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View Full Version : Quenching a weld joint?



crossthreaded
03-03-2004, 12:31 AM
I failed a bend test for a
beveled butt joint in my pipewelding class at the local JC. I had welded it outdoors on a cold (for Arizona) & windy day. It was about 45F toward evening. My instructor looked at it & said "you quenched it!" I did not quench it in water, having learned that does not enhance it's chance to pass the bend test. I just let it cool in the breeze. He commented on the fine grain structure after he broke the weld apart. He then had me heat one of the remaining coupons & slow cool it to aneal it. It passed as he had predicted. I'm going to pay more attention to preheating & slow cooling critical welds. What do you folks in COLD climates do about welds like this, or do you not find it a problem?
Mike

torker
03-03-2004, 02:52 AM
Mike...welcome to the world of welding. You better get used to failing the odd coupon. I've seen it happen to some of the best. When I do coupons I let them cool as slow as possible. You aren't really supposed to let them even sit in a breeze. HOWEVER... I've been in a rush a few times and threw red hot coupons in water and they've bent ok. My son does this all the time (thinks he's pretty smart!!) I see a lot of older guys cut their coupons out REAL slow... in other words they get the whole coupon red hot. Unless it's a dirty weld it should bend ok. They don't let us post heat coupons so we cover them up to keep them warm as long as possible. Was this a 6010 root/ hot and 7018 out?

Evan
03-03-2004, 03:15 AM
Try fixing a broken part on the snowplow at -30. I'm lucky if I can get it to stick together long enough to finish the driveway.

Preheat really makes a big difference. Use a tiger torch for big parts, cheap, runs on propane.

Thrud
03-03-2004, 04:09 AM
Mike
I don't know what you instructors are like where you are or how tough the apprenticship programs are, here in Alberta when you pass as a welder you still have a long road ahead of you to become "B" pressure certified or "A" pressure after that. The "B" pressure guys that weld on piplines are some of the very best welders in the world and their welds stand up to the scrutiny of x-ray and ultrasound NDT before being passed.

I sure as hell can't weld that good. The only way you can get that way is good teachers and lots, and lots of practice. I have known working welders with their own shops that took eight years to get a "B" pressure ticket - I used to watch one guy weld pipe over and over again, indoors and out when it was -40*C. Beautiful beads - looked like a machine laid them down.

Just keep at it and don't give up so easily.

Plain ol Bill
03-03-2004, 12:37 PM
I have taken literally a couple of hundred boiler tube test's, given another thousand or so. After burning out the coupons I always water quenched, ground and bent. Some went to xray and were not quenched. Never had a failure I could attribute to the quenching guys. Most common failure was porosity or lack of fusion. When temps were below 50 or so I preheated w/ a torch to about 200-250 before starting.

Paul Alciatore
03-03-2004, 01:06 PM
Not being a welder, I have to ask, what's a "coupon"?

Paul A.

crossthreaded
03-03-2004, 01:50 PM
I used E-7018 for the root & filler passes with an arc welder. I've been taking classes at the local JC since some of you folks admonished me to about 2 years ago. The class I'm in now is supposed to prepare you to take the ASME certification for pipewelding. I once was an Optical Engineer for 25 years; this is a new & interesting game. I'm a long way from "being there." I can now put down clean beads most of the time. Putting down nice beads in the right place & tieing them together is an art. My instructor is an "Instrument Maker" at the U of A where they build telescopes & space qualified hardware on occasion. He is an artist. God must love Community College instructors because they put up with a lot (folks like me) & don't get paid much; but I have sure learned alot from them. The test for plate is to weld two 3" X 6" beveled plates & then cut out three 1&1/2" samples across the weld; which I called coupons. They are then bent in a 10 ton press with about a 1" radius convex die into a 'U'. The 3/8" thick metal is more than strong enough to pass without cracking with even a few minor flaws, but enough will cause it to crack or in my case break open. Mine broke with a grain inside like fine powder, a sign I had changed the metal structure & made it brittle. I will hence forth pre-heat the things to a good temperature & wrap them in old welding gloves to cool, which is what my instructor recommended. If I gain any confidence & real skill I may even try water quenching them for a joke. That's in the future.
Mike

jfsmith
03-03-2004, 01:59 PM
My brother is an NDT 3 and inspect lots of welds, like bridges, building and nuclear plants.

Most welds pass, some do not. The ones that do not have to be reduced and then redone. I think is along the lines that a bad job can not be patched up.


Jerry

Carl
03-03-2004, 02:10 PM
I think I heard somewhere that they had problem with welds when they first started building the Alaska pipeline due to low ambient temperature.

Paul Gauthier
03-04-2004, 02:17 PM
"What do you folks in COLD climates do about welds like this, or do you not find it a problem?"

I weld inside where it is warm.


------------------
Paul G.

crossthreaded
03-04-2004, 04:00 PM
Jerry ,I think my lessons learned on this is that although my welds were acceptable, I allowed the metal to cool too rapidly & it become brittle. I agree bad welds have to be repaired. I got to briefly play with an air arc that does "erase" welds. It made an awful racket & threw hot slag 30-40 feet. If I had been less metally challanged, I would have done an adequate pre-heat, & slowed the cooldown as Evan suggested. The folks that built the Alska pipelins are heroes. I whine when it goes down in the teens.

Paul you are too simple & direct. I live in the Sonora Desert, where winter weather is normally balmy. I weld in my car port. If you weld indoors, how do you deal with ventilating the fumes & dust from grinding.
Mike