THE EFFECTS OF SHAFT GROUNDING ON THE CORROSION OF UNDERWATER HULLS

摘要

A reference electrode data acquisition system has been developed that allows monitoring of hull potentials at a number of locations around the underwater hull of a ship while at sea, without the need for over-the-side cables or though-hull fittings. The underwater data loggers used in this system showed that the ship to which they had been fitted was not completely protected from corrosion in the stern area, even when the ship was alongside. The loggers were also able to detect changes in configuration of the cathodic protection system that altered the current distribution around the hull of the ship. The data loggers demonstrated that the steel hull was subject to accelerated corrosion as a result of galvanic coupling to the bronze propellers through the shaft grounding systems when the cathodic protection system was shut off. Measurements placed the extent of this galvanic corrosion at 73 kg per year while at sea. This work highlighted the need for further experiments to determine the distribution of the galvanic corrosion current around the ship hull.