I hate to push this question in a different direction, but part of the answer lies in the CFR. 10CFR49 - 192 is a DOT section dealing with gas transmission lines and the realted equipment.
10CFR49, Section 192.245.c says the following: Repair of a crack or defect in a previously repaired area must be in accordance with written weld repair procedures, qualified in accordance with 192.225. Repair procedures must provide that the minimum mechanical properties specified for the welding procedure used to make the original weld are met upon completion of the final weld repair.
Section 192.225 allows qualification of a WPS under both ASME and API. API took the position that repair welds may adversely impact the properties of the base metal, therefore qualification of the WPS (after simulating repair) is required. ASME makes no distiction with regard to that position. It causes folks like us (who spend most of our time dealing with ASME governed projects) to wonder. Personally, I think it's not a bad position (API). I have a problem with some of the positions they take, but this seems reasonable to me. If I was better schooled in the fine points of metallurgy, I may have a different position. However, my depth of knowledge is pretty thin, so this seems reasonable.
Since gas line owner / operators are 100% responsible for the line (regardless of who does the construction or maintenance) they rely heavily on what they know best; which in most cases is the API code. Furthermore, they are quick to point out the CFR basis for their decision making when it is an obvious call (as they belive the repair issue is).
My rant would be this: They are quick to point to the CFR, but for some reason they overlook the allowance to use an ASME program almost every time. It usually boils down to "that's the way we've always done it."
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