Etchant for Zinc in welds 1

[unkamiko]

I am trying to find an etchant that will reveal zinc or galvanized material in a weld. The condition is for when welding over galvanized steel the zinc effects the weld. I would like to use an etchant that will show the zinc or any problems that arise from welding over galvanized steel.

 

[metengr]

Typically, when arc welding over galvanized structural steel the zinc will locally volatilize from the heat of the arc during welding versus becoming entrapped in the weld deposit. You don't need to chemically etch the surface of the weld deposit, either Liquid penetrant or wet fluorescent MT nondestructive testing will detect surface discontinuities.

I would suggest you use E6010 weld rod for welding over galvanized steel and please protect your welders from breathing in harmful zinc vapors using supplied air welding hoods.

 

[TVP]

The following link has some good information on etching zinc coatings on steel products:

http://www.struers.com/resources/elements/12/45324/AppZincEnglish.pdf

 

[Rich2001]

Mechanical wet polish with kerosene avoid any H2O. Water will react with the zinc ruining your sample.

Contact Dr. Tom Langill at the American Galvanizing Association

Thomas J. Langill, Ph.D., Technical Director
tlangill@galvanizeit.org
Phone: 720.554.0900 x14
Fax: 720.554.0909

Address:
American Galvanizers Association
6881 South Holly Circle, Suite 108
Centennial, Colorado 80112

http://www.galvanizeit.org/

____________________________________

Here are a few etchants that are typically used for Zinc.

(1) 200g CrO3, 15g Na2SO4, 1000 ml H2O
(2) 50g CrO3, 4g Na2SO4, 1000 ml H2O
(3) 200g CrO3, 1000 ml H2O

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I have seen problems with cracks in the root of fillet welds on galvanized steel.


CLEANING PRIOR TO WELDING GALVANIZED STRUCTURAL STEEL

(1) Mechanically clean the surface with a grinder.

(2) With a neutral torch heat the surface to remove any zinc residual. (A small amount of zinc will be smeared on the surface during the grinding operation.)


Vita sine litteris mors est.

 

[unkamiko]

I am currently involved with a project where welding was performed over the zinc coating. The contractor attempted a belated procedure qualification. Each attempt failed. The pull tests failed at 50% to 70% of yield in the weld. The failures generated from cracks in the root caused by zinc.

A local consultant told me that every attempt at qualifying procedures over galvanized steel fails, Every attempt.

It is a common misconception that the zinc will be burned out of the weld. This is true for light gauge steel but it is not true for heavy steel. There is very little information available on this subject and I have searched exhaustively.

The only information I have found is in the Lincoln Arc Welding procedural handbook and The AWS Handbook. The best information on this subject is in AWS handbook Vol, 4 seventh edition.

This would be an excelent research project for some one with the facilities to do it. I would do this myself but my resources are limited. I do plan on writing a paper on this subject with the information I have found. Thank you for your input and I welcome any further information that can be provided.

Thanks, Mike

 

[metengr]

unkamiko;
The research has been done. There is information regarding welding of galvanized structural steels if you simply Google "welding of galvanized structural steels"

http://www.galvanizeit.org/showContent,48,80.cfm

http://www.aisc.org/MSCTemplate.cfm...mplate=/CustomSource/Faq/SteelInterchange.cfm

(see question from 12/2004)