Mooring Integrity Monitoring System - Topside
The need for mooring integrity monitoring has of late come back under the spotlight, not least because the use of floating production systems in the offshore Oil and Gas industry has been predicted to grow at a significant rate between now and 2017 with a peak in the number of new builds expected to occur in 2016/2017. Recently, an updated industry guideline on mooring integrity has been issued by Oil & Gas UK with the support of operators, contractors and vendors. The guideline reinforces how mooring integrity management through effective monitoring and data management can provide information to help detect mooring line failure and assist with validation of mooring design strength and fatigue analyses.
Station keeping through the life of a field is of critical importance for floating production facilities in all parts of the world. The mooring system performs this function, and although it has not always been the case, current design practice is to engineer mooring systems that can withstand extreme environments with single or even multiple line failure scenarios. Even so, the offshore industry has experienced numerous unexpected mooring line failures in recent years that, in a small number of cases, have resulted in mooring system failure. On average between 2001 and 2011, there were more than two mooring system failures per year. During this period, nine were multiple line failures1 and other mooring incidents resulted in riser failures and hence extended field shut down2. Based solely on these statistics, there is a clear business case for effective mooring integrity monitoring.
One of the challenges that has emerged from these failings is the need to monitor mooring system integrity reliably for the life of the facility without the need for costly inspection or maintenance of subsea sensors. In general, most mooring line monitoring systems that have been deployed to monitor mooring line tension have themselves experienced sensors failures, and the industry is now assessing ways of monitoring mooring line break detection as opposed to measuring mooring tension in a hope that the sensors will be more robust. However, many of the challenges of installing and maintaining these types of monitoring systems still need to be addressed.