Stress Concentration Tomography
3-D Line Locating Ltd.; along with Speir Hunter Ltd offers a non-invasive pipeline inspection service based on Stress Concentration Tomography (SCT), which is a sophisticated and patented system that brings together state-of-the-art electronic engineering and geophysical modeling to assist in the provision of a commercially effective and comprehensive solution for integrity managers. SCT is a passive magnetic sensing tool that collects the magnetic data of a target pipeline and then analyzes it for self magnetic-flux leakages in the pipeline wall, which are know as Stress Concentration Zones(SCZs). Using this stress-profile information, integrity managers can make informed decisions regarding the safe operation of their pipelines.
SCT™ identifies the location and the estimated stress of each SCZ (Stress Concentration Zone) on a pipeline. An SCZ is an accumulation of localized stress in the pipeline wall that is greater than the nominal hoop stress of the pipe. SCZs are caused by corrosion, metallurgical defects resulting in wall thickness loss and mechanical sources such as twisting and sagging from poor support and ground movements. In turn, the increased localized stress within an SCZ prompts a localized realignment of magnetic domains which appear as an anomaly in the background magnetic field.
SCT™ identifies the particular magnetic signatures associated with different types of localized stress in the pipe and can differentiate between unexpected changes in stress caused by, for example, corrosion and expected changes in stress caused by girth welds. After mathematical processing, localized stress increase, no matter what the source, generates the same waveform and SCT™’s automated search algorithms can identify their locations to cm accuracy. Algorithms also have been developed and trained to examine the characteristics of each magnetic signal within the SCZ to estimate the quantity of stress causing them. Significantly this is done directly through analysis of magnetic data without any intermediary analyses of wall thickness loss calculations, any need to excavate, calibrate, verify or alter the pipeline in any way prior to or after inspection.
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