Development and Qualification of Sacrificial Anodes for Ship-Hull Corrosion Protection in Marine Environments: A Critical Narrative Review

Abstract

Sacrificial-anode cathodic protection remains integral to the corrosion management of immersed ship structures and seawater-containing compartments, yet anode selection is frequently reduced to nominal alloy capacity or laboratory electrochemical efficiency. Such a reduction overlooks the interaction between alloy activation, steel or aluminium substrates, coating deterioration, seawater chemistry, hull geometry and environmental release. This critical narrative review evaluates the development and qualification of zinc- and aluminium-based galvanic anodes for maritime service, with particular attention to ship-hull systems rather than indiscriminate extrapolation from offshore structures. Literature published principally between 2005 and 9 August 2026 was critically considered alongside foundational studies, recognised technical specifications and ecotoxicological investigations. The synthesis distinguishes three related but non-equivalent outcomes: electrochemical activity under a prescribed test, delivery of distributed protective current to a coated structure and durable protection under fluctuating service conditions. Alloying with indium, magnesium, tin, silicon or selected rare-earth elements can alter activation and dissolution morphology, but benefits are composition-, processing- and exposure-specific. Contrasting efficiencies derived from mass loss and hydrogen evolution show why apparently superior laboratory performance cannot be accepted without independent qualification. Electrical resistance, coating defects, anode location, uneven immersion and mixed-metal components create system-level constraints that alloy optimisation alone cannot resolve. Environmental evidence establishes that galvanic protection transfers metal mass into surrounding water and sediment, although bioavailability and biological response vary substantially with local chemistry and the form of the released material. A defensible development pathway therefore combines compositional control, reproducible casting, multi-method discharge testing, validated potential and current-distribution models, and field monitoring coupled with environmental assessment. The review identifies paired laboratory–field validation, realistic variable-service testing, quantitative release accounting and explicitly substrate-specific design as the most urgent research priorities. Sacrificial-anode innovation should be assessed by verified protection delivered over service life, not by isolated electrochemical indicators.