Welding Procedure Specification

Welding Procedure Specification:- ExampleWeld Procedure Number 30 P1 TIG 01 Issue A Qualifying Welding Procedure (WPAR) WP T17/A Method Of Preparation Manufacturer: National Fabs Ltd and Cleaning: 25 Lane End Parent Metal Birkenshaw Specification: Leeds Parent Metal Thickness Location: Workshop Pipe Outside Diameter Welding Process: Manual TIG Joint Type: Single Sided Butt Weld Welding Position: Welding Progression: Joint Design Run Proces s 1 2 And Subs TIG TIG Machine and Degrease Grade 304L Stainless Steel 3 to 8mm Wall 25 to 100mm All Positions Upwards Welding Sequences Size Of Curren Voltage Type Of Wire Travel Heat Filler t Current/Polarit Feed Input Metal A V y Speed Speed 1.2mm 70 - 90 N/A 1.6mm 80 - 140 DCDC- N/A N/A N/A Welding Consumables:Production Sequence Type, Designation Trade Name: BS 2901 Part 2 : 308S92 Any Special Baking or Drying: No 1. Clean weld and 25mm borders to bright metal Gas Flux: Argon 99.99% Purity using approved solvent. Gas Flow Rate - Shield: 8 - 12 LPM 2. Position items to be - Backing: 5 LPM welded ensuring good fit up and apply purge Welding Procedure Specification:- Example Weld Procedure Number 30 P1 TIG 01 Issue A Qualifying Welding Procedure (WPAR) WP T17/A Method Of Preparation Manufacturer: National Fabs Ltd and Cleaning: 25 Lane End Parent Metal Birkenshaw Specification: Leeds Parent Metal Thickness Location: Workshop Pipe Outside Diameter Welding Process: Manual TIG Joint Type: Single Sided Butt Weld Welding Position: Welding Progression: Joint Design Run Proces s 1 2 And Subs TIG TIG Machine and Degrease Grade 304L Stainless Steel 3 to 8mm Wall 25 to 100mm All Positions Upwards Welding Sequences Size Of Curren Voltage Type Of Wire Travel Heat Filler t Current/Polarit Feed Input Metal A V y Speed Speed 1.2mm 70 - 90 N/A 1.6mm 80 - 140 DCDC- N/A N/A N/A Welding Consumables:Production Sequence Type, Designation Trade Name: BS 2901 Part 2 : 308S92 Any Special Baking or Drying: No 1. Clean weld and 25mm borders to bright metal Gas Flux: Argon 99.99% Purity using approved solvent. Gas Flow Rate - Shield: 8 - 12 LPM 2. Position items to be - Backing: 5 LPM welded ensuring good fit up and apply purge Tungsten Electrode Type/ Size: 2% Thoriated 2.4mm Dia 3. Tack weld parts together Details of Back using TIG, tacks to at Welding Procedure Specification Example A WPS is a document that describes how welding is to be carried out in production. They are recommended for all welding operations and many application codes and standards make them mandatory What information should they include? Sufficient details to enable any competent person to apply the information and produce a weld of acceptable quality. The amount of detail and level of controls specified on a WPS is dependant on the application and criticality of the joint to be welded. For most applications the information required is generally similar to that recorded on a Procedure Qualification Record (PQR) or Welding Procedure Approval Record (WPAR), except that ranges are usually permitted on thicknesses, diameters, welding current, materials, joint types etc. If a WPS is used in conjunction with approved welding procedures then the ranges stated should be in accordance with the approval ranges permitted by the welding procedure. However careful consideration should be given to the ranges specified to ensure they are achievable, as the ranges given by welding procedure standards do not always represent good welding practice. For example welding positions permitted by the welding procedure standard may not be achievable or practical for certain welding processes or consumables. EN ISO 15609-1 (formally EN 288 Part 2) European Standard For Welding Procedure Specifications EN ISO 15609 Defines the contents of a Welding Procedure Specification in the form of a list of information that should be recorded. For some applications it may be necessary to supplement or reduce the list. For example only in the case of a procedure requiring heat input control would there be a necessity to quote travel speed or run-out length for manual processes. ASME IX American Boiler and Pressure Vessel Code QW 250 Lists the variables for each welding process, all the variables stated should be addressed. The range permitted by the WPS is dictated by the PQR or PQR’s used to qualify it. Typical Items That Should Be Recorded On W.P.S:- Common to all Processes .  Procedure number  Process type  Consumable Size, Type and full Codification.  Consumable Baking Requirement if applicable  Parent material grade and spec.  Thickness range.  Plate or Pipe, Diameter range  Welding Position  Joint Fit Up, Preparation, Cleaning, Dimensions etc.  Backing Strip, Back Gouging information.  Pre-Heat (Min Temp and Method)  Interpass If Required (Maximum Temperature recorded )  Post Weld Heat Treatment. If Required (Time and Temp)  Welding Technique (weaving,max run width etc.)  Arc Energy Limits should be stated if impact tests are required or if the material being welded is sensitive to heat input. MMA TIG MIG MAG FCAW Welding current yes yes yes yes Type of Welding current AC/DC Polarity yes yes yes yes Arc voltage If Auto yes yes Pulse parameters (Pulse time and peak & backgound current) If Used If Used yes yes Specific To Welding Processes Welding Speed If Mechanised SUB ARC yes † x Interstitial infomation? For more information on Mohrs Circle got to efunda.com Next Page Menu Page T Fillet Welds Next Page Menu Page Cantilever Welds Subject to both bending and shear Next Page Menu Page T Butt Weld Subject To Torsion Next Page Menu Page Butt Weld With Offset Next Page Menu Page Lap Joint Subject To Bending and Shear This is a lap joint with an offset. I could not find a calculation for this in any reference so I put this together. I have assumed that there will be a vertical shear force caused by the offset load creating a moment about the mid point between the welds (marked with the red dot), as well as a horizontal shear force. Alternative approach it gives the same answer as my method. My thanks to the person that sent this to me. Next Page Menu Page Calculating Volume Using Solids Of Revolution Some Properties of plane areas FIGURE CENTROID MOMENT OF AREA Next Page Menu Page Welding Certification, A Basic Guide The requirement for weld procedures and the coding of welders is specified in application standards such as:  BS 2971 Class 2 Arc Welding of Carbon Steel Pipework {Gas Pressures less than 17 barg}  BS 2633 Class 1 Arc Welding of Carbon Steel Pipework  BS 4677 Arc Welding Of Austenitic Steel Pipework.  BS 806 Boiler Pipe Work (Refers to BS 2971 and BS 2633)  PD 5500 Unfired Pressure Vessels (Formally BS5500)  BS 2790 Shell Boilers  BS 1113 Water Tube Boilers  BS 5169 Air Receivers Application Standards All the above application standards require welding procedures to EN ISO 15614 Part 1 (Formerly BSEN 288-3) and welders coded to BSEN 287 Part 1. Some applications of BS 2971 and BS 5169 permit welders to be qualified without procedures to BS 4872, a less stringent standard. The application standard may require tests in addition to those required by welding standards, for example most UK boiler and pressure vessel codes require all weld tensile tests for plate qualification above 10mm. UK pressure systems regulations Items that come under the UK pressure systems regulations must be 'properly designed and constructed so as to prevent danger', and items that are repaired or modified should not give rise to danger. The Health and Safety Executive Guidance Booklet to the regulations interprets this statement as meaning the manufacture or repair of any item should be carried out to suitable codes and recommends the use of British Standards or other equivalent National Standards. European Pressure Equipment Directive For inspection category 2 and above all welding procedures and welder qualifications have to be approved by a Notified Body (an Inspection Authority Notified by a European member country under the Directive), or a Third Party Organisation similarly approved under the Directive. All qualifications approved by these organisations have to be accepted by all parties for work carried out under the directive providing they are suitable for the application and technically correct. Welding Procedure Specifications This is a simple instruction sheet giving details of how the weld is to be performed, its purpose is to aid the planning and quality control of the welding operation. EN ISO 15609 (formerly EN288 Part 2) specifies the contents of such a specification in the form of a list of items that should be recorded, however only relevant information need be specified, for example only in the case of a procedure requiring heat input control would there be a necessity to quote travel speed or run out length for manual processes. A weld procedure specification may cover a range of thicknesses, diameters and materials, but the range must be specified and be compatible with the rest of the parameters on the document. I suggest that you produce a new WPS for each type of joint and keep to the ranges of thickness and diameters specified in the welding procedure standard. Welding Procedures Welding procedures are required when it is necessary to demonstrate that your company has the ability to produce welds possessing the correct mechanical and metallurgical properties. A welding procedure must qualified in accordance with the requirements of an appropriate welding procedure standard such as EN ISO 15614 Part 1 as follows:1. Produce a welding procedure specification as stated above. 2. Weld a test piece in accordance with the requirements of your specification. The joint set up, welding and visual examination of the completed weld should be witnessed by an Inspection Body. The details of the test such as the welding current, pre-heat etc., must be recorded during the test. 3. Once the welding is complete the test piece must be subject to destructive and non destructive examination such as radiography and mechanical tests as defined by the welding procedure standard. This work can be carried out in any laboratory but the Inspection Body may require to witness the tests and view any radiographs. 4. If the test is successful you or the test body complete the appropriate documents which the test bodies surveyor signs and endorses. The necessary documents are as follows:E1 Welding Procedure Approval Test Certificate This is the front sheet and only gives details of what the procedure can be used for. i.e. its range of approval. E2 Details Of Weld Test This gives details of what actually took place during the test weld it is similar to a WPS but should not include ranges of welding parameters. E3 Test Results Details of NDT and Mechanical testing Results E4 Welder Approval Test Certificate. This is the welder approval part of the qualification. Note The E1, E2, E3, E4 designations are used by some Inspection Authorities to refer to the individual forms. Examples of these forms are given in annexes of EN ISO 15614 and EN287. Forms E1, E2, E3 may be referred to as the WPAR (Welding Procedure Approval Record) or WPQR (Weld Procedure Qualification Record). In general a new welding procedure must be qualified for each of the following changes subject to the individual requirements of the appropriate standard used:-  Change in parent material type.  Change of welding process  The diameter range for pipe given by the welding standard is exceeded. Typically 0.5xD to 2xD.  The thickness range is exceeded. Typically 0.5xt to 2xt.  Any other change required by the welding standard. Welder Approval Once the procedure is approved it is necessary to demonstrate that all your welders working to it have the required knowledge and skill to put down a clean sound weld. If the welder has satisfactorily completed the procedure test then he is automatically approved but each additional welder must be approved by completing an approval test to an appropriate standard such as EN 287 part 1 as follows:Complete a weld test as stated in 2) above. The test should simulate production conditions and the welding position should be the position that the production welds are to be made in or one more severe For maximum positional approval a pipe inclined at 45 degrees (referred to as the 6G position) approves all positions except vertical down. Test the completed weld in accordance with the relevant standard to ensure that the weld is clean and fully fused. For a butt weld this is normally a visual examination followed by radiography. Once the test is completed the E4 form has to be completed by you or the test body and signed by the test bodies surveyor. Note The above changes that require a new welding procedure may also apply to the welders approval, refer to the standard for precise details. ASME 9 ASME 9 as far as the pressurised systems regulations are concerned can be considered as equivalent to EN ISO 15614-1 /EN 287. However it may not be contractually acceptable. The advantage in using ASME is that generally fewer procedure tests are required particularly when welding pipework. Welder Approval Without A procedure BS 4872 is for the qualification of welders where a weld procedure is not required either by the application standard that governs the quality of production welds or by contractual agreement. Typically applied per BS2971 for welding of boiler pipework less than 17 bar g and 200°C. Basically the same rules mentioned above for the welder approval apply. Acceptance Standards In general welds must show a neat workman like appearance. The root must be fully fused along the entire length of the weld, the profile of the cap should blend in smoothly with the parent material and the weld should be significantly free from imperfections. Reference should be made to the acceptance standard for precise details. Its a good idear to ensure that you can achieve the appropriate standard before you call in an Inspection Body. Penetration defects and lack of fusion can often be easily detected by sectioning welds and bending them. • Next Page • Welding Qualification Sub Menu Page last updated 21 March 2008 Procedure Qualification Record (PQR) PQR's are not required if Standard Welding Procedures are used, see below for details. This document contains details of the welding test, it must include details of all the parameters listed as variables in tables QW250 to QW265 for each process involved and all the destructive test results. The relevant variables for each type of welding process are clearly defined in tables QW250 to QW265. The left hand column of each table defines the section and paragraph where each variable and its application to the table is explained in the code. Welding Variables Variables used in a welding procedure test are divided into 3 categories : Essential Variables Are variables that have a significant affect on the mechanical properties of a joint. They must not be changed except within the limits specified by this code. e.g. Material thickness range, Material Group etc.  Non-Essential Variables Are variables that have no significant affect on mechanical properties. They can be changed without re qualification of the PQR.  Supplementary Variables Are variables that have an affect on the impact properties of a joint. They are classed as Non-Essential if impact testing is not required All variables listed as essential, non-essential or supplementary should be addressed on both the WPS and the PQR. If any of the variables do not apply to the particular application then they should be specified as not applicable. Joint Configuration Either plate or pipe can be used for the test piece (plate approves pipe and vice versa ref. QW211), any welding position approves all positions providing no impact tests are required ref. tables QW250 to QW265 and any joint geometry approves all geometry's, e.g. single V, double V, U prep, backed or unbacked. A butt or groove weld approves branch and fillet welds but not the converse, ref. QW202. Non pressure retaining fillet welds in pipe or plate can be tested but they must be double sided if plate and at least the dimensions illustrated in QW462.4a, ref. QW202.2c. Pressure retaining branch welds must be qualified by groove (butt) welds. Material Grouping Materials are assigned P numbers in QW420; a test in one P number approves all materials listed under that P number, except where impact tests are required then approval is restricted to materials listed in the group number within the P number. Other P number groupings are permissible ref. QW424.1 for details. Ref QW 424.1 for further details. It is normally permissible if the material is not listed in QW422 to assign it to a P number which lists materials with the same metallurgical and mechanical properties although this is not in strict conformance with the code. Typically BS1501 151 430A low carbon steel could be regarded as P1 and stainless steels such as 316, 304 as P8. Note P5, 9 & 10 are divided into sub groups eg 5A,5B etc., Treat each sub group like a separate P Number Dissimilar materials are acceptable providing they are compatible. For example P1 to P8, but this does not cover P1 to P1 or P8 to P8. Note S numbers are for pipework to B31, a P number covers an S number but not the converse Consumables The ASME code uses its own specifications for consumables SFA. which is almost identical to the AWS specification. NOTE A change in consumable is only permissible providing it has the same F number and A number (if applicable) as the P.Q.R.. Thickness Limits Thickness limits Groove welds. See QW451 for precise details.  When Impact tests are required the minimum thickness approved is restricted. See QW403.6  More than one PQR may be required to qualify dissimilar thickness The thickness little 't' of deposited weld metal for each process involved is approved from 0 to 2xt except: MIG/MAG (GMAW/FCAW) dip transfer weld of deposited thickness less than ½" approves maximum thickness of 1.1 x t only Ref: QW255 (QW403.10)  If any Pass in a single or multipass weld > ½" then the thickness approval equals 1.1xT Dissimilar Thickness QW202.4:- The thicker and thinner part must be qualified, Except P8 and P4X the thinner part can be qualified if no Impacts and test coupon > 6mm thick. Thickness limits for fillet welds as per QW462.4a or QW462.4d qualify all fillet weld sizes on all base material thicknesses and all diameters in one test. Testing Requirements (Ref QW 463 for location of specimens) Unlike EN288 there is no requirement for any non-destructive testing such as radiography or MPI/DPI, although I would recommend radiography for butt welds. The testing requirement for groove welds are as follows: Two Transverse tensile tests (QW150).  Two Root bends and Two face bends unless the plate thickness exceeds 3/8" then 4 side bends are required. All bend tests should be done to QW160 using the correct former ref. QW466 to an angle of 180 degrees. Longitudinal (all weld) bend tests are not recommended unless the base/weld materials differ markedly in bending properties. See QW 466 for exceptions and precise details. The testing requirement for fillet welds on plate is 5 macro sections only, for Pipe fillet welds 4 macro sections. No fracture test required. Welding Procedure Specifications (WPS) This document details the practical application of the Procedure Qualification Record (PQR). It should contain enough information to give direction to the welder and should address all variables associated with the welding process defined in QW250 including non essential and supplementary. A WPS can combine welding processes from other PQR's but all the relevant variables must be addressed including parent metal thickness. There is an exception to this rule for root runs from PQR's that are greater than 1.5 inches thick (38.1mm), see code for details. Standard Welding Procedures Specifications (SWP's) Standard welding procedures listed in annex E of ASME IX can be purchased from the 'American Welding Society' and used without qualifying a PQR. Section V of ASME IX gives details of essential variables and restrictions. A successful welder performance qualification must be carried out to demonstrate the SWP's before a manufacturer can use it.  Brief Introduction  Procedure Qualification Record (PQR)  Welding Performance Qualification (WPQ)  ASME definitions for welding processes, consumables and welding positions  Welding Qualifications Sub Menu Page last updated 1 September 2001 Ads Welder Performance Qualification (WPQ) Materials The purpose of this test is to determine the welders ability to deposit a sound weld therefore the base material is not considered as critical as it is in the PQR. Hence a performance test on any material in P groups 1 to 11 approves all those groups and sub groups, also P34 and P4X (P40-P49). Providing a compatible consumable exists with the same F number used in the qualification test. (QW423.1) Note a single sided weld is classed as a weld without backing and a double sided weld or weld with sealing run is classed as a weld with backing Consumables The F number cannot be changed without re qualification of the welder except that for performance qualification only using SMAW (MMA) F numbers up to and including 4 approve all lesser F numbers for double sided or welds with backing only. One Consumable from F41 To F45 approves any of these consumables, except SAW. Ref. QW404.11. Note 'A' numbers do not apply to welder approval tests. Variables For each welding process there is a list of essential variables in QW352 to QW357 and QW360 for welding operators, these are not necessarily the same as the ones for the PQR. Essential variables cannot be changed. Explanations of all these variables is given in section IV of the code. Diameter and Thickness Ranges Diameter limits for all circular welds including groove welds, branch welds and fillet welds is given in QW452.3. there are no upper limits on diameters approved and pipe covers plate Note for branch welds the diameter considered for the above limits is the one containing the weld preparation. Thickness limits, groove welds. The thickness limit only applies to the deposited weld metal thickness not the plate thickness and any groove weld approves all fillet weld sizes. For t greater than 12.5mm there is no restriction on the size that can be welded (Providing the test weld deposit contains at least 3 layers of weld). Thickness limits, fillet welds. A test on plate greater than 3/16" approves all base metal thicknesses and fillet weld sizes ref. QW452.5. (Note the above diameter limits apply unless the fillet weld is qualified by a groove weld) Joint Configuration Joint geometry, a double V (or U) is considered the same as a joint with backing and does not qualify a single V (or U) without backing, but a single full penetration joint without backing qualifies all joint configurations. Approval Range Extent of approval is very well explained in QW461.9. Take particular note of welding positions which are also explained in QW461, for example to qualify a fillet weld in the normal horizontal-vertical position with a groove weld, the groove weld must be qualified in at least the 2G position. The welding positions defined in QW461.1.& QW461.2 should be referred to in the WPS. The position designations: 1G ,2G ,3G ,4G ,5G ,6G (Groove Welds) and 1F , 2F ,3F ,4F (Fillet Welds) are test positions Period of Validity/Renewal of Qualifications (QW 322.2) Providing the welder uses the process for which he is qualified and there is no reason to question his ability then his qualification lasts indefinitely. If the welder does not use the welding process for which he is qualified for a period of 6 months or more then he must perform a new test in pipe or plate, any parent material, thickness and position, if successful all the welder approvals for that welding process are renewed in one test. Testing Requirements Test requirements for groove welds QW452 consists of either: One face bend and one root bend except for welding positions 5G & 6G which require 4 bends (Ref QW452.1 Note 4). If the plate exceeds 3/8" side bends may be used. See QW 466 for precise details and exceptions. Note:- Bend Tests can in most cases be replaced by Radiography {See Below}.  Radiography is optional and must be supplemented by bend tests when using GMAW (MIG/MAG) with dip transfer (Short Circuiting Arc) or when welding some special materials. Ref. QW304. Note:- Ultrasonic Examination in lieu of Radiography is not permitted Test requirements for fillet welds in plate ref. QW452.5: One macro section (QW 184) and One fracture test (QW182). The location where each specimen has to be taken is defined in QW463 Radiography Ref QW 191  A length of at least 6" must be examined for plate or the entire circumference for pipe.  If the pipe circumference is less than 6" then more samples must be welded up to a maximum of 4. Ref QW 302.2. Visual Examination Ref QW 302.2 & QW 190 Performance test coupons must show complete joint penetration with full fusion of the weld metal and base metal. The welder performance test must follow a properly qualified W.P.S. Once qualified the welder must always work within the extent of approval of any properly qualified W.P.S. and his W.P.Q. The welder who qualifies the P.Q.R. is automatically approved within the limits specified in QW304, QW305 and QW303. Ref QW301.2. Specialist Processes Such as corrosion resistant overlay or hard facing are covered in QW 453. Procedure variables are defined with all procedure variables in QW252 and in QW380 for welder approval. Min base thickness approved = size welded or 1", QW 453 Min Deposit Size Approved:- Point Where Chemical analysis taken No upper limit QW402.16 (462.5a) Welding Positions QW405.4 Performance Qualification approves all deposit thickness’ No min.QW381  Brief Introduction  Procedure Qualification Record (PQR)  Welding Performance Qualification (WPQ)  ASME definitions for welding processes, consumables and welding positions  Welding Qualifications Sub Menu Page last updated 01 September 2001 ASME Definitions, Consumables, Welding Positions  ASME P Material Numbers Explained ASME has adopted their own designation for welding processes, which are very different from the ISO definitions adopted by EN24063. Designation Description OFW Oxyfuel Gas Welding SMAW Shielded Metal Arc Welding (MMA) SAW Submerged Arc Welding GMAW Gas Metal Arc Welding (MIG/MAG) Welding Positions For Groove welds:Welding Position Flat Horizontal Vertical Upwards Progression Vertical Downwards Progression Overhead Pipe Fixed Horizontal Pipe Fixed @ 45 degrees Upwards Pipe Fixed @ 45 degrees Downwards Test Position 1G 2G 3G 3G 4G 5G 6G 6G ISO and EN PA PC PF PG PE PF HL045 JL045 Test Position 1F 2F 2FR 3F 3F 4F 5F ISO and EN PA PB PB PF PG PD PF Welding Positions For Fillet welds:Welding Position Flat (Weld flat joint at 45 degrees) Horizontal Horizontal Rotated Vertical Upwards Progression Vertical Downwards Progression Overhead Pipe Fixed Horizontal Welding Positions QW431.1 and QW461.2 Basically there are three inclinations involved.  Flat, which includes from 0 to 15 degrees inclination  15 - 80 degrees inclination  Vertical, 80 - 90 degrees For each of these inclinations the weld can be rotated from the flat position to Horizontal to overhead.  Brief Introduction  Procedure Qualification Record (PQR)  Welding Performance Qualification (WPQ)  ASME definitions for welding processes, consumables and welding positions  Welding Qualifications Sub Menu Page last updated 19 March 2001 Ads ASME P Material Numbers This is a general guide ASME P numbers and their equivalent EN288 groupings. Groups referred to in the Base Metal column are ASME sub groups. EN288 material groups are included for comparison only. P No. 1 EN288 1 2 3 4 5A 4 5 5 5B 5 5C 6 7 6 8 8 8 9A, B, C 10A,B,C,F,G 10 H 10J 11A Group 1 11 A Groups 9 7 ? 10 ? 7 ? Base Metal Carbon Manganese Steels, 4 Sub Groups  Group 1 up to approx 65 ksi  Group 2 Approx 70ksi  Group 3 Approx 80ksi  Group 4 ? Not Used 3 Sub Groups:- Typically half moly and half chrome half moly 2 Sub Groups:- Typically one and a quarter chrome half moly Typically two and a quarter chrome one moly 2 Sub Groups:- Typically five chrome half moly and nine chrome one moly 5 Sub Groups:- Chrome moly vanadium 6 Sub Groups:- Martensitic Stainless Steels Typically Grade 410 Ferritic Stainless Steels Typically Grade 409 Austenitic Stainless Steels, 4 Sub groups  Group1 Typically Grades 304, 316, 347  Group 2 Typically Grades 309, 310  Group 3 High manganese grades  Group 4 Typically 254 SMO type steels Typically two to four percent Nickel Steels Mixed bag of low alloy steels, 10G 36 Nickel Steel Duplex and Super Duplex Grades 31803, 32750 Typically 26 Chrome one moly 9 Nickel Steels Mixed bag of high strength low alloy steels. Ads [Home] [Failure] [Calculations] [WP's] [PED] [Fatigue] [Fracture] [Preheat] [Metallurgy] [S ymbols] [FE] [Link s] Last Modified 15 July 2001 Ads Feel free to ask me a question or comment on the site. View this site in a full size Window < are required when determining the minimum preheat level. Additions of niobium also require special consideration. For welds subject to high restraint more preheat is advisable (suggest, Incr CE by 0.3 or go down one hydrogen scale). References. EN1011 Part 2 (English version available from British Standards) This standard is highly recommended as it gives details on this preheat me and also includes methods covering fine grain and creep resisting steels. It includes practical guidance on the avoidance of other cracking mechanism Much of the data contained in this standard comes from TWI tempered by practical experience from industry. (It replaces BS5135) Welding Steels Without Hydrogen Cracking. http://www.woodheadpublishing.com/ This book is based on the original research work carried out by TWI. covers the avoidance of hydrogen cracking and preheat in great detail. preheat graphs tend to require a higher preheat than the equivalent ones in EN1011. The Welding of Structural Steels Without Preheat The Welding Journ April 2000 A very informative article covering recent TWI research into welding low hardenability steels without preheat. The article won the Lincoln foundation gold award. Preheat calculator Lincoln arc welding foundation A simple to use and inexpensive calculator. It is based on practical experi and tends to be very conservative when compared with the TWI method. Got To The Pre-Heat Calculator More information on Preheat from the Lincoln Arc Foundation [Home] [Failure] [Calculations] [WP's] [PED] [Fatigue] [Fracture] [Preheat] [Metallurgy] [S ymbols] [FE] [Link s] Last Modified 15 July 2001 Ads Pre-heat Calculator Pre-Heat Calculator to EN1011 Part 2 - Non Alloyed And Low Alloy Steels. Information on how to use this page • Heat Input OR Enter Arc Energy KJ/mm Select Welding Process Heat Input KJ/mm = • not for data input. Carbon Equivalent Enter Carbon Equivalent • Note, this box is Hydrogen Scale Select Hydrogen Scale OR • Combined Thickness Note Thickness Enter Combined Thickness mm must be 2 x T for a butt weld Calculate PreHeat • Min Pre-Heat Temperature= °C Return Page last updated 13 April 2002 Ads WELDING METALLURGY Carbon Steel ? European Steel numbering and steel designations explained Carbon Steel (AvestaPolarit), This site contains information on stainless steel ? Outokumpu.com grades, welding stainless steel + online corrosion Tables Residual Stresspdf file containing stainless steel grades and specifications ? Outokumpu.com Steel Grades - Wall Chart- European Steel Grades - Wall Chart- North American Strain Age Embrittlement ? STAINLESS STEELS: Their properties and their suitability for welding. pdf file for thePWHT pickling and cleaning of stainless steel. pdf file How to Avoid ? Handbook ? Key to Metals is a comprehensive steel properties database, also contains free useful articles. The General Effects Of Alloying Elements ? ESAB University A very comprehensive course in basic welding technology. ? Useful definitions . Stainless Steel Austenitic Stainless Steels ? Return To MainMenu Page Carbon Steel To Austenitic Page last updated 6 October 2004 Duplex Ads More articles to follow soon! The Metallurgy Of Carbon Steel The best way to understand the metallurgy of carbon steel is to study the ‘Iron Carbon Diagram’. The diagram shown below is based on the transformation that occurs as a result of slow heating. Slow cooling will reduce the transformation temperatures; for example: the A1 point would be reduced from 723°C to 690 °C. However the fast heating and cooling rates encountered in welding will have a significant influence on these temperatures, making the accurate prediction of weld metallurgy using this diagram difficult.  Austenite This phase is only possible in carbon steel at high temperature. It has a Face Centre Cubic (F.C.C) atomic structure which can contain up to 2% carbon in solution.  Ferrite This phase has a Body Centre Cubic structure (B.C.C) which can hold very little carbon; typically 0.0001% at room temperature. It can exist as either: alpha or delta ferrite.  Carbon A very small interstitial atom that tends to fit into clusters of iron atoms. It strengthens steel and gives it the ability to harden by heat treatment. It also causes major problems for welding , particularly if it exceeds 0.25% as it creates a hard microstructure that is susceptible to hydrogen cracking. Carbon forms compounds with other elements called carbides. Iron Carbide, Chrome Carbide etc.  Cementite Unlike ferrite and austenite, cementite is a very hard intermetallic compound consisting of 6.7% carbon and the remainder iron, its chemical symbol is Fe3C. Cementite is very hard, but when mixed with soft ferrite layers its average hardness is reduced considerably. Slow cooling gives course perlite; soft easy to machine but poor toughness. Faster cooling gives very fine layers of ferrite and cementite; harder and tougher  Pearlite A mixture of alternate strips of ferrite and cementite in a single grain. The distance between the plates and their thickness is dependant on the cooling rate of the material; fast cooling creates thin plates that are close together and slow cooling creates a much coarser structure possessing less toughness. The name for this structure is derived from its mother of pearl appearance under a microscope. A fully pearlitic structure occurs at 0.8% Carbon. Further increases in carbon will create cementite at the grain boundaries, which will start to weaken the steel.  Cooling of a steel below 0.8% carbon When a steel solidifies it forms austenite. When the temperature falls below the A3 point, grains of ferrite start to form. As more grains of ferrite start to form the remaining austenite becomes richer in carbon. At about 723°C the remaining austenite, which now contains 0.8% carbon, changes to pearlite. The resulting structure is a mixture consisting of white grains of ferrite mixed with darker grains of pearlite. Heating is basically the same thing in reverse.  Martensite If steel is cooled rapidly from austenite, the F.C.C structure rapidly changes to B.C.C leaving insufficient time for the carbon to form pearlite. This results in a distorted structure that has the appearance of fine needles. There is no partial transformation associated with martensite, it either forms or it doesn’t. However, only the parts of a section that cool fast enough will form martensite; in a thick section it will only form to a certain depth, and if the shape is complex it may only form in small pockets. The hardness of martensite is solely dependant on carbon content, it is normally very high, unless the carbon content is exceptionally low.  Tempering The carbon trapped in the martensite transformation can be released by heating the steel below the A1 transformation temperature. This release of carbon from nucleated areas allows the structure to deform plastically and relive some of its internal stresses. This reduces hardness and increases toughness, but it also tends to reduce tensile strength. The degree of tempering is dependant on temperature and time; temperature having the greatest influence.  Annealing This term is often used to define a heat treatment process that produces some softening of the structure. True annealing involves heating the steel to austenite and holding for some time to create a stable structure. The steel is then cooled very slowly to room temperature. This produces a very soft structure, but also creates very large grains, which are seldom desirable because of poor toughness.  Normalising Returns the structure back to normal. The steel is heated until it just starts to form austenite; it is then cooled in air. This moderately rapid transformation creates relatively fine grains with uniform pearlite.  Welding If the temperature profile for a typical weld is plotted against the carbon equilibrium diagram, a wide variety of transformation and heat treatments will be observed. Note, the carbon equilibrium diagram shown above is only for illustration, in reality it will be heavily distorted because of the rapid heating and cooling rates involved in the welding process. a) Mixture of ferrite and pearlite grains; temperature below A1, therefore microstructure not significantly affected. b) Pearlite transformed to Austenite, but not sufficient temperature available to exceed the A3 line, therefore not all ferrite grains transform to Austenite. On cooling, only the transformed grains will be normalised. c) Temperature just exceeds A3 line, full Austenite transformation. On cooling all grains will be normalised d) Temperature significantly exceeds A3 line permitting grains to grow. On cooling, ferrite will form at the grain boundaries, and a course pearlite will form inside the grains. A course grain structure is more readily hardened than a finer one, therefore if the cooling rate between 800°C to 500°C is rapid, a hard microstructure will be formed. This is why a brittle fracture is most likely to propagate in this region.  Welds The metallurgy of a weld is very different from the parent material. Welding filler metals are designed to create strong and tough welds, they contain fine oxide particles that permit the nucleation of fine grains. When a weld solidifies, its grains grow from the course HAZ grain structure, further refinement takes place within these course grains creating the typical acicular ferrite formation shown opposite. Recommended Reading  Metals and How To Weld Them :- Lincoln Arc Foundation A very cheap hard backed book covering all the basic essentials of welding metallurgy. Welding Metallurgy Training Modules:- (Devised by The Welding Institute of Canada) Published in the UK by Abington Publishing. Not cheap but the information is clearly represented in a very readable format. Return To Sub Menu Page last updated 08 May 2002 Ads Residual Stress Magnitude Of Stresses- A Simple Analogy Return To Sub Menu Page last updated 08 May 2002 Strain Age Embrittlement This phenomenon applies to carbon and low alloy steel. It involves ferrite forming a compound with nitrogen; iron-nitride (Fe4N). Temperatures around 250°C, will cause a fine precipitation of this compound to occur. It will tend to pin any dislocations in the structure that have been created by cold work or plastic deformation. Strain ageing increases tensile strength but significantly reduces ductility and toughness. Modern steels tend to have low nitrogen content, but this is not necessarily true for welds. Sufficient Nitrogen, approximately 1 to 2 ppm, can be easily picked up from the atmosphere during welding. Weld root runs are particularly at risk because of high contraction stresses causing plastic deformation. This is why impact test specimens taken from the root or first pass of a weld can give poor results. Additions of Aluminium can tie up the Nitrogen as Aluminium Nitride, but weldcooling rates are too fast for this compound to form successfully. Stress relief at around 650 degrees C will resolve the problem. Return To Sub Menu Page last updated 08 May 2002 Ads HOW TO AVOID PWHT The above picture is of a new pressure vessel that failed during its hydraulic test. The vessel had been stress relieved, but some parts of it did not reach the required temperature and consequently did not experience adequate tempering. This coupled with a small hydrogen crack, was sufficient to cause catastrophic failure under test conditions. It is therefore important when considering PWHT or its avoidance, to ensure that all possible failure modes and their consequences are carefully considered before any action is taken. The post weld heat treatment of welded steel fabrications is normally carried out to reduce the risk of brittle fracture by:  Reducing residual Stresses. These stresses are created when a weld cools and its contraction is restricted by the bulk of the material surrounding it. Weld distortion occurs when these stresses exceed the yield point. Finite element modelling of residual stresses is now possible, so that the complete welding sequence of a joint or repair can be modelled to predict and minimise these stresses.  Tempering the weld and HAZ microstructure. The microstructure, particularly in the HAZ, can be hardened by rapid cooling of the weld. This is a major problem for low and medium alloy steels containing chrome and any other constituent that slow the austenite/ferrite transformation down, as this will result in hardening of the micro structure, even at slow cooling rates. The risk of brittle fracture can be assessed by fracture mechanics. Assuming worst-case scenarios for all the relevant variables. It is then possible to predict if PWHT is required to make the fabrication safe. However, the analysis requires accurate measurement of HAZ toughness, which is not easy because of the HAZ’s small size and varying properties. Some approximation is possible from impact tests, providing the notch is taken from the point of lowest toughness. If PWHT is to be avoided, stress concentration effects such as: - backing bars, partial penetration welds, and internal defects in the weld and poor surface profile, should be avoided. Good surface and volumetric NDT is essential. Preheat may still be required to avoid hydrogen cracking and a post weld hydrogen release may also be beneficial in this respect (holding the fabrication at a temperature of around 250C for at least 2 hours, immediately after welding). Nickel based consumables can often reduce or remove the need for preheat, but their effect on the parent metal HAZ will be no different from that created by any other consumable, except that the HAZ may be slightly narrower. However, nickel based welds, like most austenitic steels, can make ultrasonic inspection very difficult. Further reduction in the risk of brittle fracture can be achieved by refining the HAZ microstructure using special temper bead welding techniques. Further Information On: - • Temper Bead Welding Technique • Fracture Mechanics (Link temporarily Disabled) • Residual Stresses • Metallurgy of Steel • Return To Menu Page Page last updated 10 June 2002 Ads Alloying Elements Manganese Increases strength and hardness; forms a carbide; increases hardenability; lowers the transformation temperature range. When in sufficient quantity produces an austenitic steel; always present in a steel to some extent because it is used as a deoxidiser Silicon Strengthens ferrite and raises the transformation temperature temperatures; has a strong graphitising tendency. Always present to some extent, because it is used with manganese as a deoxidiser Chromium Increases strength and hardness; forms hard and stable carbides. It raises the transformation temperature significantly when its content exceeds 12%. Increases hardenability; amounts in excess of 12%, render steel stainless. Good creep strength at high temperature. Nickel Strengthens steel; lowers its transformation temperature range; increases hardenability, and improves resistance to fatigue. Strong graphite forming tendency; stabilizes austenite when in sufficient quantity. Creates fine grains and gives good toughness. Nickel And Chromium Used together for austenitic stainless steels; each element counteracts disadvantages of the other. Tungsten Forms hard and stable carbides; raises the transformation temperature range, and tempering temperatures. Hardened tungsten steels resist tempering up to 6000C Molybdenum Strong carbide forming element, and also improves high temperature creep resistance; reduces temper-brittleness in Ni-Cr steels. Improves corrosion resistance and temper brittleness. Vanadium Strong carbide forming element; has a scavenging action and produces clean, inclusion free steels. Can cause re-heat cracking when added to chrome molly steels. Titanium Strong carbide forming element. Not used on its own, but added as a carbide stabiliser to some austenitic stainless steels. Phosphorus Increases strength and hardnability, reduces ductility and toughness. Increases machineability and corrosion resistance Sulphur Reduces toughness and strength and also weldabilty. Sulphur inclusions, which are normally present, are taken into solution near the fusion temperature of the weld. On cooling sulphides and remaining sulphur precipitate out and tend to segregate to the grain boundaries as liquid films, thus weakening them considerably. Such steel is referred to as burned. Manganese breaks up these films into globules of maganese sulphide; maganese to sulphur ratio > 20:1, higher carbon and/or high heat input during welding > 30:1, to reduce extent of burning. Return To Sub Menu Page last updated 02 June 2002 Austenitic stainless steels Austenitic stainless steels have high ductility, low yield stress and relatively high ultimate tensile strength, when compare to a typical carbon steel. A carbon steel on cooling transforms from Austenite to a mixture of ferrite and cementite. With austenitic stainless steel, the high chrome and nickel content suppress this transformation keeping the material fully austenite on cooling (The Nickel maintains the austenite phase on cooling and the Chrome slows the transformation down so that a fully austenitic structure can be achieved with only 8% Nickel). Heat treatment and the thermal cycle caused by welding, have little influence on mechanical properties. However strength and hardness can be increased by cold working, which will also reduce ductility. A full solution anneal (heating to around 1045°C followed by quenching or rapid cooling) will restore the material to its original condition, removing alloy segregation, sensitisation, sigma phase and restoring ductility after cold working. Unfortunately the rapid cooling will re-introduce residual stresses, which could be as high as the yield point. Distortion can also occur if the object is not properly supported during the annealing process. Austenitic steels are not susceptible to hydrogen cracking, therefore preheating is seldom required, except to reduce the risk of shrinkage stresses in thick sections. Post weld heat treatment is seldom required as this material as a high resistance to brittle fracture; occasionally stress relief is carried out to reduce the risk of stress corrosion cracking, however this is likely to cause sensitisation unless a stabilised grade is used (limited stress relief can be achieved with a low temperature of around 450°C ). Austenitic steels have a F.C.C atomic structure which provides more planes for the flow of dislocations, combined with the low level of interstitial elements (elements that lock the dislocation chain), gives this material its good ductility. This also explains why this material has no clearly defined yield point, which is why its yield stress is always expressed as a proof stress. Austenitic steels have excellent toughness down to true absolute (-273°C), with no steep ductile to brittle transition. This material has good corrosion resistance, but quite severe corrosion can occur in certain environments. The right choice of welding consumable and welding technique can be crucial as the weld metal can corrode more than the parent material. Probably the biggest cause of failure in pressure plant made of stainless steel is stress corrosion cracking (S.C.C). This type of corrosion forms deep cracks in the material and is caused by the presence of chlorides in the process fluid or heating water/steam (Good water treatment is essential ), at a temperature above 50°C, when the material is subjected to a tensile stress (this stress includes residual stress, which could be up to yield point in magnitude). Significant increases in Nickel and also Molybdenum will reduce the risk. Stainless steel has a very thin and stable oxide film rich in chrome. This film reforms rapidly by reaction with the atmosphere if damaged. If stainless steel is not adequately protected from the atmosphere during welding or is subject to very heavy grinding operations, a very thick oxide layer will form. This thick oxide layer, distinguished by its blue tint, will have a chrome depleted layer under it, which will impair corrosion resistance. Both the oxide film and depleted layer must be removed, either mechanically (grinding with a fine grit is recommended, wire brushing and shot blasting will have less effect), or chemically (acid pickle with a mixture of nitric and hydrofluoric acid). Once cleaned, the surface can be chemically passivated to enhance corrosion resistance, (passivation reduces the anodic reaction involved in the corrosion process). Carbon steel tools, also supports or even sparks from grinding carbon steel, can embed fragments into the surface of the stainless steel. These fragments can then rust if moistened. Therefore it is recommended that stainless steel fabrication be carried out in a separate designated area and special stainless steel tools used where possible. If any part of stainless-steel is heated in the range 500 degrees to 800 degrees for any reasonable time there is a risk that the chrome will form chrome carbides (a compound formed with carbon) with any carbon present in the steel. This reduces the chrome available to provide the passive film and leads to preferential corrosion, which can be severe. This is often referred to as sensitisation. Therefore it is advisable when welding stainless steel to use low heat input and restrict the maximum interpass temperature to around 175°, although sensitisation of modern low carbon grades is unlikely unless heated for prolonged periods. Small quantities of either titanium (321) or niobium (347) added to stabilise the material will inhibit the formation of chrome carbides. To resist oxidation and creep high carbon grades such as 304H or 316H are often used. Their improved creep resistance relates to the presence of carbides and the slightly coarser grain size associated with higher annealing temperatures. Because the higher carbon content inevitably leads to sensitisation, there may be a risk of corrosion during plant shut downs, for this reason stabilised grades may be preferred such as 347H. The solidification strength of austenitic stainless steel can be seriously impaired by small additions of impurities such as sulphur and phosphorous, this coupled with the materials high coefficient of expansion can cause serious solidification cracking problems. Most 304 type alloys are designed to solidify initially as delta ferrite, which has a high solubility for sulphur, transforming to austenite upon further cooling. This creates an austenitic material containing tiny patches of residual delta ferrite, therefore not a true austenitic in the strict sense of the word. Filler metal often contains further additions of delta ferrite to ensure crack free welds. The delta ferrite can transform to a very brittle phase called sigma, if heated above 550°C for very prolonged periods (Could take several thousand hours, depending on chrome level. A duplex stainless steel can form sigma phase after only a few minutes at this temperature) The very high coefficient of expansion associated with this material means that welding distortion can be quite savage. I have seen thick ring flanges on pressure vessel twist after welding to such an extent that a fluid seal is impossible. Thermal stress is another major problem associated with stainless steel; premature failure can occur on pressure plant heated by a jacket or coils attached to a cold veesel. This material has poor thermal conductivity, therefore lower welding current is required (typically 25% less than carbon steel) and narrower joint preparations can be tolerated. All common welding processes can be used successfully, however high deposition rates associated with SAW could cause solidification cracking and possibly sensitisation, unless adequate precautions are taken. To ensure good corrosion resistance of the weld root it must be protected from the atmosphere by an inert gas shield during welding and subsequent cooling. The gas shield should be contained around the root of the weld by a suitable dam, which must permit a continuous gas flow through the area. Welding should not commence until sufficient time has elapsed to allow the volume of purging gas flowing through the dam to equal at least the 6 times the volume contained in the dam (EN1011 Part 3 Recommends 10). Once purging is complete the purge flow rate should be reduced so that it only exerts a small positive pressure, sufficient to exclude air. If good corrosion resistance of the root is required the oxygen level in the dam should not exceed 0.1%(1000 ppm); for extreme corrosion resistance this should be reduced to 0.015% (150 ppm). Backing gasses are typically argon or helium; Nitrogen Is often used as an economic alternative where corrosion resistance is not critical, Nitrogrn + 10% Helium is better. A wide variety of proprietary pastes and backing materials are available than can be use to protect the root instead of a gas shield. In some applications where corrosion and oxide coking of the weld root is not important, such as large stainless steel ducting, no gas backing is used. A pdf guide to weld purging Huntingdon Fusion Techniques Limited Carbon content: 304 L grade Low Carbon, typically 0.03% Max 304 grade Medium Carbon, typically 0.08% Max 304H grade High Carbon, typically Up to 0.1% The higher the carbon content the greater the yield strength. (Hence the stength advantage in using stabilised grades) Typical Alloy Content 304 316 316 Ti 320 321 347 308 309 (18-20Cr, 8-12Ni) (16-18Cr, 10-14Ni + 2-3Mo) (316 with Titanium Added) (Same as 316Ti) (17-19Cr, 9-12Ni + Titanium) (17-19Cr, 9-13Ni + Niobium) (19-22Cr, 9-11Ni) (22-24Cr, 12-15Ni) 304 + Molybdenum 304 + Moly + Titanium 304 + Titanium 304 + Niobium 304 + Extra 2%Cr 304 + Extra 4%Cr + 4% Ni All the above stainless steel grades are basic variations of a 304. All are readily weldable and all have matching consumables, except for a 304 which is welded with a 308 or 316, 321 is welded with a 347 (Titanium is not easily transferred across the arc) and a 316Ti is normally welded with a 318. Molybdenum has the same effect on the microstructure as chrome, except that it gives better resistance to pitting corrosion. Therefore a 316 needs less chrome than a 304. 310 904L (24-26Cr,19-22Ni) True Austenitic. This material does not transform to ferrite on cooling and therefore does not contain delta ferrite. It will not suffer sigma phase embrittlement but can be tricky to weld. (20Cr,25Ni,4.5Mo) Super Austenitic Or Nickel alloy. Superior corrosion resistance providing they are welded carefully with low heat input (less than 1 kJ/mm recommended) and fast travel speeds with no weaving. Each run of weld should not be started until the metal temperature falls below 100°C. It is unlikely that a uniform distribution of alloy will be achieved throughout the weld (segregation), therefore this material should either be welded with an over-alloyed consumable such as a 625 or solution annealed after welding, if maximum corrosion resistance is required. Return To Sub Menu Carbon Steel To Austenitic Steel When a weld is made using a filler wire or consumable, there is a mixture in the weld consisting of approximately 20% parent metal and 80% filler metal alloy ( percentage depends on welding process, type of joint and welding parameters). Any reduction in alloy content of 304 / 316 type austenitics is likely to cause the formation of matensite on cooling. This could lead to cracking problems and poor ductility. To avoid this problem an overalloyed filler metal is used, such as a 309, which should still form austenite on cooling providing dilution is not excessive. The Shaeffler diagram can be used to determine the type of microstructure that can be expected when a filler metal and parent metal of differing compositions are mixed together in a weld. The Shaeffler Diagram The Nickel and other elements that form Austenite, are plotted against Chrome and other elements that form ferrite, using the following formula:Nickel Equivalent = %Ni + 30%C + 0.5%Mn Chrome Equivalent = %Cr + Mo + 1.5%Si + 0.5%Nb Example, a typical 304L = 18.2%Cr, 10.1%Ni, 1.2%Mn, 0.4%Si, 0.02%C Ni Equiv = 10.1 + 30 x 0.02 + 0.5 x 1.2 = 11.3 Cr Equiv = 18.2 + 0 + 1.5 x 0.4 + 0 = 18.8 A typical 309L welding consumable Ni Equiv = 14.35, Cr Equiv = 24.9 The main disadvantage with this diagram is that it does not represent Nitrogen, which is a very strong Austenite former. Ferrite Number The ferrite number uses magnetic attraction as a means of measuring the proportion of delta ferrite present. The ferrite number is plotted on a modified Shaeffler diagram, the Delong Diagram. The Chrome and Nickel equivalent is the same as that used for the Shaeffler diagram, except that the Nickel equivalent includes the addition of 30 times the Nitrogen content. Examples The Shaeffler diagram above illustrates a carbon steel C.S , welded with 304L filler. Point A represents the anticipated composition of the weld metal, if it consists of a mixture of filler metal and 25% parent metal. This diluted weld, according to the diagram, will contain martensite. This problem can be overcome if a higher alloyed filler is used, such as a 309L, which has a higher nickel and chrome equivalent that will tend to pull point A into the austenite region. If the welds molten pool spans two different metals the process becomes more complicated. First plot both parent metals on the shaeffler diagram and connect them with a line. If both parent metals are diluted by the same amount, plot a false point B on the diagram midway between them. (Point B represents the microstructure of the weld if no filler metal was applied.) Next, plot the consumable on the diagram, which for this example is a 309L. Draw a line from this point to false point B and mark a point A along its length equivalent to the total weld dilution. This point will give the approximate microstructure of the weld metal. The diagram below illustrates 25% total weld dilution at point A, which predicts a good microstructure of Austenite with a little ferrite. The presence of martensite can be detected by subjecting a macro section to a hardness survey, high hardness levels indicate martensite. Alternatively the weld can be subjected to a bend test ( a side bend is required by the ASME code for corrosion resistant overlays), any martensite present will tend to cause the test piece to break rather than bend. However the presence of martensite is unlikely to cause hydrogen cracking, as any hydrogen evolved during the welding process will be absorbed by the austenitic filler metal. Evaluating Dilution Causes Of High Dilution  High Travel Speed. Too much heat applied to parent metal instead of on filler metal.  High welding Current. High current welding processes, such as Submerged Arc Welding can cause high dilution.  Thin Material. Thin sheet TIG welded can give rise to high dilution levels.  Joint Preparation. Square preps generate very high dilution. This can be reduced by carefully buttering the joint face with high alloy filler metal. http://www.avestapolarit.com/upload/steel_properties/Schaeffler_l arge.jpg Large Schaeffler/Delong Diagram (Outokumpu.com) Return To Sub Menu Last Modified 19 Jan 2004 Duplex stainless steels Typically twice the yield of austenitic stainless steels. Minimum Specified UTS typically 680 to 750N/mm2 (98.6 to 108ksi). Elongation typically > 25%. Superior corrosion resistance than a 316. Good Resistance to stress corrosion cracking in a chloride environment. Duplex materials have improved over the last decade; further additions of Nitrogen have been made improving weldability. Because of the complex nature of this material it is important that it is sourced from good quality steel mills and is properly solution annealed. Castings and possibly thick sections may not cool fast when annealed causing sigma and other deleterious phases to form. The material work hardens if cold formed; even the strain produced from welding can work harden the material particularly in multi pass welding. Therefore a full solution anneal is advantageous, particularly if low service temperatures are foreseen. The high strength of this material can make joint fit up difficult. Usable temperature range restricted to, -50 to 280°C Used in Oil & Natural Gas production, chemical plants etc. Standard Duplex S31803 22Cr 5Ni 2.8Mo 0.15N PREn = 32-33 Super Duplex: Stronger and more corrosion resistant than standard duplex. S32760(Zeron 100) 25Cr 7.5Ni 3.5Mo 0.23N PREn = 40 Micro Of Standard Duplex Dark Areas:- Ferrite Light Areas:- Austenite Duplex solidifies initially as ferrite, then transforms on further cooling to a matrix of ferrite and austenite. In modern raw material the balance should be 50/50 for optimum corrosion resistance, particularly resistance to stress corrosion cracking. However the materials strength is not significantly effected by the ferrite / austenite phase balance. The main problem with Duplex is that it very easily forms brittle intermetalic phases, such as Sigma, Chi and Alpha Prime. These phases can form rapidly, typically 100 seconds at 900°C. However shorter exposure has been known to cause a drop in toughness, this has been attribute to the formation of sigma on a microscopic scale. Prolonged heating in the range 350 to 550°C can cause 475°C temper embrittlement. For this reason the maximum recommended service temperature for duplex is about 280°C. Sigma (55Fe 45Cr) can be a major problem when welding thin walled small bore pipe made of super duplex, although it can occur in thicker sections. It tends to be found in the bulk of the material rather than at the surface, therefore it probably has more effect on toughness than corrosion resistance. Sigma can also occur in thick sections, such as castings that have not been properly solution annealed (Not cooled fast enough). However most standards accept that deleterious phases, such as sigma, chi and laves, may be tolerated if the strength and corrosion resistance are satisfactory. Nitrogen is a strong austenite former and largely responsible for the balance between ferrite and austenite phases and the materials superior corrosion resistance. Nitrogen can’t be added to filler metal, as it does not transfer across the arc. It can also be lost from molten parent metal during welding. Its loss can lead to high ferrite and reduced corrosion resistance. Nitrogen can be added to the shielding gas and backing gas, Up to about 10%; however this makes welding difficult as it can cause porosity and contamination of the Tungsten electrode unless the correct welding technique is used. Too much Nitrogen will form a layer of Austenite on the weld surface. In my experience most duplex and super duplex are TIG welded using pure argon. Backing / purge gas should contain less than 25ppm Oxygen for optimum corrosion resistance. Fast cooling from molten will promote the formation of ferrite, slow cooling will promote austenite. During welding fast cooling is most likely, therefore welding consumables usually contain up to 2 - 4% extra Nickel to promote austenite formation in the weld. Duplex should never be welded without filler metal, as this will promote excessive ferrite, unless the welded component is solution annealed. Acceptable phase balance is usually 30 – 70% Ferrite Duplex welding consumables are suitable for joining duplex to austenitic stainless steel or carbon steel; they can also be used for corrosion resistant overlays. Nickel based welding consumables can be used but the weld strength will not be as good as the parent metal, particularly on super duplex.  Low levels of austenite: - Poor toughness and general corrosion resistance.  High levels of austenite: - Some Reduction in strength and reduced resistance to stress corrosion cracking. Good impact test results are a good indication that the material has been successfully welded. The parent metal usually exceeds 200J. The ductile to brittle transition temperature is about –50°C. The transition is not as steep as that of carbon steel and depends on the welding process used. Flux protected processes, such as MMA; tend to have a steeper transition curve and lower toughness. Multi run welds tend to promote austenite and thus exhibit higher toughness Tight controls and the use of arc monitors are recommended during welding and automatic or mechanised welding is preferred. Repair welding can seriously affect corrosion resistance and toughness; therefore any repairs should follow specially developed procedures. See BS4515 Part 2 for details. Production control test plates are recommended for all critical poduction welds. Welding procedures should be supplemented by additional tests, depending on the application and the requirements of any application code: A ferrite count using a Ferro scope is probably the most popular. For best accuracy the ferrite count should be performed manually and include a check for deleterious phases.  Good impact test results are also a good indication of a successful welding procedure and are mandatory in BS4515 Part 2.  A corrosion test, such as the G48 test, is highly recommended. The test may not model the exact service corrosion environment, but gives a good qualative assessment of the welds general corrosion resistance; this gives a good indication that the welding method is satisfactory. G48 test temperature for standard duplex is typically 22°C, for super duplex 35°C Typical Welding Procedure For Zeron 100 (Super Duplex) Pipe 60mm Od x 4mm Thick Maximum Interpass 100°C 1.6mm Filler Wire Position 6G Temperature at the end of welding < 250°C 85 amps 2 weld runs (Root and Cap) Arc energy 1 to 1,5 KJ/mm Travel speed 0.75 to 1 mm/sec Recommended Testing 1. Ferric Chloride Pitting Test To ASTM G48 : Method A 2. Chemical analysis of root 3. Ferrite count Return To Sub Menu Last Modified 19 March 2002 Links To Other Sites  Reference Sites The best sites I have found for technical information  Professional Bodies Standards Institutes And Professional Bodies  General information Lots of useful web sites covering a wide range of subjects  Web Site Design Sites covering web design, verification and graphics  Web Addressing A useful alternative to the address bar on your web browser.  Great Savings This site explains how you can make huge savings! REFERENCE SITES Material Properties : Matweb  Stainless Steel World  Nickel Development Institute  Nickel Cross Reference  Metal Suppliers Online  More Materia Information Calculation Software:  Xcalcs  Spreadsheet Solutions for Structural Engineers  Spreadsheets For Structural Engineering  MDSOLIDS  Free CAD Program  Free Finite Element Program  The Finite Element Method Site  Excelcalcs.com  Weld Calculations ? More Useful Links On Metallurgy ? Information & Know-How TWI Site Contains masses of free technical information in the 'Information & Know-How' Section. ? Uk welder This site access some of the practical articles from TWI's web site; also includes a list of welding related jobs. ? Lincoln Arc Welding Foundation The James F. Lincoln Arc Welding Foundation is dedicated to advancing safe,reliable, and cost-effective arc welding design and practice worldwide.Well known for its cheap books on welding, 'The Welding Procedure Handbook'is highly recommended. Further technical information Knowledge Articles ? ESAB University Free online handbooks and a courses in basic welding filler metal technology ? Aluminum Welding Technical Information For Aluminum Welding ? Pro-Fusion Lots of information on TIG & Plasma welding + tungsten electrodes and welding applications. ? Weld Reality A web site where you will find practical Welding solutions for manual / robot welding issues. ? Welding Advisors Covering Welding Processes Equipment Materials Jobs and Careers Quality Safety and Related Processes/Applications. Free Subscription and Download. Questions welcomed. ? Mechanical Engineers reference The site includes various tables and reference documents + links to a wide variety of other web sites associated with Mechanical Engineering. ? Engineering Reference Useful information on all aspects of Science, Mathematics and Engineering. ? Engineers Edge Design,Engineering & Manufacturing Resources. ? Authorizedinspector.com This site was established to promote ASME Boiler and Pressure Vessel Standards and to provide information helpful towards maintaining compliance ? Steelmaking More than 7,500 Links to Steelmaking and Steel-Related Technologies!. More Links Construction-Web-Links ? Boiler Room An On-Line Community of Manufacturers Representatives Engineers and Operators of Commercial and Industrial Steam Boilers. ? Bolting The science of bolting and gasket factors explained. Also try Tribology-ABC Lots of information on: - screw threads failure analysis and lubrication + online calculators ? Flange Info Flange dimentions and weights ? Corrosion Information on corrosion, also Nasa.gov for a simple description of the variouse types of corrosion and NACE The Corrosion Society. ? NDT Cabin The Internet Magazine for NDT professionals ? Professional Development Online Continuing Education for Engineers and Architects. ? WPSAmerica Welding Procedure Software service for major welding codes (AWS CSA ASME). ? Welding School Online A free resource to all interested in attending welding school or seeking basic to advanced welding techniques ? Weld-Class-Solutions Weld-Class-Solutions is an independent training and technical consulting organisation related to all aspects of welding engineering welding inspection and non destructive testing technology. ? Ultrasonic Impact Treatment Esonix:- the only effective technique for consistently reducing the negative effects and defects in processing metals and restoring the products base properties increasing fatigue life. Sounds good but is it true? ? On-Line Converters A range of useful conversion ? More Links A huge number of useful links <Top> ? STANDARDS INSTITUTES AND PROFESSIONAL BODIES The Welding Institute TWI - Materials Joining Technology Home Page ? British Standards British Standards Institute ? ped.eurodyn.com The official European Pressure Equipment Directive web site. ? ISO Standards International Standards Organisation. ? DIN Standards German Standards. Official DIN Web Site ? Australian Standards Standards Australia International Ltd ? Gosstandart Of Russia Russian Standards ? ANSI American National Standards Institute is a private, non-profit organization that administers and coordinates the U.S. voluntary standardization and conformity assessment system. ? ASME The American Society For Mechanical Engineering. National Board Board of Boiler and Pressure Vessel Inspectors' ? WRC The Welding Research Council ? AWS American Welding Society. Information on their publications, they even have a chat room. ? ASM The American Materials Information Society ? AISC The American Institute of Steel Construction ? TEMA Tubular Exchanger Manufacturers Association ? The Engineering Council UK body for promoting and regulating professional Engineers. ? CEOC European Confederation of Organisations for Testing ? SAFED The UK Safety Assessment Federation. Represents the interests of UK inspection bodies, originated as AOTC. ? HVCA The Heating and Ventilating Contractors' Association. ? EEMUA The engineering equipment and material users association. <Top> ? GENERAL INTEREST BBC.co.uk The BBC has the best general interest web site on the internet. Use the BBC Iplayer to watch past TV programmes, UK only ? The European Union On Line The latest news on Europe, including: European Legislation, Trade and Industry Policy, The history of the European Union, and much more! ? Language Translator This site will translate text or web pages from one language to another. ? Train Times UK Train Time Table, covers all rail operators and routes. ? Street Maps If you know most of the address of a person or business in the UK and most of the world it will draw you a street plan of where they are. Includes Aerial Views. ? RAC Route Planner Check the traffic situation and plan your route to any destination around Europe. ? Search Engine Watch Search engine watch gives details and links to most popular search Engines. ? Fact Monster Lots of interesting facts, ideal for school kids. ? Real Time True world time independent from your computers clock, also world time server ? Health Care The surgery door provides lots of information on common medical problems. Also:- Netdoctor and NHS Direct + Embarrassing Problems + Practical Back Pain info It gets to us all in the end! + Snoring Don't laugh, it's a serious problem for many ? Manage your Finances UK only. 'This is money' gives you advice how best to manage your finances. It includes advice on pensions, income tax, mortgages, savings, even choosing a cheaper gas suppler. ? Walking Websites UK only. A detailed collection of walks around Britain Walking Pages + The Ramblers association ? Beer Mad UK only. CAMRA Branches Beer Festivals etc. ? Home Check UK only. The ultimate FREE guide to flooding, subsidence, pollution, landfill sites, schools, property prices and crime rates in your neighbourhood. ? Global Rich List Did you know you earn almost as much as Bill Gates compare your salary with that of the worlds poorest people and be amazed ? Time Bank UK only. Looking for something interesting to do or want to meet new friends then why not become a volunteer! A wide range of local projects to chose from including: - conservation caring mentoring etc. ? We Are What We Do This is a new movement which inspires people to use their every day actions to change the world ? Plain English Since 1979 they have been campaigning against gobbledygook jargon and misleading public information <Top> ? WEB SITE DESIGN Bells & Whistles Useful web site embellishments, images, backgrounds, animations etc. ? Coding With Style Good looking web pages made easy ? Check Your Code Check your web pages for compatibility ? Down Load.com Free software ? html Goodies Lots of useful information on html code ? PDF file creator Free pdf file creator. It simply diverts your printer output to a pdf file. ? Dynamic Drive Scripts and components to enhance your web site! ? Home <Top> Instead of editing the web address on your browser just type it here http://www. is automatically added, just click the appropriate ending Enter Web Name www. Page last updated 30 October 2012