Would like to start a thread on this subject. Specifically TIG welding stainless steel pipe schedule 10 or 40. My experience is that the only way is to setup with a gap, to ensure complete penetration. And of course purging the inside.
Would like to hear from anyone with experience, or an opinion. Do you know of any web sites that cover this subject? Has anyone ever tried butting the pipe together and welding through with consistent results?
It is as Ernie says with the bevel. Only thing I dislike about using gap is that is shrinks very quickly to virtually no gap at all. Some jobs I have been on require filler rod some don't specify. The job I was on in Palm Springs for Arrowhead/Perrier did not require filler rod, only a completely fused weld, and the ends were square cut with a George Fischer saw. Of course, I was running an orbital welder on that job. But for the pig launcher and receiver we did not use the orbital and used just normal tig equipment with no filler and square cut ends as well. It just requires that you pay more attention to what you are doing. I have found that when I walk the cup VERY slowly I can see the puddle QUIVER so to speak and that tells me that it dropped and fused inside. You will need to practice your speed for your own knowledge. That was on 8" .135 wall stainless steel piping.
Since I purchased my Maxstar 200dx like Ernie 's, I have practiced with the pulser and it does a great job of fusing the butt welds. I also have done
12" in the SK Food plant in Lemoore, CA. with fusion, but that is ALOT harder for me. Approx. the same thickness, maybe slightly thicker, I don't recall exactly.
Well, so much depends on what results you want, and what service the pipe will be in.
Generally, you need to gap the root to insure complete penetration ahen welding manualy. If the root isn't open, a complete pen weld will melt through anyway, and you will get a keyhole ahead of the puddle. No keyhole, no full pen, as the inside didn't melt. The gap makes sure you can see the edge consume, and it is easier to control the fill so you dont suck back the root or end up with overfill on the inside. Of course, with automatic processes (orbital ube welding is most common) it isn't unusual to weld with no bevel, butted tight, no filler. Required in phamacutical process pipe, and much sanitary manufacturing piping--insures an essentialy flush and smooth surface inside, but the process takes some tuning, setup being done on test coupons to insure full pen. Not real practical to do manually, as it's damn near imposssible to get full fusion inside witout overheating spots.
For stainless, a purge is pretty much a necessity for a quality job. Purgeing isn't necessary a lot of the time for mild steel, but makes for a better job there, too.
Done light pipe without the bevel, but sch80 and heavier, bevel is pretty much needed to get the root edge to consume.
Iv'e never met anyone that can, manually, fuse Sch 40 unbeveled, but there are undoubtedly some. I have watched machines do it many times. Generally done with orbital machines, which use fairly sophisticated controls for the arc, and relatively simple (conceptualy) mechanical systems, and TIG process. Watched a robot (arm, not orbital) setup not quite able to do it- spots that didnt make full pen. Watched some amazing film from the inside of a pipe for a pharmaceutical plant being done with an orbital machine. Truly a neat sight. If you've ever sighted a weld for someone, you've seen the swirl behind the keyhole. Imagine the seeing that swirl, without a keyhole ahead of it--it looks like magic. The setup on these systems requires a lot of skill and a lot of tests.
I've done fusion roots that are ok WITH bevels, on plate, and work with people that can do fusion roots quite well with a bevel.
Pnce you get beyond tig, there are a bunch of methods that can be used, such as friction welding and swirl welding, though I don't think there are any manual ones other than gas welding. Some of th recent developments in friction processes are truely amazing.