Life Prediction Of Cr9Mo Furnace Tube After Long-term Service At High Temperature

In petrochemical industry, the heating furnaces are widely used under severe working conditions. However, the safety of the furnace tube has an important influence on the integrity and service safety of the heating furnaces and unit. Hence, in order to improve the economic and social benefits, it is very necessary and important to predict the remaining life of the furnace tube after long time service. Fortunately, the remaining life prediction of the furnace tubes is becoming a major concern of petrochemical engineering.In this paper, the performance of Cr9Mo furnace tube served for a long time in a reforming heating furnace of the aromatic factory in Yangzi Petrochemical Corporation has been evaluated by determining the damage level of material and predicting remaining life of tube. These topics can provide some scientific insights for the decision making relating to the maintenance strategy of the served furnace tubes, such as repairing and replacement, etc. Some following important results can be obtained.(1) There were no any macroscopic defects such as corrosion pits on the outer side of the furnace tube. However, the dense oxide layer has been formed during the service period. The distortion in the welding regions was relatively serious.(2) The chemical compositions of the base material and weld material have been analysed. Experimental results showed that the content of Cr element in the weld was decreased due to long-term service under the high temperature condition, which led to the low oxidation resistance of the material in this region.(3) Results of microstructure analysis showed that the high-temperature creep damage of the furnace tube was very serious. In the welded joint, the microstructure was characterized by many randomly distributed creep voids, microcracks and accumulated carbides along the grain boundaries. Using the creep damage rank assessment method, the creep damage level of the weld material was regarded to beâ…¢and the remaining life of the furnace tube is predicted about 3 to 9 years.