The High Temperature Damage Analysis And Residual Life Forecast Of The Cr5Mo Coking Heater Tube

The delayed coking plays an important role in the refinery profession, and the coking furnace is one of the key equipment to ensure the long term stable service for coking systems . Because the coking furnace operating temperature is high, its furnace tube material will have material performance degeneration phenomena under the high temperature environment, which include high-temperature oxidation,pearlyte spheroidization and so on. Specially when the coking furnace operating parameter is unstable, it will have the furnace tube short-time excess temperature , which have intensified the furnace tube material degeneration, further reduced furnace tube's service life. Therefore the development of high-temperature furnace coking loss analysis and the residual life appraisal have the important project practical significance in the explosion accident regarding the prevention and the instruction active duty furnace tube regular replacement. This article take the coking furnace tube as the object which has serviced for near 9 years, the furnace tube material is Cr5Mo, this article analyses the high temperature damage situation of the material performance, and forecast tube residual life of the furnace. Separately from the field inspection and the laboratory test two aspects, which carry on furnace tube's wall thickness examination, degree of hardness and the microstructure analysis, the chemical composition analysis, the mechanical properties experiment. The results indicated as following: after serving under the high temperature for a long time, the chemical composition of the furnace tube met the standard; under normal temperatures, the mechanical propertiesσ_b,σ_0.2 were within the standard range, the elongation ratio dropped obviously, and the degree of hardness also decreased, the impact properties reduced greatly to only 8J for the maximum value of No1 furnace tube; the spheroidization phenomena of the material was obvious when being tested in field and at lab, and the rank of spheroidization located at the different positions of furnace tubes. Based on the damage analysis of the material at the high temperature, the residual life formulae of furnace tubes were gotten with the isothermal method and the L-M extrapolated method after a long-term test. Then by these formulae, the residual life of serving furnace tubes could be calculated. Finally, the evaluation conclusion was drawn as following: under the operating temperature 670℃and the stress condition 20MPa, this batch of furnace tubes could be used for at least 3 years.