Plastic Pipes Conference Association # 2010 Vancouver
F.Scholten
Segments from 32 mm gas service pipes installed in 1975-1976 and from 40 mm water service pipes installed in 1967-1968 in Germany have been excavated and tested for residual quality. Two different HDPE resin populations discovered among the German gas pipes were also found among excavated Dutch gas pipes. Internal water pressure tests of up to 13,800 hours show that the residual quality of both HDPE gas pipe populations is still remarkably good. The times to failure in internal water pressure tests at 20, 60 and 80 °C are no lower than published regression curves. Between 1,400 and 4,300 hours at 20 °C the gas and water pipes go through an early ductile-brittle transition. This occurs however without any change in slope up to 13,800 hours, whilst published data mention a ductile-brittle transition and a knee after about 10,000 hours at 20 °C. The “MRS value” for extended operation during an additional 50 years was predicted. For the gas pipes 5.3 MPa was calculated and for the water pipes 3.9 MPa, due to much higher operational pressures over a longer period. The data also fits to Barton & Cherry’s model, which assumes a log (time) versus linear stress correlation. No oxidation effects were noted. The residual “ambient temperature thermo-oxidative lifetime” was estimated by extrapolation of test results from exposure to water and air at 60 to 95 (100) °C. No alarming results were found.
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