Dear all
In many piping systems , there is one maximum design temperature (lets name it T1) , and another minimum design temperature (lets name it T2) ,knowing that Ta is the as-installed temperature and T1>Ta>T2, The load cases are as followings:
L1 W+T1+P1 (OPE)
L2 W+T2+P1 (OPE)
L3 W+P1 (SUS)
, to analyze such systems for expansion stresses , one expansion load case for expansion shall be analyzed (L1-L3) and another load case case shall be analyzed for contraction (L2-L3).
As for for the above it is still acceptable, my question is , Is it necessary to analyze additional load case for the maximum expansion range (L1-L2) ??
My humble opinion , that this load case was invented by one lazy stress engineer who had system with many temperatures (T1In addition , the ASME B31.3 Para. 319.2.3 does not call for such systems to be analyzed for such case , since that systems will always pass through the neutral stress point (zero stress) in order to go one cycle from the maximum temperature to the minimum temperature .
My opinion is this load case (L1-L2) is not necessary and it is what so called unnecessary conservative approach.
thanks for additional opinion.

Read Interpretation 12-06.

I read it , but i am not getting the justification.
any one knows the justification, and please do not tell it is the code !!!

I will be appreciated if any body can justify it for the 2 cases
1) when 302.3.5-1a applied ( the elastic limit is maintained always and the secondary stress is limited to SY ).
2) when 302.3.5-1b applied ( The advantage of the residual compressive stress is used and the stress range is limited to 2Sy).

Thanks in advance

This is about fatigue. And metal will ago faster when you cycle it between -stress and +stress in comparison to 0stress and +stress.
BTW: also movement of equipement amongst others will give you secondary stresses, not temperature alone.

Paragraph 319.2.3(b) says use the maximum strain range when evaluating the displacement stress range. Typically, with T1 greater than ambient and T2 less than ambient, your L1-L2 would produce the range stated here.

Mr.Richard and Mr.Dave,

Is the effect of "Average axial stress" as per ASME B31.3, 319.2.3(c) for computing displacement stress range is included by default in Caesar? If not, is there is any "flag" option available in configuration file.

Please clarify...

There is a config switch to include direct axial load in the B31.3 expansion stress calculation.See SIFs and Stresses / "B31.3 Sec 319.2.3c Saxial"

Thanks Dave...

Hi Mr.Richard/Mr.Dave,

Is there is any option in caesar-II to use the allowable displacement stress range as per ASME B31.3 equ.(1a) for expansion stress in some cases and equ(1b) for other expansion stress of the same file.

For ex. in stress analysis system, let T1 and T2 be the temperatures, the load cases shall be as below,

L1 = W+P+T1 (Ope-1)
L2 = W+P+T2 (Ope-2)
L3 = W+P (Sus)
L4 = L1-L3 (Exp-1, Allowable Sa as per Equ. 1a)
L5 = L2-L3 (Exp-2, Allowable Sa as per Equ. 1a)
L6 = L1-L2 (Exp-3, Allowable Sa as per Equ. 1b)

Please clarify...

No there is no way to have both in the same file.

Regards,

Since one of our client gave their checklist for the stress analysis, which states the actual stress conditions as stated, "Is the actual stress for expansion case is limited to 90% of the allowable for operating conditions as per B31.3 equation (1a) and 90% of the allowable for maximum displacement stress range as per B31.3 equation (1b)."

So to consider this, i have to prepare two caesar-II file with applicable load cases, its an additonal time, usually not req....

The stress summary which begins each stress report lists the node with the highest ratio of calculated stress to its limit. Why not just ensure that that ratio is less than 90%?

Hi Dave,

I dont understand your reply. My actual requirement is Caesar-II have the option of using B31.3 equation (1a) & (1b) in the same load cases...

Equation (1a) is conservative. If you meet 90% of (1a), then 90% of (1b) is assured.

Equation (1a) is too much conservative for the max. displacement stress range (min. temp. to max. temp.), if we use as like mentioned by you, it requires addtional offset or loops...

90 % of allowable as per eq. 1a is a fixed value that you can easily calculate so you can manually compare the maximum stress value of L4 or L5 with this value. If not, you have to run two separate files. It will take you few minutes more.

Maybe in the future will be possible what you ask but not now.

Regards,