Dry mooring line monitoring for floating production systems

Background

Floating production systems stay at fixed positions year after year without regular dry docking. To ensure station keeping, these units are equipped with mooring systems which must be able to withstand harsh weather loadings.  Mooring systems are exposed to a wide variety of environmental conditions. Deterioration of the mooring lines over time will result in a lower resistance against breakage.  Moreover, failure mechanisms that were not anticipated during design, such as Out-of-Plane Bending, result in higher loads than were predicted resulting in a reduced mooring line reliability. 

As a result, mooring incidents have been occurring at high rate during the past decade. More than twenty incidents have happened to production vessels that are moored on-site for prolonged duration. Some of these incidents were of high consequence, such as causing the vessel to drift a short distance, riser ruptures and production shutdown [1]. These incidents are raising concerns for owners and operators.

Objective

The LifeLine initiative seeks to develop a dry mooring line monitoring system which is based on position measurements only (without subsea equipment). Monitoring of position onboard of turret moored FPSO’s have already been performed successfully [3].  Within LifeLine, a mooring monitoring system will be developed which is able to take into account the effect of the actual environmental conditions. This allows to provide the operator real-time status information on the mooring line integrity. 

Monitoring equipment will be used based on reliable and proven technology without subsea sensors. This enables application of the system on both new-built and existing units.