Anindya, that is an excellent explanation. Thankyou for taking the time to share that with me.

Since the pressure elongation is a secondary stress, it seems it would be useful if in Caesar, it was possible to select which load cases the bourdon effect was applied to. Therefore you could still run the sustained stress (W+P) withouth bourdon effects but include the bourdon in the operating and expansion case. Maybe something for Coade to consider?

I have done some futher modelling of this system using both the bourdon effect in Caesar and camparing it against using an equivalent temperature. With some modifications to the piping I am able to get the stresses in the system to pass with bourdon effect activated. In this case sustained stress was the concern as the pressure elongation is included in the sustained stress.

If i now take the same model and use an equivalent temperature and with no bourdon activated I now get a failure in the expansion case.

So I have modelled it in 2 ways and one passes and the other doesnt but which one is correct? It seems clear from the explanations others have given here that it should be treated as an expansion stress. Given this, modelling the system using the bourdon effects option in Caesar and treating the elongation as a sustained stress was not conservative as I first thought.