A Study On Security Estimation And Remnant Life Forecast For Cr5Mo Tube Of Coking Heater

The Cr5Mo steel furnace tubes were widely applied in our petrochemical field,were of considerable importance. The designed life of common equipments running under the high temperature is 100,000 hours. The Cr5Mo furnace tube in Du Shan Zi Petro chemistry Subsidiary Company have or will run out of time. Presently, the running situation, the possible damage of kept running and the residual life of the heating furnace tube are concerned by the factories. The structure, performance and creep residual life of reformer furnace tubes which have run for 7 years in Du Shan Zi Petro chemistry Subsidiary Company have been investigated using many equipments such as OM, XRD, SEM/ EXD. A reasonable and practical residual life evaluation method is found by the experiments to keep the furnace tubes running as before.The experimental results show that the microstructures of Cr5Mo furnace Tubes had been changed after a seven-year running. The changes include spherical pearlites, changes of shapes, quantity and distribution of carbides. There were no cavities and cracks. The inner and outer surface of the furnace tubes are oxides. The maximum thickness of the oxide scale layer is about 0.1~0.5mm.With the high temperature, the time will influence the strength of the materials. High temperature strength testing of the materials is a direct and reliable way to Determine the mechanical performance of the high-temperature materials, 24 specimens of reformer 11#,22#furnace tubes were used to test high-temperature persistent performance. The creep rupture test results show that although the strength of these two tubes were decreased in some sense, the residual life is more than 100,000 hours if kept running in service condition. Meanwhile, according to the micro structure, performance and residual life of Cr5Mo furnace tubes, the relation ship of the structures and high-temperature persistent performance was established to estimate the residual life in terms of the changes of the microstructures during the industrial production.