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Long-term corrosion of steel chains on pacific ocean beach sand

Paper Number: 22
Author/s: M A Watt, R E Melchers & R Jeffrey
Organisation: Centre for Infrastructure Performance and Reliability, The University of Newcastle, Australia

Abstract

The corrosion of steel exposed to seawater and sand is of interest to the offshore industry for oil production and wind farm caisson or platform mooring systems, and also for assessing the deterioration of shipwrecks. Very few data are available, particularly for long-term exposures. The present paper reports observations made recently at Catherine Hill Bay of the corrosion losses for 70mm diam. steel chain exposed since 1913 to immersion, tidal and splash zone corrosion largely whilst lying on local beach sand. The site, on the Pacific Ocean south of Newcastle, was once a coal loading facility and the chains were used to moor vessels while being loaded with coal. Observations show that, except for immersion corrosion, the rate of corrosion is not high. Corrosion tended to be uniform and there was no obvious signs of large pitting as has been observed in some cases elsewhere for mooring chains. The observations are compared with some classical data available for steels buried in sands for up to 17 years, and examined at regular intervals, that show that most corrosion tended to occur in the first 10-15 years after which the corrosion rate declined. There also are some very short-term (5 month) observations that suggest initial corrosion of metals occurs by crevice corrosion immediately adjacent to the sand particles. These observations allow for an interpretation of the new data.