Wallace, G.; Pohl, P.; Hutchinson, E.F. 1998 XClad. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 98/10 13 p.
Abstract: A description is given of the XClad instrument for the non-invasive inspection of pipes encased in insulation cladding. The instrument is designed to detect both surface corrosion of the pipes and wet insulation. The corrosion technique is based on recording the shadow cast by the pipe surface intercepting a narrow fan beam of x-rays. Because the corrosion is normally either on the top or bottom of the pipe, a dual system of x-ray sources and detectors is used which then afford measurements of deviation from a set pipe diameter. Wet insulation is more likely to occur at the bottom of a pipe, and the attenuation of the full unshaded x-ray beam is used to detect this. A prototype instrument, XClad, has been build to exploit this technique. It consists of a unit which rolls on the clad pipe, and a remote handheld control unit. Both are battery-powered, incorporate microcontrollers, and communicate by a digital radio frequency link. The remote unit has an LCD display and, in addition to the numerical information, the split screen provides rolling images of the pipe surfaces which intersect the x-ray beams. This makes the detection of external pipe corrosion immediately apparent. Sensitivities down to 0.1 mm had previously been demonstrated. (auth)