Dual grades and multi grades of material marking
Marking of pipe product means that the product is complied with more specifications.
Marking: ASTM A106 Gr. B / ASTM A53 / API 5L Gr. X52 PSL1.
So, the marking products are complied ASTM A106 Gr. B, A53 and API 5L Grade X52 PSL 1.
Marking of pipe product mean that product also complied with one more grade.
ASTM A312 TP316/316L
Means carbon content < 0.035% expressed type 316L and min. tensile strength 205 MPa expressed type 316.