PWHT heating and cooling rates for P91 material welds
PWHT heating and cooling rates for P91 material welds
(OP)
I understand ASME B31.1 Para 132.5 gives the rates of heating and cooling rate that should not be exceeded in general for all materials requiring PWHT. We have a pipe fabricator doing some heavy wall P91 welding for our power project and he is almost ready to PWHT. His PQR does not specify the heating/cooling rates.
1.Is there any particular requirement/recommendation for maintaining these rates while doing PWHT of P91 welds?
2.Does it make a difference if the rate of heating above 600F is any xxx F/hr. as long as it does not exceed 600F per B31.1.
3.Does this have to be specified when a fabricator qualifies his P91 welding procedures?
Appreciate yor inputs.
1.Is there any particular requirement/recommendation for maintaining these rates while doing PWHT of P91 welds?
2.Does it make a difference if the rate of heating above 600F is any xxx F/hr. as long as it does not exceed 600F per B31.1.
3.Does this have to be specified when a fabricator qualifies his P91 welding procedures?
Appreciate yor inputs.





RE: PWHT heating and cooling rates for P91 material welds
RE: PWHT heating and cooling rates for P91 material welds
RE: PWHT heating and cooling rates for P91 material welds
"Above 600 F the rate of heating and cooling shall not exceed 600 F/hr divided by one half the max thickness of the material in inches at the weld , but in no case shall the rate exceed 600F/hr"
- I am not aware of the 300F/hr limit stated by stanweld
- theoretically the rate of cooling should be governed by the square of the wall thickness, if one is trying to limit the developement of residual stresses caused by thermal stresses- but maybe the code has a different objective.
-please note the 600 F/hr limit for PWHT is not the same requirement as the cooling rate for P91 when cooling down from a N+T operation- if you cooled down too slowly from 1940F normalization, you would form ferrite- the minimum rate of cooling following N+T is 600 F/hr, not the maximum rate. Refer to the CCT curves for P91.
RE: PWHT heating and cooling rates for P91 material welds
RE: PWHT heating and cooling rates for P91 material welds