Residual stress measurement of high-grade steel pipeline via ultrasonic method and verification by small hole method

With the gradual formation of China's oil and gas pipeline network, pipeline safety assessment is increasingly important. On this basis, the principle of acoustic elasticity and the ultrasonic stress measurement technology were briefly introduced. In order to meet the needs of the service safety evaluation of high-grade oil and gas pipelines, a non-destructive residual stress measuring system with ultrasonic method was developed. Besides, the near-zero stress calibration technology of test blocks was also developed, which is to linearly cut the annealed zero-stress test block for further stress release, so that the zero stress can be calibrated accurately. Further, curved probes were designed according to the actual requirements of inspection. The study on nondestructive residual stress measurement of X80 pipeline was carried out with the abovementioned system, and the results were verified with the small hole method, which indicate that the test accuracy is reliable and repeatable. Thus, the study provides a good technical means for online stress measurement of oil and gas pipelines, as well as an effective technical method for pipeline operation, repair and evaluation.