Advisory Hull Monitoring System for the Bonga FPSO

Abstract

This paper describes the implementation of the Advisory Hull Monitoring System (AHMS) onboard the existing Bonga FPSO (Nigeria) during operations and production. AHMS has been developed for FPSOs in the Monitas Joint Industry Project as a fully automated system, which explains and advises on the fatigue lifetime consumption of the hull of FPSOs. The explanations and advice offered are based on a comparison between the design and the actual predicted lifetime consumption by replacing the design parameters including environmental and operational conditions with the measured data. The system differentiates between the contributions of environmental and operational conditions as well as hydro-mechanic and structural responses. The AHMS system comprises hardware and software for smart data gathering and processing. AHMS hardware includes strain- type sensors on deck and inside the Water Ballast Tanks (WBTs) and/or void spaces and interfaces with external systems including the Computer Loading Instrument (CLI), Gyro and metocean system. AHMS has generally been installed onboard newly built floaters including the Usan FPSO (Nigeria), Clov FPSO (Angola), Ichthys FPSO (Australia) and Moho Nord FPU (Congo). Being in operation since 2005, the Bonga FPSO has lived 14 of its 20-year design life. Given the constraints inherent in her design, deployment of the AHMS for the FPSO's hull fatigue life monitoring therefore presented unique installation challenges to overcome as would be expected for ageing brownfield assets. To add to this challenge, the installation was carried out during production and so required strict adherence to the stringent safety requirements of Simultaneous Operations (SIMOPs) on a live plant. This paper describes in detail, the AHMS hardware, the complexity and challenges of their installation for the Bonga FPSO and highlights lessons learned for typical brownfiled retrofit of this nature. OCTOPUS MONITAS, the software of the AHMS system for the smart data processing, calculates onboard fatigue lifetime consumption of the hull and explains the differences against design predictions. Methodology of the software is herein described, and the first set of measurements taken from the Bonga FPSO as well as preliminary results produced by the software are similarly presented.