Material in creep range 1

[Ehiman1]

Hello everyone,
I am checking a calculation of a pressure vessel, where the operating temperature is 480 C and design temperature is 510 C for SA-387 gr.11 cl.1.
In this case In accordance with ASME code the design temperature for this material is in creep range, so in my opinion design temperature should updated with Larson Miller formula to consider this thing.
In this case, with 20 years of utilization we have a design temperature of 520 C that means an higher shell thickness.
Could you please confirm my reasoning?
Because in the calculation vendor didn’t consider this modification of design temperature.

Thanks

 

[BJI]

The first step in a Level 1 assessment is to determine the max operating temperature, pressure and service time; so these must be known not assumed. For design, I wouldn't calculate any additional margins, but I would opt to check the equivalent time at temperature.

Not sure wing it would be the phrase I would use, but there are layers of conservatism in most of these assessments, which is one of the reasons the partial safety factors have all but been removed from API 579. The case discussed would pass the screening check for a level 1 assessment, without needing to calculate creep rate and damage, still permissible under a level 1 assessment; before moving on to Level 2 or Level 3 methods.