City Gas Pipeline Ring Rubber Material Aging Degree Of Testing And Remaining Life Prediction

It is the most universal way to transmit gas through pipelines. With the development of economy and urbanization, gas pipelines become the basic infrastructure of modern city. With the completion of the project of "transmitting natural gas from the west of China to the east" etc, many gas pipelines will deliver natural gas instead of man-made coal gas. Compared with man-made coal gas, natural gas is less in water vapor and aromatic hydrocarbons. Affected by aging, the change of medium and many other reasons, the leakages of gas pipelines arouse lots of accidents and the accident tendency keeps rising. Sealing failure caused by ageing of rubber seals is one of the most important reasons why gas pipelines leak out.Based on the practical situation of the gas pipelines in Hangzhou, the aging test and the residual life prediction of rubber seals are developed in this paper. The main research results are as follows:(1)The study of physical properties of rubber seals changing with aging time. Physical properties of DN150mm, DN300mm, DN400mm, DN500mm rubber seals (both new and old ones) are tested and compared. The tests results indicate that: hardness and modulus of elasticity in compression rise; tensile-strength, elongation at break, compression set and compression stress relaxation fall down. The sealing property lowers with the changes of physical property, but most of the physical properties are in the range which the standard allows.(2)The study of physical properties of rubber seals changing in drier environment. The drying device is established. The rubber seals, for test are divided into two halves. One half keeps the origin state and the other needs to be dried. Physical properties of both two halves are tested and compared. The tests results indicate that: hardness, modulus of elasticity in compression and compression stress relaxation rise; tensile-strength, elongation at break and compression set fall down. The changes of physical property bring both advantage and disadvantage to the sealing property of rubber seals. Taking everything into account, the conclusion is that the gas pipelines will maintain good sealing state in a short term.(3)Establishing the method of residual life prediction for gas pipeline rubber seals, and the residual life of DN300mm and DN400mm rubber seals are predicted. Accelerated aging tests are taken on DN300mm and DN400mm rubber seals. Through the test results, the laws of compression set changing under high temperature are obtained. Then extrapolating the laws to working condition, the laws of compression set changing under operation are got. The compression set of rubber seals yielded during the process of operation is estimated and the aging velocity can be obtained from the results of accelerated aging test. Then the residual life is predicted. The result is that: DN300mm rubber seals have a residual life of 24.13 years and DN400mm rubber seals have a residual life of 29.1 years.