Study on corrosion degradation of wire ropes in sea water

Abstract

Wire ropes used in marine environment have a great degradation due to corrosion. Accurate inspection methods for corrosion of wire ropes are necessary to ensure their safety. However, technical background data of corrosion is quite few at present, and is not sufficient for wire rope inspection. Collecting the technical data is important to establish and ensure the offshore structure's maintenance technology including wire rope inspection. A laboratory test of wire ropes degradation was carried out with seawater tanks for 5 years since 1994 to 1999. 14 kinds of ropes were used for the experiment. Further, an exposure test in real sea area was also carried out for 11 months in 1997 to acquire degradation data in dry zone above sea level, in ebb zone, and in the seawater zone. Eight kinds of ropes and 3 kinds of wires were used for the exposure test. During the test period, we examined the ropes for several times on the following characteristics. (1) appearance of ropes and strands, (2) cross section of each wire layers, (3) properties of wire: diameter, tensile strength, number of torsion, (4) mass of coating. The changes of characteristic values were approximated in the curve to eliminate fluctuation errors. We calculated the most suitable characteristics values when the experiment was finished and converted into normalized values divided by initial values. Corrosion degradation of some kinds of wire ropes was evaluated with normalized characteristics values, and appearance of their surface and their cross section.