On the basis of the metal-magnetic-memory (MMM) effect, a three-dimensional high-precision non-contact pipeline magnetism-based stress inspection (PMSI) technology is developed for trenchless inspection of buried pipeline defects. This technology is a new non-destructive testing technology, which can find the possible stress concentration area (SCA) along the buried gas transmission pipeline. Hence, we could further judge according to the testing data that the stress concentration is caused by the overpressure which results from whether the pipeline external load at the potential landslide of the soil or serious metal loss such as corrosion defects. The stress inspection method determines the relative risk of defects by directly quantifying the change level of stress, rather than calculating the geometric parameters (length, width, height) of defects. The PMSI was carried out on a 10.3 km LNG pipeline and two level-II SCAs were found. A comprehensive index F was defined to evaluate the severity quantitatively and judge the grade of the defect status as well as the sensitive. Thus, the relative stress and thereby the safety state of the pipeline are judged, and then the precise position of the relatively serious section on the pipeline is determined.

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