Fatigue Assessment for In-Service Components – A New Part for API 579-1/ASME FFS-1 Fitness-For-Service

Abstract

The third edition of API 579-1/ASME FFS-1 Fitness-For-Service will include a new Part covering fatigue assessment procedures for in-service components. Fitness-For-Service (FFS) assessments are quantitative engineering evaluations that are performed to demonstrate the structural integrity of an in-service component that may contain a flaw or damage, or that may be operating under a specific condition that might cause a failure. The API 579-1/ASME FFS-1 Standard was specifically written to cover in-service pressurized equipment typically found in the refining and petrochemical industries as well as the fossil utility industry. The new Part will cover methods used to estimate the time to crack initiation using a strain-life approach and will be written as a multi-tiered approach covering screening, current design code methods, and advanced methods that take into account the latest in technology. The screening and design code assessment methods in the new Part will be based on an updated version of the procedures in the ASME B&PV Code, Section VIII, Division 2. The advanced methods will include next generation versions for the fatigue assessment of welded joints, the Master S-N Curve Method as described in WRC 523, and the Verity Fatigue Assessment Method developed by Battelle. The advanced methods will also include a new smooth-bar fatigue assessment method that incorporates a multi-axial fatigue criterion with a critical plane approach. Cycle counting methods for both welded joint and smooth-bar fatigue methods will be provided. Methods to evaluate fatigue in the subcritical crack-growth regime in API 579-1/ASME FFS-1 using a fracture mechanics approach are also covered.