Are you preheating?
Dale Simonds
Chances are you need to pre and post heat. If you are repairing a current crack, drilling a hole at both ends helps prevent crack running.
Preheat to at least 300F; some sources say 575F, but we are getting good results on half inch WT pipe at 300F. That's what code B31-1 requires. The PWHT required in the code is 1300F to1400F, not to exceed 1480F and soak time is 1 hour per inch of WT with a minimum of 15 minutes. Remember to ramp your heat up evenly around the pipe; we are going up at a rate of 400F per hour, and bring it back down at the same rate.
We are also using the ER90S-B3 for the root and a couple of passes and filling and capping with E9018-B3 (SMAW).
We are mostly using the new Induction heat machines from Miller to pre and post. I know that an awful lot of Chrome was welded out in the past, using just a rosebud for preheat; but the fact is, the more evenly you acheive your temp. and the more uniform you maintain it, the better your weld will be. Machines are the way to go, plus you get a neat little diskette with all the charting on it.
Roybuck is spot on. No need for elaboration. chall
Thanks for all replies.
Yes, I preheat it at least 350F but considerable point is that this problem is new and it occurs immediately after welding of root pass. I was welding this case successfully before; and the WPS has a passed PQR.
By -
Date 10-26-2001 22:13
You state that the cracking is occurring immediately after completing the root pass. Is the pre-heat temperature still being applied at the stage that the cracking occurrs, or have you allowed it to cool down?
Regards
Niekie Jooste
Ted,
Just a thought,
This sounds like it may be a craftsmanship/technique Issue. 20mm is pretty thick for TIG on 6 inch pipe and I if I understand what your saying, it must be just the first pass of multiple passes that is cracking.
Is it a new welder who is experiencing this problem?
Centerline Cracks at the beginning and end might indicate inadequate wire feed (starving the puddle) or a bit too much amperage applied without wire to cool the puddle or even the welder simply moving at the wrong pace. Also a crater fill device on your powersource is no substitute for a Journeyman with a foot pedal who understands what he is looking at, In fact, I have never seen an experienced manual GTA welder use a crater fill device.
No foot pedal? than cup walking control and torch angle at the breaking of the ark may be an Issue.
Semi-automatic or chucked up to a turntable? Calibrate your wire feed & rotary speed
Keep us updated
Lawrence
Dear Lawrence
You are right. Crack just appears on root pass.
But welder is not changed and he’s experienced. He
uses crater fill just for facility.
He had welded joints successfully.no use of pedal,It's manual TIG.
Dear Niekie Jooste
Cracks appear immediately when the crater cool from red
color temperature. So the work piece is still in
preheating temperature.
thanks.
By -
Date 10-28-2001 19:23
From all you have said, I must admit that I am stumped. If you are busy applying the pre-heat as stated, and the welder's technique is good, then you should not pick up problems at the stage that you indicated. The only possibility that I can still see is that you have the wrong material. Have you performed a chemical analysis on the offending pieces of pipe?
Regards
Niekie
There are some pretty good responses to this one. Provided WPS parameters are being adhered to (including pre/post heat, electrical parameters, travel speed, etc), is the joint subject to excessive restraint during welding?
One thing you may want to check is thye joint geometry. A joint with a great depth to width ratio will cause centerline cracks. A tight groove angle and thick base metal can cause the same situation.
If the joint is in a plant that is operating I have seen situations in which vibration in the line has cause hot cracking. Or atleast when the adjacent machinery was stopped I could tack.
Good day
Gerald Austin
If this is a repair to existing links, connecting tubes or headers, is it possible there is an external load applied to the joint which could cause the cracking problem? I.E.; inadequate hanger support, damaged hangers, or rigging which is creating a load which the root pass is unable to support?
Dear Niekie 2,pipewelder and DPWeber
As you say the chemical analyze is suspicious. So I
asked to check analyze and it takes some days.
Groove angle is 70 degree. I think depth to width
ratio is suitable.
Joint is not very restraint and extra loaded but I'm not sure about vibration.
I’m following up all notes you have stated.
Regards.
