Allowable Stress Calculation and Fatigue Life Prediction for H-Class Sucker Rods

In order to effectively use the H-class sucker rod,the method of allowable stress calculation and fatigue life prediction was studied.Using the indoor tensile strength test as a starting point,the ratio of tensile strength to yield strength was calculated,by which the calculation parameter for the maximum API allowable stress of H-class sucker rod was adjusted from 0.562 5 to 0.716 3.In addition,stress-fatigue plots of H-class sucker rod by fitting method were developed,so as to determine the ultimate fatigue stress of the sucker rod at the stress ratio of 0.1.By testing the fatigue performances of H-class sucker rods in different media and different stroke frequencies,the relationship among water cut,stroke frequencies and service life of the sucker rod were obtained.The innovative techniques for the calculation of allowable stress and prediction of fatigue life of the sucker rod were applied in 10 wells in the Xingnan Area of the Changqing Oilfield,and the results showed that the stress conditions of the H-class sucker rod could be improved through the optimal design,and tap the potential of the sucker rod,so as to meet the demands of field application for stresses and service life.