Statoil pilots laser scanning on Snorre-A revamp
  from: Offshore Engineer
  by: Bruce Jenkins
  Sunday, August 01, 2004

Statoil is piloting laser scanning in anticipation of shortening a 24-month revamp of its Snorre-A platform by two to three months. If the pilot proves that laser scan data is of sufficiently high quality to support engineering, writes Bruce Jenkins*, the operator expects to be able to modify its platforms 8-12% faster as well as saving travel time and cost by reducing offshore measuring and engineering labor.

Normally when we award a contract, the contractor travels offshore with point surveying systems to document existing conditions,' points out Terje Birkenes, Statoil piping design manager. Surveying with total stations, he reports, 'takes two to five months to document the tie-in points, the main steel, and so forth'.

The new approach Birkenes is piloting is to hire a service provider 'to do laser scanning before the award of the detail engineering project, because then the contractor can start at once'. In offshore projects, there is much more room for laser scanning to accelerate schedules than to further reduce rework, according to Statoil. 'In that discipline of measuring, you don't get any credit for doing anything right, because fabrication expects you to do all that right,' Birkenes explains. 'We can't afford a lot of clashes - if that happens, they'll just throw the whole thing out. We don't have problems with the measurement technique we use now - point surveying with total stations - so laser scanning must be at least that good.'

Quality check
The Snorre-A project involves the installation of two new modules. Statoil reports it is piloting the use of laser scanning during the bid phase, and will use this experience to decide whether to require the contractor to use laser scanning-based existing conditions data for engineering once a contract is awarded.

Laser scanning was carried out in November 2003 by Norwegian design and engineering firm Hitec Framnęs using the 3Dguru scanner from Visi Image Inc.

Hitec Framnęs Asls specialist Inge Byrkeland set up a list of 15 areas to scan. 'We have a grid system marked on the platform' originally put in place to support traditional point surveying, 'so they did some testing of how to tie the laser scan into the grid system, in order to have a backup with that traditional measurement system,' he explains.

Aker Kvaerner, which installed the coordinate grid, is evaluating the quality of the laser scan data by checking it against the grid. Byrkjeland notes: 'So far the results are very good, and the deviations very small.' The scanner used has a specified accuracy of 2mm, he reports, and in scanning a module measuring 20m x 22m, 'the maximum global deviation across all registered scans is in the range of 5mm'. He believes this is extremely good, especially given that objects on a platform can move and the scans were done in rough weather.

Data and models will be extracted from the scanned clouds and stored in databases under the Hitec Framnęs-developed AsIs management system. According to Hitec Framnęs, AsIs involves two types of data: newly authored or developed data, and existing data. Comprehensive databases are developed and management techniques are employed to ensure correct information with the right revision is provided, thereby ensuring that engineering is based on correct information, the company explains.

If Aker Kvaerner's evaluation is positive and if Statoil decides to use laser scanning on the full modification project, it will commission laser scanning of all areas relevant to the two new modules being installed. It will then provide this data to contractors for their use in preparing bids, and the winner will use it to begin engineering work. The information from scanning will also be used in the last phase of front-end engineering design.

Besides accelerating the start of engineering work and reducing offshore travel, Statoil is looking to laser scanning to give bidders more complete, higherquality information than by traditional methods. By ensuring that all bidders get complete and consistent information on which to bid, laser scanning can remove one source of bid variance and thus make competing bids easier to compare.

Finding a way to import point clouds directly into PDMS is 'very important' to Statoil. The pilot project involved a total of 11 scans, each containing between 60 million and 70 million points, according to Hitec Framnęs. Software provided with the 3Dguru scanner was used to reduce each scan to 30% of its orginal size. The 3Dguru software creates a point-cloud file in a format called C3D, which contains 100% of the scan data. The 3Dguru software is then used to process the point cloud into the Leica/Cyra Cyclone PTS format. In this step, the operator specifies what percentage of the point-cloud data to bring across. This work process differs from 'decimating' - where 100% of the data is exported to the point-cloud software application, then reduced using that software - but the results are equivalent, according to Byrkjeland.

Cyclone was then used to register all 11 scans. The registered scan data was used to create 3D models of key geometry in Cyclone. Modeled geometry was exported from Cyclone in COE/DGN format to MicroStation. These DGN models were then provided to Statoil for import into its Aveva-PDMS plant design system. If this pilot project leads to production use of laser scanning, registered scan data in Cyclone format will be provided to bidders for viewing with Leica/Cyra's free Cyclone viewer software.

Byrkjeland has mixed views of Leica/Cyra's Cyclone software. 'In my opinion, Cyclone 4.1 does not handle enough points,' he says. 'I can manage to work with 15 million to 20 million points in it easily, but if I try to push it futher, I start to get problems. Cyclone is good software in many ways, especially in registration, and the modeling is also good. But we are now unhappy with Cyclone because I wish it could handle point clouds up to 100 million points easily. Then it would be extremely efficient.' Leica/Cyra has said that Cyclone 5.0, due for commercial release shortly, will readily support scan data sets of 500 million to one billion points.

Statoil, for its part, reports it is looking for a system that can import point clouds directly into PDMS. Emphasizing that this is very important, Birkenes notes: 'Nine out of ten of our projects use PDMS. Most of our modifications also use PDMS.' Aveva reported late last year that it was discussing the use of point-cloud data directly in PDMS with several leading providers of laser scanning technology.

Tie-in data responsibility
Who is contractually responsible for verifying the accuracy of tie-in data - the contractor, the owner who provided laser scan data, or the laser scanning service provider - was not disclosed. In general this responsibility lies with the subcontractor executing the work involved.

Should Statoil elect to use laser scanning on the Snorre-A module upgrade, we expect contractors who want the job will be willing to accept laser scan data for engineering. The winning bidder will probably spot-check critical areas using total station means, then use these spot checks to validate the accuracy and confidence of laser scan data for itself. OE

* Bruce Jenkins is senior analyst and principal of Spar Point Research.

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