Monitoring the integrity of buried ageing ferromagnetic pipelines is a significant problem for infrastructure operators. Typically inspection relies on pig surveys, DCVG, CIPS and contact NDT methods that often require pipes to be uncovered and often at great expense.
This paper outlines recent developments in a novel remote sensing technique to detect corrosion, metal defects and the effects of ground movement on pipeline stress by mapping variations in the earth’s magnetic field around pipelines. Magnetostriction is the process by which internal domains inside the structure of ferroelectric materials, such as carbon steel alloys, create magnetic fields when subjected to mechanical stress. Corrosion, metallurgical defects and ground movements result in areas of increased stress in pressurised pipelines. Measurement of the remote magnetic field around a pipeline due to magnetostriction allows the measurement of stress and determines the location of defects in the pipe wall. The paper first explores magnetostriction in ferromagnetic materials and then describes how measurements of remote magnetic field can be applied to define the location of defects in operational pipelines along with case studies and the benefits of using this technique. These include considerable cost savings since no modification to the line is required, no input of energy nor change to its operational parameters is needed and, crucially, no excavations are needed to calibrate preliminary results.