Update on Proposed Modifications to API 579 PART 3 Brittle Fracture Screening Procedures

Significant inconsistencies and inadequacies exist in the current brittle fracture screening procedures in the 2021 edition of API 579-1/ASME FFS-1 (API 579), Fitness-For-Service as well as the various pressure equipment and piping design codes. Results from an evaluation completed using the current published guidance could prove unsafe in some instances. In 2016, the ASME/API Joint Committee on Fitness-For-Service (FFS) initiated a project to rewrite API 579 Part 3, Assessment of Existing Equipment for Brittle Fracture. The intent of the project is to establish new Level 1 and Level 2 evaluation procedures and acceptance criteria developed using state-of-the-art fracture mechanics consistent with the Failure Assessment Diagram (FAD) approach in API 579 Part 9 Assessment of Crack-like Flaws, which is currently employed in Level 3 Fitness-For-Service assessments.

An AIChE paper published in 2019 (182d) summarized the deficiencies and concerns with current published methods for evaluating susceptibility of pressure equipment and piping to potential brittle fracture failures. The paper also offered insight on proposed modifications to the assessment procedures to mitigate those concerns through employment of modern fracture mechanics to establish new screening criterion. Subsequently, several technology enhancements were recently developed and incorporated into API 579 Part 9 and its associated annexes to reduce conservatism in previous fracture mechanics-based approaches to establish low temperature limits for equipment and piping. Those enhancements were included in the 2021 edition of API 579.

This paper will provide an update on recently proposed modifications to API 579 Part 3 brittle fracture screening assessment methods. The paper will outline alternate Level 1 and Level 2 procedures and acceptance criteria developed using the latest state-of-the-art fracture mechanics methodologies. Lastly, the paper will include case study examples to demonstrate the difference in assessment results obtained utilizing the proposed modified procedures compared to results obtained employing current brittle fracture screening methodologies.