API TR 579-B

Abstract

This research study provides background information that may be used to revise the Fitness-For-Service (FFS) document, API 579-1/ASME FFS-1 2021 (aka “API 579”), more specifically the Part 9 Level 2 Assessment, along with a new Level 3 option for Part 9. The Part 9 Level 2 crack-like flaw FFS procedure relies on the Failure Assessment Diagram (FAD) approach, which is the most widely used crack assessment methodology in the world. Several industry standards for crack assessment implement the FAD approach, including BS 7910 from the British Standards Institute and the R6 document from the British nuclear power generation industry. The FAD approach was first introduced in 1976 as a simple approximation for fracture stability assessment of structural components that experience plastic deformation prior to failure. Modern industry standards use improved versions of the FAD, but the approach still contains approximations and simplifications. The main purpose of the present work is to remove some of the approximations in the existing Part 9 Level 2 FAD procedure and thereby improve accuracy. A side benefit of this work is a new Level 3 option that is even more accurate than the improved Level 2 procedure. This study includes a large number of 3D elastic plastic Finite Element Analyses (FEA) of components with cracks.