If the base metal thickness is 1" and over, yes, PWHT is required. If you need to PWHT, butter the weld prep of the carbon steel (P-No 1) base metal with 309L filler metal. PWHT the carbon steel base metal, after buttering, following the PWHT requirements for P-No 1 base metal. After PWHT, weld the remainder of the joint using 308L with no PWHT.
ASME B31.3 Para. 331.2.2 provides exceptions to the rule. Ultimately it is up to the Owner to make that decision based on service conditions. If you are the Contractor responsible for the welding stated, you are required to PWHT the butt joint when the T of the P No. 1 material and the weld metal thickness is geater than 3/4".
now the rest of the story.very few flanges on this job,temporary caps(cs) will be welded to existing pipe,pneumatically tested with nitrogen,in some cases to 2400 psi. then removed and closure welds made ss to ss. there are no service concerns.do i still need to pwht.is brittle fracture a concern for these temporary pieces.if i butter the carbon and don't pwht do i violate 31.3,since techically its not a full pen weld.thanks for the help.
bladeo.
The P No 1 material will not be used in service and over 35 years experience in engineering B31.3 piping systems as Owner, Owner's Engineer, and Contractor. We have done this countless times.
Why would you believe that a temporary cap used for hydrotest and removed there after would be subject to B31.3 PWHT requirements?
LIKE STANWELD SAY.....NOPE...it's a temp weld and of no concern to code and I see no real concern over brittle fracture with these materials at these thickness.
especially since you should have an inch or two excess of stainless steel past the final cut and bevel point, that is this temporary weld is not at the same point of your final weld.
at least that's the way we always do temp hydrotest welds.
A further reason to not perform PWHT in your case. Sensitization will be incurred by the stainless steel pipe that will be placed in service. The PWHT will potentially compromise the integrity of the service pipe.
bladeo,
Because temporary welds may be poorly made (low concern by the welder) and you are performing a high pressure pneumatic test with probably mega ft-lbs of stored energy, I would require the temporary weld to be examined using RT or UT methods to ensure weld integrity.
we will witness fit-up,perform 100% rt and have qualified procedures. the problem is the clients inspector, he says "regardless of our quality, brittle fracture safe gards must be taken and table 331 ( i think not at work)states carbon must be pwht temporary or not. temporary is still a weld and prove to him 31.3 doesn't apply".i'm no metallurgical engineer but since we have no corrosion problem i don't think sensitizing the ss is a problem,educate me.i take these test very seriuosly and only want to do the right thing but if pwht is not required i'll agrue til the end. to make sure i didn't misled anyone the joint is 1.1 in. we will be welding a pup to the carbon cap for welding to the existing pipe and have been told by engineering we can only use the caps twice.come on fellows help me out
While the HAZ of the carbon steel will be tempered by PWHT, stress relief of the dissimilar joint will not be accomplished due to the coefficient of expansion mismatch. The Owner's Inspector is in error; however, you may be required to do as he insists as long as the Owner pays for the it.
