Stray Current Electrolytic Corrosion: An Unrecognized Enemy

Abstract

This paper examines the state of the art regarding Electrolytic Corrosion which is often mis-named as electrolysis. This corrosion of underwater metals is understood to be caused by stray currents passing through the water surrounding a vessel regardless of source. Such current flow causes corrosion (ion loss) of any immersed metals which happen to serve as the grounding conductor for any stray electrical currents. Normally, with Direct Current (DC) stray currents the ion loss at the metallic receptor (anode) is continuous, but because the majority of DC stray currents are of galvanic origin they occur at extremely low amperages (measured in milli-amps). Consequently, cumulative ion loss is slow and a long time passes before deterioration may be noticeable. To protect underwater metals against galvanic DC corrosion, cathodic protection techniques utilizing sacrificial zinc anodes were developed during the first half of the 20th century, at a time when nearly all small boats either had no onboard circuitry or only had 12 volt DC electrical systems.