Stray Current Corrosion of Steel

Abstract

Stray current corrosion has been of major concern to the Navy over the past few years. Serious corrosion attributable to stray current has occurred in seawater or brackish water on several occasions where the possibility of the corrosion having resulted from improper grounding during welding was precluded. The experimental technique used isolates the bipolar anodes and bipolar cathodes so that stray current corrosion parameters can be studied and quantized. Data have been presented on the effect of various stray direct current densities on the corrosion rates and the electrode potentials of steel both as common electrodes and as bipolar (intermediate) electrodes. The metal‐loss rates have also been compared to the theoretical values based on the reaction Fe‐2e = Fe+2 The mean dissolution potential for steel in 0.6M (3.5%) NaCl solution was approximately ‐0.7V to the Ag/AgG reference electrode, and was essentially independent of the current density. Similar values were observed for anodes, bipolar anodes, and freely corroding control specimens. Steel could not be polarized cathodically to a mean potential more negative than ‐1.015V to the Ag/AgCl reference electrode. Mean potentials either more positive than ‐0.7V or more negative than ‐1.015V were observed only when the measurement included an IR. Potential measurements were useful to detect stray current on steel only at relatively high current densities. The corrosion characteristics of steel anodes and bipolar anodes were similar at any one current density, but varied with current density.

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