The ASME Boiler and Pressure Vessel Code Committee (BPVC) has recently published Code Case N-755 that describes the requirements for the use of Polyethylene (PE) pipe for the construction of Section III, Division 1 Class 3 buried piping systems for service water applications in nuclear power plants. The code case was developed by Special Working Group–Polyethylene Pipe (SWG-PP) within Section III (Design) of the BPVC. This paper provides a critical review of the design requirements described in CC N-755 from pressure boundary integrity considerations. The various technical issues that need to be addressed for safety-critical PE piping are discussed in this paper. Specifically, the premise of allowing defects in pipe that are 10% of the wall thickness has been reviewed especially for cases involving large diameter piping [> 304.8 mm (12 inches)] that is to be operated at elevated temperatures as high as 60°C (140°F). One of the common modes of failure in PE piping under sustained internal pressure is due to slow crack growth (SCG) from manufacturing or installation defects in the pipe wall. The effect of pipe diameter and stresses on the crack driving force for a 10% deep flaw is calculated for comparison with the material resistance to SCG at elevated temperatures.

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