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Up Topic Welding Industry / General Welding Discussion / stainless pipe
- - By Henry Finkle Date 07-01-2008 00:32
what is the proper way to weld stainless steel pipe? I have about 2 years experience welding carbon w/gtaw and was wondering if there was any similarities between the two as far as technique, heat, root opening and so forth. I'm not sure but I think the pipe will be a 2" heavy wall.
Parent - By ericpratt (*) Date 07-01-2008 02:10
be sure to purge, gap will close up you so be carefull, turn down purge before finishing root so it doesnt  give you suck back.
Parent - - By sbcmweb (****) Date 07-01-2008 02:43
There's so many variables with stainless, depending on class, thickness, process....The list goes on. As far as GTAW, sure the same principles apply, but stainless is an entirely different ballgame. It reacts MUCH different than mild steel I.E. the HAZ, warpage, sugaring,(carbide precipitation) cracking, etc. I'm no expert, but that's a VERY basic introduction to doing SS as opposed to carbon steel pipe. There's some great guys on the forum who can answer the question much better that I. I'm sure many of them will offer their suggestions & experience. Good luck! S.W.
Parent - - By Henry Finkle Date 07-01-2008 03:16
what would be reasonable size gap if i'm welding with 1/8 wire
Parent - By jon20013 (*****) Date 07-01-2008 03:43
A very "general" rule of thumb is set the gap same size as filler.  Be careful though, put good tacks in and feather them nicely as your gap will want to close up on you as you come around to the opposite side.  Leave your purge going until you have a MINIMUM of two layers, or even better, 3 layers.
Parent - - By sbcmweb (****) Date 07-01-2008 03:50
What process? I'm thinking TIG & if so, that's up to you as far as the scope of parameters & procedures allow. Will this be a code quality job? Will it get UT or Radiograph tested? If so, you are going to want to be very sure you're root goes in with adequate penetration & face reinforcement on the ID side of the pipe without excessive carbide precipitation. This happens when the weld gets too hot & carbon is drawn out of the structure of the metal, forming on the surface of the weld, causing eventual weakness & lack of corrosion resistance. Some put a 1/8" land & gap on their pipe, others run a smaller gap with a little less land. I would say 3/32" would be as small as you want to go on a root gap. It's probably going to close up after you get it tacked & start welding. Every pipe I ever did in school did, in one way or another. The last thing you want is a reduced root gap, or have problems with suck in if it's too big.

The gap & land size will vary from weldor to weldor, or may be specifically spelled out by a particular process cert. in which case, you will need to follow to the letter if you don't want the weld rejected by QC when they inspect it & or watch you put that root in. You will also NEED to purge the inside of the pipe with argon, or whatever shielding gas the process requires. You will have a big mess on your hands if not. Like I said, I'm not a pipe guy, but got the basics in school. I'm going off very basic instruction, nothing more. I'm sure others will add to this who are much more experienced in this field. S.W.
Parent - - By rick harnish (***) Date 07-01-2008 03:56 Edited 07-01-2008 04:09
No land   feather it. As said watch the gap. tightest part first. I always like to be able to move my filler as needed around in the gap. If it gets too tight I blade it open.
You already have the hand, walk it in. Stainless is sweet!
Parent - - By sbcmweb (****) Date 07-01-2008 04:12
Really, no land?? I've never actually did stainless pipe, just carbon steel, so I appreciate the clarification on that one!! I was always under the impression that you put a land on it all the same. Cool! Thanks rick! S.W.
Parent - - By rick harnish (***) Date 07-01-2008 05:11
Yeppers Steve!
Parent - By sbcmweb (****) Date 07-01-2008 12:30
Nice to know. As I said, not a SS pipe guy, or much of a true pipe guy at all for that matter :-) . I thought it was all the same! So if it's pretty thick pipe, you just bevel it out & just touch the ends, gap it, & start welding? Cool......:-) S.W.

""You keep this love...." (This Love, Pantera, V.D. of P. LP)
Parent - By cmays (***) Date 07-02-2008 18:22 Edited 07-02-2008 18:26
I run a knife edge on carbon as well as stainless. Landing causes penetration problems on stainless set your amperage about 10 amps cooler than what you would on carbon and SPREAD YOUR HEAT OUT. Use a good purge and keep it going atleast till after you hot pass. Steel wool makes good purge dams as does that foil duct work tape. Use HAZ Tape where youre going to be welding to keep the adhesive from getting into your weld. If it looks black or you get sugar on the back side of the root its junk.  On some roots I will profile a step bevel on each end and butt themstraight up with no gap. With a good purge you can flow the stringer in 100% with no suck back. You have to really master machining that step bevel cause if you have any variation in the to sides your weld will favor the thinnner step and you get IP.  As said before there are so many different parameters when dealing with stainless it would take pages and pages to cover just a few methods. Good luck.
Parent - - By 3.1 Inspector Date 07-01-2008 04:57
Here is another one....
Bevel the pipes as much as the WPS let you, and then maybe a little more :)
Tack it(8 small tacks) without any root gap, and pulse it - this technique requires a little practice, but you will get a beutiful root without any miscolour.
Its very important that your pipes is perfectly alligned.

The pulse should be set at 50% for the lower amp, and the interval should be around half a second.
Parent - - By rick harnish (***) Date 07-01-2008 05:03
soaking the root. Will they allow this on a test? I love that! Golden ring!
Parent - By rick harnish (***) Date 07-01-2008 05:07
Dont know about pulsing, though. Just walk tight and slow making sure I break down the edges. Please, more info. Alas, I work off a 300D. still may learn something!
Parent - - By 3.1 Inspector Date 07-01-2008 05:07
I dont know what they allow :)
Parent - - By rick harnish (***) Date 07-01-2008 05:18 Edited 07-01-2008 05:24
Cool you would mention butting them perfect sans gap. Particularly if you are rolling it out. Perfect root. Done it countless times. In position brings new challenges, as gravity is not in your favor. Can be done with excellent results, though. The proper puddle gives an indication you are looking at a mirror. I love it when a root falls in.
Parent - - By rick harnish (***) Date 07-01-2008 05:20
I reckon Henry was looking for proper procedure, though.
Parent - - By 803056 (*****) Date 07-02-2008 18:58
The technique I use is to minimize the root face (land to some people) and leave no root opening. My root face is on the order of 1/32 inch maximum. I prefer a U-groove, but a single vee of 80-90 degrees works.

The purge is easier to maintain if no root opening is used. Penetration is not a problem and there is minimal discoloration (oxidation) on the root surface.

2% thoriated tungsten. 3/32 inch diameter, tapered end with about a 1/64 inch flat (no point). Amperage for the root pass is set to about 50 amps using the 1/32 root face. Fine control the amperage with the foot pedal if you are using one.

1/16  inch filler metal. I use the "lay wire" technique. In other words, the filler metal is rested on the bottom of the groove and pushed into the molten puddle as needed. I don't dab the puddle. The tendency is to pull the hot end of the filler metal out of the shielding gas envelop when the "dabbing" method is used. That results in adding oxides to the molten puddle the next time the filler metal is "dabbed" into the molten puddle. Bad practice, bad habit.

I've used this technique for a good while and it works well with folks learning to weld pipe. I also "walk the cup" to better control the arc. It's easier than free handing in my opinion.

Good luck and practice.

Best regards - Al
Parent - - By js55 (*****) Date 07-02-2008 19:31
The only time I've ever used the 'dab' technique is with wide gaps on root repairs or when, for whatever reason, I was keyholing. And your right, keeping it in the shield envelope is essential, and even more difficult with keyhoing since, (at least the way I did it,) a more perpendicular torch angle is used.
Parent - - By Metarinka (****) Date 07-02-2008 20:05
I primarily dab just because it's harder to get the filler deposit rate with the "constant feed" method, if the torch angle or joint setup is just right I found the filler would often burn back or fill in too much, I do use it on aluminum or certain joint profiles.  I agree keeping the end free of oxides is extremely important and it easy for that metal to get outside of the shielding coverage. 
sometimes I would "lay" the rod in the joint and just wash it out to the sides, your travel speed and heat had to be constant and at the correct values but you could get very decent root and fill passes with gtaw that way.
Parent - - By Henry Finkle Date 07-02-2008 21:13
Is it neccesary to purge the pipe while it is being tacked.
Parent - By js55 (*****) Date 07-02-2008 21:34
If you full pen tack it yes. If you bridge tack it, no. Just make sure all the tack is removed if you bridge it.
Parent - - By sbcmweb (****) Date 07-02-2008 23:58
R U alive Rick?? The forum crashed last night. Didn't know if you were aware. S.W.
Parent - - By rick harnish (***) Date 07-03-2008 17:09
Yeah, made it through another one! Ha ha!
Parent - By sbcmweb (****) Date 07-03-2008 18:04
Good deal. I hadn't read anything real recent. I haven't paid a huge amount of attention either! lol. Carry on, Bro. S.W.

"What is it? Caught in a mosh...." (Caught In A Mosh, Anthrax, Among The Living LP)
Up Topic Welding Industry / General Welding Discussion / stainless pipe

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