Disclosure to Promote the Right To Information

Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public.

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“Invent a New India Using Knowledge”

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“Step Out From the Old to the New”

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“The Right to Information, The Right to Live”

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“Knowledge is such a treasure which cannot be stolen”

“Invent a New India Using Knowledge”

है”ह”ह

IS 11812 (1986): Recommended practice for safeguardingagainst warpage and distortion of hot-dipped galvanizedarticles [MTD 24: Corrosion Protection]

IS:11812-1986

Indian Standard RECOMMENDED PRACTICE FOR

SAFEGUARDING AGAINST WARPAGE AND DISTORTION ‘OF HOT DIP GALVANIZED

ARTICLES

Hot Dip Sprayed and Diffusion Coatings Sectional Committee, SMDC 28

Chairman Representing

SERI V.R. SUBRAMANIAN Indian Hot Dip Galvanizer’s Association, New Delhi

Members

SHRI V. K. AQRAWAL Hindustan Aluminium Corporation Ltd, Renukoot SHRI N. G. SRARMA ( Alternate)

SERI P. K.-BANER JEE National Thermal Power Corporation Ltd, New Delhi

SHRI J. N. BHATTACHARYYA National Test House, Calcutta SHRI M. Y. BORKER Ministry of Defence ( DGI ), New Delhi

SHRI A. BRATTACRARYA ( Alternate ) DR A. CHAKRABORTY CHEMIST & METALLURGIST

Usha Martin Industries Ltd, Ranchi ( Bihar ) Ministry of Railways

ASSISTANT CE~M~ST & METALLURGIRT ( Alternate )

CHIEF ENGINEER ( TRANS ) Guiarat Electricity Board, Vadodara EXECUTIVE ENGINEER ( Alternate )”

SHRI J. C. ERRY Steel Authority of India Ltd ( Bokaro Steel Plant ), Borkaro Steel City

SHRI G. GANESHAN SHRI B. G. SOHONI ( Alternate )

Kamani Engineering Corporation Ltd, Bombay

SHRI BRIJLAL KHASTRIYA Steel Authority of India Ltd ( Rourkela Steel Plant ), Rourkela

SHRI J. N. BHAM~RY ( Alternate ) SHRI M. M. L. KHULLAR The Tinplate Co of India Ltd, Golmuri, Jamshedpur

SHRI P. K. BANERJEE ( Alternate ) SHRI RAMESH CHANDRA The Indian Steel and Wire Products Ltd,

MA~AJAN Jamshedpur SHRI DARSHAN SINQII ( Alternate )

DR M. D. MAHESRWARI The Indian Tube Co Ltd, Jamshedpur SHRI K. R. NATAR~JAN ( Alternate )

( Continued on page 2 )

@ Copvright 1987

INDIAN STANDARDS INSTITUTION

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.

IS : 11812 - 1986

( Conlinuedfrom page 1 )

Members

SHRI S. MAJXXUDAR

SERI P. G. MU~HERJEE DR T. MUKHERJEE

SHRI B. N. SINQH 1 Alternate ) SHRI S. NEEGAKANTAN

DR A. R. KESEAR ( Alternalc ) SRRI D. PAUL SHRI L. PU~AZHANTHY SHRI S. N. SINGE _ . .

Refircsenting

Directorate General of Technical Development, New Delhi

Indian Posts & Telegraphs Department, Calcutta The Tata Iron & Steel Co Ltd, Jamshedpur

Zenith Steel Pipes Ltd, Bombay

Guest, Keen, Williams Ltd, Calcutta Indian Lead, Zinc Information Centre, New Delhi EMC Steelal Ltd, Calcutta

SHRI PINAKI GHOSH ( Allernale ) SEIRI N. K. SINQHAL The Indian Iron and Steel Co Lid, Burnpur

SHRI A. SENGUPTA ( Allcrnate ) SHRI J. L. SONEJI Special Steel Limited, Bombay

SHRI M. R. DOCTOR ( Allernalc ) SHRI K. RaGHAvENDRAN, Director General, IS1 ( Ex-oflcio Member )

Director ( Strut & Met ) Secretary

SHRI S. K. GUPTA Deputy Director ( Metals ), @I

Hot Dip Galvanizing Subcommittee, SMDC 28 : 1

Convener

SARI V. R. SUBRAMANIAN

Membc7s

Indian Hot Dip Galvanizers’ Association, New Delhi

SHRI L. PUGAZHENTHY ( Alternate to Shri V. R. Subramanian )

SHBI V. P. ANAND EMC Steelal Ltd, Calcutta SHRI S. N. SINGH ( Alternate )

SHRI B. D. BALI Hyde1 Designs Directorate, Chandigarh SHRI J. S. BEDI Hope’s Metal Windows ( India ) Ltd, Calcutta

SRRI A. K. SOBTI ( Alternate) DIRECTOR ( TRANSMTSS~ON ) Central Electricity Authority, New Delhi

DEPUTY DIRECTOR ( TRANS- MISSION ) ( Ahrhe )

SHRI D. DUTTA The Indian Tube Co Ltd, Jamshedpur SRRI A. K. GUHA The Fort William Co Ltd, Calcutta

Sa~r S. KUIUAR ( Alternate ) JOINT DIRECTOR ( CHEM ) Ministry of Railways

JOINT DIRECTOR ( II ) - I ( Alternate) SHRI VIJAY KAPOOR Guest, Keen, Williams Ltd, Howrah SHRX R. C. MAHAJAN The Indian Steel & Wire Products Ltd, Jamshedpur

SHRI AVTAR SINGH ( Alternate ) SHRIB.MAHAPATRA Steel Authority of India Ltd ( Rourkela Steel

Plant ). Rourkela SIIRI S. N. SINHA ( Alfcrnafc )

( Continued on page 6 )

2

IS : 11812 - 1986

Indian Standard RECOMMENDED PRACTICE FOR

SAFEGUARDING AGAINST WARPAGE AND DISTORTION OF HOT DIP GALVANIZED

ARTICLES

0. FOREWORD

0.1 This Indian Standard was adopted by the Indian Standards Institution on 18 August 1986, after the draft finalized by the Hot Dip Sprayed and Diffusion Coatings Sectional Committee had been approved by the Structural and Metals Division Council.

0.2 Warpage and distortion may occur in steel assemblies and sub- assemblies fabricated by welding or riveting. In composite structural members, pipe joints, sash, weldments, etc, which are to be hot dip galvanized after fabrication, are subjected to warpage and distortion due to thermal stresses of heating and cooling incidental to the galvanizing operations. The above problem becomes more complicated when the material is to be dipped more than once to cover the entire surface.

1. SCOPE

1.1 This standard recommends the methods to be adopted for safeguarding against warpage and distortion during hot dip galvanizing of steel assemblies.

2. FACTORS IN WARPAGE AND DISTORTION

2.1 Warpage and distortion may be attributable to either or both of the following factors.

2.1.1 Thermal Stressts Set Up in Material by Diferential Exflansion and Contraction During Heating Cycle - Welded parts of unequal thicknesses, which heat and cool at different rates is one of the most common causes of this condition. A panel section composed of light gauge sheet steel ( say 1 mm ) welded to 6 mm in thickness angle iron frame, is a typical example. The difficulty is further accentuated by the use of non-sym- metrical sections. Mild steel channels, for example, usually require

3

IS:11812- 1986

straightening after hot dip galvanizing whereas ‘I’ beams, pipes, etc, which are symmetrical about both major axes, do not. Supplementing these effects are the temperature gradients set up in the product by pro- gressive immersion in the galvanizing bath or quench tank. The temperature difference between various parts on the above are least when the entire article is submerged quickIy and are greatest with IaFge items where it is’necessary to dip one-half of the article at a tL&7o complete coating coverage. Channels and other non-symmetrical sections should be avoided for the frame work of a sheet metal assembly that is to be hot dip galvanized. Whenever it is possible, symmetrical shapes or sections should be used.

2.1.2 Release of Residual Internal Stresses Remaining from Fabrication Process - During the fabrication and assembly by welding or riveting; particularly where parts are clamped or otherwise strained durl%@ fabrication processes, are subjected to stresses. These stressed i are normally released at the galvanizing temperature and frequently result in distortion. .

3. SUGGESTED PRECAUTIONS FOR ASSEMBLY

3.1 In Design and Fabrication

3.1.1 There are advantages in designing the members of the size that can be accommodated in a single dip which is guided by the size of the galvanizing bath.

3.112 The members used in an assembly should be pre-formed accu- rately to avoid springing action and force at the time of assembly.

3.1.3 If possible, all welds should be stress relieved by suitable low

temperature heat-treatment before galvanizing.

3.1.4 Parts used in assembly should be, as far as possible, of equal or near equal thickness.

3.1.5 Corners on articles such as sheet metal bins, pans, etc, should be formed with a generous radius to minimize local stress concentration.

3.1.6 Strengthening angles or stiffeners should be placed in position and held down to prevent material movement when in contact with the electrodes during welding operation. Hence, these stiffening angles or stiffeners can take care of distortion. In welding any intermediate lengths along one side of a common member, care should be taken to prevent warpage of the common member due to application of high heat on the same side.

3.1.7 All edges of tightly contacting surfaces should be completely sealed by welding. This will prevent the rusting of surfaces which are so connected that molten zinc cannot circulate through crevices to galvanize the contacting surface.

4

IS:11812 -1986

3.1.8 If the galvanizing kettle is of sufficient size to permit total immersion of the assembly in one dip; riveting of fabricated parts prior to galvanizing is not recommended because contacting surfaces will not be coated and rusting will occur due to entrapped pickling acid.

X1.9 If the structure cannot be galvanized in one go, it is better to assem&le the galvanized sheet and galvanized frame separately. Gal- vanized rivets or aluminium alloy rivets may be used for this purpose.

3.2 During Galvanizing

3.2.1 The article should be submerged as quickly as possible consistent with safety. For this purpose, vent holes should be provided ‘in cases like pressure vessels, pipe assemblies, etc. Also, in case of columns footing stiffeners, and gussets connecting base plate with the column should be clipped to provide drainage of zinc. This is also applicable in case of containers which have a tendency to form air-pockets and prevent proper galvanizing.

3.2.2 Wherever possible, the article should be dipped in such a fashion as to produce uniform heating or cooling across the sections. For example, vertical dipping of channel sections is preferable to immersing them horizontally or at an angle.

4. GENERAL FACTORS IN DESIGNING AND FABRICATION

4.1 Overlapping or Contacting Surfaces - The edges of tightly contacting surfaces should be completely sealed by welding to avoid rusting between the two hidden surfaces. It is important that no pin holes are left in welding through which pickling acids or other solutions can pass. Entrapment of liquid in recesses may generate high pressure of explosive forces at galvanizing temperature and may cause serious injury to the personnel.

4.2 Arc Welding - The use of coated electrodes frequently leave welding residues which are chemically inert to standard pickling solu- tion. Such residues should be removed prior to pickling by brushing, chipping or sand blasting. on the finished product.

Incomplete removal can result in bare spots Where the uniform galvanizing finish is requir-

ed, steels of different analysis or surface finish should not be used in the same assembly. This applies particularly to the heavily rusted or pitted steels with new materials which may result in non-uniform coating due to different pickling times required for the fresh material and for heavily rusted material. Similarly, machined surface should not be welded with hot rolled parts. In such instances, the entire piece should be shot blasted prior or after machining and then sent for pickling.

4.3 Pipe Assemblies - For pipe assemblies, such as railings, they should be provided with open mitre joints at all times. Closed or blind sections must not be included under any circumstances. Floor flanges for steel pipe railing should also be of steel and not cast iron.

5

IS : 11812 - 1986

( Continud from pap 2 )

Members

SHRI S. M~JU~~DAB

Representing

Directorate General of Technical Development, New Delhi

DEVELOPXEHT OFFICER ( HME ) ( Alternate ) SHRI M. S. MEHTA General Engineering Works, Bharatpur, Rajasthan SARI P. G. MVKHERJH~ Posts & Telegraphs Department, Calcutta

SHRI K. MITRA ( Aftmutc ) DR T. MUKHERJEE Tata Iron & Steel Co Ltd, Jamshedpur SHRI S. NEELAKANTAN

SHRI B. A. DESAI ( Altmatc j Zenith Steel Pipes Ltd, Bombay

SRRI N. D. PARIKH Kamani Engineering Corporation Ltd, Bombay SHHI A. SENaopTA The Indian Iron & Steel Co Ltd, Burnpur SHRI J. L. SONE.~~ Special Steel Ltd, Bombay

SBRI h4. R. DOCTOB ( Altmutr ) Sam IL M. TANEJA Directz;rite General of Supplies and Disposals, New

SHRI. G. P. GUPTA ( Alfcmatc )

6