Reference for citation: Kulak S. M., Neradovsky D. F., Probotyuk V. V. Patterns of magnetic stray field distribution along the surface of an underground main gas pipeline and an elastically bent pipe. Journal of Instrument Engineering. 2024. Vol. 67, N 2. P. 178—185 (in Russian). DOI: 10.17586/0021-3454-2024-67-2-178-185.

Abstract. In order to establish the causes of the periodic alternating distribution of the magnetic stray field along the surface of an underground gas pipeline, the strength of the magnetic stray field H on the surface of an extended pipe made of St20 steel with an elastically bent section in the form of an arch is investigated. H measurements are carried out both tangentially to the pipe and normal to it. It is been established that the alternating stresses arising in the wall of an elastically curved pipe are the cause of its uneven and inhomogeneous magnetization in the Earth’s magnetic field, and, consequently, the periodic alternating change in the magnetic stray field measured on its surface. The “wavelengths” of the changes in the normal and tangential components of the scattered magnetic field strength H of the pipe are shown to be comparable to the length L of the arch created on it, and their maxima are shifted relative to each other by half L. It is concluded that sections of underground oil and gas pipelines (arches), experiencing bending deformations, are magnetized in the Earth's magnetic field non-uniformly, which causes periodic changes in the magnitude and direction of the magnetic stray field on their surface. The stress state in such areas changes sharply compared to the calculated one, the state of the insulation deviates from the norm, and as a result, preconditions arise for stress-corrosion destruction. It is proposed to monitor changes in the position of the main pipeline in the ground during operation relative to the design one, as well as to monitor the seasonal dynamics of the stress state in the area of flexural deformation using the magnetic method in order to assess the service life and bearing capacity.

Keywords: magnetic stray field, deformation, stress state, gas pipeline, magnetoelastic effect, gas pipeline archway

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