Slow crack growth (SCG) under sustained loads (pressure and axial loads) is one of the limiting failure modes that affect the long term performance of High Density Polyethylene (HDPE) pressure piping identified for use in replacement of existing steel piping for Class II applications in nuclear power plants. Several different tests have shown [1] the much lower time to failure of joint HDPE material when compared to the parent HDPE material, indicative of the much lower SCG resistance of the joint HDPE material. Hence, the integrity of the HDPE pipe joints and the critical flaw size evaluation is an area of increased focus for the nuclear industry and regulators, and the plastic pipes industry. Towards this end, task and working groups have been formed within the ASME Boiler and Pressure Vessel Code Committee Sections XI, IX, and III to address the needs for the HDPE piping evaluations in nuclear safety related applications. This current study is a comparison of the resistance to the SCG exhibited by the parent and fusion HDPE materials in the SENT specimen testing. Analysis of the crack growth resistance parameter through crack-mouth- opening-displacement (CMOD), and crack-opening-angle (COA) revealed a marked difference between the parent and fusion HDPE material. The experimental analysis also revealed a similar crack growth in normalized time indicative of the same constraint in the experimental specimen, but differing fracture energy in the parent HDPE material versus the butt-fusion joint material. The findings are in line with the large difference observed in the time to failure between the parent and fusion HDPE materials from creep tests at constant load.
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