Fitness-for-Service (FFS) (also known as Fitness-for-Purpose) is an assessment according to "best-practice" standards and is part of Risk-Based Inspection in which obsolete pressure vessels and pressure lines are reassessed based on measurements and risk assessments. This allows them to remain in safe operation for longer. Using practical examples, Sjors van Kuipers shows what is involved in the assessments and what users can expect from them. The common thread here is the rules laid down in API 579.