What does the TP meaning in TP304 TP304L TP316L?

In the field of stainless steel, usually 304 is called TP304, 304L is called 304L, 316L is called TP316L. For example: ASTM A312 TP304, ASME SA213 TP304L, ASME SA213 TP316L.

So what does “TP” mean?

TP stands for Type. The reason is AISI(American Iron and Steel Institute) Classifies Stainless Steel in Type.

For the same reason, sometimes 304, 304, L316L, will be called AISI 304, AISI 304L, AISI 316L.