Fitness-for-service (FFS) assessments are quantitative engineering evaluations which are performed to demonstrate the structural integrity of an in-service component containing a flaw or damage.
The most common code in use for FFS assessments is API 579 / ASME FFS-1. This code covers assessment methods for cracks, thinned regions in shells, fire damage and creep damage assessment among other topics. The code provides for three levels of assessment with increasing complexity. The level three assessment methods requires the most detailed stress input and is thus often supplemented with Finite Element Analysis (FEA).
While the API 579 / ASME FFS-1 code is aimed at fitness-for-service of damaged equipment, it is also very helpful for setting inspection requirements for new equipment. The code methods, when applied to new equipment, permit confirmation that proposed inspection methods can find critical size defects during manufacturing and proof testing.