Experimental Study On The Low Cycle Fatigue Life Of Coke Drum Material 15CrMoR

Coke drum is the key equipment of the delayed coking process. Due to its poor working conditions, barrel and girth weld prone to bloating and cracking affects the safe operation of equipment at repeated alternating load and the changing temperature condition. Therefore, So choose appropriate model to simulate the coke tower material low cycle fatigue life prediction is very important.Butt-weld specimen has been made for coke drum material 15 CrMo R. For both parent and weld materials, uniaxial tensile tests and uniaxial ratcheting tests have been conducted under different temperatures. The OW-II kinematic hardening constitutive model has been used to predict the material ratcheting effect using the experimental data obtained. Test results show that the OW-II model can well predict ratcheting strain rates for the stable period. Based on the obtained uniaxial tensile test data, basic parameters for predicting low cycle fatigue life have been obtained. The MSRS model has been used to predict the fatigue lives of the parent material and weld metal. The predicted results are within the 2 times error band and are uniformly distributed on both sides of 45 ° line accurately. Furthermore, the ratcheting strain rate and the strain amplitude for the stable period are obtained for the parent metal and the weld metal respectively by the OW-II kinematic hardening constitutive model under the same conditions. The MSRS model predicts that the fatigue life of the parent material is significantly lower than that of the weld metal and during the stable period the ratcheting strain rate of parent material is significantly higher than that of the weld metal.Multiaxial ratcheting tests were conducted at room temperature. The effects of different load paths, shear strain amplitude, mean stress and stress amplitude have been researched. The equivalent strain approach, critical plane approach, energy approach and considering ratcheting strain approach have been used for predicted fatigue life. By comparison, consider ratcheting strain correction term of Gao-Chen model gave the best prediction.