Fitness-for-Service is a structured engineering evaluation used to determine whether in-service equipment is safe to continue operating despite flaws, damage, or deterioration. Modern FFS practices are governed by the API 579-1 / ASME FFS-1 standard.

This article provides a comprehensive, practical explanation of what turbine vibration diagnostics is, how it works, what data is needed, and why facilities rely on specialists to perform these evaluations.