|
|
we are doing a job for a refining companys alky unit the pipe in hf acid service piping low carbon steel.the xray standard is b31-3 severe cyclic pipe sizes range from 8'' down.all xrays on 2'',3'',4'' were good when we got to 6'' and 8'' thats when we started to have problems some of the 6'' was good but most failed for lack of fusion at toe of weld coming off root each pass was ground smooth before the next pass and power brushed.8'' had the same problem we put 3 passes of weld into a sch 40 joint ground each pass smooth then brushed.when grinding out for repair the lack of fusion is so small you can hardly see it.now we are welding with the lincoln stt mig process using er70s-6 wire the weld control for called for er70s2 wire but this was overrode by mgt.the fitters who cut the pipe laid back the bevels almost twice the normal angle and when welding i was carring alot of silica on top of the bead.when we were doing fitting make up those welds were good it just the fitting to pipe wekld joints we are having trouble with any help or input would be appreciated.also we just finished a job for br oil using this same process wire etc and out of 900 or so xrays we only failed 8 so any input would be helpful
Reply:Joel,I'm barely able to follow the line of questioning in your post. Using no punctuation makes it almost impossible to understand what you're saying.I can't tell if you're having trouble with STT root pass on 6-8" pipe, or if you switched to STT to solve the problems with lack of fusion?Post again with a couple simply-worded questions, and I'll try and help. But as it stands from your original post, I can't figure out what you're asking.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Same welder? Everything the same except pipe diameter? Same X-Ray technique? I've seen "ghost lack of fusion" drive us crazy before on some aluminum but not sure if it could happen on steel. Multi-pass welds resulting in percipitates of any one metal in the alloy congregating in an area can make a false lack of fusion signal.My .02Two turn tables and a microphone.
Reply:we are having problems with lack of fusion while welding 6and8'' low carbon steel pipe . the problem is after the root pass in the hot pass.the weld does not seem to be tieing into the toe of the weld at the bevel edges.now when we grind into the weld to make the repair you can hardly find the discontinuities they are linear and almost microscopic in dia.could these problems be wire?, could it be joint prep?, we grind each pass smooth; and the problems are fitting to pipe not fitting to fitting also the job spec called foe 70s2 but we are using 70s6; s6 is loaded with silica s2 has much less
Reply:Originally Posted by joelwelderwe are having problems with lack of fusion while welding 6and8'' low carbon steel pipe . the problem is after the root pass in the hot pass.the weld does not seem to be tieing into the toe of the weld at the bevel edges.now when we grind into the weld to make the repair you can hardly find the discontinuities they are linear and almost microscopic in dia.could these problems be wire?, could it be joint prep?, we grind each pass smooth; and the problems are fitting to pipe not fitting to fitting also the job spec called foe 70s2 but we are using 70s6; s6 is loaded with silica s2 has much less
Reply:Dab will do nailed it, most likely what your looking at is cold lap because your using STT for the fill passes which typically is only used for root passes, and then pulsed spray for fill. I dont know why made the decision to lay back the bevels, but I guess as long as it was within code then your ok. However it seems like a round-about way to fix the problem, as whenever it was qualified it was done with the original bevel angels. That should tell you the problem is with either the welder or weldor.Is the pipe being rotated? If so I would stick with the STT for the root, then switch to pulsed spray for the fill. However if your running 100% CO2 this might be an issue...I would also recommend that you measure the interpass temps on a 2-4" pipe and compare them to a 6-8". If you find that it is substantially lower, look at induction heating to raise the temps up before you run the first fill pass. After the first fill pass you might find that the problem goes away.Have we all gone mad?
Reply:just bought a couple of stt II's and it is my understanding that they are very sensitive to wire brand. lincoln,hobart,etc. are a little more prone to weld faults. esab and equiv. give more satisfactory results.I only drink when I'm by myself or with somebodymiller deltaweld 452 w/s62 and xr-wmiller trailblazer 302lincoln dc400 w/ln7eutectic tig rig hypertherm 900lincoln stt II w/ln742 |
|
发表于 2021-9-1 00:14:13