A battery based on Mg–AgCl with sea water as electrolyte was developed for propulsion of a naval system. In one occasion, the tie rod, conduit pipe and the copper bus rod each covered with polymer sleeve were found damaged. The copper bus rod was melted probably by amplified resistance and subsequent heating. Localized cross-sectional reduction (and thus increased resistance, R) seems to have aggravated heating by Joule heating (J = I2R) effect. Subsequently, it led to partial dissolution, embrittlement, softening and final fracture of the steel tie rod in the said sequence. There was no material deficiency. Chemical composition, microstructure and hardness values of the failed components indicate that the steel tie rod was made of the as-specified EN 24 type of low alloy steel in hardened and tempered condition, while copper bus rods were made of pure copper of 99.50% purity. Damage of the conduit tube was not related to the failure of steel tie rod and copper bus rod, although it indirectly offers clues that melting of copper happened and the molten copper reached many locations within the system.
