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Remelting zinc onto galvanized members after welding process in the field.

Dear Sir,
Typically I've sprayed cold galv paint on welded areas. Now I'm being asked to re-heat the welded area and rub a stick of zinc into the weld. I'm not talking about a lose piece of channel or angle either. This will be a three story set of stairs with all welded connections, platforms,stringers,hanrails,ect. In theory it sounds pretty good. But we both know everything should have been designed to bolt. It seems the older I get, the smarter some engineers get. Had to vent a little bit. But is this process really going to work?

Michael Ellis
steel erector - Kenner, Louisiana
January 7, 2010

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It sure won't - you would have to heat the entire staircase to the melting point of zinc! It would likely still come out like crap.

Your best bet would be to do a very thorough removal of the scale from the welding, and then apply zinc via an electrolytic brush plating process.

If, of course, you can't talk whoever thought this up out of the whole thing. :)

Dave Wichern
Consultant - The Bronx, New York
January 10, 2010

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First of two simultaneous responses --

Michael

I would very politely ask the designer to demonstrate his proposed process - then stand well back while he exposes himself to the zinc fumes this must generate!

Most welders will not touch galvanised material. Any zinc that does not fume off will be incorporated in the weld and is not likely to improve the quality one little bit. Guess who gets the blame for failed welds.

Geoff Smith
Hampshire, England
January 13, 2010

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Second of two simultaneous responses -- January 13, 2010

To The Engineers, Michael, and Dave:

There seems to be some confusion here. The "stick of zinc" is actually an ALLOY REPAIR STICK. I saw this alloy repair stick being used extensively in South Africa (in the 1980's )immediately after galvanizing and by using propane torches. It melts very much lower than zinc, perhaps having tin and/or lead in the alloy stick. The appearance of the repair is quite good. In using it, I would be very concerned it contained tin because tin is known at above 0.35% in galvanizing zinc to cause cracking in stressed steel. I would expect stressing at the welds.

I have not seen this repair stick used for some time now, but cold zinc rich spray cans of paint are commonly used. Some zinc rich spray paint (like from the hardware store) does not adhere well.

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA

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January 13, 2010

I'd be wary of these so called zinc sticks. (They go by various proprietary brand names in several countries).
We analysed one once, it contains very little zinc, mostly tin and lead. Its more like solder. It has a lot of flux in it, so that like resin cored solder, it's self fluxing.

But as for corrosion protection (that's why you galvanized right?), then it's not up to much.

If you look at ISO 1461 (International standard for galvanizing) it only allows for very small areas of ungalvanized steel to be "touched up" using this or paint etc. Whole welds so touched up won't meet the spec.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK