Floating production storage and offloading platforms (FPSOs) used in the offshore oil and gas industries are moored by several mooring lines consisting of wire rope and chain. Chain wear is an issue for mooring line safety. Herein full-scale experiments are reported for assessing the wear that may be experienced by chains under operation conditions. Since such tests are very expensive, scale experiments are being assessed as possible substitutes and to allow many more parameters to be tested. The experiments show that chain wear increases with increased axial tension and with greater inter-link angular movement. Wear is much greater when the inter-link rotations occur under dry conditions compared to continually wet conditions.
Floating production storage and offloading platforms (FPSOs), increasingly being used in the offshore oil and gas industry require a high degree of safety and redundancy to guarantee platform reliability and security. This includes reduction in risk from ‘run-away’ events and their possible consequential damages, including from crude oil and other spills. Typically FPSOs are used for deeper waters and are moored in place using an array of mooring lines tethered to chains resting on the seafloor. The mooring lines invariably consist in the upper reaches of high tensile steel chains, typically at least 76 mm diameter and sometimes 150mm or more in diameter and similar chains on the seafloor (Fig. 1). Of most concern in practice for safety issues are the upper chains, in particular in the tidal and splash zones and also where they are fastened to the vessel. There are surprisingly few studies dealing with these issues for FPSOs, although the principles are now well-established (Paik & Melchers 2008).
A recently completed joint industry project (SCORCH-JIP) has examined the likely corrosion losses for mooring chains in a variety of exposure environments including tropical and polluted seawaters. This was done using chains recovered from actual operations and specifically designed tests in a variety of seawater exposure environments, ranging from Tropical to temperate (Potts et al. 2012).