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Minimum fillet weld - light gauge steel

Minimum fillet weld - light gauge steel

Minimum fillet weld - light gauge steel

I am looking to install some new utility supports (12 Ga cold formed steel) on an existing steel column.

A cold formed manufacturer suggested using a welded connection.

I asked them what welding detail they recommended using with such a light gauge steel member.

They recommended following AWS.

So, when 12 Ga steel is being field welded to a heavier section, does anybody have any practical suggestions for a weld specification?...minimum practical weld size, etc?

RE: Minimum fillet weld - light gauge steel

AWS D1.3 covers the welding of sheet steels < 3/16" to structural members.

RE: Minimum fillet weld - light gauge steel

12 gage is modestly thick.

On your diagram, you show both joint plates (the 12 ga panels ?) to be welded on the inside of the two WF pair.
Now, 34 inches is a modest confined space - but not really adequate nor profitable place to crawl inside of and spend all day welding, so you'd cut your weld time by 80% with two external plates and a pair of interrupted seam fillets on the outside.

No confined spaces hazards and fire watch, no difficult and slooooooooooooooooooow access to the top and bottom of each small box.

RE: Minimum fillet weld - light gauge steel

I have no experience with sheet metal fabrication (in my world sheet metal is anything less than 3/4"), but it would seem difficult to produce a quality fillet weld as small as 1/16", especially in the field.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Minimum fillet weld - light gauge steel

racookpe1978, the member getting welded to the W-flanges is just a cold-formed channel section. I agree it's not the best detail, but it's just a sketch for now. In a section view, it would just get welded along the top and bottom (the 2-7/16 sides). And it's on the outside (unconnected flange-side) of the W-sections, so I don't THINK it would be considered a confined space for welding purposes.

I only have a 2008 copy of D1.3 on hand, so this may be out of date, but says that the "leg size of the T-joint fillet welds shall be equal to the thickness of the thinnest sheet steel". So that would be 0.105" (I think, 12 Ga).

I'm in the same boat at ironic_metallurgist. And that just seems like a really itty-bitty weld.

Can something like that be done in the field? Or at all?...without damaging the 12 Ga?

RE: Minimum fillet weld - light gauge steel

That’s Unistrut material or some such equal product, which the channel pipe hangers are made from. I think that stuff is welded fairly regularly, and the weld is probably more like a 1/8” fillet, but I’m not sure I like your detail. Mill tolerances will make more than half the 34” long hangers tough to get in between the flgs., and short cut hangers will make for a poor weld condition. And, I wouldn’t want some guy hanging off a bosun’s chair, pecking around with a welding stinger on the corners of the flange tips of my tower columns. At the very least, I would detail that with the Unistrut held back a bit further from the flg. tips, so the welder doesn’t get anywhere near the flg. tips, but you still have the length fit-up problem. Alternatively, you could weld a couple chairs (4” long hat sections, about 2” high) to the col. web and then bolt the pipe hanger to those, with the hanger being a little shorter than the 34” inside flg. dim. You use the notation “(TYP)” fairly liberally. What’s typical about randomly placed 1.5”, 3” and 2” RMC, except that they are round? 😊

RE: Minimum fillet weld - light gauge steel

Typical Unistrut material is galvanized or has a heavy coat of paint, consider cleaning time at the weld points. A 1/8" welding rod is recommended by Lincoln for welding 12 ga metal.

You are judged not by what you know, but by what you can do.

RE: Minimum fillet weld - light gauge steel

And watch out for galvanized metal fumes as such fumes will make the welder very sick requiring hospital stay. Provide powered air purifying respirator(PAPR)to the welder.

RE: Minimum fillet weld - light gauge steel

Your welder will need to be qualified under AWS D1.3, as this will be the controlling condition.

Yes, a very small weld can be made by a qualified welder.

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