What is the P number for A106 grade B?

There isn't a single, universally defined "P number" for A106 Grade B pipe. P-numbers are associated with specific material specifications, often related to pressure vessel design, and aren't directly tied to pipe designations like A106 Grade B. The material properties of A106 Grade B are defined within the ASTM A106 standard itself, specifying things like tensile strength, yield strength, elongation, etc. These properties are what would be used in pressure vessel or piping system design calculations, not a P-number.