The paper proposes a semi-empirical model for the seawater corrosion of six strand wire rope. The model includes the local effects of water temperature, oxygen concentration, flow velocity, together with the location of the wire within the internal rope structure and the zone location along the rope. The analytical formulation of the model is sustained by physical considerations and calibration of the model parameters is performed against a large set of experimental results available in the literature.
Steel wire rope and chain have been used for mooring floating offshore production systems since their introduction nearly 30 years ago. A recent survey (2006) prepared for the Health and Safety Executive (HSE) of past and presently operating FPS units has shown that serious incidents have occurred in the past, including loss of station. The survey has also shown that even for more up-to-date designs, deterioration of certain areas of the mooring systems may be more rapid than expected. In the majority of systems, unless fully sheathed in plastic, the life of the rope is typically less than that of the installation. This requires a policy of life prediction, inspection and replacement. For long term integrity, it is vital that wear and corrosion are correctly accounted for in the design and selection process of wire rope and chains. The present study focuses attention on corrosion modeling of wire rope.
The American Petroleum Institute (API RP 2SK) and Det Norske Veritas (DNV-OS-E301) give recommendations for life expectancy of different constructions in terms of corrosion resistance. As shown in Table 1,(Refer to the full paper) both require all wires to be galvanized though neither make reference to the different weights of galvanizing available. API, DNV, Bureau Veritas (BV-NI-493), and the International Organization for Standardization (ISO 1990–7) all identify corrosion protection measures (galvanizing, lubricant as blocking compound, sheathing, zinc anode wires) and all draw attention to the need for special protection adjacent to terminations including additional anodes and electrical isolation of the rope, and the socket.
