By Michael J. Humphries, Ph.D.
Integrity Operating Windows establish a safe operating regime for equipment and can be used to trigger a Management of Change review of any changes that might reduce equipment integrity. They can also define limits beyond which short term operation is possible, and to set a safe operating period beyond which corrective action is required. The API is currently developing a recommended practice on Integrity Operating Windows.
Carmagen Engineering, Inc. recently developed integrity operating windows for several units at a US refinery. The potential damage mechanisms for every vessel on the units were evaluated. For each applicable damage mechanism, limits were established to ensure that the service life of the equipment would be acceptable. In many cases, the limits were related to the composition of the process stream because of its impact on corrosion. In other cases, the limits were set by pressure or temperature, both because of a corrosion impact and an effect on mechanical properties.
The end product included a listing of all pressure vessels with their operating limits, and a list of process monitoring points and the limits required for them. A program of stream sampling was also identified for cases where corrosion was dependent on parameters not routinely monitored for process purposes.