Analysis Of Coiled Tubing Fatigue Life Based On Finite Element Method

Coiled tubing is a non-thread long tubing,repeatedly bending deformation occurs in every operation,prone to fatigue failure,resulting in increased application of coiled tubing costs,therefore it can not be used on large scale.In this paper,a three-dimensional finite element model of coiled tubing is established,and the fatigue life of coiled tubing is analyzed based on finite element method,which provides reference for engineering use.Considering with the actual situation of coiled tubing ground work,this paper simplifies the coiled tubing as a curved beam,utilizes the theory of bending deformation of the beam,combining the elastic plastic deformation of coiled tubing,deduces the bending moment and tension calculation formula of the coiled tubing in the drum,and the elastic-plastic limit bending moment and elasticity limit bending radius.Considering with the Finite element analysis method,a three-dimensional finite element model of coiled tubing is established,and the fatigue life of coiled tubing with different internal pressure and wall thickness is analyzed,and the results are compared with the experimental results,the finite element method is basically identical to the result obtained,and the correctness of the fatigue life of coiled tubing is analyzed by fem.Finally,the fatigue life of the non-damaged coiled tubing with different diameters and wall thicknesses under different internal pressure and axial force is analyzed.and the fatigue life of coiled tubing with different elliptical degrees,crack directions,crack length and wear degree,the variation regularity of the fatigue life of coiled tubing and damaged coiled tubing under different conditions is obtained.The results show that the fatigue life of coiled tubing increases with the increase of the diameter of coiled tubing and the wall thickness,and the fatigue life of coiled tubing decreases by about 10% when axial force increases 5 times.With the increase of internal pressure,the fatigue life of coiled tubing decreases gradually;with the increase of ellipse degree,crack and abrasion degree,the fatigue life of coiled tubing decreases obviously,the effect of cracks on the fatigue life of coiled tubing is more obvious.The fatigue life of coiled tubing with axial crack is about 8 times as long as the coiled tubing with circumferential crack.