Error Analysis and Calibration for a Novel Pipe Profiling Tool

Integrity of industrial pipework is ensured through routine inspection. Internal visual inspection tools are capable of characterising degradation in the form of corrosion, pitting, erosion and cracking. The accuracy of such inspection systems has a direct impact on decisions regarding the remaining lifetime of the asset. By minimising error margins, the asset may be operated with confidence for longer, with less uncertainty. This paper considers a probe system consisting of a laser profiler and camera that produces a textured 3D model of the internals of 2 - 6 inch pipework. The accuracy of the system is defined by the ability to extract laser projections from an image as it travels down the pipe, to accurately reconstruct these projections into 3D and to estimate the probe trajectory as it travels through the pipe. This paper presents an error model of the laser profiler. It then presents a novel calibration routine to reduce the error caused by misalignment and tolerances during fabrication of the system. A key advantage of the proposed calibration technique over alternatives is that we can calibrate for errors without manually adjusting the probe, which enables fabrication of a smaller more robust measurement system. In lab-based trials our calibration technique reduced peak sizing errors from 2.7 mm to 0.14 mm in 120 mm diameter pipes.