The following is a piping related question. Does anybody in this forum know why cast stainless steel socket weld 150# fittings (elbows) manufactured by Kingdom Precision Casting Co. Ltd. to the requirements of MSS-SP114 are not listed components in B31.3? Clause 323.1.2 states that "unlisted material may be used .....". The only thing I can think of is the manufacturing process. These MSS-SP114 fittings certainly meet or exceed the physical and chemical composition requirements of A-351 which are B31.3 listed. This forum's opinions are apprciated.