Mandatory Appendix XXVI in Section III of the ASME Code (2015 Edition) includes the requirements for the construction of Class 3 high density polyethylene (HDPE) pressure piping. Currently, there are no acceptance limits for subsurface voids in HDPE piping included in the Code. Data from recent EPRI tests conducted to determine the rate of growth of flaws in HDPE piping can be used to develop acceptance criteria for subsurface voids. The tests exposed specimens with surface flaws to sustained loads under elevated temperature and stress conditions. No failures were observed in the tests. Therefore, the results are useful to establish lower bound lifetime estimates for flawed piping under the maximum allowable temperature and stress conditions for buried pipe. The HDPE material has considerable ability to resist crack growth at temperatures well above the maximum allowable service conditions permitted in Appendix XXVI. The test data were used to establish allowable subsurface void sizes in HDPE piping. Correlations for rupture time that are based on the applied stress intensity and net section stress were used to determine an allowable subsurface void size. Because the creep failure mechanism in HDPE piping is time-dependent, an allowable void size was developed to ensure HDPE pipe integrity at the void location for a 50-year service life. The allowable flaw sizes can be used for the disposition of void indications identified in piping both before and after installation.

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