Damage Analysis And ACFM Application Research In Tools Thread Of Raise-boring

By means of theoretical derivation,numerical simulation and experimental analysis,this paper systematically studies the four stages of drill pipe stress research under reaming condition,thread stress-strain law analysis,the relationship between thread stress and crack size change,and threaded alternating current electromagnetic field test research.The main research contents are as follows:Based on the large-diameter deep vertical well engineering in complex geology,considering the factors such as the vibration load of drill bit,the interaction between drill tool and rock stratum,and accidental load,the calculation formulas of tension and torsion of reverse-well drill pipe under reaming condition are derived.Errors between theoretical and measured values of tension and torsion 4%of the errors are mainly affected by the characteristics of drilling tools,geological conditions,site construction conditions,artificial operation,mechanical losses and other factors.By means of finite element numerical simulation,the stress and strain values of the threads of the male and female joints of the reverse well drill pipe under the action of tension and torsion are calculated.It is concluded that the locations of the three threads of the large end side of the drill pipe joint,the three threads of the mother joint and the small end side of the drill pipe joint are the vulnerable dangerous areas for crack initiation and development.By means of finite element numerical simulation,an elliptical pit crack is established at the root of the first thread and the second thread of the reverse drill pipe joint,and the stress and strain around the elliptical pit crack with different lengths,depths and angles are simulated and calculated.The variation rule and trend of stress and strain around elliptical pit crack with the change of crack length,depth and angle size parameters are studied.It is concluded that stress concentration occurs at both ends of the long axis of elliptical pit crack and increases with the increase of the length and depth of elliptical pit crack.At the same time,it is concluded that the change of stress concentration is not proportional to the change of crack angle of elliptical pit and that the phenomenon of stress concentration appears at the boundary between crack and thread groove.The latest ACFM is used to detect the artificial cracks in the thread of the common joint of reverse well drill pipe.Through ACFM,the existence of artificial cracks can be detected,and the artificial cracks with different size parameters can be distinguished by₍?3? and₍?5? curves.It is concluded that the₍?5? peak-valley amplitude of the flux density component is negatively correlated with the length of the crack groove,and the₍?3?-curve Valley amplitude of the flux density component is positively correlated with the depth of the crack groove.The research results of this paper have certain application value in the calculation of load on reverse well drill pipe under reaming state,the analysis of crack damage at thread,and the visualization research of thread crack detection.