"detailed inelastic analysis" in context of ASME III.5

[EJ_]

Hi all Code-Gurus,

ASME BPVC Section III Div 5 - Nonmandatory Appendix HBB-T refers to "detailed inelastic analysis" a few times (and "simplified inelastic analysis"). (e.g. HBB-T-1331(c))
Does anyone know if & where there's any formal guidance on what's considered detailed inelastic analysis?

HBB-T-1121 seems to just imply that anything where you simplify anything to come up with conservative bounds is simplified, and conversely then implies detailed analysis would just be considering whatever sound engineering practice would consider, i.e. all relevant loads/BCs/etc.
Currently I'm just using my gut feel that by fully modelling some hot piping in FEA and applying actual time/load history with an MPC Omega creep model (from API579-1), and elastic-perfectly-plastic at hot yield (again per API579-1 guidance) this probably satisfies what they're intending.

I should clarify that I'm most certainly not designing anything nuclear! I'm just applying these creep methods to some hot piping, partly due to client request, and partly because it seems more comprehensive and clear to follow than API579-1 §10.5.2.

Thanks,
Edd

 

[TGS4]

The creep method in API 579-1/ASME FFS-1 (paragraph 10.5.2, as you mentioned) uses the Omega creep approach. Omega is a tertiary creep approach that is very good at predicting life exhaustion.

You'll need to use HBB-T-1420 (which had a major revision in the 2023 Edition, so I recommend using the 2023 Edition) for the detailed inelastic analysis. You would likely be using an isochronous stress-strain approach, as discussed in HBB-T-1800.

My recommendation to you would be to find an expert in creep analysis - these types of things can get extremely complicated quickly.

 

[EJ_]

Thanks for the info Trevor,

To clarify, I'm still applying the Sum(time/allowble-time-to-rupture) damage calculation approach per HBB-T-1420, using the modified equiv stress per HBB-T-1410 equation(10) notes and rupture data from HBB creep-rupture figs etc.
For FEA material modelling purposes I'm using the MPC Omega subroutine method to do the FEA creep strain-rate model, i.e. to predict the creep relaxation.

For past jobs for other materials (with no MPC Omega data) I've derived a power-law creep strain-rate material model for FEA purposes from isochronous curves; is this the intended/preferred method to develop an FEA creep strain-rate model?
(This is more what I was meaning in terms of what is considered suitable for a 'detailed inelastic' FEA model, i.e. material creep strain-rate modelling basis / plasticity basis etc.)

Thanks also for the heads up about the 2023 updates, will try to get it; does this have more guidance on the FEA modelling side?
Edd

 

[TGS4]

Sounds like you are on the right path.

I'd need to do a side-by-side comparison of the 2021 and 2023 Editions to see if there were differences. I just noted the (23) indication in the margin of my 2023 Edition indicating that that paragraph had been revised.