Welding Galvanized Steel Deck

[firsow]

I have specified galvanized steel and a steel roof deck over a wash bay. On site, the Superintendent mentioned that the welder has raised concerns over the fumes produced by puddle welding the steel deck. The Superintendent also said that the burn through compromises the galvanized coating on the underside of the deck.

I’ve been looking online but I have not really seen anything about the issues of welding galvanized deck. Are the fumes still a concern if the welding occurs on a roof deck? Is it typical to just call up Hilti pins instead?

 

[dik]

You typically use a zinc rich primer. Some notes for welding galvanised material.

-IF WELDING OF HDG STEEL IS REQUIRED, REMOVE ALL GALVANIZING FROM AREAS TO BE WELDED TO PROVIDE 1" MIN BASE METAL AROUND ALL WELDS. WORK SHALL BE DONE IN ACCORD WITH AWS RECOMMENDATION WZC. CLEAN FINISHED WELD AND TOUCH UP WITH TWO COATS OF ZINC RICH PRIMER. PRIMER SHALL OVERLAP EXIST GALVANISING BY 1/2" MIN

With ventilation, a headache from welding zinc fumes can be minimised. Air masks can be used. I don't know what your local health requirements are. There are health issues. Over a wash bay, I'd likely use mechanical or PAFs. Corrosion can be serious and welding can compromise the corrosion resistance.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[LittleInch]

To be frank, if the welder doesn't know you can't weld galvanised steel then I would have some doubts as to his or her ability or experience in welding.

This is a very well known issue.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[r6155]

You can use Carboweld 11 in the zones to be welded.

Regards

 

[ATSE]

1. Almost all steel metal deck (roof B deck and composite floor deck) is sheet galvanized to G60 or G90. To be clear, deck is not hot dip galv.
2. For buildings, it is very common (whether good or bad) to weld this galv deck via SMAW to black steel beams with small puddle welds - all day long. No touch up, of course.
3. Mechanical fasteners for deck to beam have gained broad acceptance in the last decade, and can be much faster with equivalent shear capacities.
4. Welding deck to HD galvanized structural steel that is also exposed to the exterior is a bad idea.
5. Most high strength mechanical fasteners for deck to steel beam fastening are not rated for exterior exposure. Fastener selection (strength, corrosion resistance) is critical.

 

[dik]

Even with Carboweld, you have to touch up the welds afterwards to help provide corrosion resistance. It will suffer with the same issue as HDG. Touching up may not get to all areas and some metal may be vulnerable. Best to use PAF or screws for minimal damage. With a wash bay, I'd seriously look at the coating system... I've seen too many of them fail. They are a specialty item that warrants extra study.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

I'm not sure about G60, but my understanding is that G90 is HDG and this should be the minimum required for a wash bay... Added: Maybe someone can help me here and confirm that both G60 and G90 are HDG. If it were my project, I'd likely be looking at a high build zinc rich epoxy system and PAF attachment (Some Coating systems can be more expensive than HDG. Carboline, noted earlier, produces some excellent coating systems.)... Hilti makes a good fastener that I've had excellent results with.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

from MetalSupermarkets...

"Grade Summary: Cold Rolled steel sheets are hot dip coated with a durable protective coating of zinc. This material is intended for uses where corrosion is a consideration and where simple bending or moderate forming is involved. They may be bent flat upon themselves (within accepted bend radii) in any direction at room temperature without cracking. Typically this material is provided with a G:90 (or Z275) coating, but it is can be available with a G:60 (or Z180) coating ."

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[EdStainless]

There is some crossover as steel and the coating get thicker where they go from electro-galv to hot-dipped.
With both there are some that better than others. And as with any coating system the surface prep and damage in shipping and installation will determine the actual performance.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dik]

I think G60 and G90 are far too thick for electro-galv. I don't consider electro-galv any sort of protection, other than for erection purposes...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Enable]

The fumes are a concern even in exterior environments as they are relatively localized and don't have a chance to disperse prior to effecting the welder. I would specify pinned fasteners and screwed laps, which can all be found in Canam tables or whoever your supplier is.

It would be a good call to swap out welding in this instance.

 

[Ron]

The fumes are not a concern for this type of welding. It is a small puddle weld and it happens quickly and you move on. As ATSE noted,this has been done forever with little affect other than localized corrosion and even that is relatively minor. I would be more concerned about the quality of the welding. If you are in the US, the welder needs to be qualified to weld sheet steel (AWS D1.3) in multiple layers (4 layers for a corner lap).

If the concern is still there, there are some good mechanical fastening systems out there that will do the job.

 

[ATSE]

Slight tangent. Re: galvanizing, there may be a difference in vernacular by region.
In the US, hot-dip galv infers ASTM A123 or A153 (fasteners only). There are several zinc-coating methods, but deck and thin sheet zinc coating usually go by the name "continuous sheet galvanizing."
AGA has a nice short summary (2-pages) comparing hot-dip galv (after fab per ASTM A123) vs continuous sheet (prior to fab per ASTM A653). See the link.
Hot dip thickness ~ 2x G90 thickness for thin plate, and hot dip galv generally has much higher bond strength and abrasion resistance (I think the spec values show this, but this is clearly observed in the field).