SCORCH JIP

Chain and steel wire rope have been used for mooring floating offshore production systems since their introduction nearly 30 years ago. A recent survey 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 moorings systems may be more rapid than expected. In the majority of systems, unless fully sheathed in plastic, the life of the rope is less than that of the installation.

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This has lead to a requirement for 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 process of wire rope and chains.

In response to this identified gap in mooring design guidance, AMOG Consulting is leading a JIP to study Seawater Corrosion of Ropes and CHain (SCORCH) in tropical waters with the aim of filling the identified technology gap between design practice and engineering analysis.

The final objectives of the JIP are to provide participants with:

• Design guidance on the specification of wire ropes and chains to maximise their design service life for the particular site conditions, in particular in tropical waters; and
• Design analytical tool, underpinned by field and test data, to estimate the design service life of steel wire mooring ropes and chains for the particular site conditions.

The JIP involves highly recognised scientists including:

• Professor R. Melchers (University of Newcastle, Australia) for corrosion technology; and
• Professor R. Chaplin (Reading University, UK) for mooring rope technology.

and partners including:

• SOFEC / MODEC which will provide access to their in-house database;
• Bureau Veritas (France) for classification of moorings and design guidance; and
• DNV for design guidance.

together with manufacturers:

• Vicinay;
• Bridon;
• Arcelormittal; and
• Onesteel.

This JIP will be of direct relevance to:

• Offshore oil and gas companies;
• Floating production or storage facility operators;
• Floating facility designers;
• Classification Societies;
• Safety Regulatory Authorities; and
• Mooring Ropes and Chain Manufacturers.

The final goal for the JIPs is to provide some guidelines and design tools for estimating the corrosion and wear of wire rope and chain. Those that are currently in design codes appear inappropriate for the results have been derived from measurements in cold waters. Experiments show that the corrosion rate grows exponentially with temperature.

JIPs will investigate the two main degradation mechanisms for chain and rope as both in-situ experiments and laboratory tests will be performed to validate models describing these phenomena, as detailed in the SCORCH JIPs proposal. A series of field tests on wires, wire ropes and chain samples will be conducted to quantify the effects of external factors driving corrosion within marine environments. Small and full scale measurements will be used to calibrate wear and corrosion models.