Study on Pipeline Spanning Detection Using Magnetic Anisotropy

Subsea pipelines often lose foundation soil support due to ocean current erosion and form spanning. Spanning greatly increases the risk of pipeline fracture. When a subsea pipeline has spanning, it is often accompanied by characteristic changes in its pipe wall stress, pipeline deflection, and pitch angle. In turn, we can analyze the three parameters to get the spanning state of the pipeline. Wherein, around using stress to detect pipeline spanning state, this paper carries out two parts of research work. (1) We conducted a stress analysis on the free-span pipeline. The results show that the stress distribution has a strong distinct relationship with the pipeline spanning state. (2) We proposed and developed a steel plate stress detection scheme based on the induced voltage method. The results show that the steel plate stress has a good linear relationship with the induced voltage of the receiving coil on its surface, and the sensitivity can reach 1mv/MPa. Therefore, the AC magnetic anisotropy measurement of stress can reliably identify the stress distribution of the spanning pipeline.