How does the Villari effect identify stress on metallic pipelines?
PureHM’s Pipe Wall Assessment (PWA) technology – which uses the Villari effect to measure stress changes in pipelines – was initially developed more than 10 years ago to address gaps with tools traditionally used to assess pipeline condition, specifically related to geotechnical concerns and unpiggable pipelines.
Pure Technologies, the parent company of PureHM, developed the original PWA system to identify elevated stress conditions on unpiggable municipal water and wastewater pipelines. Originally, this was done using an acoustic technique relying on the variation of the speed of sound through a fluid column to identify sections of pipe under elevated levels of stress. While the system worked, the practical limitations of the technique limited its operational usefulness.
Pure’s research and development team then shifted focus to the phenomenon of metal magnetic memory. The ‘Villari effect’, also known as inverse magnetostriction, relates the magnetic field properties of a pipeline to the level of stress it has been subject to.
While measuring stress was tested and validated on PureHM’s SmartBall platform, researchers found that they could best measure this difference on a buried pipeline from above ground. This discovery led to the development and application of the current PWA system on PureHM’s Spectrum XLI above-ground inspection platform. Using three sensors to measure magnetic field changes, the PWA system has now been integrated into the Spectrum XLI platform, synchronizing all the magnetic readings with GPS data.
The Villari effect is the measured change in the magnetic field due to stress on an object. Any area under concentrated stress in a pipe wall will have a different magnetic signature than an area under normal levels of stress. For pipeline operators, a stress induced magnetic field change can be caused by several pipeline condition factors such as: geotechnical issues, excessive loading or poor bedding. Identifying the root cause of stress anomalies is an important part of a pipeline integrity program that can provide owners with condition information that other integrity tools – namely ILI tools – do not provide.
This above ground inspection technology is non-invasive, and can be performed in areas that an operator believes to be under stress or may be prone to geotechnical issues. PWA can also be used alongside the traditional Spectrum XLI program which also collects many other sources of inspection data including GPS/GIS, CP CIPS, DCVG, ACVG, ACCA and soil corrosivity measurements. Since 2016, Spectrum XLI PWA has been used to screen more than 250 kilometers (150 miles) of pipeline, and is an emerging solution to help operators identify areas of elevated stress on their pipeline.