We routinely perform re-evaluation and rerating on pressure equipment and piping.

As technology experts in this area and members of relevant code committees, we not only are fully cognizant of all the standard calculations that should be performed, but we also know alternative evaluation techniques and code cases that can be used.  

Rerating can be used both to increase design pressure and temperature, and also to decrease design pressure and temperature to increase the available wall thickness for corrosion/erosion allowance.