Dear all

We have a doubt in load case building for a PSV force

Initially we built the load case as follows

L1 W+P+T+F
L2 W+P+T
L3 W+P
L4 F
L5 L2-L3(EXP)
L6 L3+L4(OCC) SCALAR COMB for Stress check

then we tried the following combination
L1 W+P+T
L2 W+P
L3 F
L4 L1-L2(EXP)
L5 L2+L3(OCC) SCALAR COMB for Stress check
L6 L1+L3(OCC) SCALAR COMB for Loads

The loads in the two cases viz., L1 of first combination and L6 of second combination were varying by large margin.Fyi there is non linearity in the form of friction.

then in the second combination we changed the combination type as algebraic for case L6 which produced the same result ( loads only) as that of Scalar

Now the two cases ,

W+P+T+F

and

W+P+T ( algebraic or scalar combination ) with F (seperately combining )

we would like to hear from you experts to clarify us why there is a difference between these two in terms of loads.

And also which combination method is right to evaluate the PSV forces in the system.

Supperposition does not apply for piping systems with non-linear boundary conditions. I suggest the following load cases:

L1 W+P+T+F
L2 W+P+T
L3 W+P
L4 L2-L3(EXP)
L5 L1-L2 (OCC) to get the effects of "F", not a stress check case
L6 L3+L5(OCC) SCALAR COMB for Stress check

Richard,

Thanks for your expert advice, My question is,should we consider these load combination for both design and operating pessure and temprataure or just the design condition is enough?

Regards,
Maryam

Typically the design conditions are used to size the pipe and components, while the operating conditions are used for the flexibility analysis. However, there are exceptions, refer to these earlier posts on this same subject:

http://65.57.255.42/ubbthreads/ubbthread...=true#Post37853

http://65.57.255.42/ubbthreads/ubbthread...=true#Post24976

http://65.57.255.42/ubbthreads/ubbthread...=true#Post18213
Make sure you note the last post in this particular thread.


There are other posts on this subject if you [Search] for them.

Dear Maryam,

Occasional load is applied when piping system undergo OPE condition. So, no need to use design conditions.

Thanks a lot Farhad.