Finite Element Analysis for Static and Thermal loads

[nara]

We are doing a solid finite element liner static study of a steel pressure vessel which is subjected to dead loads, internal pressure and a temperature load of 700°F. While the allowable stress for the material under ambient temperature is 20,000 psi, it is 18,100 psi at 700°F. While the actual stress under dead loads and internal pressure (without the thermal load) is 16,600 psi, the stress at combined dead+pressure+thermal loads is 29,300 psi. Under this scenario, I would conclude that the vessel is not structurally safe since the actual stress of 29,300 psi exceeds the allowable stress of 18,100 psi under operational conditions. However, others in my team are of the opinion that since the allowable stress at 700°F is the criterion for comparison, the effect of temperature is already taken care of and therefore, the thermal load should not be applied on the finite element model. Only dead+pressure loads should be applied and the maximum stress under this condition is to be compared with the allowable stress at 700°F to decide on structural safety. I feel this opinion opposes the very basics of Statics. Please let me know if my decision is right or wrong.

The governing code is ASME and the software used is Solidworks Simulation Professional.

I thank you all for your precious time and valued opinion.

Nara

Structural Engineer