Hi,

As a general requirement, you should follow the Project specifications and assigned design Codes requirements.
From your description and questions, I guess your piping design Code is one of the B31 piping Codes (B31.3, 31.1 etc.), and you may have some hydro-test overstress problems with your piping system.

Having this assumption, it should be stated that for all piping components, you have to follow your piping Design Code requirements, regardless you deal with very large bore or common bore pipe size.

You should be aware that B31 piping codes operate with different stress classification and qualification criteria than ASME VIII BPV Code does. Therefore, it is fully speculative to try to increase hydro-test stress allowable limit for B31 piping components because of ASME VIII-2 Section 4.1.6.2 provisions.
Going further with your reasoning, then why not to increase the allowable limit for B31 piping Sustained stresses (fixed at allowable stress Sh) because ASME VIII-2 limits resultant Pl+Pb (primary membrane local + bending stress) at the maximum between Sy and 1.5*Sh ??! (VIII-2, Sections 4.1.6.1 and 5.2.2.4)

So, the fact is you should follow Piping design Code requirements for all piping components. However, you need to use ALL design code provisions and interpretations, and to be aware of Caesar II proper settings facilities.

Hydro-Test load is classified as a primary action and the corresponding failure mode is piping component collapse. During piping system lifetime, hydro-test load is developed only few times, so that hydro-test should not be considered as a cyclic action and fatigue failure is not a characteristic for this load. This is the reason why old CII versions treated hydro-test as Occasional load. However, Hydro-Test load limit state is actually above the typical Occasional piping stress limit state (e.g. Sy > 1.15...1.33 * Sh), so that the reference Hydro-test allowable stress was corrected in accordance with actual B31 design Code provisions (0.9...1 * Sy).

For ASME B31.3 Code editions prior to 2010 edition, the Sustained and Occasional stresses assessment & qualification philosophy was detailed and implemented by B31.3 Interpretation 1-34, which provided that for Sustained and Occasional stresses calculation, only 75% of SIFs (but min. 1.00 values) may be used, OR by interpretation 6-03, which stated that SIFs may be quite omitted for Sustained stress calculation.
Consequently, for Hydro-Test stress computation, using only 75% of SIFs represented a reasonable approach. The reason is that it is unlikely hydro-test load to induce piping components fatigue failure.

ASME B31.3 2010 Edition (which appears you use on your current Project, probably with CII V. 6.10) introduced at Section 320 explicit formulas for Sustained Code stress assessment. These formulas (based upon 75% of SIFs employment) may be extended for Occasional and Hydro-Test stresses computation.
Therefore, be careful and check CII configuration file. Inside “SIF’s and Stresses” menu of Caesar II Configuration File spreadsheet, do you have ”B31.3 Sustained SIF Multiplier” parameter fixed to 0.75 value? Only in this way you'll use reduced SIFs (75%) for Sustained, Occasional and Hydro-Test (probably!) stress computation.

Moreover, you might ignore SIFs employment for non-expansion stresses (especially hydro-test load!) by fixing ”B31.3 Sustained SIF Multiplier” to 0.0001 value. In this way, you'll be in line with B31.3 6-03 interpretation.
However, in my opinion, you'll need to document in Project specifications (design basis) the SIFs omission for Hydro-Test / Occasional / Sustained stress qualification.

If you intend to reduce SIFs for Hydro-Test stresses only, you'll need to perform a separate CII run (with corresponding modified CII configuration setting) for this purpose.

ASME B31.3 2012 Ed. (implemented within CII V. 7.00) uses SSI (Sustained Stress Index) concept for Sustained (and, by extension, Occasional and Hydro-Test) stresses assessment. As per the default B31.3 provisions, the SSIs are somehow equivalent to 0.75% of SIFs approach.

If the above approach still yields to Hydro-Test overstress, then you'll need probably to carry out a detailed local stress analysis by FEA. I guess the overstress occurs at fittings' level (intersections, elbows), so that you may use PRG FEA Software package (FE Pipe, Nozzle Pro) and ASME VIII-2 qualification criteria. You need to "isolate" the fitting by upstream/downstream nodes in CII model, to identify the internal forces & moments in those nodes for Hydro-Test load, and finally to use those loads as boundary limits for the 3D Shell FEA model.
Local stress analysis shall always be based on ASME VIII-2 phylosophy, since the local FEA stress analysis quantifies the stress components of Pm, Pl, Pb, Q, F stress categories, which are not addressed by B31 piping Codes.


Best regards,