Welding Galvanized Steel

[pcronin]

I have a condition on a project where a galvanized channel was fabricated too short. They need to put a little stub on the end to close a gap and the piece is non-structal. The outside of the channel is exposed to weather, but the inside is grouted into a wall.

The steel contractor is proposing splice plates in the inside of the channel flanges to tie the peices together. I understand the glavanizing should removed and patched when complete, but do I need to worry about the heat of the weld damaging the galvanizing on the backside of the area being welded? The minimum thickness of the material is 3/8". It will be an exposed condition and the owner is fairly picky.

 

[MiketheEngineer]

Galvanizing will "boil" off at about 450F or so and the fumes it gives off can kill you!!

Find somebody who knows how to do this safely!!

 

[berkshire]

Yes you do need to worry about the heat of the weld damaging the galvanised on the back side. If possible ,grind it off first.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[CRG]

Guys, you are grossly overstating the health hazards of welding galvanized steel. The fumes are zinc oxide. The same stuff that folks use on the beach for sun block and that our bodies need for proper health. After hours of exposure it can cause "metal fume fever" which is not life threatening and does not leave any significant long term after affects. I hate the taste in my mouth though. The best way to avoid the hassles of exposure of zinc oxide fumes is not to breath it, but to my knowledge, it will not kill you.

 

[metengr]

Current information on welding fume HAZARDS

http://www.osha.gov/doc/outreachtraining/htmlfiles/weldhlth.html

It is a health hazard. So, take the necessary precautions.

 

[pcronin]

I understand the health hazards exist. I am just the EOR and the welding will be performed by a certified union welder. They are responsible for the field precautions as I will be safely in my office.

Berkshire has answered my question, Thank you. The heat through from welding can damage the galvanizing on the backside of the piece.

 

[metengr]

They are responsible for the field precautions as I will be safely in my office.

This is not something you want others to know. Your welders are just as important as you - sitting safely in your office with your cup of coffee and donut. Take care of these guys!

 

[pcronin]

The "short" channels are being picked up from the jobsite and taken back to the shop. We will see if/how they can fix/save them.

My comment about the welders in the field was sarcastic. I have no control over field safety measures as they have no control over my safety.

 

[hokie66]

If they fix the piece in the shop, they can dip it again. I agree that you can't be responsible for everybody else's safety.

 

[rmw]

Got milk???


rmw

 

[dik]

From my General Notes:



WELDING GALVANISED MATERIAL

CONTRACTOR SHALL PROVIDE A WRITTEN WELDING PROCEDURE FOR WELDING GALVANISED MATERIAL WHICH SHALL BE REVIEWED BY THE [CONSULTANT | ENGINEER]

REMOVE ALL GALVANISING FROM AREAS TO BE WELDED TO PROVIDE 1/2" MIN BASE METAL AROUND ALL WELDS

CLEAN FINISHED WELD

CLEAN AND REPAIR HDG SURFACE TO ASTM A780 A2 AND TOUCH UP WITH TWO COATS OF ZINC RICH PRIMER

PRIMER SHALL OVERLAP EXIST UNDAMAGED GALVANIZING BY 1/2" MIN

Dik

 

[TXStructural]

rmw, shouldn't that be buttermilk?

Having had metal fume fever from welding galvanized material (years before I was a safety engineer and instructor for OSHA), I would not wish it on my enemies, and it is a "health hazard" but not fatal, even if you want to die for a few hours.

Any qualified welder knows the risks of welding galvanized materials. You should specify that the material is galvanized and, as stated previously, the coating within 1/2 inch, or so, of the weld is to be removed to preserve weld integrity. Specify that more galvanizing may be removed as required to safely complete the welds, and provide the repair required for any damaged or removed coating.

Once you try telling the tradespeople how to safely do their job, you have assumed some degree of responsibility for it being done safely. For instance, if you say to "remove coatings on all sides of the channel within 1 inch of the weld to prevent creation of hazardous metal fumes" and it's not enough, you are on the hook, even if it should have been enough. If, on the other hand, you are writing a full repair procedure, then you get into hot work permitting, fire watch, fire protection equipment, ventilation, etc. [Like the guy who burned down a brand new building here after weld spatter fell between the slab and a (not quite installed) curtain wall.]