You are correct for Majority of the times it is not required but for very rare cases I had encounter one where client prefer to go for PMI for SS316L grade. (Maybe they wanted to be sure it is SS316L and not SS316 material). As a safer option it is better to have a look at client design basis 😊. This is as per best of my current understanding !
PMI is required for SS316 material to identify the qualiity of the finished product after it's manufacturing completes. The composition of the material are to be with in the tolerance limit. Especially molybdenum, chromium and nickel contents which requires for resisting the corrosion
