Coiled tubing(CT)fatigue is strain fatigue under the multiaxial load,so it is difficult to accurately predict its fatigue life,of which how to calculate the CT bending plastic strain under the pressure of the fluid in the tube is the key point.In this paper,the equiva-lent plastic strain estimation mathematical model of coiled tubing under the multiaxial load of bending and internal pressure was established.It is realized that both fluid pressure in the CT and defects on the surface of the CT will increase the plastic strain of the CT,the increase of the plastic strain caused by the fluid pressure in the tube increases exponentially with the increase of internal pressure,and the increase of the plastic strain of the CT caused by surface defects increases exponentially with the degree of defect damage.The amount of the internal pressure can be characterized by the ratio of the fluid pressure in the tube to the strength of the internal pressure strength of the coiled tubing.The degree of defect damage can be characterized by the ratio of the parameters such as the depth,width and length of the defect to the geometric dimensions of the coiled tubing.The mathematical model had been verified by fatigue testing in different pressure in CT.The fatigue life of CT can be estimated by the Miner fatigue accumulation linear criterion,and the factors such as welds and corrosive medium can be measured by coefficients.
coiled tubingplastic strainmathematical modelfatigue life prediction
万方数据
维普
