Research On Fatigue Life Prediction Of Key Components Of Pumping Unit Based On New Field Strength Method Model

The beam pumping unit which is a large,repairable and complex mechanical system is the main equipment of lifting crude oil from underground to ground.The mechanical fatigue is the main failure mode of the pumping unit because it often works under the high amplitude and high frequency alternating load.Pumping unit works in the wild with poor working conditions all the year round.Fatigue fracture of its components occurs frequently.The failure of some key components may cause the failure of the whole machine,which not only halts production but also endangers staffs around and finally brings huge economic losses to oilfield.Therefore it is necessary that we provide a reference for the replacement of the components of pumping unit by predicting the fatigue life of the key components.In addition,the process of fatigue life prediction is complex,which makes it difficult for oilfield staffs to learn.So the development of the fatigue life prediction software,which can simplify the operation and improve the efficiency of fatigue life prediction,is meaningful.This paper researchs around the topic,the fatigue life prediction of the key components of pumping unit.The main contents and conclusions are as follows:(1)Summarized the characteristics of the traditional fatigue life analysis method.After summarizing the characteristics of the traditional fatigue life analysis method like the nominal stress method,the local stress-strain method,the energy method and the volume method,it comes to a conclusion that the traditional fatigue life analysis methods have more artificial hypothesis which is not in conformity with the fatigue mechanism and as a result,the prediction accuracy is not high.So they are not suitable for pumping unit fatigue life prediction.(2)Analyzed the stress field intensity method.After summarizing the basic principle of the stress field intensity method and comparing with the traditional fatigue life analysis method,a decision was maked that the stress field intensity method would be used to predict the fatigue life of pumping unit.The reason is that the stress field intensity method takes many factors into consideration,which agrees well with the fatigue mechanism and is suitable for the high cycle fatigue of pumping unit.In addition,much attention was payed to the determination of diameter and numerical method used in the stress field intensity method.(3)Brought forward a new model of stress field intensity method.Pointed out the problems existing in the original field intensity method,then putted forward a new model of the stress field intensity method.In this model the stress contour line was proposed as the boundary of the damage zone and a new mathematical model for stress gradient was constructed.The determination of the damage zone and the direction angle were given detailedly.The results of examples show that this new method’s damage zone can vary with the load amplitude and is closer to the realistic shape and size of the damage zone.The new weight function can more accurately introduces the contribution of the points in the damage zone to the peak stress.(4)Putted forward a new technology of ANSYS secondary development based on the Qt,then developed a fatigue life prediction software of pumping unit key components.The core interface technology and auxiliary data technology between Qt and ANSYS were developed,which solved the problem of the interface between Qt and ANSYS and realized the data transmission.The friendly human-computer interaction interface was designed.Finally,the fatigue life prediction software of pumping unit was developed by encapsulating ANSYS and the stress field intensity method.(5)Predicted the fatigue life of the pumping unit key components based on the stress field intensity method.The original stress field intensity method and the improved stress field intensity method were used respectively to predict the fatigue life of the pumping unit key components,then compared with the statistical life on oil field.The results show that the prediction accuracy of the improved stress field intensity method is higher than the original stress field intensity method and the improved stress field intensity method can be used for fatigue life prediction of pumping unit.The operation process of the software show that the software is easy to operation with high prediction efficiency.