The C-SCAN system is a two-part system comprising a Generator and a Detector. The Generator is connected to a pipeline at a convenient point (CP test post, valve etc) and a remote earth (earth spike or ground point).
The generator injects a controlled current onto the pipeline, which will decrease with distance, as the current leaks through the coating. This current produces a magnetic field that is received by the Detector.
The Detector measures the characteristics of the magnetic field, giving the following information:
- Depth (if overhead)
- Cover (the depth to the top of the pipeline if the diameter is entered)
- Distance to pipeline (if not overhead – up to 10m depending on signal strength)
- Angle (the angle of the pipeline to the Detector)
- Current (the current remaining on the pipeline below the detector)
The current value and distance between survey points is used to calculate Attenuation, in milli-Bels/metre (mB/m which is one-hundredth of a deciBel, dB). The attenuation is an indication of the coating quality. Higher values indicate degraded coating.
If the pipeline diameter, wall thickness, coating type and soil resistivity are known, then an estimate of average coating Conductance can be given – see Conductance.