A Subsea Structural Deflection Monitoring System designed by RTS AS, Norway. 51st Marine Measurement Forum Adil Ali Seatronics Limited

Transcription

1 A Subsea Structural Deflection Monitoring System designed by RTS AS, Norway. 51st Marine Measurement Forum Adil Ali Seatronics Limited

2 Seatronics and RTS Seatronics Limited : Established: 1978, Aberdeen-based Marine Technology Specialists with an overseas presence in 5 continents. Core business is equipment rental ( sectors incl. positioning, geophysical, subsea construction, hydrography, Metocean, ROV tooling). RTS AS - technology partners based in Norway. Innovation, integration and installation. Technical liaison with construction companies (e.g. Subsea7, Tecnip, Saipem etc.) using existing technology for specialist monitoring and subsea structural measurement and assessment.

3 Why monitor subsea structures? Larger template structures heavy (100 s to few 1000 s tons, sizes between 20-60m). Balance between strength and weight. Avoid over-engineering. Cost! Reduced risk and time. Standard procedure in Norwegian Sector. Structures flex on lowering to seafloor, both through water column and on seabed settling using suction piles. Keep any flexing within the engineered tolerances. Lifespan between 10 and 40 years on seabed, ensures structural integrity.

4 Why SDM? Problem: Lightweight structures with a tendency to twist during deployment Deflection needs to be monitored with set limits dictating inspection regime following installation. (more flexing = more rigorous inspection regime throughout structure lifespan). Client Specification: Design, supply & support a Subsea Deflection Monitoring (SDM) package to provide:- High accuracy heading, pitch, and roll Four high precision depth sensors simultaneously polled Acoustic modem link to surface Subsea data logger for post install reply and analysis

5 Structures manifolds, riser bases, PLEMS, templates

6 Principles of Operation POSITION of Structure is determined by Compatts, LBL array, beacons. (e.g. Kongsberg MPTs) HEADING is determined by Gyro compass installation structure (Fibro Option Gyro, e.g. Ixblue ROVINS or Octans DEPTH is determined by use of pressure sensors or digiquartz sensors at each corner. Powered by internal batteries and data transmitted acoustically to modem on an ROV, with Hotstab comms as back-up. Data displayed, stored and monitored on main installation vessel.

7 Equipment Seatronics/RTS - SDM packages each comprise ixblue Octans FOG Four 700m Paroscientific Digiquartz pressure sensors (Accuracy +/-0.005% FS % Resolution) Dual underwater CDL Mini Txt displays (H and P & R) Benthos LF Modem data transmittal. DeepSea Power & Light Batteries (48hrs ops) Subsea Data Logger (16Gb) with time stamping of data Log file dumping via Ethernet Back-up system, 100% redundancy Inclinometers

8 More features Hot stab option available for redundancy purposes (data via ROV to surface) ROV Rotary switch User-friendly GUI Gyro calibration software, start up & long term logging Heading Pitch & Roll Offset settings Gyro latitude setting through surface computer Eiva NaviPac and/or QINSy data output

9 Survey equipment Digiquartz depth sensors (Z) SDM Gyro packs incl. subsea batteries, subsea displays. (heading) MPT beacon (x,y)

10 Gyro display and position on structure

11 Pre-installation control Metrology and surveying in of offsets of equipment after installation prior to vessel lifting structure onboard. Accurate xyz position input into SDM software Heading /pitch/roll of structure is measured and compared to calibration value measured from gyro for accurate C-O measurements. Structure tolerances 1-2 deg. heading and typically a few cm flex. Equipment can resolve 0.01 degree and mm depth.( z ), easily within structure tolerances.

12 Display and monitoring All survey equipment surveyed in and interconnected/integrated. Data presented real time in vessel lift control room for key personnel : Barge Captain project engineer, surveyor client rep., geologist, rep. from structure manufacturer, RTS technician Data stored and logged in subsea logger, a at surface data can be sent via RS232 to survey package e.g. Qinsy, or Eiva NaviPac etc for post installation analysis.

13 Surface display and ROV view of the SDM display

14 Real-time deflection graphs Each corner graphically displayed Inclination, pitch and roll measured, logged and displayed.

15 SDM benefits, case study 5 templates successfully installed in 320m of water 4 of the templates were 380 tonnes each 25 x 15 x 16m Client estimated that the project would take 25 days Project completed in 18 days This allowed for 36 hours crane breakdown and 48 hours weather SDM has been used on the Tyrihans and Norne projects for Acergy, Skarv for SS7 and most recently the Sequoia project for Saipem.

16 Finally Deliverables to client are screen shots, log file, and a safe, deflection- free installation of an extremely large and heavy structure. Future development - laser scanned structures can be represented 3D data files, giving a full 3D graphical representation of the structure being lowered through the water column and being sucked down onto the seabed? Real time feedback from SDM software to crane or suction piles to speed up, stop or slow down the lowering process? Depends on individual strops and blocks for each corner.

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