Abstract
This paper outlines the characteristics and field verification of a remote sensing technique developed to detect localized abnormal pipe wall stress by mapping variations in the magnetic field around pipelines. Corrosion, cracks, metallurgical defects and external forces on a pipe resulting from influences such as ground movement lead to areas of increased localized stress in pipelines that are under pressure. A direct relationship has been mathematically developed for relating magnetic field characteristics to the magnitude of this stress. The method is non-invasive and reports the geometric center of areas of localized stress in Megapascals, a 3-dimensional mapping of the pipeline route including depth of cover, changes in wall thickness and diameter and location of casings all to centimeter accuracy.
The inspection method takes a revolutionary approach to integrity management by monitoring stress without measuring the changes in mass of metal or the geometry of a pipe wall. Categorizing the type of defect, finding defect clock position or precise measurement of defect geometry are no longer needed for making maintenance decisions. Having a combination of defects such as cracks and dents at the same time can be monitored effectively and repair schedules prioritized by using this technology in conjunction with others.
Comprehensive field verifications of this inspection method have been conducted in recent years, and case studies from Europe, North America, the Middle East and China are described including a review of excavation of indications identified by this method following a survey in Europe. Observations following these excavations are detailed to demonstrate the effectiveness of the technique, notably the detection of localized stress in a pipe wall and the accuracy of its reported location. The benefits of using this method on both unpiggable and piggable pipelines are also described, in addition to its potential application for inspection of challenging lines.
