Studies On Magnetic Memory Detection Test Of Fatigue Damage And Remaining Life Prediction Method Of The Coiled Tubing

Fatigue failure is the most common failure mode of Coiled Tubing(CT),Researches on the technical method that can accurately identify and anticipate the abnormal state of the CT fatigue damage are of great significance to improve the efficiency of its use,prevent sudden fatigue fracture and ensure the safety of operation.Combining with the CT bending fatigue test,this paper studies the state of CT fatigue damage magnetic memory testing characterization method and the residual life prediction model based on test data.This thesis comprises following studies:(1)In view of shortcomings of the existing CT fatigue test equipment,the lifting mode of straightening template and the full-size CT seal structure are improved,by which the test operation is simplified.A method of CT fatigue test under the action of multiple factors is proposed.(2)CT fatigue damage testing experiment under different internal pressure,bending deflection and bending frequency is carried out,by analyzing the relationship between magnetic memory signal and degree of fatigue damage,magnetic memory characteristic parameters that can characterize the fatigue state of the tubing is determined.The results show that,with the increase of internal pressure or bending deflection,the fatigue failure and fatigue life of CT are shortened;While the lower bending frequency of 6-20 times/min has little effect on the fatigue damage of CT.(3)The timeliness of CT magnetic memory detection is investigated.The characteristics of the magnetic memory signal after the test are analyzed.Considering the characteristics of CT intermittent use in practical engineering,the bending fatigue loading test of CT sample after natural aging was secondly performed,and the magnetic memory signal changes during the test is analyzed.The results show that after two weeks of natural placement,the magnetic memory signal decreases,and after five weeks,the magnetic memory signal decreases to the minimum and stops changing.However,the timeliness of CT magnetic memory testing has little effect on its fatigue damage.(4)The grey prediction method of CT fatigue state based on magnetic memory test data is established while magnetic memory characteristic parameters obtained by the test are taken as the original samples;According to the theory of Miner linear fatigue accumulation,the cycle times are reduced to fatigue damage degree,and the prediction model of CT fatigue life is put forward,the accurate grade is close to "good" by the posterior error calculation,which satisfies the requirement of accuracy,and provides a new way to predict the residual life of CT through magnetic memory test method.