thePetroStreet

We are welding P5 to P9 (almost 10 welds in 8" NPS).
What should be the electrodes, pre-heating and PWHT temperature for this joint?

Also we have two more welds connecting SS316 to P5.
Advise required for this also.

In principal, welding of any two ferritic low alloy steels PWHT temperature should be kept as optimum as possible that is it should meet the requirement of higher alloy but must not pass the limit of low alloy. For PWHT of P5 and P9 weld joint, B31.3 has mentioned the temperature range same for both that is 704-760 deg C.

Weld P5 end with ER/E-309L and then perform PWHT. After PWHT, weld this end to SS316 with ER/E-309L. No PWHT after this.

P5 to P9 Welding:-
Use P5 welding rod and carryout PWHT as per P9 requirements. Regarding joining P5 with 316 check the temperature and there is a limit for using 309L material in high sulphur process fluid according to API582.If that is the case it is better to carryout 316 buttering on P5 and weld the same using 316 electrode.This will avoid PWHT also.
regards,

Thanks all.
piiengineers: If I use 316 to butter P5 side, PWHT is necessary to do after this or not?

No need for PWHT since the weld will be having homogenuous Austenite structure.But generally the designer wouldn't mix ASS with Alloy steel due to difference in thermal expansion and the weld will crack if it is used in high temperature service greater than 300 Deg.C