Creep design above 100,000 hours?
Creep design above 100,000 hours?
(OP)
For time dependent properties, the stress values in ASME II Part D are for up to 100,000 hours only. I need to calculate an allowable stress for 150,0000 hours using the rules in ASME II Part D Mandatory Appendix 1. I have figured out how to derive Minimum and Average Rupture Strength from API 530, however I am having trouble deriving the "Average Stress to produce a Creep Rate of 0.01% per 1000 hours".
API 579-1/ASME FFS-1 Fitness for service looks like the place to derive this stress. However in this spec when I look up a creep damage rate of 10^-7 (equal to 0.01%/1000hours) I get a corresponding stress that is very close to 0.666 times the stress in ASME II Tables.
Also the allowable Creep Damage/Strain at the end of a components life in ASME FFS-1 shall be no greater than 0.25 = 25%.
For ASME II it is 0.01 = 1%.
Why is there a difference? How do you convert information in ASME FFS-1 to an allowable stress in ASME II. Is ASME FFS-1 the correct code to use?
(I need this allowable stress for a ASME VIII Div 1 vessel.)
API 579-1/ASME FFS-1 Fitness for service looks like the place to derive this stress. However in this spec when I look up a creep damage rate of 10^-7 (equal to 0.01%/1000hours) I get a corresponding stress that is very close to 0.666 times the stress in ASME II Tables.
Also the allowable Creep Damage/Strain at the end of a components life in ASME FFS-1 shall be no greater than 0.25 = 25%.
For ASME II it is 0.01 = 1%.
Why is there a difference? How do you convert information in ASME FFS-1 to an allowable stress in ASME II. Is ASME FFS-1 the correct code to use?
(I need this allowable stress for a ASME VIII Div 1 vessel.)





RE: Creep design above 100,000 hours?
RE: Creep design above 100,000 hours?
I don't wish to introduce these additional inspections. I wish for a vessel designed from the start with the same design margins for 150,000 hours. I am having trouble re-deriving the "Average Stress to produce a Creep Rate of 0.01% per 1000 hours" from its original source.
RE: Creep design above 100,000 hours?
RE: Creep design above 100,000 hours?
"API 579-1/ASME FFS-1 Fitness for service" is for in-service inspection so probably is not the correct standard to use to calculate the ASME II average creep rate allowable stress but it is all I can find at the moment.
Do you know if this source standard for ASME II Part D is different from ASME FFS-1?
RE: Creep design above 100,000 hours?
RE: Creep design above 100,000 hours?
I am sort of already doing this type of approximation with "API 579-1/ASME FFS-1 Fitness for service" graphs.
RE: Creep design above 100,000 hours?