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RE: Welding galvanized steel

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The contractor is correct.  It is done all the time.  

The zinc has a much lower melting temperature than the steel.  The zinc will
either melt and pool or the zinc will vaporize.  The vapors are toxic.  Zinc
will not mix into the weld, but pooling zinc can cause porosity.  The
porosity of the weld will be higher than in uncoated steel, but should be
within acceptable limits.  Depending on the plate size, there is a tendency
to have more intercrystalline cracking in fillet welds.

To minimize cracking and porosity the welder should oscillate the arc with a
whipping motion ahead of the molten crater.  This volatilizes and vaporizes
the zinc prior to depositing the weld metal.  

It is best to remove the zinc for structural welds as an ounce of
precaution, but for seal welds I would not worry about it.

The zinc coating is self healing to a degree and zinc inclusions have been
shown to have a higher degree of corrosion resistance than uncoated steel.
The corrosion resistance is more of a cathodic protection as opposed to a
barrier coating.

Harold Sprague

> -----Original Message-----
> From:	Al Greene [SMTP:agreene(--nospam--at)]
> Sent:	Friday, September 15, 2000 11:36 AM
> To:	'seaint(--nospam--at)'
> Subject:	Welding galvanized steel
> I have a contractor who wants to make nonstructural weather-seal welds of
> galvanized steel without grinding off the zinc coating.  He says that it's
> done all the time.  I am concerned about the galvanic degradation of the
> weld over time with the zinc mixed into the weld metal as well as the zinc
> fume problem.  Has anyone run into this question before?  Thanks in
> advance
> for any responses.
> Al Greene, PE

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