The third edition of API 579-1/ASME FFS-1 Fitness-For-Service includes a new Part 14 covering fatigue assessment procedures for in-service components. This new part provides methods for estimating the time to crack initiation using strain-life approaches, which are important for low-cycle fatigue, and is written as a multi-tiered approach covering screening, current design code methods, and advanced methods that take into account the latest in technology. Cycle counting methods for both welded joint and smooth-bar fatigue methods are included for uniaxial and multiaxial loading histories. In addition, the multiaxial incremental plasticity correction procedure presented in the new Level 3 Assessment represents a significant update to the plasticity correction used previously. Part 14 of API 579-1/ASME FFS-1 is a procedural document that is written for accurate and practical implementation. WRC Bulletin 550 is the basis for Part 14 and provides the background and supporting documentation for its development. This paper summarizes the work that went into developing Part 14, and WRC 550, and provides a specific example of its implementation for a practical problem of interest using software developed by The Equity Engineering Group, Inc. In-depth comparisons, key findings, and limitations of the presented methods are included.

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