FFS assessments must include an evaluation of the remaining life of a component. A damaged component may be acceptable in the present, but there must be an established remaining life. This assessment is necessary to establish inspection intervals and a basis for reliability-based inspection (RBI). RBI is the assessment technique used to determine what equipment is more likely to fail first and is used to establish a priority system of equipment inspection during a turnaround. We are not going to deal much with RBI in this chapter, but it is an invaluable technique to make turnarounds more efficient and productive. Gone are the days when every single piece of equipment is opened for inspection during a turnaround. The RBI technique assesses existing inspection records and FFS assessments and the evaluations of operations personnel who rank the various pieces of equipment. Low-ranked equipment is not opened during a turnaround, thus saving many resources. Remaining life is a critical parameter in RBI, which is based on the applicable code.

Remaining life is not always easily determined. One such circumstance occurs when there is no corrosion rate data. Another circumstance occurs when there is no reliable crack growth rate. As a consequence, monitoring or remediation is used to account for any uncertainty. When there is little or no remaining life, repair is the obvious option. API 579 sets criteria for acceptance, but little is said about defining remaining life. Hence Eq. 3-18 is developed to make the process simpler.

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