Fundamental study on inspection of steel pipe covered with insulator in oil complex

In a steel pipe composed of a three layer structure, an insulator material is rolled around the initial pipe and another pipe is rolled around the whole pipe used in an oil complex. The insulator material becomes an obstacle for inspecting initial pipe. Thus, in this study, a new inspection method is proposed. An ultrasonic waveform is inputted into the transport pipe that is used for transferring fluid such as oil using a transducer. Its propagation path was inspected and it was found that the wave behaves as a cylindrical wave known as the Lamb wave. Two fundamental experiments for a steel plate and a steel pipe were carried out for its verification. Cross-correlation analysis was used to obtain propagation time, then propagation velocity was calculated. Whether both can be regarded as an equivalent of the theory was confirmed by experiments for propagation velocity in each frequency when there was no welding on the pipe structure.