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Solving "Acid Weep" in galvanizing

Q. An unattractive phenomenon that sometimes occurs in galvanizing occurs after galvanizing steel fabrications where two flat surfaces are welded together but not fully welded. Acid and alkali etc seep into the crevice formed by the flat surfaces being close but not sealed by welds, and subsequently boil dry in the immersion in zinc. This leaves oxidized dry crystalline residue behind. On the first shower of rain and water entering the crevice, a solution of iron hydroxide is formed which then seeps out leaving what looks like a rusty stain. In fact the stain is on the surface of the zinc coating, and doesn't normally compromise corrosion protection, but it looks unsightly and to the uninformed, looks like the job is "going rusty"..

One solution is to fully seal such welds so that no cleaning chemicals can enter. But this solution is not in the control of the jobbing galvanizer, and so usually doesn't happen.

Has anyone else found a workable, practical solution to this problem?

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

May 18, 2009

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A. Geoff, Maybe you just need to point out to your customer, before quoting and accepting the job, what will happen. He then has the option of fully welding. That of course could introduce the possibility of a significant volume of entrapped air with the risk of explosion in the kettle, but consideration of each case should control that. Bill Reynolds [deceased] consultant metallurgist - Ballarat, Victoria, Australia We sadly relate the news that Bill passed away on Jan. 29, 2010. A. Yes, you're right regarding the acid weeping but that occurs normally after quenching and there is no such method to control it but after 2 or 3 days when the weeping is over you can give touch up to the weeped area. SENTHIL KUMAR - Mumbai

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