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ASME BPVC accepted definition of vessel "rupture stress"

ASME BPVC accepted definition of vessel "rupture stress"

ASME BPVC accepted definition of vessel "rupture stress"

(OP)
This sounds fundamental, but I will ask anyway.

Is there an ASME BPVC accepted definition of "vessel rupture stress" that one might use in an analysis along the lines of API RP 521 5.15.1 (notably in consideration of Figures 1 and 2)?

Long story short, I am looking at an existing flare header system and its capacity relative to a fire case blowdown scenario.  In other words, I am trying to evaluate if the system can be blown down from "X" psig to "Y" psig in 15 minutes while heat is being added due to a fire, and whether or not the vessels will "rupture" before achieving the target "Y" psig.

From what I have read, "rupture stress" might mean anything from "basic allowable stress" to "yield" to "UTS" to "...stress corresponding to gross plastic deformation...".  The recommendations, of course, depend on which one accepts as the definition.

Presumably, finding pieces of pressure vessel all across the lease and neighbouring counties might be interpreted to mean "gross plastic deformation".

I don't have all of the Codes in front of me as I type this but anyone who can point me in the right direction will, of course, be thanked.

 

Regards,

SNORGY.

RE: ASME BPVC accepted definition of vessel "rupture stress"

Try Section III, Level D service limits; see if that's the kind of thing you're looking for. Level D service limits "permit gross general deformations with some consequent loss of dimensional stability and damage requiring repair, that may require removal of the component or support from service." Rupture is never allowed by code.

RE: ASME BPVC accepted definition of vessel "rupture stress"

(OP)
Thanks trottiey.

I will check that out.

I understand that "rupture" is unacceptable.  The intent is to make sure that there is enough flare system capacity to achieve fire case blowdown before "rupture" occurs.

Regards,

SNORGY.

RE: ASME BPVC accepted definition of vessel "rupture stress"

Materials are stressed at elevated temperatures until failure/rupture. A series of these tests is performed and combined with Larsen/Miller parameter. Then some fraction ( <1 ) of this stress is set as the "allowable". I don't think creep testing is done any more but you get a similar result.
For your application , I think you can work backwards from the Larsen /Miller to estimate time to rupture at much higher temp and stresses than expected in a vessel.

RE: ASME BPVC accepted definition of vessel "rupture stress"

(OP)
blacksmith37:

A possible approach...thanks for the suggestion.

For now, we just compared against three markers: Sh, Sy and UTS (corrected for temperature).

It's enough to table further analysis for discussion.  The right answer is, of course, a bigger flare header...too bad that it's already built and is the current bottleneck to development.  Hence the study.

Regards,

SNORGY.

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