TBP, You are right. I have worked many years on the other side, as an OEM. I've seen a lot of specification packages, and it seems that those who have composed a specification feel that as long as they include some reference to a piping spec, whether it is B31.1 or B31.3, that they are covered and the code will take care of them. Not knowing that there is more to it than that.
Hence my orginal question - given the level of competance, or lack of on the end user side, it would seem to me that the OEM has an obligation to point out the code requirements for nasty fluid services. Of course the OEM should get paid for this, and not be made to eat the cost as "Being Required By Code".