Corrosion of steel in tropical marine atmospheres

Abstract

The corrosion of a mild steel and a medium carbon steel has been studied at two sites in Singapore (inland and on a raft in the sea) for three periods, with two surface conditions for each steel. Corrosion of the mild steel is significantly faster on the raft than inland. The steel with the higher carbon content corroded more slowly. An attempt to relate temperature, relative humidity, time of wetness, rainfall, and solar radiation to the corrosion rate of the dry blasted mild steel at the inland site suggests that the penetration depth obtained from weight loss data for samples exposed in the winter months can be expressed as 0·1078+0·00596x μm, where x is the number of hours of wetness, with a correlation coefficient of 0·99. Examination by scanning electron microscopy showed that specimens exposed inland were covered with patches of rust, compared with continuous rust films with continuous cracks on the raft specimens. Energy dispersive spectroscopy showed the rust on the raft specimens to have higher chloride contents and atomic absorption studies suggested that the rust layers are composed of FeOOH. The long term corrosion rates of specimens exposed to the inland marine atmosphere and on the raft were found. to be 0·016 mm/year for 2 years’ exposure and 0·659 mm/year for about 0·6 years’ exposure respectively.