We present a photogrammetric endoscope to measure three dimensional (3D) shapes of inner cylindrical surfaces by fringe projection. The basic configuration includes two identical cameras aligned with the optical axis and facing each other, conical lenses, and a 360 degrees helical fringe projector. The helical fringe pattern is phase shifted and acquired by both cameras. The phase patterns are used to acquire data from the surface in a regular cylindrical mesh. A prototype was built, calibrated, and tested. We present the results and an application to inspect internal welding seams and misalignment of welded joints in 150 mm (6 in.) diameter pipelines.

This paper was presented as part of the student paper contest associated with the Annual Technical Conference and Exhibition. Abstract During fabrication of Steel Catenary Risers, the welding process is considered critical to its lifetime. Control the girth weld misalignment during fabrication would improve fatigue performance. The present work develops an optical system capable of quantifying the misalignment between the welded risers sections and to detect common geometrical welding defects like lack of fusion and excess of penetration utilizing a stereoscopic assembly. Introduction Steel catenary risers (SCR's) have been considered a strong candidate in future sub sea developments so there is an enormous effort to guarantee the structural integrity along its lifetime. In this context, inspection activities become significantly important in the manufacturing process. During SCRs fabrication the welding process is considered critical. Studies have demonstrated that misalignment between welded sections is a critical issue to SCR fatigue life. So an inspection routine is needed in order to control the misalignment during fabrication. This paper presents the concept and performance evaluation of an optical system's laboratory prototype developed to inspect the root region of the SCR weld seam during fabrication. This system has been designed to give quantitative information about the weld defects, like misalignment, lack of fusion and excess of penetration. An optical system was considered as a good choice for this application since it is fast and acquires a large amount of data related to the measured surface geometry. A stereoscopic endoscopic configuration was selected, designed and tested. This system has been developed under a joint project involving Petrobrás and the Federal University of Santa Catarina, both located in Brazil. It was planned in four stages: Stage 1 - Basic technology development. Stage 2 - Prototype design and manufacturing. Stage 3 - Prototype evaluation in laboratory. Stage 4 - Prototype evaluation in shop floor. The project has just ended stage 3. This paper deals with stages 1, 2 and 3. The complete test evaluation of the prototype in a welding plant will be reported in a future work. Basic technology development A pair of stereoscopic images is obtained when two images of the same scene are taken from slightly different viewing angles. Both images can be combined to give information about the 3D nature of the scene. That is naturally done by the brain of most animals and humans. This is the basis of stereoscopy, an already well established computer vision technique to extract 3D information from scenes.

This paper presents an endoscopic optical system to measure 3D shapes of inner cylindrical surfaces that combines photogrammetry and fringe projection. The device has two identical cameras aligned with the optical axis and facing each other, two conical lenses and one 360° helical fringe projector. The helical fringe pattern is projected in the inner surface to be measured, phase shifted and acquired by both cameras. The phase patterns are used to identify corresponding points and to reconstruct the surface in a regular cylindrical mesh using an alternative approach. A prototype was built, calibrated and tested. The paper presents the results and an application to inspect internal welding seams in 150 mm (6") diameter pipelines.

Steel catenary risers (SCRs) have been considered a strong candidate in future sub sea developments at Campos Basin (Brazil). So there is an enormous effort to guarantee the structural integrity along its lifetime. In this context, inspection activities become significantly important in the manufacturing process. The welding is considered a critical process so it is the inspection focus. Studies and analysis have demonstrated that fatigue performance of one sided girth weld is considered a critical issue, mainly in the touch down point (TDP) area. In this context, control the girth weld misalignment would improve fatigue performance during fabrication. This paper presents an optical system developed to inspect the root region of the weld during fabrication. A pair of stereoscopic images is obtained when two images of the same scene are taken from slightly different viewing angles. Both images can be combined to give information about the 3D nature of the scene. This is naturally done by the brain of most animals and humans. It is also already a very well established computer vision technique to extract 3D information from objects. The authors developed an alternative endoscopic configuration to extract and analyze stereoscopic images from the inside of pipes is presented. Two cameras are coupled with conical optics to produce a pair of endoscopic stereoscopic images of a 360° measurement ring. A light projector is used to illuminate the inner surface and, alternatively, to generate a random pattern of dots that is projected into the inner surface of a pipe to make it easier to correlate the images. Both images are analyzed by cross-correlation technique. The corresponding position of the spots in each image are found and combined to compute the 3D coordinates of points laying on the inner surface of the pipe. As a result, a dense cloud of points of the inner surface is obtained and used to extract geometrical features of the pipe. The software is capable to represent the measured surface from different angles and through different cuts. A prototype using this principle was built and tested in laboratory. Some practical considerations and early measurement results are here presented. The aim is to measure and quantify the misalignment between the pipes and to detect common welding defects like lack and excess of penetration.

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