.1 1.  the  maximum  pressure  and  temperature  may  be  195  kg/cm2  and  40oC  respectively.5 25  2.15 1.55 0.6.3 mm.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      TABLE – 2­2  Tube O.    For  this  service  also.5 Sh    Stress due to Sustained load =  Ssl        The above equation may be verified for different sizes of tubing having wall thickness as  given in Table‐2‐2 and other constants to be calculated/taken as below:    B1 = 0.2 STRESS ANALYSIS OF TUBING SYSTEMS (TUBING CONFORMING TO PB­M­17)  2. which is less than specified wall thickness of  1.38 1.  “For example.8 mm wall thickness instead for  1.  weights  and  other  sustained mechanical loads must meet the requirements of eq.6.2 10  0.62mm  which is less than specified wall thickness of 1.0 Note: It can be seen from Tables – 2­2 & 2­3 that specified wall thickness of all sizes of tubing as per PB­M­ 17  is  more  than  required  wall  thickness  as  per  ASME  Section  III  except  for  16  mm  size.29 2. 6.8             Based on the seismic analysis carried out for different tubing layouts.2.2 ANALYSIS FOR OCCASIONAL LOADS (LEVEL A&B SERVICE LIMITS)  As  per  requirement  of  ASME  –  Section  III  installed  tubing  system  should  satisfy  the  equation (5) of Section 4.2.75       The  maximum  value  of  stress  (iMc/Z)  due  to  thermal  loading  (temperature  variation  from 25oC to 310oC) for different tubing systems comes out to be 1600 kg/cm2 provided  that tubing system is supported as per recommended practices. 2615 kg/cm2).3 ANALYSIS FOR STRESS DUE TO THERMAL EXPANSION AND OTHER SUSTAINED  LOADS  As  per  requirement  of  ASME  Section  III  installed  tubing  system  should  satisfy  the  following equation   4  0.   2.6.  Thus for different sizes of tubing systems Sol value is tabulated in Table‐2‐4.  This may be seen from the table that Ste value for different sizes of tubing is less than the  value of Sh + SA (viz.8 Sh for all the sizes of tubing thus satisfying the  above equation.2.  Ste  has  been  calculated  &  tabulated  in  TABLE‐2‐3  for  different sizes of tubing.1 as given below:       1   2 1.  This can be seen that Sol is less than 1.      Tube Size  Nominal Wall  TABLE 2­3  Calculated  value to be  STE Sh + SA Nirbhay Gupta                                                                                                                                   22      . Based on the above data  and  other  parameters/constants.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      R = Bend radius  r = (Do – t)/2 = mean radius of tubing                32 –        Thus for different sizes of tubing systems Ssl value is tabulated in Table‐2‐4    2. the recommended  conservative  value  of  Mb  is  200  kg  mm  for  all  sizes  of  tubing  systems  for  SSE  level  of  earthquake. 82  2615 16  1.33 2164.2  1.5  1.33 2043.24  25  3  1. The value of   used is based on requirement such that 0.92  12  1.67   6  1.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      (OD) mm  Thickness (tn) (mm) (See note2)  used for analysis (kg/cm2)    0. P.2  1.71 0. SA = f (1. Z.25 Sh) where f = 1 & Sc = 1106 (kg/cm2)    Nirbhay Gupta                                                                                                                                   23      .65 0.67 0.94  10  1.42 0.3  20  2.33 2112.33 2205.4  Note:    1.0  3.8  1.  2. The values of MA.25 Sc + 0.33 2169.5  1.33 2045.75   should not be less than 1.65 0. Sh used for calculation of STE are same as given in Table2­4. 03  0.37  310.75    Yes  3  0.156  5  0.03  16  20  23  TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS  2008      TABLE­2­4        Nirbhay Gupta                                                                                                                                   24    .42  1.37  0.94  1.384  0.78  Yes    1558.89  1. of fitting) (kg)  8    475.8  446.466  65.  1.0  4  0.94  1.5      –    }  B2Ma   Z   2   WL (wt.5 Sh    1774.07  119.5  0.83    Yes  Yes  Yes  Yes    754.8  257.76  Whether  Sol < 1.93  1.5  12    1. of 1m of tube filled with D2O) kg/m  Z (mm3)  7  449.2  6  2  1.2  10  1  0.64  321.06  0.512  224.0  0.0  2 Wall Thickness (t) (mm)  Calculated B2  Tube size OD (Do) mm  3  115.87  383.97  1.5    Yes    347.7  154.0  536.293  0.62  310.0  1022.4  1479  2.8 Sh     Mb  (Kg mm)  Whether  Ssl < 1.315  18.32  0.775  0.34  67.5Sh (kg/cm2)  Ssl (kg/cm2)    200  Yes        32   2 B1PDo 2tn Ma(kg/mm)   9    Yes      WF (wt.25  0.21  1.61  1.27    Yes    329.8  556.8 Sh  1 1.97  1.54    Yes     1.971  0.17    Yes      463.   B2 value to be used for analysis (as B2 cannot be less than 1)  6  383.46  1.192  . Nirbhay Gupta 23 . and from the valves up to instruments they should meet at least the requirements of ANSI-B-31.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2. of tube/pipe Dmin = The min.8 Tube Bending Considerations Bend radius in instrument tubing/piping should be subject to following limitations.1. 2. For safety and safety-related systems the safety classification of instrument sensing lines including the first accessible isolating valves should at least remain the same as that of process systems. the following requirements should also be met for impulse connections for pressure/differential pressure measurement in safety and safety related systems. outside diameter of tube/pipe after bending Dmax = The max.D. SS tubes should meet the design intent of ASME Section III sub-section NB/NC. outside diameter after bending The above requirements are met if bend radius is more than 3D o.7 2008 Consideration for various forces The design of tubing/piping systems for sensing lines should take account of all the forces and moments resulting from thermal expansion and contraction and from the effects of expansion joints if any. ii) The ovality of instrument tubing/piping after bending should not exceed 8% as calculated below: Ovality (%) = 100 (D max – D min)/Do Where – Do = Nominal O.9 Special design aspects to meet the requirements of class-I tubing and tubing systems In addition to the general requirements of impulse connections as mentioned above. i) Minimum wall thickness at any point in the completed bends should not be less than required minimum wall thickness for the design pressure. 2. also prevent proper action of a protection system channel designed to protect against the condition. 20mm and 25mm. 2) NON-DESTRUCTIVE INSPECTION All finished tubing should be inspected by ultrasonic or eddy current methods or any combination of these methods in accordance with the requirements of NB-2550. Also the instrument SS tubing should be seamless.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 For seismic classification the instrument sensing lines should be of SSE Category for safety and safety-related instrumentation systems. Based on the requirements of corrosion resistance. Based on the requirements of different applications the tubing in different sizes have been specified i. 3) Based on the analysis of tubing systems carried out above for our installations the stress values for different loading (service limits) are well within the required limits. A single instrument sensing line should not be used to perform both a safetyrelated function and a non safety-related function unless the following can be shown: a. 10mm. if SS 304L instrument tubing are supplied as per specification above and installation of tubing systems is done as per recommended practices(see section-10) then instrument impulse tubing systems will be meeting the intent of ASME Section III-Sub-Section NB-Class I components. tensile strength. b. 4) Thus. austenitic stainless steel grade SS-304L material as per ASTM A-213/SA655 has been selected and specified for instrument tubing. cause an action in a non-safety-related system that results in a plant condition requiring protective action and 2. Tubing system should be such that the failure of non safety impulse line/tubing should not affect the reading of safety system. 12mm. 2.e. cold finished and full annealed. The failure of the common sensing line would not simultaneously 1. From welding consideration the tubing should have delta ferrite of 5 to 10%. Nirbhay Gupta 24 .10 CONCLUSION 1) MATERIAL SELECTION a. 16mm. OD of 6mm. hardness and weldability. OVALITY VARIATION: < 8. SIZE & THICKNESS : As per the Table below Out side dia. 10 16 1.5 + 10%. 12 20 2. TYPE TESTS a.0 Technical Requirements of SS tubes Following design requirements should be specified while ordering SS tubes.D. ELONGATION % IN 50MM GAUGE LENGTH : ≥ 35 % 11.D.2 + 15%. -0% -00+ 0. 1.2 microns FOR O. [mm] 6 1. HARDNESS TEST : On one test piece of each size and each batch as per relevant ASTM standard Nirbhay Gupta 25 . TYPE : SEAMLESS.12 Length of tube Pieces 6 meters 4. & I.0 + 10%. FLUID : Water/Steam/Lube oil 5. -0% -00 + 0.D.0% OF O. 10.8 + 10%. MATERIAL : SS 304L 3. -0% -00 + 0. AS PER ASTM-A213 2.2 + 15%. PRESSURE: 200 kg/cm2(g) 6. -0% -00 +0.5 + 10%. YIELD POINT : ≥1760 kg/cm (g) c. SURFACE FINISH: BETTER THAN 8. 8.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 3. HARDNESS : > ROCKWELL B-65 & < ROCKWELL B-80 9. TENSILE STRENGTH : ≥ 4920 kg/cm (g) 2 b. 12 25 3. MECHANICAL PROPERTIES : 2 a. -0% -00 +0.10 12 1.10 10 1. [mm] Wall thickness [min] and tolerance [mm] Tolerances on O. MAXIMUM TEMPERATURE : 320ºC 7. MAX.D. -0% -00 + 0. ASTM A 370 Standard test method and definitions for mechanical testing of steel products. EXPANSION TEST : On one sample piece of each size and each batch as per relevant ASTM standard c. Sr. No. ASTM-A-213 Seamless Ferritic & Austenitic Alloy Steel Boiler . 3. ROUTINE TESTS a. LENGTH OF EACH TUBE: 6 meters Relevant standards for SS tubes Following standards should be followed while specifying or testing SS tubes. PB-M-17 Specifications for Seamless Austenitic SS tubes Nirbhay Gupta 26 . 4. DIMENSIONAL TEST : Required to be done on 10 % of the lot 2 b. Ferritic & Austenitic Alloy steel Tubes. FLATTENING AND DOUBLING OVER TEST : On one sample piece of each size and each batch as per relevant ASTM standard e. ASTM A 262 Standard Practices for Detecting susceptibility to intergranular attack in stainless steel . 5. CHEMICAL ANALYSIS : One sample of each batch as per relevant ASTM standard 12. III NB 2550 Examination & Repair Of seam less and welded (without filler metal) tubular products and fittings 6. Code/Standard Description 1. ASME SEC. Super heater & Heat Exchanger Tubes 2. HYDROSTATIC TEST : At pressure of 300 kg/cm (g) for 10 min. required to be done on each sizes of each batch 13. ASTM-A-450 General requirement for carbon. TENSILE TEST : On one sample piece of each size and each batch as per relevant ASTM standard d.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 b. Copper is economical.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 4.0 2008 Pneumatic Tubing Copper tubes are primarily used for pneumatic connections. 3. corrosion resistant. forming and joining permits savings in installation time. Copper is lightweight. Earlier pneumatic instruments were more popular and used (controllers. With soft temper tube. This means copper costs less to transport.1 Advantages of using copper tubes Strong. and that makes copper the ideal costeffective tubing material. However now-a-days most of the instruments that are used are electronic instruments. copper tube is the leading choice for pneumatic piping. 4. Volatile organic compounds are not required for installation. indicators etc. I/P converters. material and overall costs. walls and ceilings. Smooth bends permit the tube to follow contours and corners of almost any angle. 4. No extra thickness or weight is necessary to compensate for material removed by threading. particularly when used for renovation or modernization projects. at present this is used to connect the pneumatic actuator and its accessories viz. handles more easily and. it is frequently possible to eliminate elbows and joints. Copper is formable. Easy handling. when installed. strong and leak-proof joints. Long-term performance and reliability mean fewer callbacks. they still provide a very reliable alternative to electronic instruments. These fittings save material and make smooth. positioners. Copper tube does not require the heavy thickness of ferrous or threaded pipe of the same internal diameter. Therefore. it will not carry fire through floors. solenoid valves etc. Even though the pneumatic instruments are passé. thus the use of pneumatic tubing is limited. Copper is easy to join. much less wall and ceiling space is needed. 2. Copper is safe. Because copper tube can be bent and formed. Copper tube will not burn or support combustion and decompose to toxic gases.). which are quite important from plant operation point of view. Nirbhay Gupta 27 . takes less space. neat. There are seven primary reasons for this: 1. Copper tube can be joined with capillary fittings. Pneumatic instruments are still prevalent in hazardous areas. transmitters. Thus pneumatic tubing was used widely. Still. 5. Type K tube has thicker walls than Type L tube. In the piping trades. Tube in the hard temper condition is usually joined by soldering or brazing. Nirbhay Gupta 28 . 4. Types K.2 2008 Copper is dependable. The table also shows the ASTM Standard appropriate to the use of each type along with a listing of its commercially available lengths. Copper tube is manufactured to well-defined composition standards and marked with permanent identification so you know exactly what it is and who made it. L. Each type represents a series of sizes with different wall thicknesses. and Type L walls are thicker than Type M. which means satisfied customers. “Temper” describes the strength and hardness of the tube. M. Different types of copper tubes Table 4-1 below identifies the six standard types of copper tube and their most common applications2. DWV and Medical Gas tube are designated by ASTM standard sizes. Excellent resistance to corrosion and scaling assures long. using capillary fittings or by welding. Tube in the soft temper can be joined by the same techniques and is also commonly joined by the use of flare-type and compression fittings. with the actual outside diameter always 1/8-inch larger than the standard size designation. Tube in both the hard and soft tempers can also be joined by a variety of “mechanical” joints that can be assembled without the use of the heat source required for soldering and brazing. trouble-free service. for any given diameter.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 6. Copper tube for air-conditioning and refrigeration field service (ACR) is designated by actual outside diameter. sizes and tempers. drawn temper tube is often referred to as “hard” tube and annealed as “soft” tube. All inside diameters depend on tube size and wall thickness. 7. Copper resists corrosion. It is also possible to expand the end of one tube so that it can be joined to another by soldering or brazing without a capillary fitting—a procedure that can be efficient and economical in many installations. 1. 2. When a Nirbhay Gupta 29 . although ASTM B 88 is by far the most widely used. 4. Plumbing and mechanical codes govern what types may be used. Individual manufacturers may have commercially available lengths in addition to those shown in this table. Strength. 3. 4. Tube made to other ASTM standards is also intended for plumbing applications.3 Recommendations for selection of a type of copper tube It is up to the designer to select the type of copper tube for use in a particular application. formability and other mechanical factors often determine the choice.1 There are many other copper and copper alloy tubes and pipes available for specialized applications.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Tabl e-4. Available as special order only. ASTM Standard Classification B 698 lists six plumbing tube standards including B 88. Solar Heating: See ‘Heating’ section above. Where bending is required. soil and vent lines. Fire Sprinkler Systems: Use Type M hard. Drainage and Vent System: Use Type DWV for above. suitably cleaned for oxygen service per NFPA Standard No. This plus its Nirbhay Gupta 30 . Types K or L is recommended. Type L is successfully used. Types K. b. ACR or as specified. k. use Type M for all sizes. Use Types L. l. Underground Water Service: Use Type M hard for straight lengths joined with fittings. 99. and Natural Gas Services: Use Type L or Type ACR tube with flared joints in accessible locations and brazed joints made using AWS A5. Copper tube retains excellent ductility at low temperatures to –452°F and yield strength and tensile strength increase as temperature is reduced to this point. i. Type M where straight lengths are used. L and M are all accepted by NFPA.P. d. or as specified. and Type L soft where coils are more convenient. g. Air-Conditioning and Refrigeration Systems: Copper is the preferred material for use with most refrigerants. roof and building drains and sewers. e. j.and below-ground waste. Fuel Oil. L. write CDA. f. For water heating and low-pressure steam. use Type L soft temper where coils are formed in place or prefabricated. c.8 BAg series brazing filler metals in concealed locations. Health Care Facilities. Ground Source Heat Pump Systems: Use Types L or ACR where the ground coils are formed in place or prefabricated. Low Temperature Applications – Use copper tube of Type determined by rated internal working pressures at room temperature as shown in Tables below. For condensate return lines. Nonflammable Medical Gas Systems: Use Medical Gas tube Types K or L. Heating: For radiant panel and hydronic heating and for snow melting systems. it is helpful to know which type of copper tube has and can serve successfully and economically in the following applications: a. For information on solar installation and on solar collectors. Water Distribution Systems: Use Type M for above and below ground.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 choice can be made. h. Chilled Water Main: Use Type M for all sizes. piping.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 excellent thermal conductivity makes an unusual combination of properties for heat exchangers. Brazed joints are recommended. m. and other components in cryogenic plants and other low temperature applications. Table-4-2: Rated Internal Working Pressures for Copper Tube: TYPE DWV* Table-4-3: Rated Internal Working Pressures for Copper Tube: TYPE K* Nirbhay Gupta 31 . L or M determined by the rated internal working pressures as shown in tables 4-2 to 4-9 below. Compressed Air—Use copper tube of Types K. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Table-4-4: Rated Internal Working Pressures for Copper Tube: TYPE L* Table-4-5: Rated Internal Working Pressures for Copper Tube: TYPE M* Nirbhay Gupta 32 . Nirbhay Gupta 33 . ***Types M and DWV are not normally available in the annealed temper. the corresponding annealed rating must be used. the maximum allowab le stress in tension (psi) for the indicated temperatures (°F).TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Table-4-6: Rated Internal Working Pressures for Copper Tube: TYPE ACR* NOTE: * Based on ‘S’. Shaded values are provided for guidance when drawn temper tube is b razed or welded. ** When b razing or welding is used to join drawn tube. Fluid: Air /oil / water 5. Pressure: 8.5 + 0. Elongation (%) in 50 mm Gauge Length: Nirbhay Gupta 40% 34 .20 -0 Note: Though from pressure rating consideration the thickness requirement may be less but while deciding the thickness due consideration is to be given to the strength.7% Of O. Ovality Variation : < 0. Yield Point: 2200 kg/Cm2 (g) 650 kg/cm2 (g) c.2 Microns For O.2 + 0.2 + 0. Tensile Strength: b. 9.16 -0 12 +0.D 10. in mm Tolerance On OD In mm Wall Thickness[In mm] And Tolerance 6 +0.1 -0 1.1 -0 1. Length: 15 m< L < 80 meters 3.5 kg/cm2(g) 6.D & I.1 -0 1. 2. 4. Max.12 -0 1. Max. 1.20 -0 25 +012 -0 1. Surface Finish : Better than 8.16 -0 20 +0.16 -0 10 +0. Mechanical Properties: a.2 + 0. Size (mm): Out Side Dia. Seamless copper tubes as per ASTM-B-68M.D. Temperature: up to 100oC 7. Type : Annealed Copper.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 4.4 2008 Technical Requirements of Copper tube Following parameters are to be specified while preparing the specifications for copper tubes for pneumatic piping.5 + 0. Hardness: Rockwell F50 8. bright Annealed [metric] ASTM-E-8M: Standard test Method for tension testing of metallic materials [metric] ASTM-E-18: Standard test method for Rockwell hardness and Rockwell superficial hardness of metallic materials ASTM-E-53: Method for chemical analysis of copper ASTM-B-153: Standard test method for expansion [pin test] of copper and copper alloy pipe and tubing ASTM-E-243: Standard practice for electro-magnetic [eddy current] examination of copper and copper alloy tubes.5 Applicable international standards for copper tubes Besides NPCIL specifications following international codes and standards may be referred while specifying copper tubes.2 Routine Tests a. Pneumatic Test: At a pressure 8. for 10 min. Required to be done on each size each batch c. Chemical Analysis: one sample of each batch as per ASTM-E-53 & ASTMB-55M 11. Hardness Test: On one test piece of each size and each batch as per ASTM-E-18 b.1 Type Tests a. Flattening And Doubling Over Test: On One sample piece Of Each Size and Each Batch As Per BS-2871 & ASTM-E-255 e. ASTM-B-251M: Standard specification for general requirement for wrought seamless copper and alloy tubes [metric] ASTM-E-255: Practice for sampling copper and copper alloy for determination of chemical composition. BS-2871: Copper and copper alloys tubes Nirbhay Gupta 35 . Expansion Test: On one sample piece of each size and each batch as per ASTM-B-153 c. Hydrostatic Test: At pressure of 50 kg/cm 2(g). for 10 min.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 11.5 kg/cm2 (g). Tensile Test: On one sample piece Of Each Size And Each Batch As Per ASTM-E-8M d. Dimensional Test: Required to be done on 10% of the lot b. ASTM-B-68M: Standard specification for seamless copper tube. 4. Tests 11. Required to be done on each size each batch. 0 2008 ASTM Tubing Specifications outside diameter/wall thickness It is important to understand that both of the above can affect the ferrule(s) ability to seal on the tubing. The following tables should explain the allowable variations. Wall thickness variations can affect pressure ratings and flow characteristics. ASTM Dimensional Specifications for Tubing Table-A: Permissible Variations in Outside Diameter Table-B: Permissible Variations in Wall Thickness Table-C: Permissible Variations in Wall Thickness for ASTM B68 and ASTM B75 cold drawn copper tubes Table-A Permissible Variations in Outside Diameter Nirbhay Gupta 36 .TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 5. It is recommended to order tubing manufactured to the plus (+) side of the outside diameter tolerance. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Table-B: Permissible Variations in Wall Thickness Table-C: Permissible Variations in Wall Thickness for ASTM B68 and ASTM B75 cold drawn copper tubes Nirbhay Gupta 37 . This prevents streaming of radioactivity from an active area to a non-active area Guidelines for EP Design Following general guidelines should be followed: (a) There should be enough space between two penetrations so that tube fittings (bore-through connector) can be installed easily using spanner or a suitable tool. (b) Lead shielding balls are filled in the floor penetration EPs. This serves two purposes viz.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 6. Supporting the tube Making a leak tight passage. b. Note: For further details on the EP installation refer section 12. (c) In floor penetration EPs bore through connector is installed only on the top opening of the EP. a. This hole is used to take off the Steel/lead shielding balls from the EP. 0 of this technical note. (d) In the top plate of a floor EP a hole is made and a suitable plug is installed in it. Bottom opening is left as it is. This hole is used to fill the Steel/lead shielding balls in the EP. Nirbhay Gupta 38 . This allows thermal expansion of the tube through the EP and no additional stress is caused on the EP. (e) In the bottom plate of a floor EP a hole is made and a suitable plug is installed in it.0 EMBEDDED PENETRATIONS Whenever the tubes have to pass through some floor slab or a wall a n embedded penetration is used. 2 FLARED. FLARELESS & COMPRESSION JOINTS Flareless and compression type tube fittings may be used in instrument sensing lines for the tube sizes not exceeding 25mm (1”) O. c) Socket welds should not be used where the existence of crevices could accelerate corrosion. Nirbhay Gupta 39 . they should be made of design in which the gripping members or sleeve shall grip or bite into the outer surface of the tube hold the tube against pressure (to prevent blow out) but. a) Fittings and their joints should be of compatible material with the tubing or pipe material with which they are used and should conform to the range of wall thickness and method of assembly recommended by the manufacturers. 7. While performing socket-welding.6 mm should be provided between the end of pipe/tube and bottom of socket. provided following conditions are met. The gripping member or sleeve should form a pressure seal against a fitting body.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 7. not exceeding the recommendations of the manufacturer. b) Tube fittings should be used at pressure-temperature ratings.0 METHODS OF CONNECTION OF INSTRUMENTATION TUBES Different types of connections/joints can be used in instrument sensing lines as discussed below: 7. approximately 1.1 WELDED JOINTS a) Butt-welded joints should be made wherever possible. without seriously deforming the inside diameter. before welding. b) Socket-welded joints are permitted but limited to tube/pipe size of 50 mm and less. c) Wherever compression type flareless tube fittings are used.D. Socket welded joints should conform to requirements of ANSI-B16.11. Threaded joints should not be used between the process taps and accessible isolating valves. e) Threaded connections should not be used at temperature above 495oC.3 THREADED JOINTS Threaded joints in which the threads provide the only seal may be avoided as far as possible. crevice corrosion. d) In case of steam or hot water if service temperature is more than 100 oC. stainless steel tubing should not be used with brass fittings. g) Service conditions such as vibration and thermal cycling should also be considered in the application. 7. tubing must be fully annealed and ferrule of fittings should have more hardness than tubing material.) b) Pipe threads should be taper pipe threads in accordance with applicable standard.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 d) Tube fittings should be installed in accordance with manufacturer’s recommended procedures. shock or vibrations are expected to occur. Nirbhay Gupta 40 . threaded connections should be used only if process pressure is less than 100 kg/cm2. threaded joints between accessible isolating valve and instrument may be used within the limitations specified below: a) Thread size should not exceed ¾” (N. or the complete fittings should be replaced when needed. h) Metal tubing material should be softer than fitting material. Replacement parts from different manufacturers should be qualified to meet and seal properly at the design service conditions. Suitable sealant should be used on pipe threads depending upon the type of threads.B. c) Threaded joints should not be used when severe erosion. e) The fitting parts of the original flareless tube fittings should be designed and manufactured by same company. f) The fittings selected should not degrade the inherent strength of the tubing specified. However. i) When tubing and fittings are made of the same material. For example. In neither case should the taps be more than 45 0 from the horizontal. If the liquid is clean. Location of pressure taps should be at least 5 diameters downstream from a symmetrical pipe fitting (as a reducer) and at least 10 diameters from any unsymmetrical fitting (as a tee.1. II. there are generally no problems as far as the radial position of pressure taps is concerned. taps location angle should be less than 45 0 off the vertical meridian plane. LOCATION OF PRESSURE TAPS IN HORIZONTAL PIPES/VESEL: I. should be at a point where the flow is uniform. In general the location of pressure taps in a pipe line having flowing fluid. LOCATION OF PRESSURE TAPS a. For following draining to occur.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 8. It should also be at least 2 diameters upstream from any fitting or irregularity. b.0 2008 GUIDELINES FOR TAKE OFF CONNECTIONS FOR SENSING LINES Following guidelines pertaining to the take off connections (pressure taps) should be followed. then a position above the horizontal centre line is recommended. In cases where there is considerable volume of gas in liquid line and needs special considerations a horizontal tap position should be used in conjunction with gas vent connection and gas collecting chambers in the impulse lines. GAS AS PROCESS FLUID: The location of pressure taps in the vertical meridian upwards is preferred mainly for wet gas. Nirbhay Gupta 41 . elbow or valve). LOCATION OF PRESSURE TAPS IN VERTICAL PIPES/VESSELS In case of vertical pipes/vessel. it is advisable to avoid the risk of gas in impulse line by using tap location below the pipe horizontal meridian plane. If on the other hand the liquid has significant solid content. d. LIQUID AS PROCESS FLUID: The pressure taps should be located in a meridian plane with which the horizontal meridian is forming an angle not greater than 45 O above or below according to the position of the measuring/sensing device. 8. c. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 8. They should be designed to withstand full line pressure. TURBULENCE ERRORS: It may be noted that for measurement of static pressure in above case if higher size of opening is used as static pressure tap. When dynamics effects are not important smaller tapping size and impulse tubing may be used. IV. the higher size of pressure taps are preferred for minimizing the possibility of plugging and for minimizing the error due to friction. Conversely. DYNAMIC RESPONSE CONSIDERATIONS: From measurement/accuracy considerations specially when the pipes/vessels contain compressible flowing fluids. the pressure at tap fluctuates even when the undisturbed pressure is constant. VELOCITY ERRORS: In general the measurement errors are proportional to velocity pressure. Thus the pressure at tap involves some velocity pressure and is not true static pressure. Also large tap will produce eddies in the stream and as these eddies form and break away downstream. II. it is necessary to take great care in tap construction with minimum possible tap diameter and special attention to the sharpness and squareness of the edges of the hole. With the burrs up stream. the pressure at the hole will have a positive velocity effect and the pressure at the hole will be greater than the true static pressure. MATERIAL CONSIDERATIONS: Take of connections at the source together with attaching bosses or adapters should be made of material at least equivalent to material of process pipes/vessels to which they are attached. flow is diverted away from the hole and the pressure sensed at the hole is less than the true static pressure.2. the laminar flow past the tap is affected so that the velocity of tap opening is not effectively zero. if the burr is on downstream edge of the hole. I. When the stream Nirbhay Gupta 42 . III. 2008 CONSIDERATIONS FOR PRESSURE TAP DESIGN A. CONSIDERATIONS: Following aspects should be kept in mind while designing the pressure taps for take off connections. temperature and stresses. Thus when stream velocity is high. inertia and lag in the connections while measuring dynamic pressures. The turbulence error is also a function of edge condition of pressure tap hole. response time and requirement of physical strength.5 d as measured from the inner surface of the pipe/vessels ( d = inside dia. e. In all other applications where turbulence error does not come in picture. it is recommended to use small size of pressure tap holes uniformly for HP & LP connections as recommended in ASME/PTC-9. However during steady state this loss can be neglected. Nirbhay Gupta 43 . measurement errors may be more as the nozzle drop (take off connection losses) is proportional to the square of the velocity.3. During fast transients. b. In venturi tubes/orifice plates as the low pressure tap holes are to be located in high velocity region. f. 8. Thus. reliability of measurement. Proper care should be taken while machining the pressure tap holes. accuracy. c. There should be no burrs. d. Workmanship of pressure taps holes plays an important role in accurate/reliable measurement of pressure signals. Redundant taps should be located a distance apart such that the failure of one tap does not adversely affect the reading through the other taps. Thus based on above considerations the size of pressure tap holes should be decided depending upon the process fluid condition. in the system where fast transients are expected this requirement is more crucial. Also there should be no change in the pressure tap hole diameter for at least a distance of 2. it is recommended to use 20 mm NB pressure tap holes from the consideration of reliable measurement/minimizing possibility of plugging/choking fast response and mechanical/physical strength. wire edges or other irregularities on the inside of pipe/vessel at pressure tap connections or along the edge of the hole through the pipe/vessel wall. a.5 (Flow measurement). In no case shall any fittings project beyond the inner surface of the pipe/vessel wall. of pressure tap hole). RECOMMENDATIONS FOR PRESSURE TAP DESIGN Briefly the design and sizing recommendations for pressure taps for different applications are given below.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 velocity is low. the size and workmanship of the tap hole are not so important. in case of liquid flow ii) Avoid trapping liquid in the valve structure. It is preferred to use gate valves for root valves in order to: i) Avoid trapping gas bubbles in the valve structure. h. f. in case of gas flow. Following recommendations should be followed. It is recommended that the root valves be ¾ inch unless special requirements necessitate a different size.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 9. c.0 2008 GUIDELINES FOR ROOT VALVES Isolating root valves are provided at take off connections to isolate the entire measurement system from the main pipe line/vessel when necessary. b. The root valves may or may not perform the function of the accessible isolation valve. Nirbhay Gupta 44 . g. e. d. Root valves should not affect the pressure signal during normal operation. a. Root valves should be of the same material as that of the pipe they are connected to. dependent on its location. Isolating/root valves should be located immediately following the tapping point. Root valves should be capable of withstanding the maximum working pressure and temperature of the piping/vessel system to which the take off adapters or nipples are attached. Root valve bore/should not be less than the inside diameter of impulse tubing/piping. This is detrimental from vibratory and seismic considerations. Where redundant instrument sensing lines penetrate a wall or floor the required separation (Minimum 450 mm) should be maintained. Sensing lines should be located with sufficient clearance to permit sagging. Routing of instrument sensing lines should ensure that the lines are not subjected to vibrations. They should not cause any obstructions that would prohibit personnel or traffic access. abnormal heat or stress. They should avoid hot environments or potential fire risk area.1 2008 INSTALLATION OF INSTRUMENTATION TUBING Best practices for impulse tubing installation Separation between redundant instrument sensing lines should be provided by free air space or barriers or both such that no single failure can cause the failure of more than one redundant sensing line. The speed of response is reduced for long runs b.0 10. This is good for two reasons. Care should be taken to ensure that the tubing/piping does not rest on or against any abrasive surface. As an alternate a suitable steel or concrete barrier can be used. They should be kept as short as possible. They should not interfere with the accessibility for maintenance of other items of equipment/instrument. a. Resonance frequency is increased for longer tube runs. jet forces or falling objects. Beyond this limit electrical or pneumatic transmission should be used. avoiding open or exposed area to decrease the likelihood of persons supporting themselves on the lines or of damage to the sensing lines by pipe whip. The minimum separation between redundant sensing lines should be at least 450 mm.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 10. The distance of transmission for instrumentation tubing should be limited to 16 meters only. Nirbhay Gupta 45 . Instrument sensing lines should be run along the walls. columns or ceilings wherever practicable. should be tagged at its process line root-valve connection. The number of joints should be kept to a minimum. the tray should be identified with the appropriate sensing line numbers. fire. or air seal. as a minimum. Fittings are permitted where the use of bends is not practical.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 The two impulse lines especially in case of ΔP /flow measurements should be kept close together to avoid a false pressure difference arising from a difference in temperature. If multiple sensing lines are installed in a single tray. The instrument sensing tubing or piping runs pertaining to a nuclear safetyrelated instrument channel should be identified and coded so as to identify its channel. elbows. Each instrument-sensing line and associated valves in this channel should have an identification tag showing the channel and unique line or valve identification number. care should be taken to ensure that the seal is not degraded by the sensing line's seismic or thermal movements. etc. Where tubing penetrates a radiation. water. Tubes at different temperatures should not be run together for level measurement. and at any point in between where the sensing line passes through a wall or a floor (on both sides of such penetration). Bends rather than fittings should be used to change the direction of a run of piping or tubing. at the instrument. While installing the sensing lines the bend radius of tubing should not be less than 3 Do. clips. Each valve also should be tagged. In addition. Supports. Each instrument sensing line. Sensing lines should be adequately supported along its entire length. The slope should be increased if the liquid in impulse lines is more viscous than water. A bending tool should be used when bending the tubing in cold condition. brackets. The slope should not be less than 1:12. Sharp bends should be avoided. offsets or changes in direction of sensing lines. There should be provision for thermal expansion and contraction preferably by tube/pipe bends. Sensing lines should continuously slope downwards towards the sensing instruments in case of liquid and upwards in case of gases. or hangers shall not be fastened to the instrument sensing lines for the purpose of supporting cable trays or any other equipment. the mechanical properties of the seal shall be Nirbhay Gupta 46 . This may affect the density of fluid in reference or measurement legs. colors. valves. Routing of the nuclear safety-related sensing lines shall ensure that the function of these lines is not affected by the movement of the main process (piping. etc. Sources of relative motion that should be considered are thermal expansion. and vibrational movements if its ratings equal or exceed the design requirements. One of the following methods should be used to ensure that the sensing line function is not affected: 1. Demonstrate by documented analysis or calculations that the majority of the sensing line routing is at ambient temperature. and “hot blow down” is not a design loading. ductwork. instrumentation.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 reviewed to ensure that the seal does not anchor the sensing line when a guide is required. Demonstrate by documented analysis or calculations that the process movements are negligible. One of the following methods should be used to ensure that the sensing-line function is not affected: 1.) to which the sensing line is connected. vibrations. Nirbhay Gupta 47 . equipment. Installation considerations should include maintaining slope and no low points. Routing of the nuclear safety-related sensing lines shall ensure that the function of these lines is not affected by thermal motions due to “hot blow down” of the sensing lines. supports. seismic motions. seismic. All sensing lines including trays. Instrument sensing lines and accessories inside the Containment Building shall withstand the pressure profile during containment leak-rate testing. Flexible hose may be used in sensing lines to accommodate the process thermal. Or 2. including service life. Design the sensing line routing using the process design temperature as the temperature value used in the design analysis. Or 2. The Code classification of the sensing line will determine the requirements for relative motion that shall be considered. and design-basis accidents or events. Demonstrate by documented analysis or calculations that sufficient flexibility has been provided to accommodate the process movements. and other in-line devices should be installed to avoid contact interferences caused by relative motion between the sensing line and other adjacent equipment or devices. 10.  Correct deburring tool shall be used for deburring both inside and outside edge of tube ends. If the surface requires higher degree of cleanliness then a cleaning agent should be used.  Dragging the tube across any surface that could scratch the surface can cause seal corrosion and sealing problems.  When cutting the tubing hacksaw must not be used. the correct tool is a tube cutter with a sharp blade.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Tubing Handling Imperfection on the tube OD can be potential source of problems in a tubing system. On offshore facilities scratches on tube may lead to corrosion of SS tubing from salt water pitting.  It is a good practice to visually inspect tubing to ensure it is free from scratches and other damage. Measure Exactly . (See Figure-10-1 below) Nirbhay Gupta 48 .2 Some Practical Guidelines for Tube Laying and Bending 1.Bend Accurately These are the two most important rules which must be observed when fabricating a tube line.  It is good practice to clean the tubing with dry instrument air. Handling of the tube shall be done very carefully to avoid scratches and protect the finish of the tubes. (See Figure-10-2 below) ACCURATE BENDING is necessary to achieve the exact angles required for the tube line. Tube Centerline Basis for Measurement: The centerline of the tube is the basis for all tube line measurement (See Figure10-4 below). the tube line will not fit.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 EXACT MEASUREMENT is required to insure that you obtain the desired distance between bends. Always measure from the centerline except from the first bend which Nirbhay Gupta 49 . If you do not bend accurately. If you do not measure exactly. (See Figure 10-3 below) 2. the tube line will not fit. Always try to bend in the same direction! If you backbend. Changes in plane are accomplished by rotating the tubing in the bender. 10. careful workmanship at all times. Control Accuracy Remember only you can control the accuracy of your work. To insure that the tubing is correctly placed for the desired change in plane. e. Measure and mark exactly.3 Tube Bending Check list Follow this list to insure good results on each bend. d. Nirbhay Gupta 50 . i. Open bender. Clamp tubing securely in bender. Check measurement length with tape or ruler.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 is measured from the end of the tube. The bending radius selected must be at least three times the outside diameter of the tube. Bend accurately to the desired angle plus spring back allowance. Insert tube in bender. On most benders. b. h. Remember. Double check bend angle with triangle. f. a. gain always occurs to the right side of the tube radius block. c. Use good. Keep Track of Changes of Plane Benders bend in only one direction. the edge of the radius block is at the centerline of the tube. be sure to compensate for gain or pickup. Bend Direction Mark One method for keeping track of changes in plane is to use a longitudinal or lengthwise bend direction mark. g. Check to make certain length mark is tangent to desired angle on radius block or in line with the desired degree on the link member. remove tube. 3. a reference mark on the tube is very helpful. Rules for Positioning Tubing in Bender A line which is tangent to the desired angle mark on the radius block and which passes through the measurement mark at the centerline of the tube.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 (See Figure 10-5 above)Put the mark on the side opposite the direction in which you wish to bend. Marking the Tube Whenever you make a mark on tubing. use a sharp pencil. Scratches create points where corrosion or stress concentration can ruin or dangerously weaken the tube. It also gives you a reference mark in case you must leave your work unfinished. is used to control the distance between bend centerlines. (See Figure 10-7) Don’t use grease pencils or crayons as these make too wide a line which can easily affect accuracy. (See Figure 106)This will insure that you bend in the correct direction. Measure and Mark Never use a sharp tool to scratch marks onto tubing. center the mark face up in the groove of the radius block. When you put the tube in the bender. (See Figure below) Nirbhay Gupta 51 . Use a ferrule as a guide to make measurement marks all the way around the tube so that the mark is always visible. Length mark @ 90° on link member) Horseshoe or u-bends – measure first leg.e. Thus.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Tube Positioning Rules 90° angles . tubing seems to stretch or pick up length. Test a piece of the material before you start fabricating a line to see how much it springs back on a 90° bend. 145°.e.A TUBE BENDER BENDS IT CAN NOT UNBEND. c.tangent intersects length mark at centerline. bend around to 180°. Angles less than 90° . especially with large. it is always better to underbend slightly. Always try to bend in the same direction away from the original starting end. Remember. or to 461/2° to obtain finished 45° bend. For example. Tube Stretch or Pickup When bent. position for 90°. Compensate for springback: a. 10-8 (above).tangent flush with length mark (refer to dotted line xy tangent to radius block @ 90° fig. b. (i. REMEMBER . If you reverse the direction of bending (bending towards instead of away from the original starting end) you will “trap” the stretch. i. Overbend by the amount of springback.position for a 90° bend and continue on to desired angle. You can always bend a little more if needed. but it’s almost impossible to remove or straighten a bend. This works especially well with large heavywall tubing. bend to 93° to secure a finished 90° bend. Angles more than 90° . if the material springs back 3° on a 90° bend. A good “rule of thumb” for most standard tubing materials and radius blocks is that the tubing will stretch approximately one tube diameter for each 90° bend. 135°. Nirbhay Gupta 52 . This is because it takes a curved shortcut across the inside of the angle. heavy-wall tubing. 29 1. Some radius blocks may differ. Cons ult individual radius block manufacturers for details on other radius diameters. Compensate for each bend after the first by subtracting the amount of gain from your chart for each 90° of bend to allow for stretch (Figure 4-11).TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 if you unknowingly make a reverse bend of 90°. “Rule of Thumb” Method Compensate each measurement after the first by subtracting the gain listed in table 10-1.93 3. in table 10-1 (approximately one tube O. As long as you measure and bend with the tube inserted from the left.19 .02 .04 . “pickup” will not affect your actual center-to. you will trap the gain.43 .97 1. For metric tubes the size and radius can be computed in the similar way.30 . Best Way to Measure For maximum Nirbhay Gupta Radius of Tube size (in inches) 1/8 3/16 1/4 5/16 3/8 1/2 5/8 3/4 7/8 1 1-1/4 1-1/2 2 Size 2 3 4 5 6 8 10 12 14 16 20 24 32 Bender Gain Gain (in inches) 90° 45° 3/8 7/16 9/16 11/16 15/16 1-1/2 1-7/8 2-1/4 2-5/8 3 3-3/4 4-1/2 8 . Measure the first bend from the end of the tube.64 . If bend direction for either 45° or 90° bend must be reversed. This chart (Figure 10-11) gives the accurate increase in length that occurs with the most commonly used sizes of radius blocks. the amount of stretch is related to the diameter of the radius block used.13 1.80 .24 .D.08 . Always custom measure for the last bend.19 . the correct length. Table-10-1 Pre-Measuring You may pre-measure a series of bends.11 .16 . 2.02 .61 1.10 . NOTE: 1.03 .16 .40 .center measurement.34 53 . subtract the “gain” amount listed in table 10-1.13 .02 . and measure centerline.) and increase your length between bends by that amount.06 . While our rule of thumb is approximately correct. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 accuracy, measure and bend exactly for each individual bend in the tubing line. We recommend the practice of Measure and Bend then again Measure and Bend, etc. 10.4 Characteristics of a Well-Made Tubing Circuit In a well made tubing circuit or line, bends are accurate, measurement exact. The run is plumb, square and level. Tube ends rest firmly in the fittings and entry into the fittings is straight. Straight tube entry is very important to insure that fittings are not under stress and can be assembled without leaks. (See Figure 4-13below) Remember too, that length magnifies bend angles errors. If the leg following the bend is fairly long, an error of 1° may result in the tube line missing the desired point completely. Nirbhay Gupta 54 TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Recommended Free Tubing Lengths It is important to consider the length of tubing from the end in the fitting body to the beginning of the bend. Table: 10-2 lists the recommended lengths “L” and “D” for various sizes of tubes. 10.5 2 3.25 2.65 1-1/2 2.41 1.96 1-1/4 1.94 1.61 1 1.50 1.22 7/8 1.31 1.05 3/4 1.25 .98 5/8 1.25 .98 1/2 1.19 .94 3/8 .94 .69 5/16 .88 .66 1/4 .80 .61 3/16 .75 .56 1/8 .70 .52 1/16 .38 “D” Tube Insertion Depth (inches) “L” Free Length of Strai ght Tubing (inches) .50 TUBE O.D. inches Table: 10-2 Common Causes of Imperfect Bends Figure A shows an ideal bend. Bends with little or no flattening are produced when correct equipment and methods are employed; when proper consideration is given to corelationship of the radius of the bend, material wall thickness and hardness of the tube. Figure B shows a flattened bend, caused by trying to bend too short a radius, or bending smaller diameter tube in larger radius block. Figure C shows a kinked and flattened bend, caused by the tube slipping in the bender, or by using non-annealed tubing. Tubes must be firmly clamped by clamp block to prevent slippage during bending process. Figure D shows a wrinkled bend, sometimes produced when thin wall tube is bent. Breakage will sometimes occur when mandrel is too far forward in tube, or when too short a radius is attempts with hard tube. Nirbhay Gupta 55 TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Offset Bends To form a tube offset, it is obviously necessary to make two bends. With the tube benders, it is easy to make double 45° bends. To make an offset bend simply follow the “Offset Bend Allowance” steps below to determine the proper distance between the two 45° bends. Here’s the procedure. STEP 1 First, determine the total amount of offset required (dimension “F” in the diagram). STEP 2 Next, determine the angle of offset - 30° or 45°. The latter (45°) is recommended because benders are calibrated for 45° bending. STEP 3 Figure the length of the tube required to meet your offset requirements (“L” dimension) in the diagram. For 30° bends multiply desired offset “F”x 2= 30° offset dimension “L”. For 45° bends multiply desired offset “F”x 1414=45° offset dimension “L”. STEP 4 Determine where you want the offset bend of the tube to start; and make a reference mark (A). Now measure off the “L” dimension (determined in Step 3), starting from the reference mark and make a second mark (B). You are now ready to make the bends. STEP 5 Align mark (A) with reference mark 45° on bender shoe handle (measurement end to the left) and proceed with first bend. Then align (B) with 45° mark and make second bend in proper direction (measurement end to the left). Follow previous detailed instructions for making 45° bends in one plane. Nirbhay Gupta 56 The most logical path should: Avoid excessive strain on joints . Figure-10-17 Nirbhay Gupta 57 .TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 10.6 2008 Routing of Bends Routing of lines is probably the most difficult yet most significant of these system design considerations.A strained joint will eventually leak. Proper routing involves getting a connecting line from one point to another through the most logical path. Allow for motion under load .Even some apparently rigid systems do move under load.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Figure-10-18 Allow for expansion and contraction . Nirbhay Gupta 58 .Use a “U” bend in long lines to allow for expansion and contraction. Nirbhay Gupta 59 . Pressure drop due to one 90° bend is greater than that due to two 45° bends. maintenance and repair. Have a neat appearance and allow for easy trouble shooting.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Get around obstructions without using excessive amount of 90° bends. Keep tube lines away from components that require regular maintenance. forms and fillers. Because copper is readily formed. Separation is being maintained between the pneumatic tubing used for redundant valves/instruments. Tubing should not be laid at a place where human or machine movements are expected.8 Guidelines for Copper tube bending Because of its exceptional formability. 10. The tube fitting that is used is Brass compression type single ferrule tube fitting. Copper tube. The installation procedure of brass tube fitting is more or less similar to that of SS tube fitting. brass tube fitting becomes the preferred choice. Simple hand tools employing mandrels.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 10. Because of response time considerations 6 mm tubes are for short distances whereas 10 mm tubes are used for air supply connections.7 2008 Guidelines for Copper Tube Installation Following additional guidelines for the installation of copper tubes should be followed. However galling problem of straight threads is not there to that extent as that of SS tube fittings. will not collapse on the outside of the bend and will not buckle on the inside of the bend. Tests demonstrate that the bursting strength of a bent copper tube can actually be greater than it was before bending. or power- Nirbhay Gupta 60 . Generally long runs of copper tubes are not used because of slow response. Moisture free instrument air is recommended from the consideration of corrosion of tubing. Therefore. Considering the strength and hardness of copper tubing. Pneumatic tubing for redundant instruments should be taken from different supply headers. extension of tube length is not required. dies. copper can be formed as desired at the job site. However. expansion loops and other bends necessary in an assembly are quickly and simply made if the proper method and equipment are used. properly bent. if it is needed union is used (instead of brazing and welding). As these tubes are soft they may get damaged. Brazed joints. Care must be taken to use proper welding procedures. Mechanical joints are used frequently for underground tubing. The procedure for bending copper tube with a levertype hand bender is illustrated in Figure below 10. For a guide to typical bend radii. see Table10-3.9 Copper tube Joints Soldered joints. for joints where the use of heat is impractical and for joints that may have to be disconnected from time to time. with capillary fittings. are used where greater joint strength is required or where service temperatures are as high as 350°F. for joints in refrigeration piping. The proper size of bender for each size tube must be used. are used in plumbing for water lines and for sanitary drainage. with capillary fittings. and often required. Copper tube may also be joined by butt-welding without the use of fittings. Nirbhay Gupta 61 .TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 operated bending machines can be used. Brazing is preferred. Both annealed tube and hard drawn tube can be bent with the appropriate hand benders. That being. Tube support and clamping is a necessary requirement in the fluid power industry. This criterion will be applicable for sensing lines/tubing where temperature cycling is expected. support and clamps design should include provision for seismic. supports or clamps may be subjected during normal operation.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 11. c) Instrument isolating valves or other instrumentation valves coming in the sensing lines should be supported with suitable clamps. Tube Clamping Once you’ve taken the time to make good bends and installed them. and can also be stacked. clamps. d) In the intermediate tubing runs supports should be located in such a way that the maximum unsupported span is not more than 1m. pads and spacers in contact with sensing lines should be compatible to avoid corrosion. vibration and noise free system. most manufacturers specify SAE and JIC approved components on their Nirbhay Gupta 62 . it’s not enough to just let them lay suspended in mid-air. Material for hanger. cause the fitting to loosen and leak or even allow tube to fall through fatigue.0 2008 Impulse tube/Sensing line support Following principals should be followed while designing the instrument sensing line supports. Also. The most important part of any clamping system is having enough clamps to attain the final result. From the consideration of seismic qualification the following supporting criterion should be followed: b) Supports should be placed at a distance of about 150 mm from each end of tube fittings as well as bends in the tubing layout. seismic or other credible events. When tubing is left unsupported. a well supported. pipe whip and thermal expansion of process taps and instrument sensing lines to which the hangers. From the consideration of thermal loading. in sets. Tubing can be clamped individually. Hanger. and in turn. tube fittings and bends coming in the sensing lines should not be supported. shock and vibration will cause the tubing to shake. 9 m 1.D. 5 ft.1 Alongside Table-11-1 is showing maximum permissible spacing between clamps. It is recommended to clamp as close to each bend of the tube as possible. It comes standard in steel and uses a rubber grommet around the tube for vibration dampening. 4 ft.13 mm 14 . and one must clamp each side. Parker Hannifin offers a tube clamp support system by the name of “ParKlamp”.30 mm 31 & up mm 3 ft. The best way to meet these specs concerning clamps is to utilize a clamp that employs both an upper and lower unit made of metal and a rubber split bushing which surrounds the tube or pipe and fits on the inside of the clamping units.7/8” 1” 1-1/4” & up 6 . The tube should be clamped at 1 m distance preferably.) .TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 equipment. This eliminates thrust in all directions.1/2” 3/8” . ParKlamp can clamp and support tube fro m 1/4” to 2” and pipe or hose fro m 1/4” to 1-1/2”. SPACING IN METE RS (Approx.” EQUIVALENT TUBE (mm) FOOT SPACING BETWEEN SUPPORTS 1/4” . 7 ft.2 m 1. (See class-1 Tubing design) Nirbhay Gupta 63 .5 m 2.22 mm 23 . Table-11-1 TUBE O. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 12. The open space between the pipe Figure-12-1 sleeve and the sensing lines should be filled with the suitable radiation absorbing material. Figure-12-2 Nirbhay Gupta 64 .0 2008 Impulse tube installation through EPs In case where tubing/piping are penetrating shielding wall.P. To take care of the above. care should be taken to avoid personnel exposure to radiation streaming from radioactive sources to surrounding areas through instrument sensing lines penetrations in the shielding wall. Sensing lines (tubing/piping) should pass the E. through seal plate and suitable sealing arrangement should be provided on the seal plate using suitable fittings/bore through tube fittings etc. sensing lines penetrating the shield wall should be passed through embedded parts and surrounded by a pipe sleeve in the shielding wall. The requirement that a tube fitting accomplish these two functions has been the driving factor in tube fitting design for decades. a valve. Secondly. usually on the order of up to 200 Vickers. in terms of typical commercially available tubing material.0 The tube grip and seal performance level required of the tube fitting for its intended applications. since improper make-up and tightening remain the leading causes for leakage. Low ductility makes it more difficult to deform the tubing plastically so as to achieve a desired tube grip. for example. such as for example.1 Requirements of a tube fitti ng Tube fittings that are intended for use with stainless steel tubing. Heavy wall tubing is difficult to grip because it is not only hard but it is also not particularly ductile. outside diameter and wall thickness. Any tube fitting must accomplish two important functions within the pressure. temperature and vibration criteria that the tube fitting is designed to meet. and 2.0 The characteristics of the tubing that the fitting must work with. A tube fitting has to meet the following requirements: Offer reliable installation over a range of field conditions. the tube fitting must maintain a primary seal against leakage. Stainless steel tubing is also used for high pressure applications in which the tubing wall thickness is substantial (referred to in this paper as "heavy walled" tubing). This arises from the nature of stainless steel which. whether that other member be another tube end such as through T-fittings and elbow fittings. Nirbhay Gupta 65 . are particularly challenging to design in order to achieve the desired tube grip and seal functions. including the material.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 13. First. is a very hard material. A multitude of factors influence the design of a tube fitting to meet a desired grip and seal performance criteria. the tube fitting must grip the tube end so as to prevent loss of seal or tube blow out. for example.0 TUBE FITTINGS Tube fittings are used to join or connect a tube end to another member. or a device that needs to be in fluid communication with the tube end. 13. but basic to any tube fitting design will be: 1. and thermal shock and applicable environmental conditions) or should demonstrate this by testing the fitting's ability to perform its intended function. ovality. It is recommended that compression type tube fitting should not be used for welded tubes. radiation environment.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Cope with the wide variation in tubing characteristics. This difference makes the gripping action of the ferrule Nirbhay Gupta 66 . The fittings selected should not degrade the inherent strength of the tubing specified. Fittings that require high installation torque or that vary widely in the “feel” and effort required to achieve complete pull-up may cause installers to improperly tighten components and severely degrade tube fitting performance. hardness. consistent “feel” to installers. the designer should determine that the type of fitting selected is qualified for design conditions (including vibration. pressure. during hydro test or during operating conditions) is applied on it the tube does not pull out of the grip. It should withstand the temperature and pressure cycling as per appropriate standard (PB-E-146). as long as they are in compliance with the appropriate code and system temperature and pressure requirements. Screwed joints in which pipe threads provide the only seal may be used. Generally the acceptable pull out tension load is more than four times the hydrostatic test pressure load. including differences in wall thickness. Pull Out Capability: Tube fitting should provide sufficiently robust grip on the tube such that when a tensile load (e. Thread sealant should be suitable for the required service conditions considering the process media.g. Tube fittings should be installed in accordance with manufacturer's recommendations. and compatibility with the materials of construction. Fittings should be of a compatible material with the tubing or pipe material on which they are used to avoid electrolysis and to provide acceptable weld joints. As in such type of tubes the hardness differs at the point of welding. Tube fittings should be used at pressure-temperature ratings not exceeding the recommendation of the tube fitting manufacturer and to meet the environmental and process system requirements. Deliver a predictable. In the absence of any existing standards. and burst pressures. who sometimes judge installation quality by effort (torque) rather than the recommended installation practice. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 unreliable. (This may be noted that NAPS onwards welded tubes have replaced by Seamless annealed tubing in all NPCIL plants/projects) 13.2 Construction of a tube fitting Tube fittings for stainless steel tubing typically include an assembly of a tube gripping device, often in the form of a ferrule or ferrules, or a gripping ring-like structure, and a pull-up mechanism for causing the tube gripping device to be installed on a tube end so as to grip the tube end and provide a seal against leakage. The term "pull-up" simply refers to the operation of tightening the tube fitting assembly so as to complete the assembly of the fitting onto the tube end with the desired tube grip and seal. Usually a stainless steel tube fitting is first assembled in a "finger tight" condition and then a wrench or other suitable tool is used to tighten or "pull up" the fitting to its final initial and complete assembled condition. In some cases, especially for larger tube sizes, a swaging tool is used to pre-install a ferrule onto the tubing. The pull up mechanism most commonly used is a threaded connection of a female threaded nut component and a male threaded body component, with the tube gripping device being acted upon by these two components as they are threaded and tightened together. The body includes a tube end receiving bore with an angled camming surface at the outer portion of that bore. The most commonly used camming surfaces are frusto-conical such that the term "camming angle" refers to the cone angle of the camming surface relative to the tube end longitudinal axis or outer surface. The tube end is axially inser ted into the body bore and extends past the frusto-conical camming surface. The gripping device is slipped onto the tube end and the nut is partially threaded onto the body to the finger tight position such that the tube gripping device captured axially between the camming surface and the nut. The nut typically includes an inward shoulder that drives the tube gripping device into engagement with the angled camming surface on the body as the nut and body components are threadably tightened together. The angled camming surface imparts a radial compression to the tube gripping device, forcing the tube gripping device into a gripping engagement with the tube end. The tube gripping device typically is to form a seal against the outer surface of the tubing and also against the angled camming surface. Nirbhay Gupta 67 TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 13.3 Types of tube fittings Generally following types of fittings are available: (a) (b) (c) (d) Flareless Compression Type (Single Ferrule) Flareless Compression Type (Double Ferrule) Bite Type Flared Fitting A flareless tube fitting generally refers to a type of tube fitting in which the tube end remains substantially tubular, in contrast to a flared tube fitting in which the tube end is outwardly flared over a fitting component. Flared tube ends are commonly encountered in use with plastic tubing and plastic tube fittings. The present note is not directed to plastic tubing or tube fittings because such fittings have significantly different challenges and material properties that affect the ability of the fitting to both grip the tube and provide an adequate seal. Operating pressures and temperatures are also typically substantially lower in the plastics tubing systems. In other words, with respect to tube grip and seal, whatever works in a plastic tube fitting provides little or no guidance for a non plastic tube fitting. Among the above, the recommended fitting is flareless compression type twin ferrule tube fitting. Because of its ease of installation and higher reliability this type of fitting is most commonly used. 13.4 Flared Fitting This is made up of a nut, sleeve and body with a flare or coned end. In some instances, the sleeve is used as a self-flaring option, usually on thinner wall or softer tubing materials. Compared to the original compression fitting, the flare fitting can handle higher pressures and wider system parameters. It is also available in a larger variety of materials and has a larger seal area, which provides remake capabilities in maintenance applications. However, special flaring tools are required to prepare the tubing for installation. Additionally, flaring of the tubing can cause stress risers at the base of the flare or cause axial cracks on thin or brittle tubing. Uneven tube cuts will create an uneven sealing surface. Nirbhay Gupta 68 TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 13.5 Flareless Bite type tube fitting A Flareless bite type fitting consists of a body, a special case hardened ferrule (a one-piece precision machined ferrule) and a nut, put together in a standard way. On assembly, the ferrule "bites" into the outer surface of the tube with sufficient strength to hold the tube against pressure, without significant distortion of the inside tube diameter. Hence, the name "bite type fitting". As used herein, the term "bite" refers to the plastic deformation of the ferrule into the outer surface of the tube end so as to plastically deform and indent the tubing with an almost cutting- like action to create a generally radial shoulder or wall at the front end of the ferrule. This "bite" thus serves as a strong structural feature to prevent tube blow out at high pressure, particularly for larger diameter tubing such as 1/2"and higher. As compared to ordinary compression joints, the ferrule holds the pipe in its place to give a proper seal when the nut is screwed on to the body. When it is fully tightened, the case hardened ferrule is pushed slightly in the middle where it acts as a spring. This maintains a continuous friction between the body and nut and which help prevent the nut from loosening under stress and repeated vibration. Bite-type fittings are typically single ferrule in design. This requires the nose of the ferrule to perform two functions: to bite into the tube to hold it, and to provide a sealing element for the coupling body, an action that can easily compromise on e or both functions. A two-ferrule separation of functions (the first to seal, the second to hold the tube) would solve this problem, as the separation would permit each of the elements to be designed specifically for the task. 13.6 FLARELESS COMPRESSION TYPE TUBE FITTI NG Over the years there have been numerous tube fitting designs that do not rely on a "bite" type action, but rather merely radially compress the tube gripping device against the tubing outer surface, some with the effect of indenting into the tu bing without creating a bite. The most common commercially available stainless steel tube fittings especially for high pressure applications have historically been of two radically distinct Nirbhay Gupta 69 This is accomplished usually by providing an angled drive surface on the nut shoulder that engages the back end of the single ferrule so as to radially compress the back end of the ferrule into a gripping action on the tube end. the single ferrule should be completely in three dimensional compression between the nut and the camming surface of the body. In some single ferrule designs. an outwardly bowed single ferrule fitting could be more susceptible to ferrule collapse. the outward bowing action tends to work against the effort to grip the tube at the front end of the single ferrule because. the single ferrule requires a lessened mass that is adjacent the tube gripping "bite". The bowing action helps direct the front end of the single ferrule into the tube end. Consequently. The bowing action is also used to cause the back end of the ferrule to likewise engage and grip the tube end. Additionally. the tube gripping action is usually associated with the single ferrule being designed to bow in a radially outward direction from the tube wall in the central region or mid-portion of the single ferrule body between the front and back ends thereof. Providing a back end grip actually places a counter acting tension to the single ferrule that works against the front end compression being used to provide the tube grip. loss of seal and possibly tube blow out at higher pressures. the back end of the ferrule apparently is intended to bite into the tube end. The use of a back end tube grip actually works against the effort to grip the tube end at the front end of the single ferrule. as the name implies. in order to enable the outward bowing action. This back end tube grip is sometimes used with the single ferrule in order to attempt to improve the tube fitting's performance under vibration because the back end grip attempts to isolate down-tube vibration from affecting the front end tube bite. Ideally. For single ferrule tube fittings.7 SINGLE FERRULE FLARELESS COMPRESSION TYPE TUBE FITTING A single ferrule tube fitting. The front end of the ferrule is driven against the angled camming surface of the body by the nut pushing against the back end of the ferrule. 13. Nirbhay Gupta 70 .TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 designs of the tube gripping device--single ferrule tube fittings and two ferrule tube fittings. uses a single ferrule to accomplish both the tube grip and seal functions. The outward bowing action radially displaces ferrule mass from central of the ferrule body to away from the tube end. especially in extreme environments and for sealing gas. Over the years. however. 13. The shallow camming angle has been used in single ferrule fittings to obtain a mechanical advantage because the shallow angle provides an axially elongated camming surface against which to slide and radially compress the single ferrule front end to bite into the tube end outer surface.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 In order to achieve an adequate tube grip on stainless steel tubing. Hard stainless steel tubing material necessitated this elongated sliding camming action in order to be able to get the single ferrule to create an adequate bite for tube grip. Consequently. An example of a commercially available single ferrule tube fitting that uses a case hardened ferrule and a shallow camming angle of about twenty degrees is the CPI fitting line available from Parker-Hannifin Corporation. This is because the design criteria needed to assure that the tube fitting achieves an adequate tube grip usually works against the ability of the single ferrule to also provide an effective seal. the single ferrule has been ‘through hardened’ or ‘case hardened’ so as to be significantly harder than the stainless steel tubing. however. this tube grip performance comes at the expense of having a less effective seal. This range of angles is referred to herein as "shallow" only as a term of convenience in that the angle is rather small. the shallow camming angle is still used today in such single ferrule fittings to obtain a mechanical advantage from the ferrule sliding along the camming surface to produce the "bite" so as to assure an adequate tube grip. tube gripping and sealing are at odds with each other when designing a tube fitting that can meet a desired tube grip and seal performance criteria. a non-conical camming surface has been tried whereby an attempt is made to simply press the ferrule against the outer surface of the tube end. The result in such cases however is a low grip or low-pressure-only fitting that are not well suited to stainless steel fittings. The shallow camming angle and elongated camming surface and axial movement needed to achieve an adequate tube grip with a single ferrule fitting. thereby not creating a bite. The radially outward bowing action causes a larger portion of the outer surface of the front end of the single Nirbhay Gupta 71 .8 TWIN FERRULE FLARELESS COMP RESSION TYPE TUBE FITTING It is becoming increasingly recognized that the two primary functions of a tube fitting viz. single ferrule stainless steel tube fittings have historically used a rather shallow camming angle of between 10o and 20o. compromises the ability of the single ferrule to achieve the seal function. although single ferrule fittings can achieve adequate tube grip in some cases. This is because the front end of the single ferrule attempts to make the seal against the axially elongated camming surface. In some single ferrule designs. Another example is the EO fitting line available from Ermeto GmbH that uses a through hardened single ferrule and a twelve degree camming angle. ) One result of this situation is that some single ferrule tube fittings have been designed with additional components and techniques to achieve an adequate seal. requires considerable design. This is particularly a metal to metal seal issue (as contrasted to non-metal to non-metal seals: for example. The abutment has an angle which the tube is forced into when the rings bite and drive the tube forward. 8. The result necessarily is a larger seal surface area between the outer surface of the single ferrule and the camming surface.1 Ferrule and its purpose The ferrule. metallurgy. Each ring bites in to the tube giving two separate sealing areas. to function properly. Nirbhay Gupta 72 . appears rather simple. Therefore. A further sealing point occurs at the bottom of the tube abutment. only the gripping edge of the ferrule is hardened while the rest has different. This enlarged seal area causes an unwanted distribution of the sealing force between the single ferrule and the camming surface. Less than optimum seal performance is particularly noted in single ferrule fittings that attempt to seal against gas. 13. it may not deform properly. in a plastic fitting it is usually desirable to provide an enlarged seal contact area because the more highly ductile plastic material can better form a seal between the two surfaces. tightly controlled mechanical properties. however. Also.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 ferrule to come into contact with the camming surface against which it is being driven. even in such lower pressure applications single ferrule seal performance remains less than desired. And finally. Its front edge must be harder than the tubing to grip and seal through surface scratches and defects. the hardening process must not compromise stainless steel's corrosion resistance. Not all products on the market meet these stringent requirements. The double ferrule fitting has the ability to lock onto the tube with a 'double bite' feature. For instance. and production expertise. and especially high pressure gas. Therefore. Yet it is highly engineered and. Single ferrule tube fittings thus are usually more suited to lower pressure liquid applications such as hydraulics. perhaps the most-critical component in compression fittings. the ferrule must precisely deform elastically and plastically during fitting assembly to properly grip and seal the tubing. but if the entire ferrule is too hard. and also creates a larger area for surface imperfections to allow leaks to occur. the mechanical properties of the tube are maintained. This style of fitting does so without transmitting torque or twisting the tube ensuring that the tube does not become 'stressed'. boosting safety. They also simplify assembly and maintenance. hardness and thickness of the tube wall in order to provide leak-proof connections in a large number of applications. and a mechanical or hydraulic tool compress es and deforms the fitting. 13. Swaging is a forging process.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 production processes must consistently turn out defect-free ferrules that hold tight tolerances and maintain metallurgical specifications. These tube fittings consist of four precision-machined components: body. Back and front ferrules are designed to provide leak resistant. 8. allowing fittings to be installed in seconds by simply tightening a nut. Ferrules provide a reliable. Pipe flaring machines are another example.2 Swaging Swaging is a metal-forming technique in which the dimensions of an item are altered using a die or dies. the parts loo sel y fit together. front ferrules. back ferrules. howe ver it can b e done hot. They also reduce the number of potential leak paths in the connection.000 PSI / 1. reliability and integrity. and nut.034bar. into which the item is forced. usuall y performed cold. secure and tight connections for operations at high pressures. They eliminate the time-consuming 'coning and threading' that usually needs to be performed when applying traditional high-pressure flared fittings. creating a permanent joint. These fittings provide a tight pressure seal and have a long thread area for improved resistance to pressure and load on ferrules. Long support area of back ferrules improves resistance to vibration and line loads. leak-proof connection in instrumentation and process tubing systems. Nirbhay Gupta 73 . Ferrules make up for the variation in the tubing material. Ferrules can generally handle pressures up to 15. T he most common use of swaging is to attach fittings to pipes or cables ( also calle d wire rope s). and create the primary tubing seal. Thus the relatively "softer" front ferrule achieves an excellent seal. This is because the front ferrule does not need to slide excessively on the camming surface in order to achieve a tube grip function. A swaged piece is created by placing the tube inside a die that applies compressive force by hammering radially. In a two-ferrule tube fitting design. The ostensible angle of this camming surface is forty-five degrees. Flared piece of pipes are sometimes known as "swage nipples. The front end of the back ferrule cams against a frusto-conical camming surface formed in the back end of the front ferrule.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Swaging is a process that is used to reduce or increase the diameter of tubes. Function of a Back Ferrule The back ferrule achieves the tube grip function in the two ferrule tube fitting. Although the effective camming angle for the back ferrule is shallow. but due to the sliding movement of the front ferrule. the inner tube diameter can be a different shape.3 Operation of a twin ferrule tube fitting Function of Front ferrule In the two ferrule fitting. the front ferrule is not case hardened because the primary purpose of the front ferrule is to seal and is not to bite into the tube end. the back ferrule moves the front ferrule forward to spring load the fitting assembly. and the back or rear ferrule provides an excellent tube grip. and the outer is still circular. the back ferrule is not required to provide a primary seal (although it can form secondary or backup seals). for example a hexagon. even though the body conical camming surface presents a camming angle of about twenty degrees.8. burnish and seal with the fitting body. the tube grip and seal functions also are separately achieved by the use of two ferrules. through the swage process. The front ferrule achieves an excellent seal by camming against a shallow camming surface angle such as twenty degrees. particularly against gas. The back ferrule also does not exhibit the undesired bowing action but rather grips Nirbhay Gupta 74 . Thus." "pipe swages. The forward or front ferrule provides an excellent seal even against gas. 13. the effective camming angle is actually a shallow angle of about fifteen to twenty degrees. Likewise." "swedge nipples." or "reducing nipples". The back ferrule is case hardened to be substantially harder than the tube end. Swaging can be further expanded by placing a mandrel inside the tube and applying radial compressive forces on the outer diameter. Tube fittings depend on a balance of factors to ensure proper installation and performance. 2. Complete surface hardening of the back ferrule: The use of complete surface hardening on a conventional back ferrule can have several drawbacks. the back ferrule’s leading edge must be sufficiently harder than the tube. this softer center section acts as a hinge point when force is applied to the flange. Instead. the two ferrule tube fitting achieves tremendous tube grip and seal functions. This condition can potentially damage the tubing and fitting body and compromise the front ferrule action required for consistent gas-tight remakes. Thus. the effective shallow camming angle not only does not compromise the fitting seal capability. First. This hinging mechanism helps limit the amount of torque required by the installer. In manufacturing back ferrules selectively hardening the nose of the back ferrule is done. more torque typically is required. it must be wedged into position using installer torque. To swage and grip the tube properly. the term "hinging" refers to a controlled deformation of the ferrule such that a central region or mid-portion of the ferrule body undergoes an inwardly radial compression. Two methods of producing this differential hardness may be employed— 1. conventional back ferrule is unable to flex or “hinge” downward to improve swaging action on the tube. As used herein. The improved engineered hinging action of the back ferrule (Figure 4. Selectively hardened back ferrule: Use of a selectively hardened back ferrule. The back ferrule also swages the tube to provide the grip needed to keep the fitting and tubing firmly in place. and as a result. By using separate ferrules for each to achiev e primaril y only one of the key tube fitting functions. because it is not engineered to hinge and absorb installer torque on remakes.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 the tube end as a function of a radially inward hinging action. it typically increases installation torque because a surface-hardened. yet the center section and rear flange are left softer. as distinctly contrasted to a bowing or radially outward displacement. a conventional surface-hardened back ferrule can tend to overdrive the front ferrule when remade. Second. Swagelok reduced installation torque while providing the swaging and gripping action needed to perform in combination with a wide variation of commercial grade tubing. it actually substantially enhances the overall performance of the tube fitting especially for stainless steel tubing. During make-up. yet delivers the right amount of swaging action through the nose of the back ferrule. next page) provides several benefits: Nirbhay Gupta 75 . TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 It advances and seals the front ferrule predictably and accurately. it reduces the potential for improper installation and leakage in cases where the fitting is less than properly tightened. titanium and aluminum. to name some add itional examples. Fi gure 13-4: 316 SS A dvanc ed S wage lo k Tube Fi t ti ng Pri o r to Make -up The elements of the fitting are depicted in cross-section prior to make-up: the fitting nut (top). For example. An important aspect of the cho ice of material s is that the ferrule preferably should be cas e or through hardened to a ratio of at least about 3.3 and preferably 4 or more times harder than the hardest tubing material that the fitting will be used with. and the fitting body (right). Nirbhay Gupta 76 . such as magnesium. Its proprietary metallurgy and hinging action can absorb excess torque inputs to help prevent overdriving of the front ferrule. It flexes to maintain installation torque at a predictable and manageable level. Therefore. the front ferrule (center). It smoothly and efficiently delivers more swaging energy earlier in the pull-up process. even on hard materials. the ferrule need not be made of the same material as the tubing itself. the advanced geometry back ferrule (left). The tube wall section is shown belo w the ferrules and body. the ferrule may b e s elected from the stainless stee l material s or other suitab le materi als that can be case hardened. thus ensuring more predictable gas-tight sealing during remakes. As a result. The back ferrule geo metry allo ws for an improved engineering hinging action that translates axial (forward) mo tion into radial swaging ac tion on the tube. preventing the exposed vibration stress riser that is typical of bitetype fittings. the front ferrule (center) is driven into the body of the fitting (right) and the tube (botto m) to create primary seals (tube and body). The improved radial colleting ac tion of the back ferrule (the area to the left of the swage point) isolates and pro tects the swaged area of the tube. Nirbhay Gupta 77 . yet operates with a low input force (torque) requirement. A distinct advantage of the contoured back ferrule is that pull up forces between the nut drive surface and the contoured face of the Back ferrule are more uniformly distributed across the surface of the back ferrule. This further reduction of force concentrations on the drive nut reduces pull up torque and reduces galling. thus reducing and substantially eliminating force concentrations. thus facilitating re-make of the fitting.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Fi gure 13-5: 316 SS A dvanc ed S wage lo k Tube Fi t ti ng A fter Make -up During make-up. while the bac k ferrule (left) hinges inward to create a strong grip on the tube. Nirbhay Gupta 78 . Swaging considerations For swaging over thickness may lead to unreliable joint and in very thin tube it may lead to distortion of tube leading to leakage. reducing the chance of coining out surface defects. optimal thickness should be selected when use of compression type of tube fittings is envisaged. The tube should generally have a hardness of no more than 80 on the Rockwell 'B' scale. allowing the ferrules to coin out minor surface imperfections.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 13. This is subject to certain constraints on the wall thickness of the tube. A heavy wall tube resists ferrule action more than a thin wall tube.8. If the wall is too heavy the rings will not bite. the tube will collapse rather than allow the rings to bite fully. Tube thickness is decided by following factors a. A thin wall tube offers less resistance to ferrule action during installation.4 Effect of Tube thickness on Swagi ng The strength of the fitting is such that the tube contained will burst before the fitting shows any sign of a leak or movement. Thus considering all the above factors. Corrosion/Threading allowance c. Within the applicable suggested allowable working pressure table. select a tube wall thickness whose working pressure is outside of the shaded areas. When the tube wall is too thin. such as scratches. Pressure rating b. Reference to the manufacturers' product information should be made in all instances. thes e c alcu latio ns of f er a cons erv ativ e es tim ate of the tube’ s pres s ure -cont ain ing ability .TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Advanced Swagelok Fitting The adv a nced S w a gelok tw o -f errul e tu be f itti ng of f ers predict abl e. In addit ion. bu t als o to de liv er grea ter s w agin g actio n thro ugho ut th e pu ll -up proces s . there by ens urin g relia ble op erati on an d gas s eal f or repeat ed rem akes . this f ittin g red uces th e pot ent ial f or im prop er ins tall atio n an d s y s tem leakage . leak f ree co nn ectio n. s tain les s s tee l tu bin g m an uf actur ers do not a lw ay s run t heir proc es s es f or the m in im um requir ed m at erial s tre ngth v al ues ci ted by AS TM and other s ta ndar ds f or determ ini ng t he ru ptur e pres s ure of a tube. th is des ign r edu ces th e pot enti al f or ov erdriv ing t he f ront f errul e. Th e res ul t is s tronger. s uc h as Lam e’ s f orm ula f or determ ini ng m inim um ru ptur e pres s ure of a tu be . Nirbhay Gupta 79 . d es pit e their i ncre as ed s trengt h an d adv anc ed m ech anic al prop erti es . E nhanced Gas Seal : The b ack f errul e h ing e d eliv ers s teady f orce to s eal t he f ront f err ule c ons is ten tly on a w ide ran ge of tu bin g. l eak f ree perf orm ance up to t he b urs t pres s ure of ANS I 316 and 304 s tai nles s s teel tu bin g. us e th e m inim um al low abl e ult im ate t ens il e s treng th. Appl i cabi li ty to New Al l oys: The adv an ced S w ag elok f ittin g dem ons trat es it is practic al to dev el op an eas y -to ins tall. s uch as s uper d upl ex s teel. How ev er . A s um m ary of its benef its includ e: Wi der Targ et for Pr oper Ins tal l ati on: The e ngi ne ered hi ngi ng actio n of t he back f errul e d eliv ers en ergy to not only s eal t he f ront f errul e. I n ad ditio n. This coll etin g prote cts the s w aged ar ea of the tub e m ore ef f ectiv ely f rom s y s tem v ibration and f atig ue . Greate r Marg i n of Performan ce on C omme rci al Tubi ng : Textbook calc ula tions . hig h. Vi brati on Fati g ue R esi s tance: T he e ngi ne ered back f errul e h ing ing act ion de liv ers a m or e co ns is tent radial col let ing ac tion to giv e im prov e d s upport to th e tub e beh ind t he poi nt of grip.perf orm anc e tu be f itti ng t hat c an b e bu ilt us i ng a dv ance d all oy s . w hat ev ery ins tall er w il l no tic e is a m ore cons is te nt f e el. As a r es ult. av ailab le t ubi ng m at erials . h arder t ubi ng w ith b urs t pres s ures of ten s ign if ican tl y high er tha n w hat occurs und er leas t c as e cond itio ns . t he adv anc ed S w ag elok f ittin g us es th e s am e ins tall atio n ins p ectio n ga uges as bef ore . C ompati bi l i ty wi th Ori g i nal Desi g n Swag el ok Tube Fi tti ng s: Th e adv an ced S w ag elok f itti ng p ulls up us ing th e s am e one-an d-one-q uart er .turn proc ed ure as the origi nal d es ign S w age lok tube f itti ng. The adv a nce d S w agelok t ube f itti ng is robus t e noug h to grip a nd e xc eed the b urs t pres s ure of th es e s trong er. t he unif orm s urf ace -har de ned des ign of the ba ck f er rule of f ers high corros ion res is tanc e. In r eali ty . ev e n in cas es w here the f itti ng w as les s than prop erly tighte ne d. an d m axim um al low abl e out er diam eter f or tub e burs t c alcu latio ns —as they s hould. How ev er. f rom a m ore c ons is ten t ra nge of torq ue on ev ery pull-u p to an ev e n m ore cons is tent . B eca us e th e adv a nce d back f err ule c an hin ge a nd a bs orb m ore e nergy th an a conv ent iona l hard en ed b ack f errul e. m inim um allow abl e w all t hick nes s .  Never turn the fitting body.  Additional tubing considerations: Always use an insert with extremely soft or pliable plastic tubing.. In NPCIL a Nickel compound based sealant is used (Never Siege compound) to avoid galling  Do not mix materials or fitting components from various manufacturers— tubing. hold the fitting body and turn the nut.  Avoid unnecessary disassembly of unused fittings.  Use the gap inspection gauge to ensure sufficient pull-up upon initial installation. is noted for its lubrication and anti-seizing properties.5 Safety precautions for tube fitting installation Following safety precautions should be taken while installing the tube fitting1  Do not bleed the system by loosening the fitting nut or fitting plug. Wall thickness should always be checked against the fitting manufacturer’s suggested minimum and maximum wall thickness limitations. 8.  LUBRICATION Stainless-steel parts that rub together under high pressure have a strong tendency to cold weld and seize. The result is low assembly torque and consistent performance.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 13. Solid molybdenum disulfide readily adheres to surfaces. leak-free tubing connections. Instead.  Make sure that the tubing rests firmly on the shoulder of the tube fitting body before tightening the nut. Nirbhay Gupta 80 . which exacerbate seizing. ferrules. and the solid does not squeeze out like liquid or soft. waxy lubricants under extreme pressure. To prevent seizing and ensure only linear ferrule movement. even with repeated remakes.  Do not make up and tighten fittings when the system is pressurized. ferrules must only slide forward during assembly and not rotate with the nut. All mating surfaces must be smooth and free of defects. nuts. And to form high-integrity. A bonded molybdenum-disulfide coating is the recommended lubricant for many compression fittings.  Always use proper thread sealants on tapered pipe threads. surface conditions and lubrication at the nut/ferrule and nut/body interfaces should be precisely controlled.  Never allow problems to go unreported. and fitting bodies. etc. Tubing that is oval and will not easily fit through fitting nuts. or other surface defect will be difficult to seal. particularly in gas service. As tube outside diameter (OD) increases. Nirbhay Gupta 81 . The following table indicates the minimum straight length required. The most successful connection for gas service will occur if all installation instructions are carefully followed and the heavier wall thicknesses of tubing on the tables-1-3 to 1-10 are selected. so does th e likelihood of a scratch or other surface defect interfering with proper sealing. raised portion. helium. Some surface defects on the tubing can provide such a leak path. there must be a sufficient straight length of tubing to allow the tube to be Bottomed in the fitting (see figure-13-7). nitrogen. hydrogen. Figure 13-7: Tube fitting at a bend Special precautions for Gas Service Gases (air.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Surface finish is very important to proper sealing. and bodies should never be forced into the fitting. When installing fittings near tube bends. Tubing with any kind of depression. ferrules. scratch.) have very small molecules that can escape through even the most minute leak path. 9 Repeated assembly and Disassembly of tube fitting Figure-13-8: Tube fitting in assembled condition Repeated assembly and disassembly of the tube fitting causes the reduction in the distance between the two ferrules. Therefore it is necessary to keep this gap under check and whenever this gap is found to be very little the new tube fitting and swaging should be used. Nirbhay Gupta 82 . The figure:13-8 shows this type of action. As the distance between the two ferrules reduces over a period of time the back ferrule’s spring action diminishes and a time comes when both the ferrules touch each other and the leak tightness provided by this assembly is no longer assured.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 13. 2. twin ferrule : SS-316 as per ASTMA-A-314 .2. duration = 10 min.1.2 Routine Tests 8. hardness) : Required.26. 1. 2 and 2.1 8.5 g.3 8. Pressure Maximum Temperature Overall Dimensions Hardness 8. nut and ferrules should be tested for physical properties (i.1.1.10 SPECIFICATIONS FOR SS TUBE FITTI NGS 1 2 Type Material / type : Flareless compression. Before and after the test the fitting assembly should be tested and should qualify all the other tests.4 Pneumatic leak 8.1 : > Rockwell B-90 : Incoming material as per ASTM-A-314 : On each size of ferrule as per ASTM-A-3145 : Raw material for body.2.2.75 Hz Peak acceleration should be 3.2 Nirbhay Gupta : As per ANSI-B-1.5 Hz should preferably be between 1g and 3.3 Overall Dimension Thread Check for End Connections Hydrostatic test 8. % elongation. Frequency should be increased in step of 1/3 octave in the specified frequency range 1-33 Hz.forged 3 4 5 : water / steam/lube oil : 200 kg/cm2 (g) : 320 °C 7 Fluid Max. 83 .1 Chemical Composition test Ferrule Hardness Test Test on Raw Material 6 8. : Required to be done on 1% items of each type : : At pressure of 300 kg/cm2 (g). For and beyond 3. Test duration should be 30 seconds at each frequency.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 13.2 8.0 Tests 8.1 Type Test 8.4 Seismic Test 8. Peak acceleration at frequencies 1.e.20. 1. tensile strength. duration = 10 min. Vibration should be in the frequency range from 1-33 Hz.5g or capability of shake table.59.1. Required to be done on 10% items of each type : At a pressure of 4 kg/cm2 (g). TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 8.2.). Standard specification for stainless steels forgings Hydraulic tube fittings ASTM-A-269 ISOR-206 Nirbhay Gupta 84 .20.5 test Reassembly Test 9.1 ANSI-B.1 2008 (required to be done on 10% items of each type.0 Applicable codes & standards: ASME Boiler and Pressure vessel code ANSI-B-1. 2 nos. Sub section NB for Class I components.1 ANSI-B-1. Unified inch screw threads (UN AND UNR thread form) equivalent for tube end Pipe threads. Division I. Standard specification for stainless steels bars &shapes. from each lot.2 ASTM-A-213 ASTM-A-262 ASTM-A-276 ASTM-A-314 ASTM-A-473 SAE – J -514 ANSI-B-31.) : Required to be done 25 times on 1% items (min.20. As per section III. Standard specification for stainless steels billets and bars for forging. general purpose Standard specification for seamless ferritic & austenitic alloy steel boiler super heater and Heat exchanger tubes Standard practice for detecting susceptibility to inter granular attack in austenitic stainless Steels.1. . : Required to be done on 1% items of each type : Required to be done on 1% items of each type : At a pressure of 60 kg/cm2 (g).26. duration = 10 min.3 Overall Dimension Thread Check for End Connections Hydrostatic test 8. Peak acceleration at frequencies 1.5g or capability of shake table.e.11 SPECIFICATIONS FOR BRASS TUBE FITTINGS 1 2 Type Material / type : Flareless compression.2.1 Chemical Composition test Ferrule Hardness Test Test on Raw Material 6 8.5 Hz should preferably be between 1g and 3.0 Tests 8. required to be done on 10% items of each type : At a pressure of 4 kg/cm2 (g).4 Pneumatic leak 8.2. Pressure Maximum Temperature Overall Dimensions Hardness 8.1. Vibration should be in the frequency range from 1-33 Hz.1 Type Test 8. Before and after the test the fitting assembly should be tested and should qualify all the other tests.2 Routine Tests 8.2.2 8. Test duration should be 30 seconds at each frequency.1.20.1 8.75 Hz Peak acceleration should be 3. % elongation.2 Nirbhay Gupta : As per ANSI-B-1. nut and ferrules should be tested for physical properties (i. tensile strength. 85 .2. 1. 2 and 2. Frequency should be increased in step of 1/3 octave in the specified frequency range 1-33 Hz.3 8. 1. hardness) : Required.4 Seismic Test 8.59.1.5 g.1 : > Rockwell B-90 : Incoming Material as per ASTM-E-54/478 : On each size of Ferrule as per ASTM-B-124 : Raw material for body.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 13. twin ferrule : Brass as Per ASTM-B-124 / Forged 3 4 5 : Air : 40 kg/cm2 (g) @ ambient temperature : 320 °C 7 Fluid Max.1. For and beyond 3. duration = 10 min. This test should be performed on limited samples taken from the lot.2 SAE J 514 2008 (required to be done on 10% items of each type.0 Applicable codes & standards: ASTM-B-124 ANSI-B-1.20. Nirbhay Gupta 86 ..1.1 ANSI-B-1. IS 4218 Indian standard for Metric Straight Pipe Threads Notes: 1. 2 nos. Needs the above seismic test is required on 1% of each type of fitting. pneumatic test) Copper and copper alloy forging rod bar and shapes Unified inch screw threads (UN AND UNR thread form) equivalent for tube end Pipe threads. Pipe threads should be NPT threads as per ANSI-B-1.) : Required to be done on 1% items (min.1 2. general purpose Hydraulic Tube fittings ASTM-B-16 Free cutting brass rod.20. from each lot.20.1 ANSI-B.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 8.5 test Reassembly Test 9. six times after sixth. bar and shapes for use in screw machine.2. NPT has a tapered male and female thread which seals with Teflon tape or jointing compound. Sir Joseph Whitworth devised a uniform threading system in 1841 to address the incompatibility problem. Type of Threads Pipe threads used in hydraulic circuits can be divided into two types: I.0 2008 THREADS USED FOR TUBE FITTINGS Different types of screw threads have evolved for fastening. Jointing threads – are pipe threads for joints made pressure tight by sealing on the threads and are taper external and parallel or taper internal threads. His 60 degree thread angle. and hydraulic systems. As a result.1. Of special concern are plastic-to-metal. The Whitworth thread is now used internationally as a standard thread for jointing low carbon steel pipes. This became known as the British Standard Pipe thread (BSP Taper or BSP Parallel thread). taper/parallel threaded joints in hydraulic circuits. or NPT Thread. The sealing effect is improved by using a jointing compound.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 14. A discussion and recommendations are provided to create an awareness of diff erent types of threads and how they are used. The Whitworth thread form is based on a 55 degree thread angle with rounded roots and crests. in common use by early American clockmakers. and screws which became the National Pipe Tapered (NPT) Thread in 1864. 14. Evolution of threads In the nineteenth century. many different types of screw threads were required for hydraulic and pneumatic circuits as well as fastening components. These thread forms later became the American National Standard. The best known and most widely used connection where the pipe thread provides both the mechanical joint and the hydraulic seal is the American National Pipe Tapered Thread. enabled the American Industrial Revolution. bolts. manufacturers started to devise their own fastening systems. In America. which was made self sealing by cutting at least one of the threads on a taper. William Sellers set the standard for nuts. The Whitworth thread form was selected as a connecting thread for pipes. 14. The English mechanical engineer and inventor.2. Nirbhay Gupta 87 . This resulted in compatibility problems. The bottoms of the threads aren't on a cylinder. For example.1 and SAE J476 standards. instead of these distances. type of sealants used. Both threads are parallel and sealing is affected by compression of a soft material onto the external thread. For workers. This is accomplished by the tapered thread form of the male matching the thread form of the female tapered thread and the use of pipe sealant to fill any voids between the two threads which could cause a spiral leak. the p ipe has a left hand thread. “1/2 – 14 NPT” identifies a pipe thread with a nominal inside diameter of 1/2 inch and 14 threads to the inch. they taper. this is the length of the thread which makes the seal on a conventional machined pipe thread. If “LH” is added. The most common global pipe thread forms are: NPT NPSC NPTR NPSM NPSL NPTF BSPP BSPT American Standard Pipe Taper Thread American Standard Straight Coupling Pipe Thread American Standard Taper Railing Pipe Thread American Standard Straight Mechanical Pipe Thread American Standard Straight Locknut Pipe Thread American Standard Pipe Thread Tapered (Dryseal) British Standard Pipe Thread Parallel British Standard Pipe Thread Tapered Plastic injection molded thread forms are manufactured to ANSI B2.3.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS II. and Nirbhay Gupta 88 . Many pipe threads must make not only a mechanical joint but also a leak proof hydraulic seal. made according to the NPT standard. or a flat gasket. it is more convenient to know how many turns to make by hand and how many with a wrench. Because of the taper. 2008 Fastening threads – are pipe threads where pressure tight joints are not made on the threads. A simple rule of thumb for installing tapered pipe threads. both metal and plastic. Sizes Pipe thread sizes are based on an inside diameter (ID) or flow size. It also specifies another distance – the effective thread. but a cone. but due to the variations involved in pipe joints such as dissimilar materials of male and female threads. 14. the distance the pipe thread can be screwed in by hand. is finger tight plus one to two turns with a wrench. which is the same as 3/4 inch in a foot. Torque installation values can be determined as per application. The taper is 1⁄16 inch in an inch. The standard specifies this distance as the length of hand tight engagement. a pipe thread can only screw into a fitting a certain distance before it jams. The word “tapered” in several of the above names points to the big difference between many pipe threads and those on bolts and screws. Nominal size 1/8 1⁄4 3/8 1/2 3/4 1 Table-XVI-American Standard Taper Pipe External Thread Actual Threads Length of engagement Length of OD per inch (tightened by hand) effective thread 0. A pressure tight joint is achieved by the compression in the threads resulting from tightening. Taper/Parallel Threaded Joints Despite the standards created to maintain uniform fittings.4 turns 0.546 1.327 11.248 ≈ 3.124 ≈ 3.534 1.6 turns 0.172 ≈ 3.313 ≈ 3. material from both the male and female threads deform into each other.546 18 0.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 internal variations in product wall thickness.060 14 0. This table shows the distances and number of turns called for in the standard.7 turns 0.260 0. and in pract ice threads are often routinely cut shorter than the standard specifies.1 turns 0. All dimensions are in inches.3 turns 0. The area where the crest and the root of the thread meet can form a spiral leak path no amount of tightening will eliminate.408 0. A tolerance of plus or minus one turn is allowed.407 27 0.4. tapered pipe threads are inexact and during the course of use and repair the threads can become damaged and susceptible to leakage. Variations between injection molded plastic and machined metal thread forms can occur due to different manufacturing processes. This ensures full thread contact which minimizes spiral leakages.682 14. a standard torque specificatio n cannot be generically applied.267 ≈ 3.681 18 0. This compression and sealing occurs in the first few turns of the internal thread.184 ≈ 3. As wrenching takes place. Nirbhay Gupta 89 .401 0.3 turns 0.5 0.850 14 0. Liquid Teflon based sealants are also used successfully to ensure a pressure tight seal. Variation in crests and roots may cause a mismatch in the thread and create a spiral leak. the use of a Teflon based sealant is recommended on all plastic pipe threads. See figure -141. A number of variations of the NPT thread have been introduced to overcome the problem of spiral leakage and are known as Dryseal threads (See SAE standard J476). For this reason. With the use of thermoplastics and plastic injection molding in the manufacture of plastic pipe thread forms. Using both tapered male and female BSPT threads would offer a better chance of sealing since you are now matching the taper of the male and female thread. You can see the crest of both the male and female thread flanks meet. there are controls on the crests and roots of both the male and the female threads to ensure the crest crushes or displaces material into the root of the mating thread. With this thread design. a pressure tight joint would be easier to accomplish.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Pipe threads were originally designed as machined thread forms. It is always important to use care when applying sealants to avoid introducing the sealant material into the system flow path. but with thread sealant. Nirbhay Gupta 90 . Crest and root control is still missing. When a BSP tapered male thread is tightened into a straight female thread (BSPP) the seal can only be made at the base of the female port with 1 or 2 threads. The most common form of sealant is Teflon tape wrapped 2 to 3 turns around the male thread before assembly. Thread sealant is required to seal this combination. See figure-14-2. Figure 14-3 shows an NPTF male tightened into an NPTF female hand tight. Sealing is compromised by the lack of thread form control in BSP specifications. The best known is the NPTF (F for Fuel). The following sections show examples of how different threads are used and issues that can arise in attempting to create a leak free connection. This offers more threads a chance of sealing against spiral leakage. mold shrinkage and plastic sink make it difficult to insure leak free joints. seals against spiral leakage. The interference fit between the crest of one thread and the root of the other along with the thread flanks matching. It is used for internal threads and a NPTF external thread can be screwed into it to provide a satisfactory mechanical connection and a hydraulic seal. The combination of a parallel and tapered is not regarded as ideal but is widely used.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Figure 14-4 shows the NPTF male and female threads tightened approximately 1 turn past hand tight. and 3/8” sizes have a dissimilar pitch. Although these threads are considered Dryseal. NPT has a 60° thread where the BSP has a 55° thread. A variation of the Dryseal thread is the NPSF (National Pipe Straight Fuel). BSP thread is commonly used for low pressure plumbing. Nirbhay Gupta 91 . Because of the smaller size of the BSPP and the pitch difference. they both have 14 threads per inch. covered by British Standard 21. Figure 14-5 shows a male NPT tightened into a BSPP. High quality plastic quick disconnect couplings typically use NPT threads. and you can see the flanks meet and the crests are displaced into the roots. The 1/16”. Problems arise when threading a NPT male thread form into a BSP female straight thread form. but is not recommended for medium and high pressure hydraulic systems. However. or BSP. The Teflon works as a lubricant to avoid galling of the material when tightening the two threads together and also fills any voids that may cause leakage. the NPT tightens with only a few turns. a Teflon tape or liquid is still recommended to aid in the assembly process. 1/8”. This form uses the Whitworth thread with an angle of 55°and a 1 in 16 taper. The flank angles of the threads are also different between NPT and BSP. which causes a misalignment of the threads. Another tapered thread is the British Standard Pipe taper. It is not interchangeable with the American NPT thread. 1/4”. though at the 1/2" and 3/4" size. in Nuclear power plants Teflon is not used since its properties deteriorate very fast under radiation conditions. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Figure 14-6 shows an NPT tightened into a BSPT. The NPT thread to engage further, but pitch difference eventually causes a binding of the threads. Pitch and thread angle differences will allow spiral leakage. The 1/2” and 3/4” sizes in the NPT and BSP are all 14 threads per inch, and the NPT will engage the BSP fairly well. Although these threads are the same pitch and engage well there are still issues with the tread form. The thread angles and the crest and root tolerances being different will allow spiral leakage as shown in figure 14-6. These threads might be used effectively together if an appropriate thread sealant is incorporated. Many issues arise when plastic quick disconnect couplings, with their corresponding injection plumbed into metal piped hydraulic systems. Leaks and plastic thread form failures may occur if care is not taken. When investigating a metal to plastic pipe joint failure, two factors viz. chemical attack and over tightening, need to be considered. Chemical attack can occur when improper thread sealants are used. Thread sealing is an attempt to block the spiral leak path which occurs when the crests and roots of the thread forms do not match. Anaerobic thread sealants should be avoided when sealing plastic thread forms. These sealants contain chemicals which may attack plastics. Use of a Teflonbased pipe thread sealant is a better choice for plastic threads. Over tightening of any plastic pipe thread will have adverse affects on the function of the joint. The major difference between plastics and metals is the behavior of polymers. Injection-molded plastic parts continue to deform if they are held under a constant load e.g. creep. Creep is the continued extension or deformation of a plastic part under continuous load. Typically the plastic material in an injection-molded plastic pipe thread form will creep from being over tightened into a female tapered port. The deformation of the part’s internal features can lead to part failure. Nirbhay Gupta 92 TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 14.5. Dry Seal NPTF Threads Dryseal pipe threads are based on the USA (American) pipe thread; however, they differ from the USA (American) pipe thread in that they are designed to seal pressure tight joints without the necessity of using sealing compounds. To accomplish this some modification of thread form and greater accuracy in manufacture is required. The roots of both external and internal threads are truncated slightly more than the crest, i.e. roots have wider flats than the crests, so that metal to metal contact occurs as the crests and the roots coincident with or prior to flank contact, see figure -14-7. Thus as the threads are assembled wrenching, the roots of the threads crush the sharper +crests of the mating threads .This sealing action at both the major and minor diameters tends to prevent spiral leakage and pressure tight without the necessity of using sealing compounds, provided that the mating threads are in accordance with standard specification and tolerance and are damaged by galling in the assembly. The control of crest and root truncation is simplified by the use of properly designed threading tools. Also it is desirable that both for the length. However, where not functionally objectionable, the use of a compatible lubricant or sealant may be used to minimize the possibility of galling. This is desirable in assembling dryseal pipe threads in refrigeration and other systems to affect a pressure tight seal. In order to obtain a pressure tight seal using dryseal pipe threads without a sealer, it is necessary to hold crest and truncation of both internal and e xternal threads within the limits specified. Unless this is done by use of threading tools with the crest and root truncation controlled so assure reproduction on the product of threads, it is necessary to use a system of measuring or a system of gauging and measuring to determine conformance. There are two classes of Dryseal pipe threads viz. Class-I and Class-II Dryseal pipe threads. The classes differ only in inspection requirements. For class -I threads, inspection of roots and crest is not required while for class-Ii threads these inspections are required. External Dryseal threads are tapered only while internal Dryseal threads may be either straight or tapered. Also, the thread lengths may be either standard or short depending on the requirement of the application. Short threads are obtained by shortening the length of the standard thread by one pitch. Nirbhay Gupta 93 TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 The minimum material condition as shown at the left is established by having the mating crests and roots of equal truncation so as to assure metal to metal contact at these points coincident with flank contact. The condition is established at the sharpest root and the flattest crest and gives no clearance. Tolerances at the crests and the roots are established in the direction of interference only, therefore the maximum material condition shown at the right is established by having the extreme combination of sharpest crests and flattest roots, which provide the maximum interference. When threaded joints are made wrench tight, it is intended that the flanks and crests and roots shall be in contact. Nirbhay Gupta 94 TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Figure14-8-: Basic dimensions of NPTF threads Nirbhay Gupta 95 . the use of a backing gas is mandatory. This lowers the dissolved chromium content in these areas and thus lowers their corrosion resistance. The “L” series (extra low carbon) stainless steels are often used for this purpose. It should be noted that in welding the relatively small fitting sizes. it is recommended that backing gas be used. Weld fittings are made from a select 316 series with carbon content in the low range of 0.1 300 Series Stainless Steels May be welded by the TIG. Carbide Precipitation When un-stabilized stainless steels are heated to 800° . 15. As scale formation remains a problem.07 percent. All weld fittings in stainless steel are supplied in the solutiontreated condition. stick and oxyacetylene methods. the chromium in the steel combines with the carbon to form chrome carbides which tend to form along the grain boundaries of the metal (carbide precipitation). In all cases where stick welding is used.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 15. MIG. making them vulnerable to intergranular corrosion. Nirbhay Gupta 96 . but their use reduces system design stress by approximately 15%. MIG. filler deposition rate economies are not a factor and therefore the MIG method is not commonly applied. Stick arc welding is not recommended in many cases because of the likelihood of excessive burn-through and improper root penetration. the use of a backing gas is still recommended. This results in a welded fitting with good corrosion resistance and a high strength factor.0 Welding Methods 15. This limits the amount of carbon available to combine with the chromium. MIG welding gives the same characteristics as stick electrode welding with faster deposition of the filler material.2 C1018 Steel Fittings May be welded by the TIG. TIG welding is recommended as being best for welding Weld fitting systems because it allows better operator control of heat penetration and filler material deposition. As this process runs “hotter” than the stick process. Carbide precipitation is reduced by holding the carbon content of the material to a very low value. or stick arc-weld process.04 to 0. capable of passing ASTM-A-262 Tests for Detecting Susceptibility to Intergranular Corrosion.1500° F during welding. So nowadays. Stainless steels like 304. It is considered more difficult than other arc welding processes because it requires the use of both hands. or a mixture of the two. copper alloys like Nibral bronze and pure copper. People still call it TIG and even Heliarc. But before it was called TIG" it was given the name "Heliarc" because helium was the gas that was used when the process was invented. The arc is very smooth and quiet and clean when DC current is used. The word "Inert" no longer held true so it was decided that a new name was required. The heat the melts the metal and makes the weld puddle comes from the arc that is created between the tungsten electrode and the work piece. All can be welding using the TIG welding process. Nickel alloys like inconel 718 and Hastelloy X. Nirbhay Gupta 97 . Often times a foot pedal amperage control is also used which adds another layer of difficulty. Titanium alloys like commercially pure. it is slightly more noisy but still clean and smooth. and 6al4v. 321. What Metals can be welded using the TIG process? Almost any metal can be welded with TIG.3 TIG WELDING The "TIG" in TIG welding stands for Tungsten Inert Gas. When the TIG welding machine is set on Alternating current. Magnesium alloys like az31b. Sometimes for certain alloys. Carbon and low alloys steels like 1010 carbon steel and 4130 chromoly steel. Cobalt alloys like Stellite 6b and l605. The tungsten electrode is sharpened for applications where the arc needs to be pinpointed and for very low amperage.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 15. The arc is shielded by argon. A TIG torch can be either water cooled or air cooled and is designed to provide shielding gas as well as welding current through a tungsten electrode. 5052. hydrogen is added in small percentages to improve the way the puddle flows. A ceramic nozzle directs the shielding gas to the weld puddle and internal copper parts like the collet and collet body hold the electrode in place. TIG welding is akin to gas welding as far as welding technique in that the torch is held in one hand and the filler rod is manipulated with the other hand. helium. and 17-7ph. But wait. But then someone discovered that argon worked better and so it was called TIG because inert gas could refer to either helium or argon. the technical term for what used to be called ‘TIG’ and ‘Heliarc’ is Gas Tungsten Arc Welding or "GTAW". In fact more people call it TIG welding than Gas Tungsten Arc Welding. then someone else discovered that small additions of hydrogen worked well for some metals. Aluminum alloys like 6061. Orbital welding became practical for many industries in the early 1980's when combination power supply/control systems were developed that operated from 240 VAC and were physically small enough to be carried from place to place on a construction site for multiple in-place welds. The skills of a certified welder are thus built into the welding system. The arc welding current was regulated with a control system thus automating the entire process.4 2008 ORBITAL TUBE WELDING Orbital welding was first used in the 1960's when the aerospace industry recognized the need for a superior joining technique for aerospace hydraulic lines. A mechanism was developed in which the arc from a tungsten electrode was rotated around the tubing weld joint.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 15. Nirbhay Gupta 98 . Modern day orbital welding systems offer computer control where welding parameters for a variety of applications can be stored in memory and called up when needed for a specific application. The result was a more precision and reliable method than the manual welding method it replaced. producing enormous numbers of identical welds and leaving significantly less room for error or defects. Once a weld program has been established an orbital welding system can repeatedly perform the same weld hundreds of times.154 inches (3. An orbital welding system consists of a power supply and an orbital weldhead. Quality. An orbital welding system will drastically outperform manual welders. The quality of a weld created by an orbital welding system with the correct weld program will be superior to that of manual welding. In applications such as semiconductor or pharmaceutical tube welding.4. many times paying for the cost of the orbital equipment in a single job. errors and defects of manual welding.9mm) Larger diameters and wall thickness' can be accommodated with open style weld heads. Consistency. Certified welders are increasingly hard to find. With orbital welding equipment you don't need a certified welding operator. tubes/pipes are clamped in place and an orbital weldhead rotates an electrode and electric arc around the weld joint to make the required weld. inconsistencies.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 15. All it takes is a skilled mechanic with some weld training. Standard enclosed orbital weld heads are practical in welding tube sizes from 1/16 inch (1. the arc welding current.1 Orbital Welding Equipment In the orbital welding process. The power supply provides the control parameters. eliminating the normal variability. Power Supply: The power supply/control system supplies and controls the welding parameters according to the specific weld program created or recalled from memory. consistent welds repeatedly at a speed close to the maximum weld speed offer many benefits to the user: Productivity.4. The ability to make high quality.6mm) to 6 inches (152mm) with wall thickness' of up to . the power to drive the motor in the weld head and switches the shield gas(es) on/off as necessary. 15. Skill level. Nirbhay Gupta 99 . Weld Head: Orbital weld heads are normally of the enclosed type and provide an inert atmosphere chamber that surrounds the weld joint. orbital welding is the only means to reach the weld quality requirements.2 Reasons for Using Orbital Welding Equipment There are many reasons for using orbital welding equipment. For maximum piping system efficiency the tubing must be as smooth as possible. Hydraulic Nirbhay Gupta 100 . 15.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Orbital welding may be used in applications where a tube or pipe to be welded cannot be rotated or where rotation of the part is not practical. The high pressure systems of a single plane can have over 1.500 welded joints.3 Industrial Applications for Orbital Welding Aerospace: As noted earlier. all automatically created with orbital equipment.4. Examples are applications where inspection of the internal weld is not practical for each weld created. Compact orbital weld heads can be clamped in place between rows of heat exchanger tubing where a manual welder would experience severe difficulty making repeatable welds. By making a sample weld coupon that passes certification. the aerospace industry was the first industry to recognize the requirement for orbital welding. that successive welds created by an automatic machine with the same input parameters should also be sound. crack or incomplete weld joint can form a place for the fluid inside the tubing to be trapped and form a bacteria harbor. dairy and beverage industries require consistent full penetration welds on all weld joints. Nuclear Piping/Tubing: The nuclear industry with its severe operating environment and associated specifications for high quality welds has long been an advocate of orbital welding. Weld heads may be used in rows of boiler tubing where it would be difficult for a manual welder to use a welding torch or view the weld joint. Most of these tubing/piping systems have schedules for cleaning and sterilization in place. crevice. Any pit. Orbital welding may be used in applications where access space restrictions limit the physical size of the welding device. Food. Many other reasons exist for the use of orbital equipment over manual welding. Offshore Applications: Sub-sea hydraulic lines use materials whose properties can be altered during the thermal changes that are normal with a weld cycle. Dairy and Beverage Industries: The food. the logic holds that if the sample weld is acceptable. Boiler Tube: Boiler tube installation and repairs offer a perfect application for orbital welding. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 joints welded with orbital equipment offer superior corrosion resistance and mechanical properties. Here the orbital weldhead provides the ability to produce high quality welds in applications with restricted access to the weld joint. tip geometry and surface condition may already be written into a specification covering the specific application. Pharmaceutical Industry: Pharmaceutical process lines and piping systems deliver high quality water to their processes. Sometimes the tubing may be welded in place to a valve or regulator body. the base material to be welded. Each orbital welding equipment supplier differs slightly in recommended welding practices and procedures. Orbital welding ensures full penetration welds with no overheating occurring that could undermine the corrosion resistance of the final weld zone. Where possible. and tungsten electrode material. 15. Semiconductor Industry: The semiconductor industry requires piping/tubing systems with extremely smooth internal surface finish in order to prevent contaminant buildup on the tubing walls or weld joints. This section is intended as a guideline for those applications where no specification exists and the engineer responsible for the welding must create the welding set-up.4 General Guidelines for Orbital Tube Welding For orbital welding in many precision or high purity applications. arc length. and derive the welding parameters in order to arrive at the optimum welding solution. and liquid and gas delivery systems all require tubing with connector fittings. Nirbhay Gupta 101 . rust or other contaminant. Once large enough. Tube/Pipe Fittings. follow the recommendations of your orbital equipment supplier for equipment set-up and use. Orbital systems provide a means to ensure high productivity of welding and improved weld quality. a build up of particulate. the tube diameter(s). Valves and Regulators: Hydraulic lines. shield gas type and purity. especially in areas that pertain to warranty issues. weld joint and part fit -up requirements. moisture or contaminant could release and ruin the batch process.4. This requires high quality welds to ensur e a source of water from the tubes that is uncontaminated by bacteria. Minor changes in amperage may be required to return the weld to its original profile. For co mplex applications a significant amount of testing will be necessary to ensure the long term suitability of the chosen material from a functionality and cost viewpoint.5 The Physics of the GTAW Process The orbital welding process uses the Gas Tungsten Arc Welding process (GTAW) as the source of the electric arc that melts the base material and forms the weld. 15. When a change in heat number is made a test coupon should be made for the new heat.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 15.6 Material Weldability The material selected varies according to the application and environment the tubing must survive. These trace elements can vary the conductivity and melting characteristics slightly for each heat. 400 series stainless steels are often weldable but may require post weld heat treatment. The power supply responds to the demand and provides weld current to keep the arc established. In general. To start the arc. thermal. No additional filler material is used in this process of welding. which reduces the arc voltage to a level where the power supply can then supply current for the arc. an RF or high voltage signal (usually 3. stability. Accommodation must be made for the potential differences of different material heats. the most commonly used 300 series stainless steels have a high degree of weldability with the exception of 303/303SE which contain additives for ease of machining.4. Nirbhay Gupta 102 . In the GTAW process (also referred to as the Tungsten Inert Gas process . The metal to be welded is melted by the intense heat of the arc and fuses together. and corrosion resistance requirements of the application will dictate the material chosen.4.5 to 7 KV) is used to break down (ionize) the insulation properties of the shield gas and make it electrically conductive in order to pass through a tiny amount of current.TIG) an electric arc is established between a Tungsten electrode and the part to be welded. A capacitor dumps current into this electrical path. The chemical composition of each heat batch number will have minor differences in the concentration of alloying and trace elements. The mechanical. Differences in tube diameter or out -of-roundness will cause weld joint mismatch and arc gap v ariations from one welding set up to another.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 It is important that certain elements of the material be held to close tolerances. Minor deviations in elements such as sulfur can vary the fluid flow in the weld pool thus completely changing the weld profile and also causing arc wander. If no specification exists the laws of physics will require that the molten material flow and compensate for tube mismatch and any gap in the weld joint.4. Both the ID and OD should be burr free with no chamfer. Tubing is produced according to tolerances that are rigid or loose according to the application for which the tube was purchased. It is important that the wall thickness is repeatabl e at the weld joint from part to part. Nirbhay Gupta 103 . reinforcement and drop through. weld concavity.7 Weld Joint Fit-Up Weld joint fit-up is dependent on the weld specification requirements on tube straightness. Tube and pipe end prep facing equipment is recommended in order to help ensure end squareness and end flatness. 15. It is possible to weld with gaps of up to 10% (or greater) of wall thickness. two of the main considerations are mismatch and gaps. ultra high purity gas or gas with a local purifier are employed. Nirbhay Gupta 104 . As a general rule use 100% argon gas. the following rules apply: Any gap should be less than 5% of the wall thickness. This system also removes the mechanical requirement of aligning the tubes from the orbital weldhead. Argon is the most commonly used shield gas (for the OD of the tube)and the purge gas (for the ID of the tube). In these applications. commercial grade argon gas may be used. often causing hydrogen embrittlement in the resultant weld.4. the resultant quality of weld will suffer greatly and repeatability will also become a significant issue. 90% Argon/10% Hydrogen or 75% Helium/25% Argon my be used when the wall thickness to be welded is heavy (. but the resultant quality of weld will suffer greatly and repeatability will also become a significant challenge. Again. Using mixtures of 95% Argon/5% Hydrogen is incompatible with carbon steels and some exotic alloys. Alignment mismatch (high-low) should be avoided by using engineering stands and clamps to align the two tubes to be welded. Gas purity is dictated by the application. The objective of the welder should be to create a weld which has zero tint at the weld zone ID.8 Shield Gas (es) An inert gas is required on the tube OD and ID during welding to prevent the molten material from combining with the oxygen in the ambient atmosphere. For non-critical applications.1" or above). for simplicity and reduction of shield gas cost. Mixed gases such as 98% Argon/2% Hydrogen.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 When two tubes are butted together for welding. 95% Argon/5% Hydrogen. 15. In general. the laws of physics will allow welding with mismatch of up to 25% of wall thickness if this is the only challenge but again. such as semiconductor and pharmaceutical applications. Helium is often used for welding on copper material. For high purity situations where the concern for micro-contamination is paramount. the shield and purge gases must minimize the heat tint that could otherwise be undesirable. Wall thickness variations at the weld zone should not be more than ± 5% of nominal wall thickness. Recommended Electrode Materials: Cerium. While the radioactivity is of a low level. the most commonly used electrode materials are 2% thoriated tungsten and 2% ceriated tungsten. While no one would refute the importance of the ignition device on an automobile airbag. In the orbital welding industry. Safety: The safety issues of tungsten electrode material are now being looked at more closely.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 15. more and more companies are looking for ways to ensure that their Nirbhay Gupta 105 . the source of the welding arc.9 Tungsten Electrode The tungsten welding electrode. is one of the most important elements of the welding system that is most commonly ignored by welding systems users. as a base material. Electrode Tip Geometry: Given the ever increasing weld quality requirements of the final weld. it is always best to follow the advice of your orbital equipment manufacturer. While these materials are commercially available they have been largely ignored until recently. such as 2% ceriated electrodes. Users continue to manually grind and wonder why they produce inconsistent results.4. it brings an issue of danger especially with the radioactive dust generated when grinding the electrodes to a point for welding. this is the area where manufacturing organizations can improve the consistency of their welding output with minor effort. non-radioactive tungsten materials are now available. Electrode Materials: For quite some time. 2% ceriated and 2% thoriated electrodes are the most commonly recommended materials for orbital welding equipment. a radioactive element added to the tungsten. has a lower work function than thorium. However. Thus. Whether in manual or automatic welding. they also improve the arc starting ability of the orbital equipment. not only do ceriated electrodes offer an advance in electrode safety. The objective for the choice of tungsten parameters is to balance the benefits of a clean arc start and reduced arc wander with good weld penetration and a satisfactory electrode life. tungsten manufacturers have added an oxide to pure tungsten to improve the arc starting characteristics and the longevity of pure tungsten electrodes. Many users of the TIG welding process do not realize that the welding electrode they use contains Thorium. thus it offers superior emission characteristics. the rip cord for a parachute. or quality tires f or automobiles. as mentioned earlier. Alternative. the importance of tungsten electrode for quality welding is often overlooked. which often offer superior arc welding. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 weld quality is up to par. The surface finish (ground or polished) of the electrode grind must b e consistent. The shape and quality of the tungsten electrode tip is finally being recognized as a vital process variable. The electrode tip dimensions shown must be held to close tolerances 3.4. However. the following guidelines apply: A. Once a weld procedure has been established. because they have usually performed a significant amount of qualifying and troubleshooting work to optimize electrode preparation for their equipment. Electrode Taper . Consistency and repeatability are key to welding applications. Below is a summary chart that illustrates how different tapers offer different arc shapes and features: Nirbhay Gupta 106 .10 Welding Basics and Set-Up Figure-15-5: We ld Electrode tip di ameter To produce high consistent welds the Tungsten electrode must provide the following: 1. it is important that consistent electrode material. 15.This is usually called out in degrees of included angle (usually anywhere between 14º and 60º). High quality electrode material 2. Welders should follow an equipment supplier's suggested procedures and dimensions first. where these specifications do not exist or the welder or engineer would like to change those settings to possibly improve and optimize their welding. tip geometry and surface condition be used. Figure-15-6: Arc Shapes and resultant weld profiles B. Larger and smaller tip diameters offer the following trade-offs: Nirbhay Gupta 107 . Electrode Tip Diameter . to demonstrate graphically how the taper selection will affect the size of the weld bead and the amount of penetration. However in most cases it is best for a welder to leave a flat spot or tip diameter at the end of electrode.Grinding an electrode to a point is sometimes desirable for certain applications. especially where arc starting is difficult or short duration welds on small parts are performed.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS Sharper Electrodes Blunter Electrodes Easy arc starting Usually harder to start the arc Handle less amperage Handle more amperage Wider arc shape Narrower arc shape Good arc stability Potential for more arc wander Less weld penetration Better weld penetration Shorter electrode life Longer electrode life 2008 In addition. This reduces erosion at the thin part of a point and reduces the concern that the tip may fall into the weld. below is a drawing that shows typical representations of the arc shape and resultant weld profile for different tapers. In addition. many manufacturing organizations have chosen to purchase electrodes pre-ground. Nirbhay Gupta 108 . 5.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS Smaller Tip Larger Tip Easier arc starting Usually harder to start the arc Potential for more arc wander Good arc stability Less weld penetration More weld penetration Shorter electrode life More electrode life 2008 Tungsten Electrode Grinders and Pre-Ground Electrodes: Using electrodes pre-ground to requirements or a dedicated commercial electrode grinder to provide electrode tip quality and consistency offers the following benefits to the user in their welding process: 1. since a small difference in the dimensions of an orbital electrode can produce a big difference in the weld results. 4. Longer electrode life before electrode wear or contamination. Reduction of tungsten shedding. pre-ground electrodes are the preferred electrode choice to maintain the consistency of your welding. This low cost option ensures that the electrode material quality. Improved arc starting. 2. 3. increased arc stability and more consistent weld penetration. Pre-Ground Electrodes: Rather than risk electrode radioactivity issues and also constantly endure the variability of each operator grinding the electrodes with a slightly different touch. This minimizes the possibility of Tungsten inclusions in the weld. tip geometry and ground electrode surface input to the welding process is constant. Tungsten electrode grinding equipment requires less skill to ensure that the tungsten electrode is ground correctly and with more consistency. A dedicated electrode grinder helps ensure that the welding electrodes will not become contaminated by residue or material left on a standard shop grinder wheel. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Consult electrode charts or a pre-ground electrode supplier to obtain the electrode diameter and tip geometry that is most suitable for your welding application. Fi gur e. Note: The "rules of thumb" noted below are general guidelines only and will not apply to every welding application and mix of parameters chosen. arc stability and tube concentricity/ovality.11 Welding Parameter Development Many welding equipment suppliers offer a series of pre-calculated weld programs for a variety of tube diameters. it is impossible for the equipment suppliers to have welding procedures for every welding application and there will always exist a trade off in maximum weld speed possible versus weld quality and repeatability. Experimentation and experience will determine the final weld parameters. The objective of the welding engineer is to keep the electrode at a constant distance from the tube surface with sufficient gap to avoid stubbing out.7: Us i ng p re -g rou nd el ec tro des ens u re t ha t th e el ect rod e ma te ri al qual i ty . ti p geom et ry an d gro un d el ect rod e s urf ace i np ut to th e w el di ng p ro c ess i s c o nstant 15. because they have usually performed a significant amount of qualifying and troubleshooting work to optimize electrode preparation for their equipment. Welders should always follow an equipment supplier's suggested procedures first.4.15. However. Although the welding parameters are often chosen and changed according to the specific needs of the application. Where weld parameter specifications do not exist or the welder or engineer would like to change those settings to possibly improve or optimize their welding. wall thicknesses and materials. the guidelines noted below give information on how to modify the welding parameters for a desired result. Nirbhay Gupta 109 . there are some industry standards that have been developed as starting points. Arc Length The arc gap setting is dependent on weld current. As a good starting point. the weld penetration would increase as the weld progressed around the tube. Nirbhay Gupta 110 .010" + . weld speed. For a wall thickness/penetration requirement of . The objective is to weld as fast as possible while still yielding a quality output.015" = . The objective is to achieve full penetration.080" Weld Speed The weld speed is dependent on flow rate of material to be welded.070" = 0. Thus for a 0. If the weld current used to initially penetrate the tubing was held at the same level for the complete weld. Thus if the tube wall is . wall thickness.010" + 0.10 inches per minute with the faster welding speeds used for thinner wall materials and the slower welding speeds used for heavy wall thickness.010" and add to this half the penetration required (usually the tube wall thickness) expressed in thousandths of an inch.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 As a "rule of thumb" use a base arc gap of 0.030" wall tubing the average weld current will be 30 amps in the first level. and wall thickness. Welding Current The welding current is dependent on the material to be welded. and the shield gas chosen.001" wall thickness if the material is stainless steel.025". As a starting point the tungsten surface speed should be 4 . As a starting point use 1 ampere current per 0. defect free welds. use 5 inches per minute. Weld Current Levels Orbital welding normally uses multiple levels of weld current to compensate for heat building up in the tube during the welding process.154" the arc gap would be 0.030" then a good starting arc gap would be 0. producing too much penetration. SS tube.D. This technique reduces the overall heat input to the base material and can also allow for increases in weld speed. often Nirbhay Gupta 111 . It may be noted that in the weld program chosen by the welder. Arc Pulsing Arc pulsing involves using the welding power supply to rapidly alternate the weld current from a high (peak current) to a low (background current) value. This welding technique brings many benefits to the welding procedure. This creates a seam of overlapping spot welds. Figures 15-9 and 15-10 depict a typical weld program current profile for a 10 mm O. Orbital welding normally uses a minimum of 4 levels of weld time with each level decreasing in weld amperage as the tube heats up during the welding process Normally orbital welding uses a minimum of 4 levels of weld time with each level decreasing in weld amperage Starting parameters: Set weld level 4 to be at 80% of weld level 1 amperages.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Figure15-8: A Typical Weld Program current Profile ( This weld profile shows a single level of weld time). the time for each level is same (Impulse rate) and the average current decreases with each level. Set weld level 2 and weld level 3 to gradually decrease the current from level 1 to level 4. TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 improving weld quality and repeatability. The result is impro ved weld quality and increased output. Figure 15-9: Weld program data sheet of a typical weld in RAPP-6 Nirbhay Gupta 112 . In some cases materials and weld joints with poor fit-up that are difficult to successfully weld with a non-pulsed arc can easily be welded with a pulsed arc technique. minimizes the weld sagging at the 12 and 6 o clock positions. pulse width (duty cycle). at the lower background current the puddle can solidify before becoming liquid at the next peak current pulse. Arc Pulsing Parameters: Arc pulsing involves four welding parameters: peak current. This diminishes the effect of gravity on the molten weld. Here Nirbhay Gupta 113 . and pulse frequency. The arc pulsing technique thus becomes more advantageous as the wall thickness increases resulting in a larger weld puddle.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 In orbital welding. When pulsing at peak current the base material(s) melt and flow together. background current. and reduces the molten weld puddle running/slumping downhill at the 3 and 9 o'clock positions and effectively alters the electrode to weld puddle distance. arc pulsing also offers another advantage due to the fact that the gravity pulls the weld puddle in different directions as the weld is created around the tube. A good starting point is to use 3:1 ratios. A good starting parameters would be to set a pulse width of 35%. Weld Speed = 5 ipm surface speed RPM = ipm/(3. Welding Parameter Development Example for 1" Tube/.030") = .TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 again. Pulse rate for thin wall tube is often equal to the weld speed in ipm (5 ipm = 5 pps) {pps: pulse per second} Pulse Width: The pulse width (the percentage of time spent on the peak current) is dependent on heat sensitivity of material and available current from power supply.) Starting Parameters: 5/(3.001" of wall thickness for level 1 current Level 4 = 80% of Level 1 current Levels 2 and 3 gradually decrease the current from Level 1 to Level 4 Starting Parameters: Nirbhay Gupta 114 .010" + (0.5 x penetration required) Starting Parameters: . The primary objective is to use the benefits of weld pulsation to improve weld quality and output. opinions vary from one welding organization to another and indeed from welder to welder.5 x . Good starting parameters are to attempt for a 75% spot overlap. It is important to understand how to choose convenient weld development starting parameters and the effect on the weld by changing each parameter.1415 x 1") = 1.025" 2. make the required weld and test other parameters to see if any benefit can be gained. Standard pulse widths are often 20% to 50%. Industry usage generally varies from 2:1 ratios to 5:1 ratios.010" + (0. Welding Current Levels Level 1 = 1 amp per .59 RPM 3. Arc Length/Gap = . Pulse Frequency: The pulse frequency is dependent on spot overlap required.1415 x dia. Peak/Background Current Ratios: The peak to background current ratios basically provides a means for the welding current to pulse from one level to another. Higher heat sensitivity requires lower pulse width % on peak current.030" Tube Wall Thickness: 1. Many welders arrive at the same welding result having somewhat different welding parameters. Nirbhay Gupta 115 .Use your equipment manufacturer's specifications or consult your pre-ground electrode supplier The above data gives starting parameters. Tungsten Electrode Diameter & Tip Geometry .030" wall thickness = 30 amps Level 4 Peak Current = 30 amps x 80% = 24 amps Level 2 Peak Current = 28 amps Level 3 Peak Current = 26 amps Background Current will be 1/3rd of peak current.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 Level 1 Peak Current = . the parameters will be modified to obtain the final result desired. Pulse width/duty cycle is 35% 4. On completion of the first test weld. “Is your bend good enough”. 4. IS-1239 (part-II)-1982. Division-ISubsection NB: Class 1 Components 18.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 16. ANSI/ASME B1. PB-E-44: Specifications for Brass compression type (flareless)tube fittings 15. Dryseal Pipe Threads Nirbhay Gupta 116 . Eric Lundin. 10. 11.1-1980: Power piping 3. Pro-Fusion technologies. ASME Section-III.02(1996): Nuclear safety related instrument sensing line piping and tubing.20. Specification for mild steel tubes. 8. 20. 1993: recommendation note on impulse connections and their installations 7. An installer’s pocket guide for Swagelok tube fittings: Swagelok instruction manual. 1993: Design note on Class-I Instrument tubing.Rules for construction of Nuclear Power Plant Components. ANSI/ASME B1. Tubular and other Wrought steel fittings 17. 13.20. PB-E-344: Specifications for SS tubes 12.1-1983. “Fundamentals of orbital tube welding”. SA 655: Specification for special requirements for pipe and tubing for nuclear and other special applications. PB-E-146: Specifications for SS compression type twin ferrule (flareless)tube fittings. 6. Pipe Threads. PB-M-23: Specifications for Seamless Copper tubing for 500 MWe 14. TAPP-3&4/60610/93/B/4670 dated 9th June. ASME PTC code 19.02. BS-4368-Part-I-1972. 9. 2. ANSI/ASME B31. General purpose (inch) 16. ISO-2186-1973 (2001): Fluid flow in closed conduits. The Fabricator. 5. Carbon and Stainless Steel Compression Couplings for Tubes 19. ASME PTC code 19.2: Pressure measurement. Inc. TAPP-3&4/60610/93/B/4671 dated 9th June.connections for pressure signal transmissions between primary and secondary elements.4-1976.5: Flow measurement. ISA-S 67.0 REFERENCES AND SUGGESTED READING 1. 24. Green. Swagelok Manual on Orbital tube welding machine SWS D-100. Jody Collier. D. 22. Nirbhay Gupta 117 . Charles Wick. Robert H. 23. Brochure of Tubes and Tube fittings. Swagelok SWS Orbital tube welding machine training notes. Parker Hannifin. 25. USA.W. “Perry’s chemical Engineers’ Handbook”. “TIG Welding Basics-for TIG Welders. 26.TECHNICAL DOCUMENT ON INSTRUMENTATION TUBING AND THEIR CONNECTIONS 2008 21. Perry. Managers and Technicians”. Tom Drozda. by a TIG Welder”. “Tools and Manufacturing Engineer’s Handbook: A Reference Book for Engineers.