| China began to use polyethylene(PE) pipes in urban cities since the 1980s, and widely used them in the mid-1990s, therefore, they have been used for more than 30 years so far. After a long time of trial, research and extension, PE pipes have replaced the traditionalstation of the past gas pipelines such as steel pipes, cast iron pipes, etc. in the low-pressure gas pipelines network because of its advantages of long life (up to 50 years), corrosion resistance, good flexibility (seismic and adaptation settlement), lightweight, easy connection and so on. What’s more, it has become the first choice of "town gas design specification"(GB50028-2006), and is also gradually began to applying the high-pressure gas pipelines. The usage of PE pipes has become one of the indicators to measure a regional gas technology level, and by 2005, the proportion of the usage of PE pipes in the low-pressure pipe network construction has reached 50%. However, the PE pipes belong to organic material after all, so the aging problem is inevitable. Once an explosion occurred causedby rupture in urban areas, it will cause severe injury and economic loss. Therefore, the research of PE pipes for aging law has great economic and industry significance.But up to now, the researches of aging laws on PE pipes is not perfect.In this paper, PE100 and PE80 pipes material which mainly used for urban gas have been chosen as the research objects.The experiments are conducted on the self-built thermal oxygen accelerated agingplatform based on thermal aging methods.Then, a different aging time of PE pipes under different pressures are selected, and the regularity of PE80 and PE100 pipes are studiedin a detail.From the tensile tests, thetensile properties of PE specimens obtained by the above thermal oxygen accelerated aging experimentgradually weaken with the increasingaging time and pressure;and at lower heating temperature and pressure, the performance of PE pipes changes slowly.But with the gradual increase in the temperature and pressure, the stability of PE pipes changes significantly.When the temperature increases by 10 degrees, the performance weakensby a geometric shape. Then usingthe linear kinetic curve method to fit the data, and an aging prediction model of PE pipes with pressure and without pressure is proposed. As a result, the data is in a good agreement with the thermal oxygen accelerated aging experimental model. The results show that the mechanical properties of PE pipes changes significant with the thermal aging temperature, pressure, time, and the breaking point load also changes dramatically.When the test pressure is 0.1 MPa, the life of PE pipes with pressure is reduced by 9.6%than those without pressure.From the experimental study of melt flow rate,the performance of PE specimens changes significantly withthe thermal aging temperature and time, and the performance parameter is one of the indicators to judge whether the aging of the test tubes happens or not. Then through collecting and analyzingthe data,the material properties before and after the aging are contrasted, to verify the correctness of the thermal oxygen accelerated aging test.From the experimental study of differential scanning calorimetry(DSC),the performance of PE specimens changes significantly with the thermal aging temperature and time, and its performance parameter is also one of the indicators to judge whether the aging of the test tube happened or not. Then through collecting and analyzingthe data, thematerial properties before and after the aging are contrasted, to verify the correctness of the thermal oxygen accelerated aging test.Results of this study can be used to guide the remaining life of evaluation and treatment of PE pipes. |
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