The essential variables include:
a) Welding Process
b) base metal A (P number 11)
c) base metal B (P number 8)
d) Filler Metal C (F number "X")
e) Weld Chemistry D (A number "Y")
f) other essential variable dependent on welding process and other considerations
Any time you change an essential variable, i.e., P number, F number, A, number, etc., a new procedure has to be qualified.
Welding two P11 base metals together does not replicate what will be done in production. As a matter of fact, welding two P11 base metals together with 316 filler metal would probably resulting in a potential cracking problem due to insufficient ferrite.
Best regards - Al
I agree with Al. The procedure should replicate what you're going to weld.
If and only if p11 and 316 stainless materials were in the same material group of the Code could you use both p11 tubes as your test plates, provided that your filler metal is acceptable per the Code.
Keith