Quantitative study on the propagation characteristics of MMM signal for stress internal detection of long distance oil and gas pipeline

The metal magnetic memory (MMM) detection technology has great application potential in the field of stress internal detection of long distance oil and gas pipeline due to the non-contact online detection to stress damage; however, the scientific significance of the pipeline stress internal detection results is questioned because the detection signal is affected by the medium during propagation. To study the propagation characteristics of MMM signal, a three-dimensional magnetic balanced magneto-mechanical model is set up based on magnetic charge theory. In this paper, the distribution characteristics of the scattered magnetic field in the stress concentration region are exposed and the propagation characteristics of different components of MMM signal are quantitatively analyzed. Further, the influence of different media on MMM signal propagation is compared, and a systematic experimental study is conducted. The results indicate that MMM signal shows a first-order exponential decay with increasing propagation distance. During the propagation, the tangential signal decays rapidly, and the normal signal is stable and suitable for locating the stress concentration regions. MMM signal decays faster in ferromagnetic medium than in non-ferromagnetic medium.