RefineryMechEng
Mechanical
Let's say you have a pressure vessel that has been in service for 5 years, and it had a shell cylinder wall thickness of 1.5 inches when it was installed new. You want to know how thin you can allow the vessel wall to become before you have to replace it, so you calculate the thickness required to keep the stress in the vessel wall from exceeding the allowable stress for the material, and you find that it is 1.2 inches. What is the proper way to determine the MDMT for the vessel at its minimum required thickness (tr) of 1.2 inches using UCS-66. Do you let tn = 1.2 inches and then plug in zero for corrosion allowance in [tr E]/[tn - c] or Do you let tn = 1.5 inches and plug in .3 for corrosion allowance in [tr E]/[tn - c]?