pipe clamping

[larry53]

I have been welding sch. 10 stainless pipe about 45 inches in length 4 inch diameter, then a reducer down to 3 inch diameter, then another reducer down to 2 inch diameter. Each pipe was about the same 45 inch in length pipe. On each one there were three holes that a 2 inch pipe was welded too.
The 2 inch pipe was scallop to fit the radius of the large pipe. The problem I was having was that I clamp the two inch pipe to keep it from moving, and later found out that the pipe that the two inch pipe was welded to was be deformed. This show up more at the ends of the pipe where the pipe draw in about 1/8 of a inch causing a problem keeping the reducer straight without alot of grinding. The question I have is there a better way to clamp the 2 inch pipe? Thanks for any suggestions

[Farmers Machine]

How long are the 2" pipes, What process are you welding with,how good is the fit where the 2" mates into the 4", do you own a machine shop or have a good buddy with one who could make a V block tie down with clearance to weld around the pipe with out unclamping.
Heat input is your main reason for warping. Molten metal shrinks when it cools so the least amount of input filler metal to do the job will minimize the drawing effect. you might machine a 1" thick round circle to insert into the end of the pipe to keep it from deforming, drill and tap for 1" 8tpi and use a slide hammer to remove it. Every action has an equal and opposite reaction. you may have to take a torch and apply the same amount of heat opposite the weld to counter act the pull from cooling. Reply with some more particluars on how you are clamping the pipe and we will come up with something. good luck the Farmer

[larry53]

The process I am using is tig welding. The job varys in size of the main pipe that the 2 inch pipe is welded too. The first thing I do is bore the main pipe the size of the inside dimension of the 2 inch pipe. Then I cut the 2 inch pipe the radius of the main pipe, which is a good fit. Then I place the main pipe on Vee blocks and use a clamp and a piece of flat metal to clamp the 2 inch pipe to the main pipe. Then the ends are welded on the main pipe. There are several 2 inch pipes welded to the main pipe, these 2 inch pipes are spaced as the customer requires. The shop is my own, which I make all the parts that go into the finish product. Thanks Larry

[Madclicker]

Thin wall stainless pipe is going to shrink. The hotter you get it, the more it will shrink. Clamping won't help. Just keep it from getting any hotter than necessary. Weld small segments and stagger them around the seam. Let it get cool before the next segment(s). Not real good for production, but you can get some really crappy results with thinwall if you just weld it out all at one time. Not to mention the carbide precipitation and later rust problems you create.

[larry53]

Thanks for the reply.

[larry53]

Welding in small steps is alot better then welding a longer piece. I can use a level and see the pipe moving back square if I allow it to cool. It looks to me the clamp is doing nonthing more than to hold it in place until it is spotted in place. I can see why a pipe fitter must control the heat of the weld and placement of welds to help draw a part back into square.

[Farmers Machine]

I have a Lincoln Precison Tig 375 that has pulsing ability. I have fused a 3/8" stainless tube approx .035 wall to 4140 1" Od pipe thread at 195 amps with the power on 50% and background current at 30%. focus the heat on the heavy part and let the puddle flow to the thin part. Using a 1/8" filler rod on your tube you could focus heat on filler and get it just hot enough to let the puddle bond to the pipes. Linclon also builds the power mig 350 single phase multi process mig welder that has pulsed mig for thin wall welding with no spatter. If it is as good as tig machine it will be OK!!. waiting for my new one to get out of 1 year demo at local college, they said maybe another month. The main thing is heat and the best fit up possible will help reduce input heat.Good luck the Farmer.