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Time Dependency of Stress/Strain on 304 SST

thread367-65962

Time Dependency of Stress/Strain on 304 SST

Time Dependency of Stress/Strain on 304 SST

(OP)
I'm looking for information on the effect of very rapid stress onset on 304 SST.  We have a pressure vessel which was subjected to an internal explosion and I'd like find out if we can use the lack of deformation of the vessel as proof that the vessel was not overpressurized. Essentially I'd like to make sure that the material couldn't approach UTS without getting some yielding.  The overall time scale for the stress peak was probably a few milliseconds.

RE: Time Dependency of Stress/Strain on 304 SST

The heat generated by the deformation raises the material temperature since it cannot be dissipated. This dramatically reduces the austenite instability which generates much of the work-hardening of this grade. This means less martensite is formed and the material has a markedly lower tensile strength. A drop from over 90KSI to 80 to 85KSI would be expected.

RE: Time Dependency of Stress/Strain on 304 SST

(OP)
I had read a bit on martensite generation.  If I understand correctly, we would need to have gotten some plastic deformation to generate the heat necessary for this to occur.  Is that correct?

RE: Time Dependency of Stress/Strain on 304 SST

AlphaT,
There are a lot of material and environmental parameters that affect fracture behavior.
E. g., were the welds annealed, was the contained solution something that might cause embrittlement or intergranular corrosion.  What was T & P and for how long?  A very major question is where did the failure originate? Along some seam?  Surface analysis of the initial fracture surface might be invaluable.

mcguire,
Wouldn’t less martensite mean more plastic deformation?

RE: Time Dependency of Stress/Strain on 304 SST

You are on the right track. Lack of yielding means that no transformation to martensite has occurred. Your tank has proven itself. This material will deform before fracture at even very high strain rates. The deformation mode is not thermally activated as it is in BCC steels ( carbon steels and ferritic stainless steels ), so it is only strain rate dependent as far as the adiabatic heating effect I mentionned above.

RE: Time Dependency of Stress/Strain on 304 SST

My apologies, I interpreted the question as one of brittle failure.

RE: Time Dependency of Stress/Strain on 304 SST

(OP)
Thank you very much for your response.  I feel a lot better about being able to make a case for keeping this vessel in service.

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