Large standoff magnetometry (LSM), a novel screening technology, has shown strong industry relevanc e in s everal pipeline integrity inves tigations . LSM is used to detect changes in the magnetic field of a pipeline due to changes in the magnetic susceptibility of steel. These changes are known as inverse magnetostriction (a.k.a. the Villari effect) and occur when a ferromagnetic material (steel) is subjected to mechanical stress, such as the presence of stress on the wall of a pipeline. Geometric anomalies (ovalities, dents, wrinkles), hoop stress, ground and slope movement, bend strain, thermal expansion, cracks, and material defects are examples of potential sources of stress that LSM can detect from aboveground.
This paper summarizes the use of LSM as a complimentary tool in several pipeline integrity assessments conducted on oil and gas pipelines, in this case, to pinpoint a lost inline inspection pig and to identify dents, cracks, buckles, slope movement, casing ends, unknown valve locations and other pipeline integrity and direct assessment applications. Ongoing development programs and lessons learnt from practical, real-life projects and validations of the technology are presented to demonstrate the effectiveness of LSM for pipeline integrity investigations.
Large Standoff Magnetometry (LSM) is an emerging, innovative, non-intrusive, aboveground, indirect inspection technology that is currently employed to pinpoint stress concentration zones. This is very useful on difficult-to-pig pipelines that can be challenging for other robust inspection methods. LSM is a non-contact, passive, geo-magnetization flux leakage measurement technology for identifying and locating elevated levels of stress through the measurement of the magnetic field surrounding steel pipelines, regardless of the ability to pig or whether the pipeline is buried, exposed, or elevated. A change in the magnetic field can indicate the presence of stress in the pipe wall. A change in materialsize, volume, type, age, etc., of a ferromagnetic material during magnetization is characterized as magnetostriction. Inverse magnetostriction, known as the Villari effect, characterizes a change in the magnetic susceptibility of a material when mechanical stresses are applied. For instance, it has been employed in the identification of unknown buried structures, such as valves, taps, etc., by measuring changes in the magnetic field across the buried structure. This change in the magnetic field due to mechanical stress is what LSM technology can detect1–3.