Hi,
It is a codal requirement to use cold modulus(reference modulus of elasticity: Ea) in stress calculation(B31.3, Cl. 319.4.4 (a)).

However, hot modulus can be used for Loads/reactions.

Most stress analysis software use Cold modulus for Loads on Restraints, However options are available for user to use hot modulus instead of cold modulus. Using hot modulus especially for > 300 deg C systems will have significant reduction in Loads on Nozzle and supports.