Characteristic of Magnetic Fluctuation of Underground Passing Pig Labeled with Magnets

Abstract

During the pigging process, a pig labeled with magnets can be effectively detected by monitoring the magnetic fluctuation (MF) introduced when the pig passes by. In order to analyze the influence of various factors on the MF, the principle for magnetic fluctuation detection (MFD) is described, and a detection model is established here. The influence of model parameters, such as pipeline geometries, geomagnetic characteristics, as well as permeability of pipeline, on the magnetic anomaly distribution along the measured line is analyzed. The study reveals that with the increase in pipeline parameters (thickness, permeability, and outer diameter), the MF detected decreases. The pipeline length will have little influence on the MF. With an increased number of magnets, the MF increases while remaining almost unchanged at two ends of the measuring line. Attention should be paid to the installation of magnets to ensure the consistency of the magnetic moments. With the increase in geomagnetic intensity and declination, the MF will be almost unaffected, while the change of geomagnetic inclination will introduce an obvious change to the MF. In field application, measuring points can be set along and above the pipeline with a certain interval. From the magnetic anomaly measured, it can be determined whether the pig has passed by the point or not.