IS-2629

IS : 2629 - 1985(Reaffirmed 2001) ( Reaffirmed 2006 ) Edition 2.3 (2001-01) Indian Standard RECOMMENDED PRACTICE FOR HOT-DIP GALVANIZING OF IRON AND STEEL ( First Revision ) (Incorporating Amendment Nos. 1, 2 & 3) UDC 669.1 : 669.586.5 © BIS 2004 BUREAU MANAK BHAVAN , 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002 OF INDIAN STANDARDS Price Group 7 IS : 2629 - 1985 Indian Standard RECOMMENDED PRACTICE FOR HOT-DIP GALVANIZING OF IRON AND STEEL ( First Revision ) Hot-Dip, Sprayed and Diffusion Coatings Sectional Committee, SMDC 28 Chairman SHRI V. R. SUBRAMANIAN Members SHRI P. K. BANERJEE SHRI K. S. BANNINTHAYA SHRI J. N. BHATTACHARYYA CHEMIST & METALLURGIST ASSISTANT CHEMIST & METALLURGIST ( Alternate ) SHRI G. GANESHAN SHRI B. G. SOHONI ( Alternate ) SHRI BRIJLAL KHASTRIYA SHRI J. N. BHAMBRY ( Alternate ) SHRI RAMESH CHANDRA MAHAJAN The Tinplate Co of India Ltd, Golmuri Steel Authority of India Ltd (R & D Centre for Iron & Steel), Ranchi National Test House, Calcutta Ministry of Railways, New Delhi Representing Indian Hot Dip Galvanizer’s Association, New Delhi Kamani Engineering Corporation Ltd, Bombay Steel Authority of India Ltd (Rourkela Steel Plant), Rourkela The Indian Steel Jamshedpur and Wire Products Ltd, SHRI DARSHAN SINGH ( Alternate ) Zenith Steel Pipes Ltd, Bombay SHRI S. NEELAKANTAN DR A. R. KESKAR ( Alternate ) Guest, Keen, Williams Ltd, Calcutta SHRI D. PAUL SHRI L. PUGAZHENTHY Indian Lead Zinc Information Centre, New Delhi Ministry of Defence (DGI), New Delhi SHRI B. N. SAHA SHRI A BHATTACHARYA ( Alternate ) SHRI S. N. SINGH Elecrtrical Manufacturing Co Ltd, Calcutta SHRI M. M. MALHOTRA ( Alternate ) SHRI N. K. SINGHAL Indian Iron and Steel Co Ltd, Burnpur SHRI A. SENGUPTA ( Alternate ) Special Steels Ltd, Bombay SHRI J. L. SONEJI SHRI M. R. DOCTOR ( Alternate ) ( Continued on page 2 ) © BIS 2004 BUREAU OF INDIAN STANDARDS This publication is protected under the Indian Copyright Act (XIV of 1957) and reproduction in whole or in part by any means except with written permission of the publisher shall be deemed to be an infringement of copyright under the said Act. GUPTA ( Alternate ) Guest. NEELAKANTAN Zenith Steel Pipes Ltd. Bokaro Steel City Director General. Calcutta SHRI S. DUTTA The Indian Tube Co Ltd. New Delhi SHRI G. A. ISI Hot-Dip Galvanizing Subcommittee. C. ANAND Elecrtrical Manufacturing Co Pvt Ltd. New Delhi DEPUTY DIRECTOR ( Alternate ) SHRI D. Howrah SHRI VIJAY KAPOOR 2 . Members SHRI L. G. Calcutta SHRI S. Keen. Calcutta SHRI P. SHANBHAG Special Steels Ltd. Bombay SHRI N. MUKHERJEE SHRI K. K. K. MEHTA ( Alternate ) DIRECTOR Central Electricity Authority. S. SMDC 28 : 1 Convener SHRI V. Bombay SHRI S. Burnpur SHRI K. SUBRAMANIAN Indian Hot New Delhi Dip Galvanizer’s Association. Calcutta SHRI J. R. Subramanian ) SHRI V. S. S. MURANJAN ( Alternate ) SHRI A. MAJUMDAR Directorate General of Technical Development. S. Director (Struc & Met) Representing Steel Authority of India Ltd (Bokaro Steel Ltd). TANEJA Directorate General of Supplies & Disposals. SINGH ( Alternate ) SHRI B. New Delhi Posts & Telegraph Department. Jamshedpur SHRI N. Bharatpur SHRI D. MAHAPATRA Plant). GUHA The Fort William Co Ltd. R. Rourkela SHRI S. ERRY ( Alternate ) SHRI K. Chandigarh Hope’s Metal Windows (India) Ltd. TUDEKAR SHRI J. Jamshedpur DR T. SENGUPTA The Indian Iron & Steel Co Ltd. K. C. BHULLAR SHRI M. PUGAZHENTHY ( Alternate to Shri V.1985 ( Continued from page 1 ) Members SHRI S. MUKHERJEE SHRI S. M. MAHAJAN Jamshedpur SHRI AVTAR SINGH ( Alternate ) Steel Authority of India Ltd (Rourkela Steel SHRI B. R. KUMAR ( Alternate ) Ministry of Railways JOINT DIRECTOR (CHEM) JOINT DIRECTOR (TI)-1 ( Alternate ) The Indian Steel & Wire Products Ltd. SINHA ( Alternate ) SHRI S. M. BEDI SHRI A. SOBTI ( Alternate ) General Engineering Works. PARIKH SHRI R.IS : 2629 . P. RAGHAVENDRAN. ISI ( Ex-officio Member ) Secretary SHRI S. G. BALI Hydel Designs Directorate. R. GUPTA Deputy Director (Metals). SHRI R. S. NATARAJAN ( Alternate ) SHRI A. Williams Ltd. D. MITRA ( Alternate ) The Tata Iron & Steel Co Ltd. N. D. Bombay DR A. KESKAR ( Alternate ) Kamani Engineering Corporation Ltd. 3. The zinc coating firstly protects the base metal by acting as an impervious shield between the metal and the atmosphere and secondly affords sacrificial protection even when moderately sized areas (4 mm dia. The intermediate alloy layer provides a strong bond between the ferrous base material and the pure zinc and also resists corrosion and abrasion in the event of the pure zinc layer being removed. (b) dry process. Under same conditions of process or composition of the material the whole coating may consist of zinc-iron alloy layers. F O R E W O R D 0.1985 Indian Standard RECOMMENDED PRACTICE FOR HOT-DIP GALVANIZING OF IRON AND STEEL ( First Revision ) 0.1 This Indian Standard (First Revision) was adopted by the Indian Standards Institution on 20 June 1985. when 3 .3 Hot-dip galvanizing is an old and well known process of applying zinc coating to iron or steel surface for protection against corrosion. The typical photographs for the various defects in galvanized coatings on iron and steel have also been included in Appendix A.1 When a thoroughly cleaned article is immersed in a galvanizing bath. namely (a) wet process.IS : 2629 . After galvanizing.3. As the article is withdrawn from the bath. and (c) a combination of dry and wet process by continuous or batch galvanizing. 0.2 The galvanizing process can be grouped together under three categories. 0. The present revision has been prepared in the light of the experience gained since its first publication and further technical developments in this field. it picks up pure zinc which solidifies on cooling and forms the outer layer. Continuous galvanizing process consists of cleaning base steel surface by first oxidizing and subsequently reducing the surface oxides under controlled atmosphere or by any other in-line cleaning method. The strip is heat-treated in line annealing/normalizing furnace followed by continuous feeding through molten zinc bath and passivating treatment by suitable agent like chromic acid. the metal surface reacts with molten zinc to form a zinc-iron alloy. The continuous galvanizing process has been included in this revision. Sprayed and Diffusion Coatings Sectional Committee had been approved by the Structural and Metals Division Council. 0. for example) of the base metal surface are exposed. after the draft finalized by the Hot-Dip. 0.2 This standard was first published in 1966. The primary purpose of the flux is to help in keeping the surface of both work and molten zinc free from oxide at the time of reaction. The former is formed as a result of oxidation of clear zinc on the bath surface and when the oxide is skimmed off. SCOPE 1. 2 (March 1995) and Amendment No.0 For the purpose of this standard. their causes and remedial measures are given in Appendix A.3. 0. 1 (December 1988). 4 . forms in the galvanizing bath as a result of the reaction of molten zinc with iron or iron salts and settles down at the bottom of the bath. commonly met with in the hot-dip galvanizing practice. 2.5 Working conditions and safety measures which should be observed in galvanizing plants are given in Appendix B.1985 the sheet emerges from the zinc bath. 0. There is no fluxing in this process. better surface appearance. 0. Side bar indicates modification of the text as the result of incorporation of the amendments. uniformity of coating along the length. which is a complex mixture of zinc and iron.1 Ash — A mixture of zinc oxide and varying quantities of metallic zinc. the following definitions shall apply. the excess molten zinc on them is wiped off by air or gas jets.2 Dross — An intermetallic compound (FeZn13). a certain amount of metallic zinc gets entrapped and removed along with it.3 Flux — A chemical compound applied in the form of an aqueous solution and dried on to the work in the dry process or spread as a molten blanket over the zinc bath in the wet process. 1.IS : 2629 . In this appendix. 3 (January 2001). Amendment No. along with the typical photographs for illustration. control of coating thickness. 2. less dross formation. 2. 0.6 This edition 2. TERMINOLOGY 2. the information given in the last column aids inspectors in interpreting the appearance of the article and help them in arriving at a correct decision for accepting or rejecting the finished material.3 incorporates Amendment No.3 Continuous galvanizing process has got advantages over both wet and dry processes with respect to high productivity.4 A summary of defects. 2. etc. better coating adherence. Zinc content in dross will vary between 94 to 97 percent depending on the quantity of metallic zinc entrained in dross during its removal from the pot. In both the galvanizing processes fluxing helps maintaining the surface of work free from oxides.1 This standard recommends important guidelines for general hot-dip galvanizing of iron and steel. etc. PREPARATION OF THE METAL SURFACE FOR GALVANIZING 4. If necessary. Several proprietary reagents are available. threaded sections. 3.5 Inhibitor — A substance added to pickling solution to prevent undue attack on clean metal without affecting the scale removing property of the pickling solution. This effect. 3.2 Cast Iron — Cast iron react with zinc differently depending on the exact composition. however.1985 2. 2. pretreatment in special solvents will be necessary for their removal. the temperature of the solution may be usually kept between 85 and 90°C and the immersion time varying from 1 to 20 minutes depending on the nature and degree of contamination. When using sodium hydroxide solution. Generally a sodium hydroxide solution obtained by dissolving 10 to 15 kg of sodium hydroxide in 100 litres of water is used.1 Steel — Mild steel is the most common material that is galvanized and the variations in the range of compositions used have little influence on the galvanizing process.1 Carbon and silicon tend to increase the rate of reaction between steel and molten zinc. etc.1 Cleaning — If an article is contaminated by oil.1 The work should be so handled in the degreasing bath as to allow free circulation of liquid over all parts. BASE METAL FOR GALVANIZING 3. The steel. should contain minimum amount of segregation. the silicon and phosphorus contents. 4. 2. slag inclusions. that accumulates on the galvanized surface exposed to water film or moist atmosphere. taking care to clean the scum that may collect.4 Over-Pickling — The undue attack of the underlying ferrous surface by the pickling solution after the removal of scale. manufacturers’ recommendation should be followed.7 Wetting Agent — A substance added to pickling and prefluxing solutions to facilitate wetting of the work surface. mainly containing zinc oxide and basic zinc carbonate. grease or paint. 5 . the work should be raised and lowered in order to allow the degreasing solution to enter inaccessible areas. in particular. 3.IS : 2629 .1. 2. rolled-in millscale. however.1. is not so apparent in the range of compositions encountered in mild steels as in high carbon and high silicon steels. for a thorough cleaning action.6 White Rust — A white corrosion product. 4. When using other proprietary degreasing agents. 3. 4.2 Cleaning of Castings — Grey iron and malleable iron castings if not properly cleaned before annealing.1 A hydrofluoric acid pickle leaves a gelatinous layer on the surface of the castings which shall be thoroughly removed by hosing with water and scrapping and brushing.2.1.1 ) and sulphuric acid ( see 4. 4. the inlet should be at the bottom of the tank and water should overflow from the top. Since this is an expensive and difficult process.1. all castings should be shot or grit blasted prior to galvanizing. 4. a solution consisting of 4 parts of dilute hydrochloric acid (1 : 1) and 1 part of hydrofluoric acid may be used. 4 parts by volume of technical grade hydrochloric acid ( see IS : 265-1976* ) and 40 parts by volume of water may also by used for pickling.2 ) solutions may be used for pickling.2. ranging from one volume of acid and 59 volumes of water for a very weak pickle to one volume of acid and 9 volumes of water for a very strong solution.2 Solution containing 6 parts by volume of commercial hydrofluoric acid. the work should be rinsed in hot water (60°C) followed. 6 . It is generally recommended to give a quick rinse in running water followed by cleaning with one of the pickling acids. by a final rinse in cold running water. the commercial acid is diluted to various strengths. This way the rinse water is in a dynamic state thereby ensuring an efficient and a thorough rinsing operation. For use.2 When lubricating materials have contaminated with the surface of the metal. When pickling of castings is done occasionally. Except in the case of light castings which would be damaged. if possible. With a weak solution pickling may take as long as 24 hours. it may be necessary to heat the part to bluing or scaling temperature in order to burn off the offending material. Hydrochloric acid is used at room temperature while with sulphuric acid best results are obtained when it is hot (60 to 80°C).1.2. prior care should be taken to avoid such contamination.3. 4.1. It is then processed according to normal fluxing practice 4. 4.1985 4.3 Pickling — Both hydrochloric acid ( see 4. An ideal arrangement for rinsing would be to provide an inlet and outlet on two opposite sides of the rinsing tank. while the strong solution should pickle satisfactorily in 10 to 30 minutes.1 An alternative but less efficient method of cleaning castings with burnt-on sand is to employ a pickle solution containing hydrofluoric acid.1.1 Immediately after degreasing. *Specification for hydrochloric acid ( second revision ). develop burnt-on and patches at the surface which are not removed by normal pickling.IS : 2629 . The casting shall then go through the ordinary pickling process. the solution should be discarded. 4. 4. 4.3. The strength of the solution should be maintained by periodic addition of fresh concentrated acid. 4.1985 4.2 Sulphuric Acid Solution ( 100-150 g/l ) — Dilute 6 to 8 ml of technical grade acid conforming to IS : 266-1977† to 100 ml. the temperature of the bath and the time of immersion will depend on the nature of the work to be pickled. Two rinse tanks are preferable. The solution should be tested for acid and iron contents at regular intervals in accordance with the methods given in Appendix C.3. The iron salts in the pickling bath gradually accumulate with continued working and when the iron content reaches to about 100 to 120 g/l.1 A suitable inhibitor should be used with hydrochloric acid.2. the water cascading from one 7 .1. Raise or lower the work once or twice to change the acid layer in contact with the work.4 Control of the Acid Solution — To make the best use of the solution.3 Agitation — Mild agitation of the work in the pickling tank reduces the time of pickling. 4.3. the article should be rinsed in running water.3. 4.3.1 Hydrochloric Acid Solution ( 100-150 g/l ) — Dilute technical grade acid conforming to IS : 265-1976* with an equal volume of water.4 Rinsing — After pickling. reasonably close control of its acid content is necessary.3. 4. Air agitation is not recommended. The actual concentration of sulphuric acid solutions. The actual concentration of hydrochloric acid solutions and the time of immersion will depend on the nature of the work to be pickled.3.IS : 2629 . Where this is not done the pickling solution should be neutralized before dumping into sewers or streams.5 Disposals of Waste Liquor — The acid and iron compounds may be recovered from the waste pickling solution.1 A suitable inhibitor should be used with sulphuric acid. . . drainage)  bolt holes.  ature by  Only Remove work  agreement slowly  Keep articles  separated  prior   flux burnt  Stale on during  dipping Flux  Surface resiinclusions  dues on steel picked up  Flux from top of  bath  Flux stain if left  over on the job after flux removal. Check steel pre.IS : 2629 . etc  in  Articles  contact during  withdrawal Remove work   slowly Increase temper.1985 FIGURE DEFECTS CAUSES RECOMMENDED ACTIONS GUIDANCE FOR ACCEPTANCE/ REJECTION  Withdrawal  speed too high  Cold galvanizLumpiness  ing bath and runs  Delayed runoff (uneven  seams. joints. is not considered paration  as flux inclusion Skim before  and hence should withdrawal  not be rejected  Refresh or renew flux blanket (A microstructure of flux inclusion) 16 . from design and fab. compared to a free zinc)  gen  during tor  solidification  bright coating. or lim con. Skim bath before  if in gross lumps  withdrawal   (A microstructure of ash inclusion)   Not if due to steel  Steel composi.  tion (high siliphostion in order to  condition. In coating (all  ing alloy no  Release of ab.  seams  and rication Rust stains  folds  May be accepted  Storage near Check storage   rusty material  condition   17 . environ  acidic   ment.IS : 2629 . composition or ply for composi. (Under a microscope. the cross section)  ‘Weeping’ of Check product   acid. etc. use inhibi. only displeasing to  Slow ing. adjust for gal. fact.Check steel sup. is  of coating  abrasion resistant   and is chemically   more protective in environ  some   ment for instance.1985 FIGURE DEFECTS CAUSES RECOMMENDED ACTIONS GUIDANCE FOR ACCEPTANCE/ REJECTION    Ash inclusions     Ash burnt on during dipping Ash picked up from top of bath Skim bath before   dipping  May be rejected.  sorbed hydroling.  cold work  Grey coating is cooling Avoid hot stak.Avoid overpick. quench  the eye and is. grey coating. not Dull grey  after galvaniz a defect at all. Control by vanizing  bon) or severe  prior agreement. ited to occasional  phorus or carareas.  before accepting or  porary protec.Use shot blast   Effect  times obser.  ings bined carbon   May be caused near surface of   by  Yes. include de.have no com. deposits can be  close packed lated conditions.1985 FIGURE DEFECTS CAUSES RECOMMENDED ACTIONS GUIDANCE FOR ACCEPTANCE/ REJECTION  Confinement of Store and ship in  No.IS : 2629 . if deposits A temporary  are heavier. etc. A tem.  removed by hand  articles under separate arti.  Yes.  ing. they Bulky white   treatment like  shall be removed deposit chromating is  and the zinc coat(wet stor. Check steel   ing pickling supply    Improper mal.   Packing of Dry before pack.ment.  sorbed durkle.  ved on que. should be tested white  articles while thickness ing.instead of pickle. if general zing practice  leablizing (for   malleable   iron castings   only (A blister under microscope) Tiny blisters some. ablizing treat. rejecting the white  tive treatment  rust attacked gal  like chromating  vanized products  is recommended   (White rust under microscope) Blisters  Expansion of Check steel quality  entrapped hy drogen and  moisture in flaws  Driving off of Use shot blast   hydrogen abinstead of pic. rubbing. thin white dry well-venti.  notably mal.  malle. Should   leable cast.  ing recommended beneath age stain. brush damp condi tions cles with spacer. if blistering is casting gas wide evolved from  generally  the  spread work  resulting   from absor  bed hydrogen   or breakdown   of combined    carbon near   surface   18 .Check malleabli. for rust)  damp siccant.Check  nched work. . . . . . . 1985 APPENDIX B ( Clause 0. Where possible. B-2.3 While cleaning the articles with sodium hydroxide solution. the operators should be warned that it produces severe flash burns. B-2. B-2. and f) long rubber or PVC or neoprene gloves. e) rubber and leather aprons. b) rubber boots. gloves and aprons. be carefully handled by wearing rubber boots.1 All safety measures should be properly exhibited. therefore. 19 .2 ) is dangerous and causes very sever burns and sores when it comes in contact with the skin. WORKING CONDITIONS B-1. B-2. Special precautions should be taken to protect them from splashes of sodium hydroxide solution. SAFETY MEASURES B-2. B-2. d) leather or leather on woollen base gloves.2 The workers at the galvanizing bath should be provided with: a) eye or face shield.IS : 2629 .4 Hydrofluoric acid sometimes used for pickling of castings ( see 4.5 Arrangement should be made to protect the galvanizer from the fumes over the zinc bath.1 The galvanizing shop should be kept neat and tidy.5 ) WORKING CONDITIONS AND SAFETY MEASURES B-1. c) steel-capped boots. It should. increased use should be made of hoods. extraction ducts and exhaust fans to give as good an atmosphere as possible. 5 N.5 × B × 49 Mass of sulphuric acid in g/l = A --------------------------2.1. C-3.1 Standard Sodium Carbonate Solution — Approximately 0.1. C-2. *Specification for water for general laboratory use ( second revision ).3.1 Reagents C-2. DETERMINATION OF ACID CONTENT OF THE PICKLING SOLUTION C-2.6. Pipette out 25 ml of this solution in a 250 ml conical flask.3 Calculation × B × 36. QUALITY OF REAGENTS C-1. C-2. C-2.5 Mass of hydrochloric acid in g/l = A -------------------------------2. NOTE — ‘Pure chemicals’ shall mean chemicals that do not contain impurities which affect the results of analysis.3. and B = normality of the standard sodium carbonate solution. Add a few drops of methyl orange indicator and titrate it with the standard sodium carbonate solution to yellow end point.IS : 2629 . pure chemicals shall be employed in tests and distilled water ( see IS : 1070-1977* ) shall be used when the use of water as a reagent is intended.1985 APPENDIX C ( Clauses 4.2 Procedure — Filter exactly 25 ml sample of the pickle liquor into 250-ml measuring cylinder and make up to 250 ml by adding distilled water mix thoroughly. 20 .4 and 4.2 Methyl Orange Indicator Solution — Dissolve 0.1 Measure density of the pickling solution with a hydrometer.1 ) TEST METHODS C-1.5 where A = volume in ml of the standard sodium carbonate solution required. C-2.05 g of methyl orange in 100 ml of alcohol. DETERMINATION OF IRON CONTENT OF THE PICKLING SOLUTION C-3.1 Unless otherwise specified. FIG. 2 NOMOGRAPH RELATING THE IRON CONTENT OF SULPHURIC ACID PICKLE TO THE ACID CONTENT AND DENSITY 21 .IS : 2629 . join with a transparent ruler the point representing this reading shown on the left hand line with the point on the right hand line representing the acid content of the pickle. Read off the iron content on the middle line. 2 and 3 ) depending on the acid used for pickling.1985 then on the corresponding nomograph ( see Fig. 1985 FIG.IS : 2629 . 3 NOMOGRAPH RELATING THE IRON CONTENT OF HYDROCHLORIC ACID PICKLE TO THE ACID CONTENT AND DENSITY 22 . No. New Delhi 110002.Bureau of Indian Standards BIS is a statutory institution established under the Bureau of Indian Standards Act. Andheri (East) MUMBAI 400093 BANGALORE. I. I. 2 Amd. 323 33 75. GHAZIABAD. HYDERABAD. Telephones: 323 01 31. NALAGARH. marking and quality certification of goods and attending to connected matters in the country. CHENNAI 600113 Western : Manakalaya. 832 78 58   832 78 91. FARIDABAD. BIS. 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