Experimental Study On Residual Life In Tubular Reactor Of Ultrahigh Pressure Polyethylene In Service

Owing to long-term service in the harsh environment, such as the high temperature and pressure, the safety performance of the autofrettaged reactor of ultrahigh pressure polyethylene is decreasing, which often leads to the fatigue and corrosion fracture. It comes that the accidents such as the leakage, fire and explosion, seriously threat the safe production of the enterprises and the life of personals. Parts of ultrahigh pressure tubular reactors in Chinese enterprises have reached the last stage of design life. However, direct decommission will not only cause huge waste, but also affect the production capacity of the polyethylene. Therefore, it has great significance to carry out the study on residual life of tubular reactor of ultrahigh pressure polyethylene in service, thus to reduce the risk and safeguard the personal safety and property.In this paper, the conclusions were obtained by taking the tubular reactor of ultrahigh pressure polyethylene in service for 29 years as the research object. The assessment of the residual life is based on the re-autofrettage test, ANSYS finite element simulation and analysis of the different operation conditions. The main contents are as follows:(1)Based on the re-autofrettage test with the same initial autofrettage pressure, the decay rate of residual strain and the variation of the stress at different locations were obtained. According to the results of external loop strain, the experimental comparison method, nominal stress method and local stress-strain method were used for assessment of residual life. By comparison, the nominal stress method is more reliable, which provides basis for evaluating the life of tubular reactor in service.(2)According to the decay rate of residual strain, two hypotheses were proposed, one of which is equivalent transformation of elastoplastic interface, the other is same proportion of attenuation of the residual stress both inside and outside wall. Therefore the stress level of the tubular reactor after service is reflected in the numerical simulation of ANSYS, which realizes the assessment of the residual life of tubular reactor in service through the finite element simulation method, as well as expands residual life evaluation theories and methods of the tubular reactor in service. By comparison, results derived from the second assumption tends to be safer.(3)On the basis of approximate transformation of stress level of the tubular reactor after service, the stress distribution under different pressure and temperature variations were analyzed. The residual life of the tubular reactor under different service conditions was assessed, by the Manson and Shigley approximation methods, providing the reliable data for the further study of the effect of different temperature and pressure variations on the residual life of tubular reactor.The analysis of influence factors and prediction of the residual life of ultrahigh pressure polyethylene tubular reactor in service, provides an important reference for the enterprises to implement saftey monitoring and reduce potential accidents.