pipe distortion!!!!!!!!!!!!!!!!!!!!!!!!!

Date 07-28-2003 21:11

i would still like to here from anybody on this subject. in the shop we have a set of chaih clamps that we use.the chains lock around the pipe and by tightening a piece af allthread attached to a piece of angle opposite your weld o let . these do a fair job. i`ve clamped them and still had the pipe warp like a bannana.this distortion causes alot of water to be trapped in a fire sprinkler system(this is somthing that really pisses my fitters in the field off).also its not good craftmanship and can cause alot of problems.90% of the time we use sch. 10 pipe mild steel.any suggestions would be appreciated.im an apprentice welding for around 50 other fitters and apprentices who have no ideas about welding.i would like to rid myself of this distortion problem.

By CHGuilford (****)

Date 07-28-2003 22:03

If your welding is mostly on one side of the pipe,you could try back bowing the pipe in the direction opposite from the way it tends to warp. A little experimentation should get you pretty close to straight.

My second thought is to use heat straightening after welding if your back bow wasn't enough. Make sure heating your pipe to dull red (around 1100 - 1200 degrees F) won't violate code restrictions first. If it's OK then heat spots on the side of the pipe where you need to cause the metal to shrink to bring everything straight. Start out small and conservatively until you get the hang of it because it's easy to go too far.
It might help to picture where you might like to saw cut a small vee out of the pipe to be able to bend it where you want. That's where you should put the heat spot. Generally, it doesn't work to heat the same spot twice.

Don't be alarmed if it looks like heating is bending the pipe the wrong way. It does that. Just wait until it cools enough to put your hand on it and you will see it actually curves toward the side you heated. Also don't overheat, dull red is enough.

You could also make line heats running the length of the pipe (or portions thereof). Think of it as connecting the spot heats together. Long runs work best if you have a motorized unit like a Bug-O where you can dial in a speed until you can run one pass and get your pipe straight.

There's my 2 cents worth. I hope it helps and I'm sure other people have some ideas for you.

Chet Guilford

By insp76

Date 07-28-2003 22:29

Blue, grab a torch and put a hot spot 180 deg. opposite the olet your about to weld,about the size of the olet,when the steel starts to turn yellow it`s hot enough.Make the weld emediately after applying the heat. This should even out the distortion. With a little trial and error on your part you`ll figure out on your own exactly how much heat you need to apply. If you don`t like that idea try tacking a strong back 180 deg.from the olet in a longitudinal direction prior to welding. Flat bar or plate 3/8"X3"X12" should get you started. Let the weld erea completly cool before removing the strong back. I have seen pipes of large diameter lashed down with comealongs and chains to huge I-beams fail.The point I`m making is chains have a little slack in them no matter how tight you get them,but when you tack a strong back of a good enough size to the back side of the pipe it`s not going to budge.The quickest and easiest way for your situation that I suggest is the hot spot technique. I`m suprised no one at your shop has suggested this to you by now. Good luck and have a good day.