Research On Early Warning Method Of Thermal Mechanical Fatigue Damage Of Coke Drum

Coke drum is a critical equipment in delayed coking plants,which is operated under severe thermal-mechanical conditions by cyclic heating and quenching processes.The thermal stress generated by temperature fluctuations is the main cause of structural failure.Cracks are usually developed during service because of severe plastic deformation and low-cycle fatigue.Thus,the assessment of the deformation severity and remaining life is important for safety operating of the coke drums.At present,most of the traditional shutdown inspection methods are used in China,and foreign research institutions and inspection companies have begun to apply three-dimensional laser scanning to detection and life analysis.A long-term service carbon steel coke drum was used as the research object in this paper,Using the laser scanning method and strain fatigue test data,a method was proposed to evaluate the universality of the bulged coke drums.The results can be used as a reference for the life evaluation and detection of coke drums in service.Comprehensive consideration of many influencing factors is of great significance for accurately predicting the remaining life of coke drums.The main contents are as follows:(1)The deformed coke drum was processed into a finite element geometric model by internal laser scanning detection.The thermal mechanical coupled finite element analysis was performed on the two regions with large deformation based on the dynamic thermal boundary method.The stresses and strains of the perfect geometry were analyzed and compared.The stress and strain distribution levels of different bulging patterns are obtained.The maximum stress and the maximum strain of the deformed region were increased by 35% and 77%,respectively,compared with the perfect geometry.(2)A thermal-mechanical fatigue test was performed to simulate complex loading condition experienced by the coke drum.The thermal-mechanical fatigue life curve of the fabrication material was obtained.The fatigue life of the coke drum was assessed by the Coffin-Manson-Basquin's relationship.A reasonable life of the coke drum can be obtained by using the thermal-mechanical fatigue properties and laser scanning approach.(3)The cold spots were applied to the two regions with large deformation,and compared with the undeformed coke drum model,the maximum stresses in local bulges and band bulges have increased by 10.3% and 12.8%.These models have different degrees of bulging,and the bulging of the deformed model is more serious.Compared with one cold spot,the equivalent stress of the two models increases when the two cold spots are arranged axially.For the deformed model and the undeformed model,the equivalent stress decreases with the increase of the cooling water temperature,and increases with the increase of the water inlet speed.The operating parameters have a more significant effect on the deformed model.(4)When the radiation is applied to the coke drum,it is found that the temperature distribution at the hot box is more uniform when considering the thermal radiation.According to the actual laser scanning results,two ideal simplified bulging models are proposed.After analysis,it is found that one side of the axial stress in the bulging region is tensile stress and the other side is compressive stress.The maximum equivalent stress of the bulging model increases with the increase of bulging size.