Best way to remove galvanizing from mild steel

[cvis]

Hi

Could anybody perhaps shed some light on what is the correct procedure to follow to remove existing galvanizing from mild steel so as to have it properly re-galvanized?

Thanks

 

[swall]

Ask your galvanizer. In lieu of that, 30-50% Hydrochloric works.

 

[amorrison]

Better you should post to forum135

Also - please request this thread be deleted so you won't get nailed for double posting.

 

[cvis]

Ok, thanks very much.

 

[ornerynorsk]

We do small batches of stripping with Muriatic acid that we buy at the local hardware/plumbing supply. It's basically hydrochloric acid. Does a very nice job of it. You need to be careful though, the byproduct is hydrogen gas, which can provide some additional entertainment, provided we're outdoors. I would have to officially recommend that you let your plater do this, however.

 

[patprimmer]

Heating to red hot removes it, but may create other problems like distortion and evolution of toxic gas.

Why remove it before hand. If it is dipped in molten zinc, the original coating should melt and mix with the bath.

Regards
Pat
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[transmissiontowers]

I also need to know how to remove old galvanizing from a steel angle in a transmission tower. Sometimes a car hits one of our towers and we have to replace a leg member. They would like to weld in a new piece but I am reluctant to let them weld on the old leg. A bucket of acid 30 feet in the air is not a great idea so can they grind off the galvanizing?

_____________________________________
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[patprimmer]

I always have and I'm still OK, but I also weld over gal, taking care to be upwind and well ventilated.

30" in the air sounds well ventilated

Regards
Pat
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[berkshire]

patprimmer.
"Why remove it before hand. If it is dipped in molten zinc, the original coating should melt and mix with the bath."

Sometimes the reason for removing Galvanised before re coating is because the metal was not properly prepped before dipping. The resultant coating does not adhere very well to the parent metal and peels later.
Re dipping does not cure that problem.
B.E.

 

[rob768]

Patprimmer,

welding over zinc can lead to liquid metal embrtllement, as the zinc will penetrate in the metal in the haz.
Seen this in a case where they forgot to normalize a zinc-plated object prior to galvanizing, and decided to do this afterwards.
The hydrochloric acid, with the necessary precautions, would do the trick, but personnaly I would have it done by a more experienced company because of the health risks involved.

 

[patprimmer]

For welding insitu, if it's thin gal over thick metal, I normally weld over it and you can see it burn away about 1/2" ahead of the weld. If the gal is thick or the metal thin, I would grind first to do it insitu.

If it could be dismantled, for welding I might treat with inhibited hydrochloric acid and or grind the area, depending on quality requirements and size of job and size of weld and stress on the joint.

The OP does not specify why it if faulty, but if the problem was actually faulty pretreatment,then obviously a pickling/proper pretreatment process would be better.

Regards
Pat
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[MiketheEngineer]

There are "spray on" galvanizers that claim they work.. No experience but have been sold for years.

 

[transmissiontowers]

Thanks for the tips. I'm feeling much better about welding in the field but I still want to specify that they grind off the zinc before welding so they don't burn the zinc into fumes and get sick. The guy in the field can't afford to lose too many IQ points.

_____________________________________
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[Adalius]

There's also a rod produced by Cronatron (although they were recently bought out by Lawson), I can't remember the number on it, but it's designed for welding galvanized. We've used it on a number of bridge jobs and had very pleasing results compared to just using a plain 7018 like Lincoln Excalibur or others.

 

[patprimmer]

I also think you can get welders masks with filters or respirators for welding over zinc.

You can do local repairs at the weld by wiping the weld with a rod of zinc while the area is still hot enough to melt the zinc, but not hot enough to burn it. A poorer treatment is zinc rich paint.

Regards
Pat
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