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Up Topic Welding Industry / General Welding Discussion / Lincoln STT for welding pipe piles
- - By Pablo van Dam Date 05-05-2007 14:40
I am in  Venezuela so I dont want to make a mistake when purchasing expensive welding machines such as Lincoln power wave and semia automatic feeders.
Have to circumferentially weld 40"diameter pipe joints from 5/8"to 1" in mild steel. Some misalignent or uneven gaps are possible. The reason I am considering STT is I want to weld from outside only. After finishing root pass I want to fill in by SAW. Can I get a good appearance on the inside of the pipe. I also need good support for the SAW. Will have pipe on turning rolls so flat to 45 degree welding is possible.  Am I going the right way with thinking STT?
Parent - - By cmays (***) Date 05-05-2007 15:15
We use STT day in and day out for open grove butt welding of pipe with no problems. The STT was really specifially designed for open grove butt welding. Ive seen the power wave 455 running a Fanuc robotics system that was set up for STT in .045 on open grove butts followed by GMAW-P for fill and caps and its amazing. This was on 2" to 16" sch 40 and up pipe. It produced the best looking stringers Ive ever seen. When the parts were tacked up all the operator had to do was feather out all four tacks and thats it! The STT melted right through the tacks with no problem. If that was done by hand I would have had to cut out my tack completely to get the same result. Its really an excelent process.
Parent - - By welder5354 (**) Date 05-07-2007 00:01
I have the Powerwave455 STT in our shop at present, which is there temporarily from my lincoln sales rep.
We have the dual setup; STT for roots on one side (works excellent).  On the waveform side we are having difficulty getting it programed.  We (including salesman) have been trying to program the waveform side, either with CV or GMAWp, but no luck so far with good results.   So try before you buy.
Cmays, what program are u using to weld GMAW-P with.  Would u be willing to share with us the program that u are using and all the parameters associated with welding the 2"-16" pipe.
Thanks
Parent - By js55 (*****) Date 05-07-2007 14:35
The STT can certainly do what you are looking for it to do, but then so will much less expensive standard CV's. IMO, unless you are planning on running all position GMAW roots on (especially with high alloys) standard CV is a more economical choice.
I've seen STT called for with low ID spatter applications as well, but quite frankly a well adjusted CV in the hands of the right welder can eliminate spatter.
Its not like the CV guys sat on their hands doing nothing while the STT guys came out with the new show pony. CV's are smoother now too.
Parent - - By welder53 (*) Date 07-05-2007 12:54
CMAYS, are you running the STT program on stainless steel. 
If you are, are purging?  I have completed several stainless steel plates using the STT program>open roots (no purging) and filled with flux cored  and the results were good.  I did root bends and side bends, but no tensiles, yet.
I would like to know, if anybody has been welding stainless steel pipe, using the STT program (open roots) without purging.
thanks
Parent - - By Lawrence (*****) Date 07-05-2007 14:04
Hey 53

No purge on Stainless open roots?

I don't understand... How does it matter if it's STT, GTAW, Short Circuit CV, or SMAW?

Air gets to the molten backside of an open root and no backing even with STT ...  Are you grinding off the sugar and doing the bends at that point?

Tell us more
Parent - By ssbn727 (*****) Date 07-05-2007 19:56
Hi Larry!

Good questions!!! this thread has definitely caught my attention!!!

Having been one that has welded together many stainless pipe joints of various grades and different diameters/schedules, I've seen more than once what can occur when there's no purging gas used, or when there's a sudden loss of purging gas at the joint location and economically speaking, a whole lot more man hours alone would have to be included, not to mention operating costs, especially if we're talking about certain pipe diameters and schedules that do not facilitate the use of removing the "sugar' infested root faces within the line... What a mess that would be!!! Talk about a clusterblank!!! FUBAR!!!

I just do'nt see how one can get "sugar free", uncontaminated roots with STT or any other process where no flux is incorporated in to the process - without the use of purging gas... Am I missing something here???

Respectfully,
Henry
Parent - - By welder5354 (**) Date 07-06-2007 03:30
Lawrence, am i reading you right.  Do you purge your stainless steel, open root joints when using the SMAW process?
Parent - By Lawrence (*****) Date 07-06-2007 04:48
Honestly,   I've never done an open root smaw with stainless electrodes..... Don't see how it would matter though....

Just having a hard time getting my brain around non purged open roots with SS.
Parent - By ssbn727 (*****) Date 07-07-2007 01:19 Edited 07-07-2007 05:47
STT is'nt SMAW...

I believe that's the GMAW process variant being used. ;)

Just curious as to why no sugaring in the root... Is there anything different in the joint preparation/configuration??? I would agree that the results from the tensiles would justify the need to qualify the procedure. Is this API or ASME B31.1 or B31.3???

Respectfully,
Henry
Parent - - By cmays (***) Date 07-06-2007 01:06 Edited 07-06-2007 01:09
Have not run it nor seen how it runs on stainless. I would be very interested to see how it runs. I cant believe it would be capable of putting down "sugar" free stringers with out purging.
Parent - - By welder5354 (**) Date 07-06-2007 03:25 Edited 07-07-2007 04:30
Well, it looks like nobody out there is using the STT process on S Steel.open root joints.
To my surprise the root pass did not sugar.  It was a little black, but when i brushed it with a stainless steel brush it came off.  The root went in beautifully.  I did two root bends and two side bends/no flaws.
The rood bends showed the little crease down the middle as if it were done by tig.  When i get the time, i'm gonna do some tensiles.  If that works out to my satisfaction then i will approach the welding inspector to do a procedure.  Will let you know the results in about six weeks.  Inspector is on vacation.
Has anybody got anymore feedback?
Parent - - By cmays (***) Date 07-08-2007 21:39
Post some pics if you can.
Parent - By welder5354 (**) Date 12-16-2007 06:15
STT procedure update.
Hi all, just an update to the STT procedure on 304L material using 3/8" plate.
Completed the procedure and sent it to a independent company for tensiles and bends.
Tensiles fractured in a ductile manner in the weld at 83,500 & 84,000.
Both face bends showed no individual open discontunities.
R1 showed no individual open discontunities.
R2 fail the bend test.
I will change a few variables the next time and try it again.  The root pass looked excellent and i did not use any purging.
Previous to that, i welded samples in the shop and did side bends and root bends and they were fine.
Next time i'll wear my glasses so i can find the root gap, while welding(age do play a factor)!!
Excellent machine and runs a very nice clean root pass with excellent penetration.
I put my failure to human error or wrong parameters.  Any suggestions out there?
dan
Up Topic Welding Industry / General Welding Discussion / Lincoln STT for welding pipe piles

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