Analyses and verifications of magnetic shielding of long pipelines aiming for pipeline orientation measurements

So far, none of conventional magnetic shielding models can model a field long pipeline consisting of many welded short sections with different permeabilities. This paper demonstrates the magnetic shielding model of long pipelines via simulation analyses based on the finite element method (FEM) and experimental verifications of the magnetic shielding of short pipes, torus pipes, and field long pipelines. The radial and axial shielding factors of a finite pipe can be accurately calculated by the FEM. As the pipe length increases, the axial factor rapidly converges to a value less than 1, and the convergence value is independent of the pipe length because of the magnetic charges at the two ends. For a long pipeline consisting of many short sections, the averaged shielding factors over a couple of adjacent sections are equal to that of an ideal infinite pipeline, and the axial factor is always equal to 1. An “average” strategy for field pipeline orientations that employs the averaged magnetic fields and shielding factors over several sections is then proposed and demonstrated. As the geomagnetic field is taken as the absolute reference, this orientation measurement method has no risk of divergence over a long time and distance. Index Terms—cylindrical magnetic shield, magnetic fields, pipeline orientation.