Pipeline Inclination Measurements Based on a Spherical Detector With Magnetic Proximity Switches

Spherical detector (SD) is a novel and promising magnetic shielding-based approach for long subsea pipeline orientation and localization with low risk of blockage. As not all the shielding factors can be accurately obtained, large errors of inclination measurements can be caused. This paper proposes a new inclination measurement method without utilizing the magnetic shielding model of the pipeline. A tiny magnet and a Hall sensor is installed on the SD to form a magnetic proximity switch (MPS) to determine the moment when the sensitive axis of the accelerometer perpendicularly points to the pipe wall. The acceleration value at that moment and the phase difference between the acceleration and magnetic signals are used to calculate the pipeline inclination. Numerical simulations are carried out to analyze and design reasonable structural parameters of the carrier for fixing the MPS and the accelerometer. The carrier can be driven to roll inside the pipe to mimic the rolling of the SD. Through measuring a couple of pipe inclinations both upward and downward, it is demonstrated that the proposed method can distinguish the rising and descending pipe sections, and most of the measurement errors are less than 0.5 degrees over the range of 0 degrees-90 degrees. In case if the MPS is not on the middle circle plane of the SD, a circumferential MPS array can be deployed in field applications to cover a large range and obtain a small liftoff value, so that the proximity moment can still be captured by at least one MPS.