The primary goal of floating systems life extension efforts is to project how the system or components will behave in the future beyond the original design life. This predicted behavior can then be used to determine the practicality of the proposed life extension in terms of safety, environmental and economic risk. Often, these predictions are limited to reviewing inspection data (which has a limited ability to predict future response) or analysis (which is dependent on various assumptions). Measured data from in-situ monitoring systems provides accurate system response information which, in conjunction with mathematical modeling and inspection data, can be used to determine past and future behavior. The full potential of measured data for life extension activities has not been realized thus far.
Some uses of measured data in life extension efforts are illustrated through examples in this paper. The first example highlights ongoing fatigue assessment of a mooring line chain jack system using line tension measurements. The second example describes how uncertainty was greatly reduced in a polyester rope fatigue assessment by utilizing measured mooring line tension data. The third example demonstrates use of measured vortex induced motion response of a floating system to reduce the conservative assumptions provided during the design phase. The results of all of these examples show that measured data can provide insight into floating production system (FPS) response that cannot be attained otherwise, allowing for significantly reduced conservatism in life extension engineering assessments. Without the availability and use of this data it would be difficult to demonstrate the fitness for service of these facilities.
The examples of utilizing measured data to enhance life extension efforts provide concrete demonstrations as to how life extension of FPS components can be justified where uncertainty in analytical prediction is high. In such situations, demonstrating fitness for service beyond the design life would prove exceedingly difficult if measured data was not available. Continued service feasibility is most effectively demonstrated by augmenting inspection and analysis efforts with field monitoring data.
McNeill, S., Maniar, D., Renzi, D., Del Vecchio, C., “Measured Data Provides Insight for Floating Systems Life Extension,” Proceedings of the Offshore Technology Conference Brasil 2017 (OTC-28044-MS), Rio de Janeiro, Brazil, October 24 – 26, 2017.