Stud welding on galvanized member

[dozer]

We want to weld studs to a hot-dip galvanized platform frame for grating clips but I've read that you should not stud weld directly to galvanized steel. This leaves two options.

1) Stud weld before galvanizing. The fabricator is saying the studs will get knocked off during hot-dip galvanizing. This seems like utter nonsense to me. Just be careful. Am I making it easier than it really is? Does he have a valid point? I can see them getting damaged during shipping but again, just be more careful.

2) After galvanizing grind the spot where the stud goes, weld it on, then touch up affected area. I've never heard such b'ing & m'ing when this option was presented to the shop guys.

The obvious answer is don't stud weld, use some other method for attaching grating. The problem is our client has only given us two choices. Stud weld or use Hilti stainless steel disk. These babies along with the powder-actuated fastener are $20 apiece! Don't even get me going on, "How could they possibly cost that much?" Anyway, anybody have any experience with a solution to problem?

 

[Mr168]

Studs damaged during shipping - all the time. Studs falling off during shipping, you've got bigger quality issues than worrying about your coatings.

 

[Duwe6]

Stud weld first, and actually use a Welding Inspector and actually test the in-process stud welding in accordance with AWS D1.1. Poorly 'shot' studs fall off all the time. Properly shot studs are sturdy enough that they can be bent almost flat and still not break loose. Impossible to visually detect a mediocre-but-good stud weld vs. a poorly fused stud weld. Somebody has to QC those studs during fabrication, by bending them with a sledge hammer or a heavy-wall pipe. Hard, repetitive work, boring & necessary.

 

[moltenmetal]

Put the grating down with powder actuated fasteners- forget about welding! Hilti makes an excellent grating clip fastener. No fuss, no muss- but of course, also no good if you need zero clearance removal of the grating as the studs themselves are in permanently (as would be your stud-welded studs, so no problems there). Either that, or you drill and tap to bolt on the clips, assuming your member will tolerate that.

 

[Duwe6]

Second the 'shoot it down w/Hilti fasteners'. One type is a threaded stud that will end up slightly below the top-of-grating. Add a clip and nut and the grating is now removable and the fasteners are below the top of the grating bars. These 'nails' pierce the flange of the steel so rapidly that it is plastic deformation, making them impossible to pull out, and allowing the galv to seal around the stud and prevent rust staining. Excellent system, and the work goes fast. CAVEAT: clear the area below the guy shooting. If he gets a miss, that stud is traveling at a large fraction of the velocity of a pistol round, and is pointy enough to easily penetrate a hardhat or a bone.

 

[darthsoilsguy2]

sounds like the shop doesn't want to coordinate clip locations.

Do you need structural connections?
if so, you're 2 approaches are all you have.... unless...

the contractor has a WPS for burning through HDG to make this weld, PQR test records for that burn-through WPS, and WPQR's welder certs and test records for each welder to make those field connections.... i bet against the house that the Contractor does NOT and i win every time. i'm assuming you've specified AWS welds, which the galvanized coatings kill all the Pre-Qualified Welds available, as it is an essential variable.

The Hilti system will give you lots of headaches if you have to shoot into or near the web, or if you have steel shapes of varying thickness to punch into. i fail about 3% of them. But, you could meet halfway and say.... Shoot them, and the one's you mess up (or don't work here), clean the metal and weld.

 

[holdpt]

We are in the middle of galvanizing CS material that will have 304L material welded to it. To prevent grinding the zinc we masked the areas for welding. Our testing demonstrated that duct tape, secured with not only its adhesive backing but also with a spray on adhesive (we used Loctite and 3M) before applying the tape will prevent that area from galvanizing the best. It took 3 layers of duct tape with the 2nd and 3rd layers not needing the spray adhesive. After the galvanizing process, wire brush the area and its ready for welding.
If the tape is not applied tightly to the substrate, the caustic dip, HCl dip, or the flux dip will get between the tape and substrate and it will fall off before it reaches the kettle. It sounds silly but this work is for a power plant so we have taken it very seriously. Zinc in a stainless weld causes cracking which causes companies to go out of business.
Maskote may work for your application but it was too messy and time consuming for us.

 

[dozer]

Thanks for all the replies. We are going to go with the Hilti fastening system. It's price just seems outrageous to me though.

 

[moltenmetal]

If you think your labour is cheaper than Hilti's materials, then drilling and tapping is your option. Building in a shop environment, we always drill and tap some fasteners on each sheet, then go around with the Hilti and bang the rest down after hours when the noise won't bother as many people.