13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Thermal Mechanical Fatigue of Coke Drum Materials Jie Chen1, Zihui Xia1* 1 Department of Mechanical Engineering, University of Alberta, Edmonton T6G 2G8, Canada * Corresponding author: zihui.xia@ualberta.ca Abstract Coke drums are vertical pressure vessels used in the delayed coking process in petroleum refineries. Significant temperature variation during the delayed coking process causes damage in coke drums in the form of bulging and cracking. There were some studies on the fatigue life estimation for the coke drums, but most of them were based on strain-fatigue life curves at constant temperatures which do not consider simultaneous cyclic temperature and mechanical loading conditions. In this study, a thermal-mechanical material testing system is successfully designed and implemented. A selected set of base and clad materials of coke drums are investigated under isothermal cyclic loadings. In addition, a comparative study between isothermal and thermal mechanical fatigue lives of clad materials is conducted. Some of these fatigue tests are similar to the actual loading scenario experienced by the coke drums. The experimental findings lead to better understanding of the damage mechanisms occurring in coke drums and more accurate prediction of fatigue life of coke drum materials. Keywords: Coke drums, Low cycle fatigue, Isothermal mechanical fatigue, Thermal mechanical fatigue 1. Introduction Coke drums are vertical pressure vessels used in the delayed coking process in petroleum refineries and oil sands plants. They are normally constructed of carbon or low carbon alloy steels and internally clad with SA 240 Type 410S or Type 405 stainless steel to protect the coke drums from corrosion. They range in size from 4 to over 9 meters in diameter and 25 to over 40 meters in height. The maximum shell thickness varies from 14 to 42 millimeters. The maximum operating temperature ranges from 427 to 482°C [1]. First, heavy residual is imported into a coker heater and heated to approximately 482°C. Before direct the heavy oil into the coke drum, the drum is preheated by flowing vapour from the bottom of the drum to the top. (Temperature rises from approximate 150 °C to 360 °C). Then, the hot heavy oil is directed into the coke drum to begin the fill cycle. The fill cycle usually takes 14-18 hours. When the filling is completed, light hydrocarbon from the coke produced during the thermal cracking process is removed by steam stripping. (Temperature drops from 450 °C to 250 °C approximately) After that, high rate of quench water is injected into the coke drum cooling the vessel and possibly extracting the solid coke. After soaking, the solid coke is cut by applying the high-pressure water steams. After all the coke is removed from the drum, the coke drum is reheated and checked in order to prepare for a new operation cycle. [1] The severe cyclic thermal-mechanical load makes coke drums susceptible to damage. It is also found that shell bulging is one of the causes contributing to cracking and failure in the vessel shell
RkJQdWJsaXNoZXIy MjM0NDE=