Research on Axial Stress Ultrasonic Measurement Method for In-service Pipes Based on Bi-directional Probe

Abstract There is a linear relationship between the change in ultrasonic critical refraction longitudinal wave time of flight and the change in stress, and the change in ultrasonic time of flight of the outer wall surface of the in-service pipe and the zero stress calibration specimen can be measured to calculate the axial stress of the pipe during operation. The difference between the calibration specimen and the measured pipeline steel batch and yielding degree will lead to inaccurate ultrasonic time of flight measurement results of zero stress, which in turn will reduce the reliability of stress measurement results. In order to solve the errors caused by calibration problems in the ultrasonic stress measurement process, this paper firstly deduces the calculation formula for axial stress ultrasonic measurement in the bi-directional stress state of the pipe wall, and proves that axial stress measurement requires both axial and circumferential ultrasonic time of flight measurements. Preparation of X80 spiral welded seam steel pipe axial and circumferential plate specimens, the first measurement of ultrasonic time of flight in different directions under zero stress state; followed by axial and transverse plate specimens one-way tensile test, respectively, to calibrate the relationship between stress and ultrasonic time of flight of the two specimens; finally, based on the results of anisotropic ultrasonic time of flight measurement of pipeline steel specimens and axial and transverse plate specimens one-way Finally, based on the anisotropic ultrasonic time of flight measurement results of pipeline steel specimens and the calibration experimental results of axial and transverse plate specimens in one-way tensile test, an axial stress ultrasonic measurement method is proposed for the bi-directional stress state of pipeline wall. The usability of the measurement results of the method was verified by pipeline pressure testing using bi-directional ultrasonic probes.