stainless railing + tig = bad distortion

greets all. started today on a 20' stainless steel indoor railing (stairs) -- and have finished the first 6' with ugly results.. and after all that
notching/fitting.
don't know where to post pictures -- but a quick description: the rail is composed of 3 horizontal 3/4" thinwalled stainless steel tubes, spaced about 6" apart, with short (6" long) 3/8" thinwalled SS tube vertical pieces to tie the horizontal ones together.. spaced about 3' apart, and offset between each horizontal tube.. think "brick wall" pattern: 3/4" horizontals and 3/8" verticals.
to keep the SS looking nice i'd laid the first section on a sheet of plywood and used blocks/woodscrews to hold the pieces in place. cut, fish-mouthed, and fitted all the pieces.. it was looking great.. tackwelded everything in place (small tacks on each tube end 180deg apart to try to keep them from moving)..
flipped the 6' section over (remarkably light), and started in with the tig. 1/16" tungsten to get as small and inconspicuous a bead i could. tig @ about 50 Amps. welded one side (halfway around each tube, connecting the tacks from before), flipped it, closed the welds on the other side.
i stood back.. and i saw it. the whole thing bent up like a noodle. it stayed flat (in the plane of the railing), but my 3/4" horizontal tubes now look like waves.
tried to do my best to keep the heat down.. but what did i do wrong? and how can i keep this from happening on the rest of the railing? (heavier walled tubing would've probably helped, but i've already got it all here in the shop)
any thoughts/suggestions greatly appreciated -tony
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Hi Tony Welcome to the real world , SS is a problem , even for the old timers , about the best you can hope for is to try to out smart the SS , you said that you had a fixture to hold your tube in alignment , this is good and I commend you for it , you now have an idea as to how much warpage you can expect and so back to your fixture and over bend the tube in the direction needed to have it zero out after welding , SS is very warp prone and if you start out at zero , you know it will not bow away from the weld , only in , some of the tube aircraft that were welded in fixtures , had to be hit with a large rubber hammer to get back near zero , you are not the first or last to fall victim to SS warp, don't feel bad , I have welded T sections of SS and after a few tries I could shim the center and the T came out nearly flat . Good Luck Phil

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Good Morning
Now you know why welders love to hate handrail, it can be troublesome..
Small welds are a good thing, however it is a good idea to weld only a quarter of the tube at one time and stagger your welds so the stress is balanced. It is common practice where I am to weld the rail while it is laying flat on benches or a table, this requires flipping the rail several times in order to balance your welds. My personal choice is to stand the rail up on its posts, as it would be when installed. Depending on the length of rail and the amount of weld required I will shim the end posts up from 1/8" (3mm) to 1/2" (12mm). Weld the center posts first in quarter segments to balance the weld, push or pull the center post down tight against the work surface and tack in place if possible. This will help in achieving a rail that has a nice straight line in one direction when finished welding, balanced welding will take care of the second direction.
Now for the problem with weld shrinkage and heat input creating a wave in the intermediate rails, can be a source of great frustration. there are a couple of options: 1) use a Oxyfuel torch to straighten the parts by selectively shrinking the tubes, I've never tried this with stainless and would not venture to guess the outcome if tried by someone without some experience with heat shaping steel. 2) Start welding from the center tube of the rail and work you way our from there, finishing the weld on each section before moving to the next. On one particularly bad rail I resorted to a little trickery to get things straight, after one end of the tube was welded I would let it cool then break the tacks at the other end to release any accumulated stress. Realign the part tack and weld as before, much more work but the residual stress in the end appeared to be lower i.e. a straighter segment of rail.
For anyone who wants to try their hand a heat straightening steel I would recommend they pick up a copy of the AWS standard C4.4 / C4.4M ;2004 "recommended practices for heat shaping and straightening with Oxyfuel gas torches". a little pricey for some people but it has good examples of how to curve several steel shapes., along with a great deal about torch use and safety.
John

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John Noon wrote:

sounds good
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Yeah. For definite. Scientific / technical reason is * s.s. has twice(?) the thermal expansion coefficient compared to mild steel * s.s. has half(?) the thermal conductivity compared to mild steel
Combine concentrated heat with high expansion and you get what you have just seen - hideous warping. It really leaps out at you - nothing subtle to observe here. In my teeny bit of experience now some time ago - only a few designs in s.s. would work where with mild steel there would be plenty of approaches which worked just fine.
Richard S.
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One additional problem is that the tubes should be no more than 4" apart to keep children from slipping thru them or getting their head caught between them. It's a federal requirement in the USA, and similar guidelines exist in England and Germany, don't know about other countries.
outofstepper wrote:

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guys, thanks for the good and bad news. i have another 8' section to tackle.. i'll see if i dont have some luck trying to overbend a bit. i guess now, at least, i know how much distortion to expect.
the remaining piece is S shaped.. still the same brickwork pattern, but now i wont be able to lay it down on my welding table. this jig is going to be a nightmare.
john, i've heard about flamestraightening but have never tried it. wouldnt think to put a torch to this current project.. but i've got some scrap left over.. might be interesting to weld up some T joints and play with the torch.
any tips? i imagine i'll be heating up the curved side (opposite the T weld) and watching what happens when it cools?
-tony
Robert Ball wrote:

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outofstepper wrote:

I have used heat somewhat sucessfully to correct warping. If the rail is warping around the post you can heat on the oppoite,top side, to a dull red. when color is achieved try cooling the opposite side. This is a trial and error procedure, so good luck.

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Check out my solution to this problem
<http://www.stagesmith.com/gallery/shop_projects/rail_tube_weld_clamp/ind ex.html>
It is a common problem
--
Welding Instructor - South Seattle Comm. Coll.
- Divers Institute of Technology
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Go to the best european website concerning stainless steel matters
http://www.euro-inox.org /
There you can find you way out to load down a guideline for welding stainless steels. Stainless steels is used much more in Europe then in the US and therefore there are more knowledge collactable there. Elsewhere you can always try to contact the Technical sales people at the stainless steel producers. Try for example Outokumpu. www.outokumpu.com
//Roger
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