Underground modeling with B31.3

I needed to model some underground piping to ASME B31.3. In the Code there is a warning (319.2.3-c) you need to consider the average axial diplacement stress. This is the case for buried service where the longitudinal compressive stress can be high in restrain portion of the pipe. Does anyone know if Caesar account for these compressive stress in the analysis?

The answer here is "maybe".

Simply burying a model will not cause C2 to alter the B31.3 stress computations. However, you could also:

a) Throw the "Include F/A" switch in the Configuration, or
b) Throw the "Use Appendix P" switch in the Configuration.

I'd suggest playing with a very small model to get an understanding of what is going on before jumping in to your real model with both feet .

Richard,

Thanks but two additional questions:

1) How does Caesar calculated the hoop stress? When I do a run, SUS (W+P) I get an answer very close to my hand caculation but OPE (W+P+T) the hoop stress number is 30% less.

2) When Casaer does a tmin check will it add in the compressive stress?

1) For Hoop Stress, check the Help Text in the Configuration Module for the various computation options. For B31.3, I can't see the hoop stress value changing between OPE and SUS, assuming the same "P" is used in both load cases.

2)No.

Richard,

I still am at a loss why Caesar is reporting two different hoop stress values for W+P vesus W+P+T case? I have only one pressure specified for the file.

E-mail the job to techsupport@coade.com.

GGM,

B31.3 uses corrosion allowance for the sustained and occasional load cases, but not for the operating case. As a result, your hoop stress is higher in the sustained case. If you go to the configure/setup->SIFs and Stresses and turn on the switch for "All Cases Corroded" then re-run the analysis you will have the same hoop stress for all load cases.

Because Caesar does not consider the axial compressive stress in B31.3, I would need to calculate the compressive longitudinal stress (fully restrained) = Modulus of elasticity* liner coefficient of expansion*(delta Temp) + Poisson ratio*Hoop stress. This would combine with the axial stress and compared to EXP allowable as a secondary stress. Another possible option would be run B31.4 case which accounts for this loading and compare to B31.3 allowable. Any thoughts on the best approach using Caesar?

GCM,

You can check the item in Configure/Setup->SIFs and Stresses called "Include F/A in Stresses" and Caesar II will indeed include the axial compressive stress in the code stress for the EXP case and compare it to the allowable.