World Pipelines Magazine, The magnetic dimension

Frequent inspections of oil and gas pipelines are critical to ensure their operational safety, to protect people and the environment. A significant portion of the global network, estimated at 30%, cannot be inspected through traditional techniques, i.e. inline inspection (ILI). The alternatives currently available on the market are not satisfactory either from an efficiency or from an operational standpoint. Skipper NDT has therefore developed a novel, contactless magnetic technology, with proprietary and patented field protocols designed to ensure operational safety while optimising maintenance costs. On one hand, it aims at identifying stress concentration zones as well as metal defects on pipelines, such as dents and corrosions. On the other hand, it precisely geolocates the pipeline network. The results observed in real field conditions were confirmed by an R&D programme launched in collaboration with the French energy majors TOTAL and TEREGA.

Skipper NDT magnetic contactless technology
Villari effect

Magnetic non-destructive testing technologies have received a great deal of interest and are extensively adopted to ensure the operational safety of pipelines. Over the last few decades, this subject has been investigated by many researchers and several techniques have emerged, including magnetic flux leakage (MFL), magnetic Barkhausen noise (MBN), magnetoacoustic emission (MAE), and stress induced magnetic anisotropy (SMA). Unlike approaches which may be ascribed to active magnetic test methods, in which a strong magnetic field is applied, the large standoff magnetometry (LSM) method is considered a passive one. It uses the natural surrounding magnetic field as stimulus to locate stress concentration zones as well as potential metal defects on pipelines.

This disruptive technology, optimised by Skipper NDT through four years of R&D, is based on the inverse magnetostrictive effect, also known as the Villari effect. An applied stress causes a change in magnetisation of ferromagnetic materials (Figure 1). This change can be remotely measured in the magnetic field surrounding the steel pipeline, using magnetic sensors capable of detecting weak magnetisation changes. The LSM technique offers several advantages; non-intrusive, above ground inspection combined with a precise geolocation of the structure including its depth of cover.