Corrosive-wear of buoy chain

Abstract : Corrosive-wear, which is responsible for the majority of buoy chain degradation, was investigated in two laboratory studies. The objective of the first study was to isolate the two components, corrosion and wear, in order to determine each of their influences on the corrosive-wear process on steels. The second study was designed to produce uniform wear on the steel's surface, providing more accurate data on the steel's wear resistance and to determine the effects of alloy additions. The steel presently being used for buoy chain, which is similar in composition to ASTM 1022 steel, was compared to ASTM 4140, 4340, 8740, and a heat-treatment 4140 steel in order to identify a material which would provide a longer life buoy chain. The results of the experiments showed that the wear component contributed material losses of one to two orders of magnitude greater than the corrosion process. It was also determined that the 4340 steel would be the most suitable material for longer life buoy chain. This alloy's high nickel content would reduce the potential for pitting attack, which can be extremely damaging to a mooring. The microstructure of the 4340, with a low ferrite to pearlite ratio and fine grain size, would provide an increased wear resistance of up to four times greater than the 1022 steel. (Author)