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Online Companion Guide to the ASME Boiler and Pressure Vessel Codes: Criteria and Commentary on Select Aspects of the Boiler & Pressure Vessel Codes

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ASME Press
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This chapter discusses the evaluation of flaws in nuclear power plant components using the methods and criteria in ASME Code Section XI. It describes flaw acceptance based on the use of predefined acceptance standards and the use of detailed fracture mechanics evaluation. The chapter covers topics such as the evaluation of examination results (IWA-3000), flaw characterization, and flaw acceptance standards (IWB-3500). It begins with a discussion on the evaluation of component flaw (Class 1 components, IWB-3600 and reactor pressure vessel, IWB-3660), evaluation of piping flaw (for austenitic and ferritic materials, IWB-3640), and the evaluation of piping wall thinning, such as wall loss by flow-assisted corrosion. The chapter presents rules for characterizing planar, laminar flaws, as well as linear indications. It also presents a discussion on temporary acceptance of flaws for justifying continued operation until repairs could be performed in moderate energy systems. The chapter provides information on the evaluation of plant operating events, providing rules for performing assessments to ensure that initial Code margins are maintained. In addition, it examines the procedures for evaluating situations where design bases for the original plant may have been exceeded. Evaluation of Classes 2, 3, MC, and NF components are also covered. The chapter closes with a summary of some specific short-term activities and recent developments that are ongoing in the Section XI committees responsible for the evaluation and acceptance of flaws detected during inservice inspections.

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