Introduction
Modifying an existing offshore platform (or any facility for that matter) can be a daunting task. Any engineering company, owner operator or construction contractor who has tackled an offshore retrofit is well aware of this challenge. Tight spaces, densely packed equipment and a difficult operating environment combined with a tight timeframe for field construction creates engineering challenges that often carry a high penalty when errors occur. And errors do occur! Most platform owners, engineering firms, equipment vendors and construction companies have experienced significant difficulties with retrofit projects at one time or another. The results are major cost overruns and/or schedule delays as well as ‘field compromises’ required to get the platform back online as quickly as possible.
These construction issues and delays can frequently be traced back to either inaccurate or missing as-built information used as critical input to the design and construction/demolition planning of the retrofit. The root causes of the poor quality as-built information lie, in turn, in the traditional methods for gathering as-built information: engineers extract ‘as-built’ information from original design/ construction drawings and supplement this information by taking additional as-built measurements manually. Both these techniques are prone to error. Existing drawings are rarely, if ever, accurate, and good manual measurements are extremely difficult to obtain. In addition, even when accurate manual measurements can be taken, many critical measurements may be missed due to oversight or later changes in design/scope. The result is field construction interferences, fit-up problems and costly on-site changes.
Today, these problems (and costs) can be avoided with the use of Cyrax Laser Scanning technology.
What is Cyrax Laser Scanning ?
Cyrax Technologies, a San Ramon, California-based company and subsidiary of Leica Geosystems AG, introduced Cyrax® laser scanning in 1998 and is the largest supplier in the laser scanning industry with over 300 systems shipped through December 2002. The tripod-mounted Cyrax laser scanner sweeps a pulsing laser over the facility, collecting up to 1,000 individual surface geometry measurements per second. By measuring precisely the time of flight for the laser pulse (distance) and two angles (horizontal and vertical rotating mirrors), a rich, dense ‘three-dimensional (3-D) point cloud’ of facility geometry is created. Each individual point measurement is accurate within +/- 6mm up to a range of 50 metres. By averaging thousands of points on surfaces, a few millimetres precision can typically be achieved when point clouds are processed into as-built models and drawings.
Figure 1: Offshore Platform Scan
To capture full 3-D geometry of the area(s) of interest, the laser scanner is moved around the platform or facility as needed. Once multiple scans of a facility (offshore or onshore) are collected, they are ‘registered’ together and typically tied to a local co-ordinate system using several known survey points. The registration process can utilise both known common points (target registration) as well as matching of common surfaces within the point clouds (cloud-to-cloud registration). Even large structures such as offshore platforms can be scanned easily and the scan data tied together accurately, as shown in Figure 1. This project consisted of 43 scans (roughly 43 million measurements) capturing the areas of critical interest for the retrofit. The scans were collected in less than two days.
Since the laser scanner literally ‘blankets’ the scene, designers can easily identify all objects (valves, flanges, strainers, structural elements) they are working with (see Figure 2). The point clouds can be used within Cyra’s Cyclone™ software for rapid creation of accurate, complete as-built models, or, with Cyra’s CloudWorx software, the points can be used directly within the AutoCAD or Microstation design environment to extract measurements or create as-built drawings. This allows designers to model existing piping, structures and equipment easily using familiar design tools while referencing the point cloud as an accurate ‘3-D road-map’. Through CloudWorx, plant design software such as PDS, AutoPLANT, CADWorx and Plant4D can all take advantage of rich point clouds for creation of accurate as-builts for interference-free design.
Figure 2: Point Cloud Shrinkwrap
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