Abstract
Abstract The Floating Product Systems (FPS) fleet has increased steadily over the last 2decades and is expected to continue to grow with developments in the world'sdeepwater basins. One of the issues with floating installation is that they aremoored to the seabed and therefore subject to the forces exerted during stormyconditions. These exceptional forces can cause deterioration of the mooringlines and in some circumstances result in mooring line breaks. This has obviousimplications for personnel, asset and environmental safety. Being able to monitor the tension experienced by the mooring lines enables FPSoperational personnel to proactively take the required measures to maintainmooring line integrity. This paper details the design and installation of a newmooring line monitoring system allowing such mooring integrity monitoring on a FloatingProduction Storage Offloading (FPSO) vessel operating offshore Brazil. Introduction SBM supplied the FPSO for deployment in Brazilian waters. The vessel is mooredusing 9 mooring lines bundled in 3 sets of 3 lines at 120° from each otheraround the turret chaintable. A new mooring line monitoring system was specified for this project. Thepurpose of the system was not only to notify the operations team in the eventof a line break but also to record the line tension experienced over time sothe mooring line performance could be evaluated. The project specification also called for thesystem to have the capability to identify progressive degradation such as linecreep and quantify the need for line retensioning. Technical Challenges Many of the systems used in the past to monitor anchor leg load have offeredlimited reliability. Load cells need to be mounted in the load path which leadsto difficulties when maintaining them. Shear pins require modifications to thechain which can affect chain integrity. Strain gauges have issues with water leakage. Moreover the cables required to connect these sensors to the data collectionsystem could become trapped and severed during a subsea intervention like riserpull-in. When developing the system reliability and robustness was foremost in thespecification. Therefore Pulse decided to use inclinometers in the developmentof the system. An inclinometer was attached to the chain hawse of each leg. This meant that the sensor was outside the load path, enabling straightforward maintenance ofthe sensor. Furthermore, each anchor leg chain can be pulled through the chainhawse to re-tension the chain without affecting the operation of theinclinometer. In order to avoid the problems associated with cables connecting the system, Pulse used acoustic communication to relay the measured data to the controlroom. Figure 1 shows the type of acoustic receiver used.
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