The issue of selecting temperature for stress calculation
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Should pipeline stress calculations be done using the design temperature or the operating temperature? We have always used two types of operating conditions: design condition and operational condition. But are the spring parameters chosen for the design conditions or for the operating conditions?
Reply 1# caobingqin: It is generally calculated based on the operating temperature
The highest temperature that can be reached in the piping system
Regarding this issue, I consulted Beijing AESF by phone, and their advice was to choose the value based on the design temperature. Although in actual operating conditions these conditions are generally not met, since we have specified these design conditions, the pipeline system designed should fulfill them; it is also a relatively conservative approach. Personally, I think the design temperature should be used.
The design temperature is a value that is higher than the highest temperature that the pipeline might reach; using this temperature means assuming that the piping system is always under extreme conditions, which is too conservative
I think it is more appropriate to choose springs based on the operating temperature conditions, especially when there is a significant difference between the operating temperature and the design temperature. For example, in chemical industry flare pipelines, using springs designed for the design temperature would be rather conservative in such cases.
The selection of the spring should be based on the operating conditions; the design conditions only need to provide the load values.
It depends on the stress analysis regulations of your company. It should generally be included inside. Our company uses operating temperature and design pressure. The spring isn’t a big issue; the spring you chose for 250° can be used just fine at 270° as well. It’s just that there is load transfer.
Based on inquiries from various parties, including some major domestic first-class engineering firms, it is believed that this should be the highest operating temperature (or the temperature that may occur), that is, the condition under the most severe circumstances. Sometimes, the operating temperature of pipelines differs significantly from the design temperature; in such cases, it is up to the designer to make a judgment. If the difference isn’t large, for example, if the operating temperature of a steam pipeline is 280° while the design temperature is 310°, and the purge steam comes from another workshop at a temperature of 300°, then it would be more conservative to use the design temperature of 310° as the basis for design.
It might be a bit conservative, but I consulted experts from the East China Institute and the Luoyang Institute, and their general advice was to use the design temperature and design pressure for calculations.