I have a friend that is using a new semi auto GMAW machine. He is welding 2" schedule 80 pipe, open root, knife edge bevel. He is running Esab ER70S-6 wire with 90/10 mix. He has been using this for a few months now and has operator qualifications. Everything has been going well, x-rays on the welds previously without issues.
He started welding this 2" and after having the components x-rayed they found horizontal cracks in the welds, pipe to pipe. All of the cracks are in the tack weld. He was using a brand new spool of wire so old wire is out of the picture. He is welding inside a shop that is climate controlled, temp set at 70 degrees. I asked him this because it was about 15 degrees outside when he called. The pipe is being welded in the 5G position, mounted on a machine to hold the pipe. I am unsure of any settings as far as volts and wire feed speed.
When we last spoke he was going to try and pin down when the cracks occurred by putting in tacks, have them x-rayed, then weld a root, again x-ray, then fill, x-ray and finish with the cap.
I figured I would put this on here to see if anybody has seen this or has any other additional ideas on causes. As I said he has had no problems on schedule 40 pipe.
If you have any thoughts on this I would be interested in hearing them and pass the information along.
thank you,
Shawn
Ooh, that evil "Crack" thing.
1) First off, are we sure it is a crack? Has it been cut apart and evaluated further to truly identify the "transverse linear indication"?
2) Did the recurrent problem start with the use of the new machine or when the sch. 80 change took place?
3) Were all settings duplicated with the new machine and independently verified with calibrated meters to ensure consistent electrical settings.
4) Same gun and nozzle as was used on the sch. 40?
My first thoughts are that this is a lack of fusion from the feathering of the tacks.
Nozzle might not be allowing the same electrical stick-out on the thicker walled pipe.
1) First off, are we sure it is a crack? Has it been cut apart and evaluated further to truly identify the "transverse linear indication"?
No, I do not believe so, they were x-rayed and shown to have cracks. I questioned him about cutting out the tacks and trying a nick or tensile to separate it to look inside, some other means of a visual
2) Did the recurrent problem start with the use of the new machine or when the sch. 80 change took place? Started with the sch. 80, all pipe work done before on sch. 40 was clean.
3) Were all settings duplicated with the new machine and independently verified with calibrated meters to ensure consistent electrical settings. It's a Miller set up and they came out and educated them on use, trained, etc. Not sure about the calibrations, figured the Miller guy or the qualifying inspector might have checked that, info I do not have
4) Same gun and nozzle as was used on the sch. 40? I will check on that. Didn't think about stick out myself but good point
SuperFlux is thinking along the same lines as I am.
Is the root pass Short Circuiting Transfer ?
Are we using a fancy RMD or STT for the Root?
If short circuit:
Is a smaller nozzle being utilized for access/stickout considerations ?
Is the contact tip set 1/8" beyond the nozzle ?
You mention "Semi-Automatic" GMAW. All GMAW done by hand is semi-automatic, is there something else meant by that term, or are you just telling us that it's not a robot? Best to ask... not trying to be snippy :)
Lack of fusion on restarts is the curse of GMAW, especially short circuit and low current pulsing. I would also look further with the radiographic interpreter about defining the defect as a crack or a lack of fusion on a restart. If distortion caused a tack to crack during the root pass (consistently) I would think the operator would be able to see it as he places the weld over it at least some of the time.
By the way: You did a great job of detailing the issue for your friend :)
Sorry Lawrence, it is a Mig on a machine. Mount the pipe, set your parameters and whatever else, flick the switch and it welds away. He is more of an operator on this thing as opposed to a welder. I was out there months ago when they were talking about getting it and was back once to visit with my friend and saw it, that's about the extent of my knowledge. Talked with him about it the other day and told him that I was sure somebody here has seen it before and could at least give more direction than I could.
"By the way: You did a great job of detailing the issue for your friend :)" LOL, I've been coming here for years and have learned when questioned about a weld to ask the basics! Forgot to ask about his settings but I don't even know what set up he is using. Cost more than I'll ever spend on a welding machine.
Just because I am a pedantic Welding Engineer - this would actually be referred to as mechanized GMAW (GMAW-ME). Sine the operator has "some" limited control of puddle (or so it seems from the description) it would not be automatic GMA (GMAW-AU).
As I said, I do not know what it is called, have never operated it, only saw it. Will never own one so the importance of it becomes even less on my list of things to know.
I knew he didn't hold it in his hand, it was mounted, the pipe spins mechanically, he said he can change speed I think, speed of what I could not say.
Not sure what you mean by horizontal cracks.
Pipe set in the 5g position, cracks go left to right, horizontally not vertically with the weld.
Transverse cracks such as that are almost always due to hydrogen. The only reason I would doubt that is the material and the thickness are favorable to preventing hydrogen cracking. But nonetheless I think that is where you need to start.
Have you suggested trying the tacks only, inspecting (maybe MT), and welding with progressive inspection. Transverse cracking that occurs at the tacks only could be a type of crater cracking or cracks that are occurring as the joint is welded.
Gerald
Yes, that was my initial thought when talking to him, tack it and mag test or xray, mag test because it's cheaper then move out from there. I talked with him yesterday and he was talking to a guy who thought it might be lack of fusion at the restart on the tack weld, cold lap I think. I know I've experienced this on FCAW with the big wire.
Thanks to all for the excellent responses!
At a quick glance it didn't look like anyone asked what the base material type and thickness were that your man was welding on? Was he following a WPS that was qualified?
A53 and the wire combo shouldn't be cracking. What pipe size sched 80 off chance?
Can you post the Xray film? Id like to see what you're actually seeing. Also how far are the crack propagating outside the root into the pipe?
I don't have it. Posted the question here for a welder friend of mine that called me with questions. Actually I haven't even seen the films.
If the cracks are not too out stretched or dramatic, I would think perhaps the stress pulling on a circular object along perhaps crater cracks. Or even an elongated keyhole edge flexing during stress and a crack branching out from that. I am interested in what you find out. A feathered tack that eventually gets ran over but not fully consumed I would think could cause a crack to go in that direction.
Jordan
Hey Shawn,
I have limited pipe experience. Is a knife edge bevel common? Could that cause issues?
Tyrone
