Question

What is CET for Pressure Vessels including heat exchangers and pressure storage spheres?

Answer 1

The CET for pressure vessels is determined from the anticipated process and atmospheric conditions.

The CET is defined as the lowest metal temperature at which a component will be subjected to a general primary membrane tensile stress greater than 55.2 MPa (8 ksi).  The CET may also be defined according to the following options:

• The minimum metal temperature at which a component could be subjected to a pressure greater than 40 percent of the design pressure for vessels constructed to ASME SEC VIII D1.
• The minimum metal temperature at which a component could be subjected to a pressure greater than 35 percent of the design pressure for vessels constructed to ASME SEC VIII D1, with a 3.5 safety factor as recognized in the 1999 addenda.
• The minimum metal temperature at which a component could be subjected to a pressure greater than 30 percent of the design pressure for vessels constructed to ASME SEC VIII D2.
• For pressure vessels designed to a higher allowable stress than that permitted in these codes, the CET may be taken as the lowest metal temperature at which the vessel will be subjected to a pressure no greater than 25 percent of the design pressure, or a membrane stress of no greater than 55.2 MPa (8 ksi).

Answer 2

Additional CET for Piping:

The CET for systems constructed to the ASME B31.3 Piping Code is defined as the lowest metal temperature at which a component will be subject to either 30 percent of the MAWP at ambient temperature or a combined total longitudinal stress due to pressure, weight effects and displacement strains which does not exceed 55.2 MPa (8 ksi).  The CET for piping is determined from the anticipated process and atmospheric conditions.