The Safety Assessment Of Pipe In Equipment For Hydrogenation And Deacidification

The pipe was built in 1990 and it was put into service in 1996,the specific parameters are:the material is 1Cr18Ni9Ti;the size isφ219×20.62;the operating pressure is 4.5MPa;the operating temperature is 230～270℃;the transporting fluid is decompression line oil,and it contains hydrogen,hydrogen sulfide and chloride ion.The pipe has been operated for eleven years,and the material may degenerate,so it is urgent to assess the safety of the pipe from the aspects of corrosion and fatigue.It is found in the macro-detection that there is brown corrosion layer on its internal surface,and great deals of small cracks are distributed circumferentially.A micro-structure detection of the corrosion layer and metallurgical structure for the pipeline material was carried on.And the results prove great quantities of banded structures were caused in the fabrication process,so that there is internal stress in the micro-structure.The internal stress and the corrosive environment,especially the chloride ion,made the pipe corroded.In this paper,the tests for the life of low cycle fatigue at high temperature are carried on under multiaxial state with the cylindrical specimens of different notches.The stress and strain fields of the specimens are analyzed by the FEM software ANSYS,and the equivalent plastic strain ranges of danger point are calculated through the Von Mises equivalent theory. According to the results,the Manson—Coffin equation and the least-square regression method,the equations to evaluate the life of low cycle fatigue at high temperature are obtained.By the software ANSYS the model of the pipe is established and the operating state is simulated,so the stress/strain fields of the pipe in real operation are calculated.And then the remaining life is evaluated through bringing the equivalent plastic strain range into the equation for life of low cycle fatigue at high temperature.