In-line inspection technology of oil and gas long-distance pipeline based on alternating current field measurement

Alternating current field measurement (ACFM) has advantages of fast inspection speed, high efficiency, sensitive inspection, and easy quantification. In this study, a probe based on ACFM has been carried out, trying to inspect cracks on the inner wall of pipeline with high precision. An inspection tool which is working according to ACFM is developed in order to determine the stress corrosion cracking. The lift-off distance and excitation frequency parameters are optimized, and the influence of uneven magnetic permeability of the pipeline on the test results is analyzed. In addition, experiments are carried out to test the practicality of the tool. The minimum axial crack length that the probe can detect is 15 mm and the minimal depth is 1 mm. The research results show that the probe has the ability to quantitatively evaluate the axial cracks on the inner surface of the pipeline, which has certain guiding significance for the design and development of the AC electromagnetic field inspection probe.