Are there any manuals for the fabrication of tube welding? This is all 7ga. 304 s/s. No pressure vessel at all.The dia. size range from 28 in.- 144 in. More voulme flow than anything. Very large project, hunderd,s of yards of tubing! None of us have much background on general fab. requirments for tubing. We are making our own tubing,stright and elbows and don,t know about seam alinement. We have cut alot of elbows apart trying to not have the seams inline. DOES IT REALLY MATTER? Need some kind of reference documentation as to it does or does not matter! We are waisting alot of time.
By Tommyjoking 
Date 11-16-2009 01:17
Edited 11-18-2009 07:10
As far as having your seams in line .....I have never seen much of anything to discourage that unless it was a customer requirement. I understand why you would not want to and I would think it is preferable but I have never seen it required except in containment vessels and pressure vessels. Someone here can probably reference some eng specs that refer to it.
That must be an interesting project from a fab standpoint....
(sic)
Regards
Tommy
What's the application? I would think that if it's a) stainless and b) large diameter, then it must be some sort of exhaust duct. I can't see why anyone wouldn't want the seam to line up, form a purely aesthetic point of view. Is there some sort of heat input/expansion requirement?
By Superflux
Date 11-16-2009 19:11
Edited 11-16-2009 19:13
If there are no specs dictating otherwise, for ease of fabrication and aesthetics I would stagger them at 180 degrees. On this large of diameter, the difficulties of aligning the seams would be cost prohibitive (major PITA) labor wise if not near impossible.
I personally think it would be very appealing to be able to keep all the seams true, but Wow, what a nightmare to accomplish this. Better be a T and M job.
Just one word of warning. When welding two pieces of tube together, good engineering practice says that the longitudinal welds must not coincide; rather, they should be staggered. How much? Use your good engineering judgement. How about 15º?
When welding two miters of the same elbow, the welds must be 180º apart from each other, i.e., one on the widest side of the miter and the other on the narrowest side.
Giovanni S. Crisi
Sao Paulo - Brazil
Convinced me!
I have never done structural mitering, only in ventilation ducting and cosmetic flashing. The only time I didn't stagger seams is when the piece was highly visible, and usually stainless steel at that. The reasoning behind the stagger is heat distribution, especially when dealing with thin gauge stainless. which wants to warp like mad even with staggered seams. But those admirals love to see uniformity. :)
