PROTECTION AGAINST LOCAL FAILURE ASME SECVIII DIV 2
PROTECTION AGAINST LOCAL FAILURE ASME SECVIII DIV 2
(OP)
dear member
I'm going to design a FSE (thick wall expansion joint) and a nozzle to shell junction by ASME SEC VIII DIV 2 .
in addition to an elastic analysis (PROTECTION AGAINST PLASTIC COLLAPSE)our client asked to
check PROTECTION AGAINST LOCAL FAILURE,but I found that principals stress to be extracted
when/where stress are primary. am I right?(I mean primary principal stress)
- if yes ,it seems that protection against local failure is not applicable in FSE, while most of stress
are secondary (PL, PL +Q ),because of discontinuity and temperature specially in load cases (4,5,6,7 see ASME SEC 8 UHX part).
- for analyzing stress in nozzle to shell WRC 107 is not applicable in this case therefore Nozzle-pro (PRG software )is used
but I want to know if I should consider local failure too ? I mean check (S1+S2+S3)option
I'm going to design a FSE (thick wall expansion joint) and a nozzle to shell junction by ASME SEC VIII DIV 2 .
in addition to an elastic analysis (PROTECTION AGAINST PLASTIC COLLAPSE)our client asked to
check PROTECTION AGAINST LOCAL FAILURE,but I found that principals stress to be extracted
when/where stress are primary. am I right?(I mean primary principal stress)
- if yes ,it seems that protection against local failure is not applicable in FSE, while most of stress
are secondary (PL, PL +Q ),because of discontinuity and temperature specially in load cases (4,5,6,7 see ASME SEC 8 UHX part).
- for analyzing stress in nozzle to shell WRC 107 is not applicable in this case therefore Nozzle-pro (PRG software )is used
but I want to know if I should consider local failure too ? I mean check (S1+S2+S3)option





RE: PROTECTION AGAINST LOCAL FAILURE ASME SECVIII DIV 2
For your nozzle example, I suspect that you could exempt yourself as I described above.
In general, I follow the advice provided by PTB-1 (2014) and always use the Elastic-Plastic Analysis method. For your thick-wall expansion joint, I think that you would probably want to use the elastic-plastic analysis method for demonstrating Protection Against Plastic Collapse, as well, since the classification of the stresses could be complicated and/or ambiguous. Remember the caution in 5.2.1.2...
RE: PROTECTION AGAINST LOCAL FAILURE ASME SECVIII DIV 2
actually I'm not expert in elastic - plastic analysis .
ASME SEC 8 DIV2 2015
5.3.1.2 Two analysis methodologies are provided for evaluating protection against local failure under applied design loads.When protection against plastic collapse is satisfied by the method in 5.2.3,either method listed below is acceptable.
5.3.2 Elastic Analysis–Triaxial Stress Limit.
5.3.3 Elastic-Plastic Analysis–Local Strain Limit.
according to latest version of ASME it seems this two method are acceptable when limit load analyses is used . is it right?
if ,a local criterion based on elastic analysis may not meaningful, so why software like PRG (nozzle pro)consider it in elastic analysis?
ASME Sec8-1 PART UHX table-uhx 17 help to classify stress for FSE also TEMA 9th
give us a procedure to analyses.
RE: PROTECTION AGAINST LOCAL FAILURE ASME SECVIII DIV 2
The wording currently in VIII-2 was there from the original 2007, which itself was a controversial compromise. Because of the historical aspects of the elastic method - which, as described in the original Criteria of the ASME Boiler and Pressure Vessel Code For Design By Analysis in Sections III and VIII, Division 2 it was decided for the 2007 Edition to retain the elastic analysis method, despite a complete lack of engineering rigor on its application, as discussed in PTB-1.
Commercial software, such as Nozzle Pro (and others) perform this analysis because it is, strictly-speaking, permitted by the Code. However, my personal engineering judgement, based on the extensive discussion that have been going on for the last 10+ years, as well as the commentary in ASME PTB-1, is that I will not use it and my recommendation is to not use it. You can take that for what it's worth.
Be forewarned that just because you have a classification guide from the likes of UHX or TEMA, that this will allow you to properly classify the stresses from an FEA. Heed the warning in 5.2.1.2.