API 5L X56

Allow?

Can any body give me information that why B31.1 is not allow this material for power plant use . But same time it gives allowablee for API 5L Grade B, Grade 65 , grade 72

Ultimate strength.

Materials are tested to B31.1. They either meet specification, or are deemed not robust enough to be listed.

If an available material is not listed, don't use it.

Doing otherwise could prove catastrophic.

I'm guessing it is dependednt on how much H2S there is in the product stream. The more H2S there is, the lower the hardness and therefore the yield needs to be to prevent Stress Corrosion Cracking in the material. (see NACE MR-0172 or it's ISO replacement which the number eludes me at the moment, hey it's monday morning for me. Coffee hasn't kicked in yet.). A106 Gr B if memory serves is pretty darn soft, with a yield in the neighborhood of 32ksi if memory serves. This is an instance where stronger is not better. Pretty common situation where SCC is a possibility.