Abstract
The influence of quantity of dewing and interval of dew-cycle on the corrosion of mild steel panel exposed in an atmosphere of 20ppm SO2, 95-100% R. H. was investigated and evaluated from the viewpoint of similarity to field test, acceleration of test and reproducibility of test result.
The grade of dewing was classified into the critical dewing (temperature difference between specimen and atmosphere: TD≅0), the light dewing (TD=2°C) and the heavy dewing (TD=5°C).
As dewing period (min)/drying period (min)15/15, 30/30, 60/60 and 120/120 were selected, besides continuous dewing during the test period of 24hr.
In heavy dewing, the shortest interval of 15min/15min showed the largest amount of corrosion, but the similarity to the corrosion pattern of field test was weak. The reproducibility under the condition of the cyclic heavy and light dewing was very good, while that in the cyclic critical dewing was unstable. Continuous dewing except critical one had the tendency to reduce acceleration and similarity.
To satisfy the similarity, acceleration and reproducibility in the laboratory test, the condition of light dewing and comparatively rapid dew-cycle as 30min/30min was recognized to be optimum.
