I agree with js. However, his answer is very short and chances are that someone (especially someone whose mother language isn't English) doesn't understand exactly what he meant.
So, I'll take the liberty of explaining that what he wanted to say is that the Engineer (whether a person or a company) that has designed the pipeline and/or specified its construction, based on his knowledge, expertise, experience and good judgement, should determine whether or not to accept one standard in lieu of another one, as BS in lieu of ISO.
Example: back im my days of erector engineer I'd been in charge of the construction of a natural gas compressing station in the south of Argentina (S.A.). All of the welders were qualified to API 1104. When it came the time to make a few structural steel field welds, all of them belonging to the station building and pipe supports, the client and me agreed that the correct qualifying standard in this case would be AWS D1.1. After a few minutes of discussion, though, we decided that a welder who's been qualified under API 1104 was a good welder; that the structural welds to be done were minor ones (largest structural shape was 4 inches), and so the welders didn't need to be requalified to AWS D1.1.
js, have I interpreted correctly what you meant?
Giovanni S. Crisi
Sao Paulo - Brazil