Api 579

An Introduction to API RP 579: Section 9, Assessment of Crack like Flaws

REACTOR SAFETY DIVISION BHABHA ATOMIC RESEARCH CENTRE MUMBAI

INDIAN NUCLEAR SOCIETY LECTURES ON WELDING, NDE AND INTEGRITY ASSESSMENT September 18-22, 2006

rrastogi@barc.gov.in
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Lectures on Welding, NDE and Integrity Assessment

 

ROHIT RASTOGI

Lecture number 19 a, Page 1 of 33

INDEX 1. Introductionto API RP 579 2. Overview of API 579, Section 9 (Assessment of crack like flaws) 2.1 General 2.2 Applicability And Limitations Of The Procedure 3. Flaw Characterization 3.1 Characterization Of Flaw Length 3.2 Characterization Of Flaw Depth 4. Level 1 Assessment 5. Level 2 Assessment 6. Level 3 Assessment 7. Remaining Life Assessment 8. Leak Before Break Analysis 9. Remediation 10. In-ServiceMonitoring 11. Documentation 12. Example Calculation 13. References 3 7 7 7 9 10 13 15 17 23 25 27 29 30 30 32 33

Lectures on Welding, NDE and Integrity Assessment

Lecture number 19 a, Page 2 of 33

1. Introduction to API RP 579
In classical engineering design, an applied stress is compared with the appropriate material resistance expressed in terms of a limit stress, such as the yieldstrength or fatigue endurance limit. As long as the material resistance exceeds the applied stress, integrity of the component is assured. It is implicitly assumed that the component is defect-free but design margins provide some protection against defects. Modern design and operation philosophies, however, take explicit account of the possible presence of defects in engineering components. Suchdefects may arise from fabrication, e.g., during casting, welding, or forming processes, or may develop during operation. They may extend during operation and eventually lead to failure, which in the ideal case occurs beyond the design life of the component. The analytical methods for safety evaluation of flaws are based on stress analysis, but they also require information on equipment operations,nondestructive examination (NDE), and material properties. Stress analysis may be performed using standard handbook or design code formulas or by means of finite element analysis (FEA). With modern computer technology, the use of FEA is quite common. Fitness for service assessment requires both knowledge of past operating conditions and a forecast of future operating conditions. Interaction withoperations personnel is required to obtain these data. NDE is used to locate, size, and characterize flaws. The material properties should include information of material damage mechanisms and behavior in the service environment, especially on the effects of corrosion and temperature. The draft of API RP (American Petroleum Institute Recommended Practice) 579 [1] was started in 1994, and the firstedition was published in January 2000. API 579 has been developed to provide guidance for conducting fitness for service (FFS) assessments of flaws commonly encountered in the refining and petrochemical industry, which occur in pressure vessels, piping, and tanks. However, the assessment procedures can also be applied to flaws encountered in other industries such as the pulp and paper industry, fossilfuel utility industry, and nuclear industry. The guidelines provided in API 579 can be used to make run-repairreplace decisions to ensure that pressurized equipment containing flaws that has been identified during an inspection can continue to be operated safely. API RP 579 is organized in modular fashion based on type of material damage or flaw to facilitate its use and updating. It incorporatesa three-level assessment approach. The level of conservatism decreases with increasing level of assessment, but detail of analysis and data increase with increasing level of assessment. An inspector or a plant engineer can perform level 1 assessment. Level 2 assessment requires at least a plant engineer, whereas Level 3 assessment must be performed by an expert engineers or by a team of...