Weld joint P11 to P91

[kahoot]

Hi,
Our contractor is going to weld P11(P4) to P91(P15E), they have PQR but i have still doubt for PWHT,and looking for expert advise.
PWHT is required after welding,and they used 750c holding Temp.however recomended temp from ASMEB31.1 650 to 705 for P11 and 735 to 775 for P91.
my question if they use 750 deg.C for P11//P91 weldment,sure they temp beyond the limit of P11 material,So Question is if they go beyond the ASME recomendation what risk involve, what effects on material properties ?//??/remember this piping for Steam (137bar 537 C)
what do you suggest as safe or good engineering practice???
thanks,

 

[weldstan]

I believe the Code requires that the P91 temp governs. The lower critical of the P11 material will be exceeded and this has been done many, many times in boiler construction. You can weld a P22 intermediate material between the P11 and P91 to alleviate your concern.

 

I have not had direct experience with this combination but weldstan makes sense.
Choose the filler metal with caution; matching the P-91 base metal could lead to undesirable effects at the interface on the P11 side of the weld.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[kahoot]

thank you wledstan,apericiated your response,thats one option(P22) i had given already but a contractor insisting,that 775c is lower critical temp for P11 so if apply 750c for PWHT its convenient.
can u encompass what maximum changes in microstucture can occur if used 750c PWHT for P11/P91 weldment??

 

u?

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[weldstan]

Also recommend the lower limit PWHT temp for P91 stated.

 

[davefitz]

It is possible that you could evaluate ( in specific cases) whether to "safe end" the P91 with inconel filler first,use P91 PWHT, then weld the P11 to the safe end. TBD

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[weldstan]

There was a famous documented failure of this joint using B9 filler metal. The P4 fusion line and nearby HAZ was denuded of carbon which moved to the B9 filler. Because the P4 material was subject to greatest stress, failure occurred along the denuded area. We used B3 filler metal for this joint and a 1350 F +20F -0F PWHT.