Abstract
Three dimensional (3D) optical measurement systems have seen ongoing development with regards to both technologies and applications. While previously targeted primarily toward manufacturing and quality control environments, significant benefits have been recognized for utilizing precision optical metrology systems across the oil and gas industry. Specific applications have developed in field and facility defect assessment and mapping, NDE services, failure analysis, evidence preservation, and forensic reconstruction.
This paper presents recent work and research comparing 3D laser scanning technologies to traditional inspection techniques for mapping of corrosion, dents, and dent/gouge combinations. Included is a comparison study consisting of a typical corroded region of pipe, comparing accuracy, speed of measurement, and data processing applications for traditional pit gauge measurements with those processed from a 3D laser scanner. Review and comparison of alternative techniques and technologies, such as structured light, and photogrammetry is also presented.
Introduction
Recent advances in laser scanning technology have allowed laser scanning devices to conduct the same damage mapping and assessment tasks as traditional techniques in less time and with more accuracy and precision. The laser and structured light devices come in a variety of types, ranges, and accuracies which each have their own strengths and weaknesses. Knowing the various abilities of the current generation of laser scanning devices will allow the user to make informed decisions regarding the right device for their particular need. This paper will inform the reader of each type of laser scanning device, how they work, their strengths and weaknesses, as well as potential applications. Specific models will not be reviewed in detail, and recommendations will be given with respect to the type of laser scanner, rather than to individual models.
Types of Devices
In this paper, laser scanners are divided into 4 types: long range rotating heads, arm based laser line probes, hand-held units, and structured light scanners. It is recognized that some specialized units may not fit into these categories; however, these types are the primary units which are used in pipeline inspection. All these units operate on the same general principal. A laser is emitted from the unit onto the object being scanned. A sensor on the scanning unit will then, based on the position of the laser, detect the position of the object being illuminated. Beyond this, each type differs in exact method of measurement.
