wnrf piperTo be honest I never really gave it much thought, strangely never an issue for me.
Ill start by saying that I have not worked in the oil and gas sector, just pharmaceuticals and heavy industry. With regards to HAZ it must be industry or process specific because its never been an issue for any line I have worked on. When you have slip on flange there are 2 welds in close proximity, any fitting on seam welded pipe has over lapping welds on 45 deg elbows the welds can also be quite close, so I never really understood that one. I always worked on the principal as long as the welds dont touch your ok. Comes from a BS standard. So I dont think thats the reason. The only thing I can think of is that for the larger sizes on site to get a square cut you need to have some straight pipe either side of the cut to be able mount the jig for gas cutting the pipe.