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Subsea 7 Spool Metrology

2G Robotics enabled Subsea 7 to scan multiple spools as well as the surrounding area, creating both a detailed model for metrology measurements.

Introduction

UTEC StarNet, Seatronics, and 2G Robotics completed a spool metrology project for Subsea 7 using underwater laser scanning as part of the overall solution to achieve the required measurement accuracy that could not be attained using acoustic techniques.  The end customer’s objective was to design five spool pieces to connect a newly installed bundle towhead to five previously laid spool pieces.

To obtain towhead and spool piece positions and headings, acoustic LBL was used. Survey specifications, however, dictated that a 6 metre long acoustic baseline to derive at an acoustic heading was insufficient. 2G Robotics’ ULS-500 high precision laser scanner provided the additional dimensional control needed to obtain the necessary measurement accuracy that could not be achieved using a 6 metre long acoustic baseline.

Methodology

The metrology was conducted in the North Sea at a depth of 90m; two of 2G Robotics’ ULS-500 laser systems were utilized. The ULS-500 with rotary actuator and tripod was deployed by the WROV. A gripping frame was added to the standard mount location of the ULS-500 so that the WROV’s manipulators could grab the system to position it on the seabed. The system was tethered to the WROV and the WROV’s fibre optic umbilical cable was used to communicate with topside operators for real-time data acquisition.

The center flange was positioned within the LBL acoustic array using the two saddle mounted transponders with control spheres that were deployed onto the largest of the five spools by the WROV. To complete the high precision dimensional control survey of the towhead structure with flanges, 2G Robotics’ ULS-500 performed 360° scans at multiple locations around the spools, with each scan capturing both the key flange pipeline components and the control spheres attached to the two pipeline saddles.

Cost Savings and Efficiencies

The traditional LBL survey approach would have required an entire day for this operation. With the ULS-500, in only eight scans and 3.5 hours, the scanner captured the flanges, bundle towhead, beacons, control spheres, and surrounding environment. Since 2G Robotics’ ULS-500 system is factory calibrated, no time-consuming calibrations were needed during deployment. Whereas the traditional approach would have yielded only one point per beacon, the laser scanning approach generated a complete 3D model comprised of 14.6 million points, notably improving the accuracy for designing the spools.

“The operational time savings will be motivation to use this system again. There will no doubt be many other subsea situations for which highly accurate dimensional detail is required where 2G Robotics’ laser system would fit in perfectly.”

Pieter Jansen

Survey and Subsea Data Manager, Subsea 7

 

 

 
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