Effect of Acid Rain on Corrosion of Carbon Steel

摘要

In view of scarcity of data as to whether or not acid rain that falls in unpolluted areas accelerates atmospheric corrosion of carbon steel, a series of atmospheric exposure test was conducted in the unaffected atmosphere of Maebashi, where specimens were tested with and without periodic exposures to artificial acid or neutral rain. Exposures to acid (pH 3.5) and neutral 5 percent NaCl solutions 3 times a week as artificial rains accelerated corrosion by 25 times regardless of the pH of the rains. Twice a week exposures to artificial sea water diluted to 1/6 and 1/30 and acidified to pH 2.5 resulted corrosion about 3 times larger than similar exposure to corresponding neutral artificial rains, demonstrating accelerating effect of acid rain. The cause of this acceleration was attributed to the detrimental effect of acid rain on the protective nature of the rust films to atmospheric corrosion. This is caused either by the destructive action of acid rain during its contact or the formation of anion nests by the constituents of acid rain during subsequent atmospheric exposure, but the mechanism has not been specified by this study. From the present data and scanty literature, it is deduced that atmospheric corrosion of carbon steel is accelerated several times when the sea salt deposition is less than moderate and the adverse effect of acid rain is considerable.