What design temperature should I us 1

[newobserver]

What design temperature should I use for stress analysis of existing steam piping downstream of a desuperheater if:
- the steam generator's design temperature is 500 degF
- the desuperheater's design steam temperature is 400 degF.

The piping is designed per B31.1.

Per B31.1 (101.3.2): "Where a fluid passes through heat exchangers in series, the design temperature of the piping in each section of the system shall conform to the most severe temperature condition expected to be produced by the heat exchangers in that section of the system".

Does this statement mean that I could use the desuperheater design temperature but not that of the steam generator?

Thank you!

 

[metengr]

I would use the 500 deg F steam design temperature in the event spray is not valved in during service.

 

[pennpiper]

newobserver,
You asked, "What design temperature should I use for stress analysis"
You will get many different opinions on this question.
Here is mine.
(a) The "Design" temperature is a fictitious number
(b) The Maximum Operating Temperature is a real and verifiable number
(c) Using a fictitious number for calculations results in Over Design
(D) Over Design results in higher Costs

Therefore, the Maximum Operating Temperature should be the only temperature used for Stress Analysis.


Sometimes its possible to do all the right things and still get bad results

 

[newobserver]

Thank you gentlemen,

Do you know what is correct per B31.1?

 

[metengr]

500 deg F.

 

[davefitz]

meteng is correct, and the key item in the initial post is that the purpose is pipeline stress analysis. If the piping expansion limits and supports were based on 400 C yet it was exposed to 500 C due to a mal-operating spray attemporator then bumper clearances would be exceeded and pipeline stresses would increase dramatically.

"In this bright future, you can't forget your past..." Bob Marley