Optimization of magnetic anomaly detection with single-axis sensor for pig locating in low latitude areas

When a pig mounted with permanent magnets gets stuck in the pipeline, it can be located by detecting the magnetic anomalies on the ground using a single-axis magnetic sensor. In order to collect the magnetic anomaly efficiently through single-axis magnetic sensor, a geometric detection model and calculation method for single-axis magnetic anomaly detection is established in this paper. The distribution of magnetic inclination and declination of the measuring points is obtained. The results indicate that the magnetic inclination of all measuring points vary within a small range of 2°, and this value is highly dependent on the magnetic sensor which is configured aboveground around the geomagnetic inclination. However, the magnetic declination at different points of detection surface is subject to the geomagnetic components and the Y-axis component of the magnetic field of magnets. The magnetic declinations distribute irregularly and vary in a wide range. Therefore, to achieve a high-efficiency detection with the single-axis sensor, the sensor shall be placed in such a manner that the magnetic inclination thereof coincides with the geomagnetic inclination. The magnetic declination of the sensor can be calculated using s, the superposed Y-axis component induced by the permanent magnets, and the corresponding formula given in this paper. The article demonstrates the feasibility of locating a blocked pig in the pipeline based on the single-axis magnetic anomaly detection. It will have a practical significance in guiding the engineering detection. © 2019