Fatigue Life Experiment Of Coiled Tubing&Research In Evaluation

The technology of Coiled tubing known as "Universal Operating Equipment" involved in its wide range of applications,coiled tubing(CT)in the process of each job bear the plastic deformation at least six times.After several job,these deformation leads to lowcycle fatigue,which is a continuous tube of typical failure modes.So the prediction of the fatigue life is very important.In this paper,the coiled tubing deal with the complex state of the underground work.The CMT5105 which is a test machine of electronic universal tensile designed a special pressurized equipment,fixtures,molds,bend,straighten the workpiece and other test devices,which carried out 2-3/8",1-1/4"non-destructive and a typical initial damage test.By consulting the literature and field research and statistics,summed up the three failure modes of coiled tubing:Deformation of fracture failure,partial perforation failure to come to affect the coiled tubing fatigue life of six geometric parameters(thickness,the ellipticity,depression,depth,pits or holes,the axial length,the circumferential length and depth).According to Coiled tubing working status established ground coiled tubing(through the rolls,guide frame,into the head office),model and calculation method from the state of the working process,in order to get the bending stress axial stress and hoop stress;and formed a spiral bending analysis of coiled tubing in the underground,the coiled tubing spiral bending of the bending stress.Based on fatigue experimental data of coiled tubing,Failure model was created a different form of the initial damage of coiled tubing,coiled tubing ovality,wall thickness and defect geometry size with work stress and strain,the number of cycles change the formula.Three-parameter power function of energy law establish a non-destructive and damage coiled tubing fatigue life prediction model and calculation formula of the coiled tubing in the initial damage conditions(including ovality,wall thickness,the surface of the local pit,did not penetrate axial and circumferential crack)fatigue life calculation method.Comparison with experiment,theoretical approach based on established theoretical calculations on the six sets of specimens.The experimentally measured bend straightened number of cycles with the theoretical calculation results in line with rates greater than 80%,the theory of damage values(ellipticity,wall thickness,surface local pit,did not penetrate the axial and circumferential cracks)and the experimental results relative error is generally less than 10%.Three wells testing(La gas wells 106,La gas wells 108,wall thickness and ovality value of the South 1-11-P023 wells),as well as theoretical analysis of this project method calculated the coiled tubing wall thickness and oval The degree of value shows that the relative error is generally less than 20%.The fatigue life in accordance with established theory on the coiled tubing fracturing,acidizing,flushing,gas lift working condition when the remaining fatigue life will predict,and provide a theoretical for the site safe and reliable construction.