Prabhat Krishnaswamy, May 2018
Proposed Allowable Scratch Depth for High-Density Polyethylene (HDPE) Pipes in Safety-Related Nuclear ApplicationsAuthor(s): P. Krishnaswamy1, S. Kalyanam1, Y. Hioe1, S. Pothana1, P. Raynaud2Affiliation:1Engineering Mechanics Corporation of Columbus3518 Riverside Drive, Suite 202, Columbus, OH 43221kswamy@emc-sq.com, sureshk@emc-sq.com, yhioe@emc-sq.com, spothana@emc-sq.com2United States Nuclear Regulatory CommissionRockville, Maryland Patrick.raynaud@nrc.gov The topic of flaw acceptance for HDPE pipes installed in safety-related applications of a nuclear power plant has been of interest over the last decade. From initial analysis and tests on slow crack growth (SCG) in coupon specimens to hydrostatic Notched Pipe Tests (NPT), verification studies have been conducted by several researchers. Recently, the Electric Power Research Institute (EPRI) proposed a flaw acceptance criterion for HDPE pipe based on observations from several rounds of tests on various HDPE resins. The present study proposes acceptable flaw sizes for a range of pipe diameters and thicknesses. The flaw acceptance analyses use the renowned Brown model to transfer PENT values to service life/failure time estimations, evaluate the stress-intensity factors (SIF or KI) for infinitely long axial outer diameter (OD) surface cracks (most conservative approach for flaw acceptance determination), and analyze EPRI NPT data. It is also noted that the Brown PENT model does not accurately incorporate pipe or component geometry effects, and hence needs to be modified to predict the service life of pipes. However, this model can easily be used to determine maximum allowable SIF (KI) for pipes with the same geometry but different PENT values at the same service temperature, using NPT data. The allowable flaw size (scratch depth) analysis method is presented, and the flaw acceptance criteria for various postulated pipe geometries are discussed. In addition, the allowable flaw size method is demonstrated with the example of the largest pipe diameter with the thickest wall installed to-date. In summary, a rigorous conservative approach has been developed using existing data (from EPRI), the Brown PENT model, and a fracture mechanics approach for KI, to determine the maximum allowable axial external scratch depths (flaw sizes) in HDPE parent pipe for all diameters, all wall thicknesses, and PENT ratings from 2,000 to 10,000 hours.