Analysis of Forward and Measured Magnetic Anomalies of Submarine Pipeline

The theoretical calculation model of magnetic anomaly of submarine pipeline is derived by Poisson formula method of gravity and magnetic field. For two known submarine gas pipelines, the forward simulation calculation and sea test verification are carried out. The forward results show that positive magnetic anomalies with a span of about 20.0 m and up to 329.8 nT and 362.4 nT respectively are produced on an observation plane of about 8.0 m from the submarine pipeline. The measured distribution spans of magnetic anomalies of submarine pipeline are consistent with the results of forward modeling, but the details of their distributions are different. Both positive and negative magnetic anomalies exist. By analyzing the distribution characteristics of the extreme points of magnetic anomalies, it is speculated that the thermal residual magnetism at the junctions of the pipeline may lead to the detailed characteristics of the measured magnetic anomalies.