Design Temperature Versus Maximum Operating Temperature which do you use for stress analysis?

[rhino27]

I am curious to read the input from others regarding the following issue.

For years, I have used the design temperature in my pipe stress analysis models for calculating the wall thickness and for expansion stresses. In addition, I have had Notified Body's or third party reviewers check my stress analysis and require me to put the design temperature into my stress analysis.

Recently, I have been told that some engineers only use the design temperature to calculate the wall thickness of the pipe. They then only use the maximum operating temperature for their stress analysis.
This relates to the last sentence under S301.1 in B31.3 Example in Appendix S Piping System Stress Analysis Examples which I have attached.

Please provide your current practice and thoughts on this issue.

For example:

Design temperature = 1200 F
Maximum Operating = 1150 F

I would use the 1200 F to calculate my minimum wall thickness and select the schedule of pipe required.

After my wall thickness is found, I would then only use 1150 F for thermal expansion calculations in my Caesar model.

 

[davefitz]

It would depend on whether the stress is to be used for static purposes or for fatigue analysis.
In the case of fatigue analysis and for specifying required clearances to bumpers and columns, the max expected event temperature ( including temporary overheats during startups) would be needed to be used if you really wish to model the event. Ignoring the extra growth that occurs during such overheats could lead to contact with bumpers or columns, and the pipeline stresses dramatically increase in those events.
Examples I have seen are related to gross overheats during startups of coal fired supercritical steam generators; from that experience I would design the clearances based on a temporary 100F overheat, although officially such overheats are never supposed to occur.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick