Plastic Pipes Conference Association # 2010 Vancouver
P.Krishnaswamy
The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Codes Committee (BPVC) has 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 PE Pipe (SWG-PP) within Section III (Design) of the BPVC. The U S Nuclear Regulatory Commission (U SNRC) has not as yet approved this Code Case for use in regulatory decisions. However, two Relief Requests for installation of PE Piping in safety-related applications at US Nuclear Power plants have been approved by the USNRC. The paper focuses on the susceptibility of PE pipe to premature failure due to slow crack growth (SCG) - specifically, the various forecasting models and accelerated testing protocols that are used to analyze short term experimental results to predict long term (50 years and beyond) service life. A critical review of these models with regard to the acceleration factors for temperature, stress, and stress intensity factors is provided in the paper. As expected, elevated service temperature has the most significant impact on the predicted service life using the various models. Areas where improvements are needed in these forecasting models for newer generation PE100 or PE4710 bimodal resins are identified.
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