310 Stainless Cracking Mechanism(s)

[SMF1964]

I've got a 310 stainless steel sootblower nozzle that failed in service and was found in the bottom ash system some time later. The fracture is intergranular (I'm thinking creep, given that the unit has a history of cooking their sootblower long retracts) on both the outer and inner surfaces (more severe on the outer sruface). However, within the (rampant) intergranular cracking on the outer surface of the nozzle, I see transgranular cracking that is more indicative of SCC. I don't see this fine t/g cracking on the ID surface, so I'm of the opinion that this cracking is not something that occurred following immersion in the bottom ash slurry (else it would be present on all exposed surfaces).

Any thoughts? I can attach pictures as soon as I can remember how to do it.

 

[metengr]

Sounds like creep/fatigue to me.