Potts, A.E., Kurts, P., Jayasinghe, K., Kilner, A., Melchers, R., Lee, T., Chaplin, C.R., Paper Number OTC-28737, Proceedings of Offshore Technology Conference, April 30 - May 3, Houston, Texas, USA, 2018.
Abstract
Operators have, in the past, experienced high rates of corrosion for mooring systems in warm waters above those allowed for in traditional design guidance. The Joint Industry Project (JIP) for Seawater Corrosion of wire Rope and mooring Chain (SCORCH) was carried out with the participation of over twenty five offshore platform operators, equipment manufacturers, regulators and classification societies to address gaps in industry knowledge on the corrosion of steel wire rope and mooring chain, particularly in tropical waters.
The fiveyear project involved a broad range of research from literature review through to field experiments, examination of recovered inservice components and derivation of generalised corrosion models. Coupons of several grades of chain were deployed for a two year period at a number of sites to account for variation in temperature, oxygenation, current/wave action and water quality. Fullsize chain links and lengths of smaller chain were also deployed for comparison, with special laboratory tests to investigate the effect of nutrient content on microbiologically influenced corrosion (MIC). Wire rope tests were carried out for a similar variation of environmental conditions as the chain tests. A range of specimens including individual wire strands, and wire rope sections with varying levels of blocking compound, jacketing and galvanic protection were subject to exposure for a period of three years and 6 months.
An extensive industrywide survey of inservice and retired mooring components was also carried out to supplement these experiments. A standardised procedure for corrosion inspection was distributed to participants and a database of detailed wire rope and chain corrosion measurements was collated from approximately 30 floating production units (FPUs) operating in tropical waters in Asia, Africa and the Americas. Some recovered specimens were subject to more extensive examination, including 3D laser scanning and tensile break tests.
The SCORCH JIP advanced knowledge in the field of mooring corrosion by providing guidance on inspection and integrity management methodologies, unique insight into the factors affecting the corrosion performance of steel wire rope and mooring chain, and generalised predictive corrosion models for the assessment of mooring corrosion. These recommendations are presented in the following paper.
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