Hi all,

I am supposed to analyze a piping system of 24” NB produced gas distribution network from sub-sea interface to onshore terminal through launching arrangement for intelligent pigging.
System is consists of two ASME piping code as B31.3 and B31.8.
I have modeled the system by changing applicable code at the points per design and run the system.
From output report I notice some results which are not explainable or understandable to me. I need your kind assistance….
Observations are listed below..
In code compliance report,

1. Code allowable in ‘EXP’ case are not shown, but it should be equal to 0.72(SMYS) per code.

2. Code allowable in ‘SUS’ case is showing as SMYS, but it should be equal to 0.75(SMYS).F.T per code. (In my case T=1.0, F=0.5).

3. Code allowable in all ‘OPE’ case is showing as SMYS. Why should we check operating stresses?

Code allowable for the part B31.3 is showing perfect per code. My question is how to comply pipe stresses for this type of dual code systems. My senior's suggestion is, to analyze the whole system in B31.3 only, will be on conservative side. His supporting logic is that material allowable for code B31.3 is much lower than that of the code B31.8.
But I am not satisfied with this explanation because SIF and flexibility factors are different for both code and will results different induced stresses (code stresses) on the piping element.
Please advise.
Thanks in advance.

sudhakar

Analyse the system in 2 files

first file in B31.3 and set to zero the stresses on B31.8 portion of the system and viceversa on the second file.

Regards

Muthu

Yes you can analyze the entire system in one model, with part denoted as B31.3 and part denoted as B31.8. There are no problems running multiple Codes in the same model in CAESAR II.

B31.8 is a little special in that the stresses and allowables are different based on whether the pipe element is restrained or unrestrained. In addition, there is an OPEerating stress and corresponding allowable. So everything you've stated above makes sense. Take a look at this Code to see what is required. For the 2003 edition, restrained pipe has no EXPansion case and unrestrained pipe has no OPErating case. So for these conditions CAESAR II will report the allowable as zero.