Hello All,

I have confusion point for EXP load combinations on B31.3 code.
Generally we use load combination as below on piping analysis.
L1) [OPE] W+T1+P1
L2) [OPE] W+T2+P1
L3) [SUS] W+P1
L4) [EXP] L1-L3
L5) [EXP] L2-L3
L6) [EXP] L4-L5 ( for Cold pipe line )

My questions are for L4~L6.

First, L4 and L5 case are used on piping stress check. But, I want to know why dead load (W) is not included in these EXP case. I think that only thermal case without dead load will not occur on site. I think this EXP case is not realistic. Is it specified on B31.3 code why we should use this load case?

Second, I think that L6 case also is not realistic. If stress ratio of L4 is 90%, and stress ratio of L5 is 50%, L6 load case will be failure with 140%. (I assume that L4 is hot temperature, and L5 is cold temperature.)
Is it specified on B31.3 code why we should use this load case?

Could someone please resolve my confusion?
Thank you,