Valve pressure calculation at higher temperature (to be used for thickness calculation)

[MoReSo]

Hello,

I need to calculate the thickness of gate valve for unlisted material based on ASME B31.3 - 304.1.
In this case as the valve is unlisted I don't have the related pressure to consider for the equation.

My question is that how can I calculate pressure for each temperature (100F, 200F,...)?
Is there any way to calculate pressure based on stress values for each temperature?

thank you,

MRSohrabi;
Materials and Welding Eng.