An application of the coulostatic method to corrosion rate measurements

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Abstract
The coulostatic method avoids some of the essential short‐comings of the polarization resistance method; in particular, it enables the time to be reduced because in most cases it is sufficient to follow potential decay down to 50% of the original value (this requires less than 0.1 sec). Experiments in 1 n sulfuric acid (with iron) in deionized water, in aerated and deaerated 0.1 m sodium chloride solutions and in an aerated solution containing 0.05 m NaCl + 0.1 m sodium hydrogen carbonate + 0.03 m sodium sulfate (with steel) yield corrosion losses which are well reproducible with the results of other methods, even when surface layers are formed on the metals. Tests with steel 304 in ferric chloride solution and (under crevice corrosion conditions) with steel 403 in 5% NaCl‐solution show that the coulostatic method yields reproducible results even in the case of local corrosion with very small amounts of corrosion products being formed. Reliable results are obtained under the conditions of subsurface corrosion, too, so that a rapid screaming of the protective value of various coatings systems becomes feasible.

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