Abstract
The similarity between results of dew-cycle corrosion tests and the results of field exposure has been evaluated by comparing the corrosion rate of mild steel with that of weathering steel at several dew-cycle conditions in 20ppm SO2. It was known that both the similarity and acceleration of tests are, particularly in the case of steel, largely dependent on the drying process.
An attempt was made to convert the corrosion quantity vs. testing time curve, which was generally used, into the curve of corrosion quantity vs. total dewing time, that is testing time minus drying time. If Fe (II) rust, formed during wet or dew period, is sufficiently oxidized to Fe (III) rust in the process of drying, the slope of corrosion quantity vs. total dewind time should become sharper. This is because the reduction of Fe (III) rust to Fe (II) during the succeeding dew period induces the corrosion of steel. The period 30 minutes of light dewing (temp. of specimen: 35°C; atmosphere: 37°C, 100% RH) showed a good similarity between the test results and the results of field exposure. And the corresponding optimum drying period seemed to exist between 30 to 60 minutes.
