Evaluation of Plastic Pipes by Hot Water Circulation, Stress Rupture, and Immersion Tests

 

Papers # 2014 Chicago

The polymer electrolyte fuel cells (PEFC) cogeneration system has been commercialized in Japan. The number of commercialized PEFC residential cogeneration systems have reached 100, 000 in total at the end of last year. The waste heat can be used for hot water supply and central heating. Hot water distribution pipes connecting a gas cogeneration system with the water heater and terminal appliances are very important. As the advanced residential cogeneration system is expensive, the longer lifetime of the heating and hot water supply system is required for consumers, the reliable plastic pipes have been developed. In this paper, plastic pipes such as PEX and PE-RT for heating and hot water supply were tested by the hot water circulation at the pressure of 0.4 MPa in inlet and 0.2 MPa in outlet, the stress rupture at the pressure of 0.2 MPa at 110 °C and the simple hot water immersion and hot air exposure at 60, 80, 100(98), and 120 °C for 7000 hours or more. There were some failures for PE-RT pipes in hot water circulation and stress rupture tests. The tensile test for dumbbell specimens cut out from plastic pipes after hot water circulation, stress rupture, hot water immersion and hot air exposure was conducted to evaluate the effect of hot water flow in a pipe and applied pressure to a pipe. ‘he yield stress increased and the elongation at break decreased for plastic pipes due to increment of degree of crystallization after hot water circulation, stress rupture, hot water immersion and hot air exposure. There was a rough degradation layer at the inner surface after hot water circulation for PEX and PE-RT pipes for 7000 hours. The initial oxidation temperature (IOT) at the inner surface and the middle of a pipe after hot water circulation was also measured to evaluate remaining antioxidants. As the [OT decreased at the inner surface of a pipe after hot water circulation, it was found that antioxidants were deactivated and eluded into hot water.

Related keywords : PE-RT. Oxidation, PEX, stress, rupture, pressure, antioxidants, IOT.
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