Q. Cyclic Service for vessels?

The required service for all vessels shall include consideration of cyclic service. Batch operation vessels, for example, quite frequently fall into this category. The following guidelines are recommended as a starting point in the process of determining if cyclic analysis may be required.

Number of Cycles

Vessels should be considered to be in cyclic service, when the total number of cycles in (1)+(2)+(3) below will exceed 1000 cycles in the desired design life of the vessel:

1. The expected number of full range (design) pressure cycles, including start-ups and shutdowns.

2. The expected number of operating pressure cycles in which the range of pressure variation exceeds 20% of the design pressure.

3. The expected number of thermal cycles, where the metal temperature differential between any two adjacent points exceeds 50^oF (29^oC).