". . . QA controls based on conformance to the WPS. That's how modern QA systems work. "
Sorry, but it does NOT. And when we Eng types try for the "1-size will fit all welds, trust me" or the "we know better than you, you unschooled, non-engineering welder" we are FORCING the actual folks doing the actual work to work outside of the tolerances. Because we didn't allow enough freedom to perform the work within tolerance.
Anywhere in a fab shop within 50-ft of a door requires a gas-lens cup to be used, and usually one or two sizes larger than the minimum cup diameter for good gas coverage in 100% still air.
Running argon requires a small increase of the flow for overhead 4G work, and that increase may make the argon flow too fast & turbulent for working on flat 1G work. A deep weld bevel on a pipe at the upper end of the WPS thickness will require a narrower and longer cup than a bevel on Sch10. A large diameter pipe >12NPS [or plate] 'responds better' - gives better heat tint 'color' - than the biggest one that is usable on a 1NPS pipe that is listed on the WPS. Sorry, but these are FACTS. Spend time in the weld shop before you tell professional welders, with pride in their workmanship, how to do their job.
IF the job is repetitive, like joining fuel tubing, all similar [or same] diameter and wall thicknesses in a 'tight' fabshop, then yes you can develop a highly restrictive WPS that can specify the torch gas flow rate at 22-24 scfm, the 'backing' purge gas at 1-3 scfm, and the cup size as a conventional-length #6 w/gas lens, volts = 14, amps 70-78, footpedal amp control not allowed, preflow at 3 seconds minimum, postflow at 5 seconds minimum, each bead to be performed in less than 21-seconds to limit heat input to less than 18,000 joules/inch.
And the way you arrived at these stringent variables was to watch several identical joints being welded and working with them to optimize these variable factors.
Just ain't possible on field work. EXAMPLE: Callaway Nuke plant piping on the reactor coolant loop; about 5 field welds were made, on each of 4 loops. Each set of welds was at a different distance from the construction opening in the Reactor Containment bldg., about 20-ft x 30-ft. Different minimum cup diameters required to handle the unavoidable air movement. Different wind conditions on each day that welding was done on these 20 FW's. As the welders progressed out in the Extended-Land J-Bevel weld prep, the cup diameter needed to increase and the cup length was dropped from long-nose to conventional geometry. Big cup deep in the prep groove means bad visualization of weld puddle, means probability of 'bad' bead that has to be ground out. Too small a cup gives poor gas coverage and the color going from the 'perfect silver & gold' to the 'OK purple' to the 'start grinding grey' to the 'your fired as a welder scaly grey-black.' Depending on the day's temperature, the amps used on the Automatic GTAW dwell on the sidewalls had to be adjusted up and down significantly to compensate for the basemetal temperature and heat loss between beads. Cold outside = weld slightly hotter to compensate, and to maintain a nice 'hot' bead with toe angles of 120° or better. Then the weld cap requires a different travel speed and filler feed rate, with different amps and volts, highly dependent on the base metal temp. It makes a big difference if the 304 pipe is at 55°F or 340° when trying to make a beautiful cap. And these guys got two tries at it. We ran two welding crews on the loops, and eachweld was unique, so 1 weld to 'learn on' and one more to do, than the that phase of heavy-wall stainless welding was OVER. For a 6-year $1.2B project. Yes these welds had been mocked-up, in a shop with only a foot or three of pipe attached. So the mock-ups were very similar to reality, but they were not 'reality'. Each highly-critical weld was slightly different, each welder had slightly different techniques to achieve superb results, temperatures differed, etc. Nothing was identical, thus a 'tight' stringent WPS would never have allowed excellent work to have been done on each of these 20 welds. The WPS was 'snug' and we had to trust the welders to change with the changing conditions.
