tempering parameter for PWHT of P22- hardness vs ductility
tempering parameter for PWHT of P22- hardness vs ductility
(OP)
We have multiple cases of craze cracking near the butt welds downstream of attemporator spray nozzles at our HRSG's. The hardness of the zone near the P22 butt weld is consistently harder than the parent metal, and I suspect this is related to the lower ductility near the weld zone. The lower ductility would lead to increased vulnerability to craze cracking.
Other recent published correlations for P91 "tempering parameter" indicates that for P91 there is a LMP larson miller paremeneter that correlates PHWT Temp, time, and hardness , and I suspct this same parameter can predict ductility for P91 and other materials , including P22.
Kindly advise if there is a known tempering parameter for P22 that correlates PWHT temp, time and hardenss. In lieu of this parameter I expect we will simply double the PWHT min dwell time over the code-required minimum time in order to improve the ductility for those butt welds immediately downstream of a spray.
Other recent published correlations for P91 "tempering parameter" indicates that for P91 there is a LMP larson miller paremeneter that correlates PHWT Temp, time, and hardness , and I suspct this same parameter can predict ductility for P91 and other materials , including P22.
Kindly advise if there is a known tempering parameter for P22 that correlates PWHT temp, time and hardenss. In lieu of this parameter I expect we will simply double the PWHT min dwell time over the code-required minimum time in order to improve the ductility for those butt welds immediately downstream of a spray.
"Whom the gods would destroy, they first make mad "





RE: tempering parameter for PWHT of P22- hardness vs ductility
"Whom the gods would destroy, they first make mad "
RE: tempering parameter for PWHT of P22- hardness vs ductility
"Whom the gods would destroy, they first make mad "
RE: tempering parameter for PWHT of P22- hardness vs ductility
RE: tempering parameter for PWHT of P22- hardness vs ductility
Yes, there is a tempering parameter for Grade 22 steel. It is well defined. As mentioned by stanweld, P22 can become thermally embrittled with loss of ductility. However, before I would venture down this path or become involved with paralysis by analysis, you should have this confirmed by proper met analysis - sample removal. It sounds to me this could be thermal fatigue.
RE: tempering parameter for PWHT of P22- hardness vs ductility
Yes,it is thermal fatigue, but in several cases the cracking only develops near the butt weld zone ( or reheat zone) that was PWHT'd ( +/- 4" from weld line), and hardness readings show that zone uniformly has a higher hardness than parent metal further away.
We will send the damaged pipe sections to SI and request a determination of impact energy for both parent metal and the reheated zone and an analysis of carbides in each, perhaps to determine if there is a preferred PWHT procedure that would better retain ductility so as to avoid the fatigue cracking. The major thru wall cracks are circumferential , while a large number of randomly oriented craze craks are at the ID.
Thermographs of typical spray stations ( reheat dump to ACC, interstage reheater )show tremendous thermal gradients ( axial and circumferntial) downtream of the spray nozzles, implying bending moments in the piping that would be consistent with a circumferential failure.
The Chauvy paper includes a plot of toughness vs LMP ( used as a tempering parameter, calculated for PWHT hold times), showing a sharp drop off in toughness at an LMP=19500 for P11, and I suspect the same is true for P22. If this loss of RT ductility is the cause of the major failure cracks, then the residual sresses are formed at operating temperatures ( due to excessive thernmal gradients )and the cracks are occurring during outages.
"Whom the gods would destroy, they first make mad "
RE: tempering parameter for PWHT of P22- hardness vs ductility