ASME Section XI Case N-513-6, Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping and Gate Values [1], is one of the most widely implemented code cases within the U.S. nuclear industry. The primary purpose of the Code Case is to provide evaluation criteria for flaws within moderate energy, safety-related piping to allow for continued plant operation without repair/replacement until the next scheduled refueling outage. Utilities may avoid an unscheduled plant shutdown provided structural integrity is demonstrated and other requirements are met. Periodic examinations of the flaw during the temporary acceptance period are required by N-513 to ensure the flaw has not grown beyond the acceptable flaw size. N-513 is typically implemented to disposition flaws found in service water piping made of carbon steel that is exposed to raw water where active corrosion mechanisms exist. The Code Case can also be applied to stainless steel and nonferrous material components.

The purpose of this paper is to provide a history of N-513, its technical scope, current ASME Code and U.S. regulatory status, as well as proposed changes for an upcoming revision. This paper also provides a secondary benefit of consolidating the history and development of this important nuclear industry flaw evaluation methodology for traceability and knowledge transfer purposes.

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