循环弯曲和内压作用下连续油管壁厚变化规律试验研究

连续油管作业期间，除受到循环弯曲载荷作用外，管内还常受内压作用，从而产生严重的塑性变形，会出现壁厚减薄和截面椭圆化，而大多数情况的疲劳裂纹都是源于壁厚减薄处。采用自制的连续油管疲劳试验机进行室内试验，模拟全尺寸连续油管在实际工况中受到的循环弯曲和内压作用，利用超声波测厚仪检测不同循环次数下的油管壁厚值。在300mm最大弯曲行程、20MPa内压下，连续油管壁厚变化率成抛物线下降趋势，得到壁厚变化率与循环次数拟合关系，可为预判连油管工作寿命提供依据。

Experimental study on the change of wall thickness for coiled tubing under cyclic bending and internal pressure

During coiled tubing operations, in addition subjected to cyclic bending loads, it often subjected to the internal pressure in the pipe. That will result in severe plastic deformation and appear wall thinning and cross-sec- tional ovalization, most cases of fatigue cracks are derived fromwall thickness thinning department. Laboratory test was conducted by homemade coiled tubing fatigue testing machine to simulate coiled tubing in the actual working conditions by cyclic bending and internal pressure, and the values of wall thickness for cycles tubing under different cycle numbers were measured by ultrasonic thickness tester under the 300ram maximum bending trip and 20MPa in- ternal pressure conditions, the changing rate of coiled tubing wall thickness showed a parabolic decline, and the fit- ting relation between changing rate of wall thickness and cycle number was obtanined. It can provide the basis to predict even the tubing working life.