Welding Tips and Tricks

If I tig stainless without having gas on the other side of the weld and then grind both sides of the weld to be flush with the base metal (with a flap disk or something) will this cause for a weak weld or would there be any downsides besides oxidation? This is not for a structural weight bearing object. Would grinding the oxidation layers off reveal new stainless that would not rust?

it will make the weld weaker but that may be perfectly fine. i've seen kitchen sinks done like that, weld it on the inside so they can grind the sugar off the outside where they can get to it easily.

rust is totally different. bare stainless actually rusts because you expose the iron in the stainless steel. this is why you pickling/passivate the stainless with acid, it removes that iron from the surface.

Ok, thank you!

tweake wrote: ↑Thu Aug 22, 2024 12:11 am it will make the weld weaker but that may be perfectly fine. i've seen kitchen sinks done like that, weld it on the inside so they can grind the sugar off the outside where they can get to it easily.

rust is totally different. bare stainless actually rusts because you expose the iron in the stainless steel. this is why you pickling/passivate the stainless with acid, it removes that iron from the surface.

Stainless doesn't all oxidize equally. 304 rusts. 308L, not so much. 316L is actual marine grade SS. I think the main (only) differences are the level of chromium and L for low carbon. I TIG welded rusted out stainless steel airplane mufflers which was almost impossible without blowing more holes in it (especially with the output frequency fixed at 60 cycles as it always was back then). I assume the mufflers were 304.

Timmy_Tiggs wrote: ↑Thu Sep 19, 2024 9:53 am
Stainless doesn't all oxidize equally. 304 rusts. 308L, not so much. 316L is actual marine grade SS. I think the main (only) differences are the level of chromium and L for low carbon. I TIG welded rusted out stainless steel airplane mufflers which was almost impossible without blowing more holes in it (especially with the output frequency fixed at 60 cycles as it always was back then). I assume the mufflers were 304.

true, in normal conditions 304 rusts more than 316. however welding makes it rusts, even 316, hence the need to pickle/passivate.
i have some parts at work where someone welded then ground off the heat tint etc. its all rusted and thats inside a nice dry factory.

All stainless is prone to rust if you weld it and create “sugaring”. Sanitary piping is all 316 and must be fully purged, autogenous mostly. If you even think about welding it without a purge, you will fail every inspection.

That's good to know. I had been welding almost strictly aluminum for about a year and a half and I was recently called upon to weld a couple of SS gutters for a commercial building. 18ga.
There was no time for research and little time for practice. It's mostly fusion, no purging, just chill blocks. #5 cup because it didn't occur to me that a larger cup might be better until I watched a couple of Jody's videos afterwards -- D'OH!
I'm sure I have pictures of the gutters, but I don't have them available right now and I don't think I could upload them to this terminal (I'm at work now). I'd be very keen to know what you guys think.

Fortunately, this is a rain gutter and not sanitary piping. I'd still like to do a better job of it. My concern is for the structural integrity and the visual look. I'll post pictures when I get home (I'm at work) if I don't get a "page unavailable" situation.

Brace yourselves. I hope nobody is turned into a pillar of salt by viewing my welds...
I thought I had more pictures but there was a big hurry to get these out of the door. I'll start off light, with the tacks.

Since those are stainless and you did not use a backside purge, you’d better passivate them or they will rust through after 1-2 seasons.

You can do a search for “pickling” or “passivation” options that are pretty inexpensive. But you’d better do that before shipping them out or you can expect an unhappy customer before too long.

#8 cup would work fine. Whenever you use a large cup on an edge, the argon is split and is less effective than you think. A smaller cup in this instance actually produces a better weld, given the thin nature of the material and the edge application.

And crank up the post flow to 1.5-2 seconds per 10 amps of welding amperage. This will leave your weld and tungsten very clean so you only need worry about the backside.

They totally sprung this on me. It was due at the site by the time they got me the parts. I finished welding it, turned around and it was gone. Unless I can get someone to passivate it on a building several stories above the ground, I guess we're screwed in 2 years (sigh).
I actually used a #5 cup because that's what I use on aluminum and I hadn't welded SS for about 2 years except for a little practice.
We removed the oxidation with a wire wheel but I guess that doesn't amount to passivation.

Getting a good fit up on this was more time consuming and painstaking than it looks.
[edit] Looking at it later, I should point out that i added tacks later and dollied the seam with a plastic hammer to take out the gaps visible in this photo. Otherwise, forget about fuse welding .0478" stainless. [/edit]

cj737 wrote: ↑Fri Sep 20, 2024 7:44 am All stainless is prone to rust if you weld it and create “sugaring”. Sanitary piping is all 316 and must be fully purged, autogenous mostly. If you even think about welding it without a purge, you will fail every inspection.

a lot of sanitary pipe is 304, it depends on the industry. you can often buy fittings in either spec. tho some places will only sell 316 because they don't wan the cost of stocking both.
for me 316 is a lot more expensive so its only used if i have to.

Timmy_Tiggs wrote: ↑Fri Sep 20, 2024 4:55 pm They totally sprung this on me. It was due at the site by the time they got me the parts. I finished welding it, turned around and it was gone. Unless I can get someone to passivate it on a building several stories above the ground, I guess we're screwed in 2 years (sigh).
I actually used a #5 cup because that's what I use on aluminum and I hadn't welded SS for about 2 years except for a little practice.
We removed the oxidation with a wire wheel but I guess that doesn't amount to passivation.

i don't know if it will rust right through. my stuff is all inside work, i don't know the effect of outdoor. however it will rust and be unsightly. they might not notice depending on where its installed. if they can get to it, applying acid in the field is possible.

The sugaring is all inside, so it would only be visible if you were a bird (I doubt they care) or a drone. From the outside, as long as it isn't leaking or visibly rust from 40 feet, it should actually be OK. I'll try to load a couple more pictures -- getting a few 500 errors lately.

tweake wrote: ↑Fri Sep 20, 2024 6:14 pm a lot of sanitary pipe is 304, it depends on the industry.

Never seen 304 used for sanitary pipe. Here it doesn’t meet the criteria, and sanitary piping that I’ve welded is either Water treatment or Food Grade. And that is all 316.

tweake wrote: ↑Fri Sep 20, 2024 6:14 pm

cj737 wrote: ↑Fri Sep 20, 2024 7:44 am All stainless is prone to rust if you weld it and create “sugaring”. Sanitary piping is all 316 and must be fully purged, autogenous mostly. If you even think about welding it without a purge, you will fail every inspection.

a lot of sanitary pipe is 304, it depends on the industry. you can often buy fittings in either spec. tho some places will only sell 316 because they don't wan the cost of stocking both.
for me 316 is a lot more expensive so its only used if i have to.

Many years ago I worked at a place that made large SS vessels for pharmaceutical and vitamin companies as well as Sinks. The sinks were 304. I sink that is fine for FDA use, like at your local supermarket. The vessels were often 308L, 316 and 316L. I have a horror story about that place, but that's for another thread.

tweake wrote: ↑Fri Sep 20, 2024 6:14 pm

cj737 wrote: ↑Fri Sep 20, 2024 7:44 am All stainless is prone to rust if you weld it and create “sugaring”. Sanitary piping is all 316 and must be fully purged, autogenous mostly. If you even think about welding it without a purge, you will fail every inspection.

a lot of sanitary pipe is 304, it depends on the industry. you can often buy fittings in either spec. tho some places will only sell 316 because they don't wan the cost of stocking both.
for me 316 is a lot more expensive so its only used if i have to.

Many years ago I worked at a place that made large SS vessels for pharmaceutical and vitamin companies as well as Sinks. The sinks were 304. I sink that is fine for FDA use, like at your local supermarket. The vessels were often 308L, 316 and 316L. I have a horror story about that place, but that's for another thread.

Snuck this past the error 500 gremlin -- I think. I'm sure I welded this horizontally and repositioned it to weld the seam that's now on top before taking the pic. I would like to have more pictures but I was trying to beat the clock and taking a lot of pictures in that case would not be a good look. I'm pretty sure I got colors fusing 1.2mm SS a couple of years ago, but they were small parts and could be positioned like an upside down V on a thick piece of (brass) angle. I used a piece of 1/2" aluminum plate in this case. And at the time I was more concerned with oil canning than oxidation of the outside corners.

The fit up on this was terrible. I wasn't involved in fabrication. The used a jigsaw/ saber saw. For crying out loud, guys, just run down to the local hardware store -- no shortage of them here -- and pick up a hole saw! This was jagged and there was a gap that got as wide as 1/8". Material is18 gauge (308?) stainless against a 1/2" aluminum chill plate. Fortunately, one of the things I learned from jd's WT&T videos is that you can leave the wire in the weld pool and keep pushing it in, if that's what it takes. That had not occurred to me, previously. I was going up and down, to wherever the sheet metal was receding, following it with the tungsten. Using .040 308L wire, 3/32" 2% lanthanated tungsten, standard stubby collet, #5 cup (probably wrong, but we can discuss that later) in a weldcraft W-250 torch.

Because life is never enough of a challenge...
The tube was a piece of flat 18 ga. SS that was formed into a 'C' by a computerized sheet metal brake. I then formed from a 'C' to an 'O' using clamps, a tape measure, a plastic hammer, a large bench vice, and a bit of determination and patience and fused on a 1" aluminum half-round chill bar. SS tubing would have added to the manufacturing cost, you see.

Looking at this picture, at first I thought "I should have added cosmetic tungsten wash" Then I looked again and realized that I had. There would be no color at all if I had not. The hole that they cut reminded me of an old movie: The Texas Chainsaw Massacre. Yeah, they assume I can perform miracles. So, we're fillet welding 0.0478" thick material with gaps of up to 1/8" -- what could possibly go wrong? Leaving the wire in the weld pool was the only way it was humanly possible to do this. Half inch aluminum plate underneath. If I hadn't been in a hurry, I probably could have bent a 1/8" thk aluminum mill plate for the back, but I was, so I didn't.

This is the kind of job where something like solarflux-b works great to prevent sugaring: https://www.harrisproductsgroup.com/en/Products/s0fb01

Add some alcohol to the powder (methanol is the preferred), mix up a paste and smear a little on the back of a weld area. It will cover the back of the weld with a glass-like coat in the end and prevent any oxygen getting to it. It can also be used as a normal flux for oxy-acetylene welding on both the front and back in that case.

It's not a useful product for sanitary/food grade jobs as it leaves a residue, but for jobs like this it can be a lifesaver as you can protect the back of such welds without needing a back-purge setup that can sometimes be tricky to use on bigger and 'open' parts.

Used it in the past on some stainless exhaust systems and especially mufflers that were just too big to back-purge without wasting lots of argon.

Bye, Arno.

Thanks for the tip, Arno.