A guided wave is created by restricting the propagation of sound or electromagnetic waves in one or two dimensions. A particular frequency of the wave can travel -- with little attenuation -- for very long distances. Changes in the dimensions of the restrictions can cause partial reflections that can be analysed to find the location of the change. -SBC
In 1998, pipeline operators began to use a form of instrumented inspection technology that has evolved into what is known at present as guided wave testing (GWT), which detects changes in the cross-sectional area of the pipe wall. Test equipment software provides a percent estimate of the change (gain or loss) and is often expressed as percent estimated cross-sectional loss. These changes include metal loss indications, anomalies, or defects such as corrosion, gouges, etc., or metal pickup such as welds, valves, flanges, etc. When properly applied, GWT can monitor cross-sectional loss over time, and provide economic benefits and efficiencies in integrity assessments.