Welding of A217 C12A cast steel to A 335 Grade 91?

[Arkaprava Ghosh]

Is Welding of A217 c12A cast to A335 Grade P91 possible? What consumbales shall be used? What other critical factors shall be kept in mind while developing WPS?

 

[metengr]

Yes, the C12A is indeed weldable to Grade 91. The filler metal should be B9 chemical composition which matches the Grade 91 and C12A base materials. Make sure you receive material certifications on the welding rod and the 91 casting to ensure proper selection of PWHT temperature. Qualify the WPS per Section IX.

 

[Arkaprava Ghosh]

Metengr , Thank you very much.

 

[weldstan]

The one concern that you should have, is casting flaws that only become apparent when Radiography of the weld is done and the potential for costly repairs.

 

[davefitz]

C12A is the cast form of grade P91, typically used for thick walled valve bodies, els, tees, wyes, etc. One issue that does not seem to be completely addressed by US codes is that this material needs to be cooled ( or quenched) following N+T such that the rate of cooling is at least -9F/min in the temperature range 2000 to 1200 F, in order to ensure martensite is formed. If this rule is not followed, then "soft" zones of pearlite and ferrite are formed, which are not as strong as the martensite regions.This implies tdhat a proper QC spec will require that each cast item in the batch being N+T'd needs to have a monitoring thermocouple , and a have a hardness survey completed at the end of heat treatment.

Likewise, if there are voids formed in the casting process, there shoud be completed another N+T following weld repair of the void. That detail is disliked by the casting outfit. This also imples the QC spec should include volumetric testing of the part prior to shipment to client.

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

 

[sandeepKumar63]

The recommended filler wire for P91 is E8018-B8. What the base for B9 recommendation?
Any specific reason please

 

[metengr]

The recommended filler wire for P91 is E8018-B8.

Recommended by whom? Maybe for 9Cr-1Mo material.
Actually, in the 2015 Edition of ASME Section II, Part C, SFA 5.5, B91 (previously known as B9), chemical composition matches the Grade 91 cast or wrought material.

 

[davefitz]

another detail often lost is that when welding a thin wall P91 pipe to a thick wall casting is that the weld geometry should be improved if the part is to be used in thermal cycling service. Rather than use the default 30 degree slope in wall thickness at the OD transition , a max slope of 18 degrees at the OD is recommended in the european codes for such a weld in cyclic service.

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

 

[bruv]

Note that ASTM A217 also imposes restrictions on the chemistry of weld consumables for the weld repair of C12A castings. Your customer might want to impose the same restrictions on any fabrications.

 

[metengr]

The new ASTM specification for Grade 91 castings is ASTM A 1091. C12A will be removed from SA 217 shortly, and called C91. Second, ASME has a code case for use of ASTM A 1091 as SA 1091. This is what you should be specifying, it is much improved for weld repairs.