Fatigue Crack Growth Eqns in API 579
Fatigue Crack Growth Eqns in API 579
(OP)
Hello all,
I had a particular question concerning the fatigue crack growth data listed in Appendix F of API 579-1/ASME FFS-1 (2007 ed).
I am analyzing a pressure vessel constructed out of SA-302 Gr. B (mod.) material with a yield strength (Sy) of 100 ksi. Typically we use the Paris Law to determine our number number of cycles to failure using API 579 as a source for fatigue crack growth data. The constants C, n, and Eyr is determined based on Sy of the material, composition (grain structure), temperature, and outside environment that the material is exposed to. Since Sy is 100 ksi, I have to refer to Section F.5.3.3 to get my constants, but how do I determine if SA-302 Gr. B is a martensitic steel or ferritic-pearlite steel? Can that be determined simply by chemical composition, or if the material has been heat treated, etc.? Thanks in advance.
I had a particular question concerning the fatigue crack growth data listed in Appendix F of API 579-1/ASME FFS-1 (2007 ed).
I am analyzing a pressure vessel constructed out of SA-302 Gr. B (mod.) material with a yield strength (Sy) of 100 ksi. Typically we use the Paris Law to determine our number number of cycles to failure using API 579 as a source for fatigue crack growth data. The constants C, n, and Eyr is determined based on Sy of the material, composition (grain structure), temperature, and outside environment that the material is exposed to. Since Sy is 100 ksi, I have to refer to Section F.5.3.3 to get my constants, but how do I determine if SA-302 Gr. B is a martensitic steel or ferritic-pearlite steel? Can that be determined simply by chemical composition, or if the material has been heat treated, etc.? Thanks in advance.





RE: Fatigue Crack Growth Eqns in API 579
RE: Fatigue Crack Growth Eqns in API 579
RE: Fatigue Crack Growth Eqns in API 579
So just to understand, in order to get a martensitic microstructure, it would have to depend on whether the steel has been heat-treated or not...? Do you get a martensitic microstructure for stainless steel only? Isn't normalizing a type of heat treatment, just removed from the furnace for air-cooling? What if the pressure vessel has experienced post-weld heat treatment?
RE: Fatigue Crack Growth Eqns in API 579
Normalizing is exactly as you described it. This steady cooling heat treatment will allow the steel to form mainly pearlite.
PWHT for this alloy is probably going to be around 1150 F and is used to stress relieve the welds (which have cooled quickly). If carried out properly, it will not significantly alter the base metal.
RE: Fatigue Crack Growth Eqns in API 579