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09-02-2012, 09:00 AM #1
Problem welding thin wall SS tubing: warping
I am having problems TIG welding 1 inch thin wall .065 stainless tubing. Pretty sure it is 316. The joints are all
coped pieces. We tacked the joints together. To try to control warpage, I am only welding about 1/4 of the
lenght, taking less than 45 seconds, then immediatly cooling with water. Even with this procedure, we are still
getting minor warping.
Please give me some suggestions.
09-02-2012, 09:27 AM #2
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09-02-2012, 10:26 AM #3
Like vette said,dunking it in water will cause more warping.Best you can do is tack it in several places then stager your welds and do it as fast as you can till it is welded all the way around and then most importantly,let it cool slowly at room temperature.
Something else I have done that seems to help is to preheat the material up to a couple hundred degrees or so to take the "chill" out of the part.It seems to help with warping also because your not creating a hot spot from welding while the material next to the weld is cold.
Also as vette said...it's SS and on top of that it is thin wall SS..it's gonna have some warp no matter what you do,all you can do is minimize it.
09-02-2012, 11:01 AM #4
Ditto on the water, don't do it.
The fit up of the joints is EVERYTHING. Take your time and file fit your copes, mitres, to contact each other as tight as possible.It is worth all the extra time spent in a nice finish product.
4 tacks 90 degrees apart is enough, the other thing is to use a .035 filler rod.
If your joint fit is poor you might have to go to .065 filler and lay it in there. Another thing to try is to not point the tungsten at 90 degrees to the work, lay the torch over and let some of the heat blow over the tube. It will let you navigate around the tube a little easier as a one inch tube is alot of hand movement quickly with the thin wall.
It sounds like 45 seconds for a quarter of the tube is slow, which could be a problem too. When things are right , the fit , the heat, the technique, it should be like 15 seconds for the 1/4 weld.
Once you get the hang of it all, on thin wall stuff , speed is your friend, going slow thinking it will help doesn't usually work. It just means your putting more heat in the joint over all.
Another tip is to pay attention to the color of the weld when cool, it should be from a straw color, yellow , to deep red or light blue coloring, if it's getting darker than that it's too much heat.
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09-02-2012, 11:20 AM #5
I have been helping a friend do sanitary brewery pipe welding with stainless steel schedule 10 pipe, which is very thin. In brewery work, the welds must be perfect. He doesnt even use filler rod at all. Instead, absolute perfect fitup, usually with a cold saw, and then a very low amp pulsed machine, like a Maxstar or a Dynasty, that can accurately run at low amperages.
as mentioned, tack at 4 compass points, then weld. Lowest possible heat input is the best.
09-02-2012, 03:47 PM #6
Expect some distortion, which possibly may be dealt with by pre-stressing, depending on the joint.
No description of the joints or part assembly?
Guess it's 316 SS?
Backpurge or solar flux?
The coped joints need to be really good fit.
Big deal--fire off on the filler-not the parent material.
Pulsing can help a bunch, but is not a crutch for those with little bench time on SS TIG.
If machine doesn't allow tailoring of the peak/low/time of pulse --then slow pulsing works better than fast--like around 5 cps.
09-02-2012, 04:13 PM #7
I have done a fair bit of pipe at those thickness's. The comments about 45 seconds a 1/4 being too slow is spot on IMHO. I would not like to say 15 seconds, but you should be noticeably moving a lot faster than 45 seconds for less than a inch of weld. Other thing is, assuming the joint is a 90 degree T, i would not weld it in quarters aligned with the line across the top of the T, Lay it down on the bench Weld each side, then weld the inside corners of the T as it were. Don't just weld every quarter in the same direction, try and alternate between clockwise and counter clockwise. Just helps make for a more even joint. Equally don't try and make too big a fillet, bigger the fillet the more the shrinkage - distortion. Keep the tungsten in close and don't add to much filler. I would be using a 1/16 tungsten sharpened about 3 diameters to as sharp a point as i can get it, you need good tight arc control on thin stuff like this. At a guess 45 ish amps plus or minus a little depending on how it goes - joint geometry. Too low a current and your fighting for a puddle putting more heat in than you need. As to pulse, have played with it a lot, you get it set just right and its wonderful, makes a real difference. To slow - fast and too low - high and its a real pain. IMHO pulse on a tig just makes it faster to make good welds on challenging things, it does not let you do anything you can't with simply less current manually. Really more for production type jobs is what i feel suits it best. Were you can get a real move on.
Another thing i do for stainless if the welds going to just be polished or passivated - not ground out is go to a larger gas lens. Its not text book but it really helps reduce scaling - heat stain. Keep the filler in the gas stream at all times and run a decent amount of post flow keeping the torch + filler on the part. You can damn near get only a slightly yellow weld bead that polishes up easy if you take care - do it indoors out the breeze.
Comments about good joint fit up are worth noting too, as is everything should be clean, no cutting oil residue or grinder grit. You don't need to brush the part like Alu but you do want grease and oil free so it welds nice and easy.
09-02-2012, 05:30 PM #8
What size filler rod are you using? It doesn't take a lot of amps to weld that thin stuff and if you are using filler that is too thick you are putting more heat into it than you need to. That being said welding coped rounds isn't a place I would expect to get warping, you have round parts with 3D welds, stresses are well distributed.
09-02-2012, 09:32 PM #9
Something I have been doing building handrails is to use a chunk of ss angle iron with a flat welded on the top so you can clamp it on the handrail with some reverse bend in it by using a half a piece of the next size tubing on top at the position of the vertical stanchion. I do this after tacking the top corners . This prevents the hump that normally occurs on the top as I can't always get perfect fit and perfect weld technique .
09-03-2012, 10:19 AM #10
Thanks for all the replies. Jim, that hump is exactly my problem. I will make up a sample and try your fixture.
I am also going to test plan B: a short lenght of schedule 40 pipe, OD turned to 1 inch with 1/2 inch turned to fit inside the tubing and then butt welded. This makes for an extra joint to be ground and polished, but I only have 8 joints on this pulpit.
09-03-2012, 11:02 AM #11
I took a photo of the jig it is 13 inch long and I use it for thin wall tubing and schedule 40 ss pipe . Just clamp it enough to put reverse bend in it before welding
Last edited by Jim Moser; 09-03-2012 at 02:01 PM.
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09-03-2012, 12:35 PM #12
We used to make alot of handrail out of 1 1/4 schedule 40 SS, when we were through welding we had made a device that looked like a large bearing puller only the arms that usually a 90 degree foot on them had hooks that wrapped around the horizontal rail approx 16 inches apart, the screw in the center had a piece of angle on the screw/swivel.
So we would clamp it on the horz. piece after welding and "pull the hump" back out of it--------------- worked well and was quick to use.
09-27-2012, 01:00 PM #13
Just a follow up. I used Mark's idea and built a puller. It worked great in taking the "humps" out.
Attached are pictures of the puller and the completed pulpit.
09-27-2012, 09:40 PM #14
That is just like what we used only ours had deeper / longer arms with a acme threaded push screw. Then it had a slip rod on top for a handle-------------- nothing wrong with yours, it will make it easy work and you can stand up a 100 feet of handrail and make it look good too !