Fatigue Crack Initiation And Propagation Prediction Of 15CrMoR Coke Drums

Coke drums are key equipments of the delayed coking process in the petroleum industry. As coke drums experience severe thermal cycles, there will be fatigue crack initiation after a certain number of years. The subsequent crack propagation will lead to shutdown of production and even the risk of severe accident if there is no much attention to these issues. Therefore, the fatigue crack initiation and propagation prediction are important to actual operation of coke drums.A coke drum in Guangzhou Branch of Sinopec was taken into analysis. The temperature field and stress field in the coke drum wall were simulated by using the finite element ANSYS software. The results show that the peak stress occurs at the area between the skirt and the cylinder or the weld seams. For high stresses always lead to fatigue crack initiation, so the above areas were taken as the monitored locations.The prediction of fatigue crack initiation was based on the Manson-Coffin equation. The fatigue properties of the material were obtained by low-cycle fatigue test. As the stress varies every cycle, the predicted results with the maximum, minimum or mean strain amplitude of a single cycle could not agree with the actual situation. Thus the crack initiation prediction was conducted with the statistical data from a batch of cycles based on Miner Damage Accumulation theory.Based on the Paris law, the material parameters related to the crack propagation were obtained by fatigue tests. The propagation of a crack with certain initial size was predicted according to the Miner theory with data from number of cycles. Moreover, a probabilistic crack propagation prediction was conducted by applying Monte Carlo simulation. The predicted results of the two methods were compared.