The Influence of the Inclination and Direction of Specimen Surface on Atmospheric Corrosion of Steels

The corrosion rate of a steel and the morphology of the rust formed are influenced by the inclination and direction of the steel surface exposed to the atmosphere. Sheets of a carbon steel and a low alloy steel one side of the surfaces of which was coated by resin paint were positioned at the inclinations of 0, 30, 60 and 90 degrees to the horizon, facing skywards and groundwards. Atmospheric exposure test has been carried for two years. Corrosion rate of steels, sulfate content of rust, and retained water content of rust layer after rain fall have been studied. The results are as follows; (1) Corrosion rates of the groundward surfaces were greater than those of the skyward surfaces and decreased with steepening the inclination of the surfaces. Corrosion rates of the skyward surfaces positioned horizontally and vertically were greater than those of the surfaces inclined at the intermediate angles. (2) The sulfate content of rust varied with the inclinations of the surfaces on which the rust was formed. This fact seems to relate to the amount of rain running along the surface of the specimens. (3) The sulfate content of the rust could explain the dependency of corrosion rates of the groundward surfaces on the inclinations of the surfaces. As to the corrosion behavior of the skyward surfaces, however, the water retaining property of the rust layer after rain fall, which shows the same dependency on the exposure inclinations as the corrosion rates, must be taken into consideration.