B31.3 allows not to include average axial stress in displacement stress range calculations because of its insignificant magnitude in ordinary piping configurations. However in special conditions where these have significant value like double wall pipes the Code requires to consider these stresses (Para 319.2.3c), but is silent about how to "consider" these stresses. Does the Code have intent to treat these stresses same as ordinary displacement stresses comparing these with the allowable stress range given in Para 302.3.5d? However following goes against this assumption
1- The stresses are not localized
2- Elastic Shakedown is not guaranteed because of instability of pipe under compression
If these are valid concerns then how to evaluate these stresses?

I don't think the code offers guidance in this regard. I have seen various references in literature on the considerations for jacketed piping. I don't have them handy. Suffice it to say, it is not a simple analysis.

Tanveer,

I fully agree with your views.The objective of the code is to keep things simple and as such does not delve into the complications of such situations.Such situations have to be analysed on a case by case basis . You can find some interesting discussions in PAUL VOORHAR'S website.


However regarding the method of combination we can follow what is prescribed in ASME Sec VIII as

Primary + secondary stress intensity, involving both membrane and bending stresses <=3.0 average allowable stress intensity


Anindya Bhattacharya

Stress Analyst

Bechtel Corporation