Many processing plants, such as refineries, chemical plants, and electric power generation plants, use networks of pipelines. Failure of these pipelines can cause major disruption of plant operation and an unscheduled outage. To ensure safe operation of such plants, there is a need for on-line non destructive testing methods to inspect and monitor pipelines.
One effective method for inspecting and monitoring a long length of pipelines is guided wave testing (GWT) using magnetostrictive sensor (MsS) technology. A common implementation of this method uses primarily torsional waves (T-waves) that are generated in a thin ferromagnetic strip placed around and coupled to the pipe under test. If the generated waves are coupled to the pipe, the waves propagate along the pipe and are partially reflected by geometric irregularities present in the pipeline, such as welds or corrosion defects.
The reflected signals are then detected in a pulse-echo mode. From the arrival time of the reflected signal and the signal amplitude, the axial location of the irregularity and its severity are determined. In above-ground pipelines, this method can detect 2 to 3% defects over 500 feet from an MsS sensor location. The % refers to the defect's cross-sectional area relative to the total cross section of the pipe wall.
Magnetostrictive testing, although especially useful for testing pipelines, is not limited that type of testing. Magnetostrictive testing has been adapted for testing of structures of other shapes, and in general, can be used to test for defects in any shape, even to plate structures.