Development of an optical system for geometric inspection of external surface of pipelines

This paper presents a new configuration of an optical measurement system using fringe projection for 3D shape measurement using active photogrammetry. The system was optimized to measure 3D geometries of external surfaces of pipes. The system was mainly designed for periodic inspections of pipelines submitted to environmental induced corrosion and local dents. It has a compact design and it is suitable to inspect pipes with diameters 250 mm (10”) and up. The software is able to compute geometric parameters of the inspected area like depth, volume and length of the damaged areas. The developed system uses a special compact fringe projector composed of an acrylic tube printed with two sinusoidal fringe patterns with two different frequencies, a set of LEDs forming a line light source and a special phase shifting approach with absolute phase calculation procedure. The three-dimensional surface of the pipe is measured and displayed using virtual reality techniques. The measured area is 300 mm x 200 mm. The paper also presents results of quantitative evaluations as well application results.