Introduction

Seawater is inherently corrosive. If a vessel’s hull and submerged steel components are not adequately corrosion-resistant, the safety implications are obvious. To address this, corrosion-resistant materials and cathodic protection measures—such as zinc sacrificial anodes—are commonly applied. What are the performance characteristics of marine zinc anodes and where are they most suitable? Industry experts provide the answers below.

Principle of Sacrificial Anode Protection

Experts specializing in aluminum and zinc alloy anode development explain that sacrificial (galvanic) cathodic protection works by electrically connecting a more active metal or alloy to the steel structure to be protected. The more active metal (for example, zinc) acts as the anode and corrodes preferentially, thereby protecting the steel (which becomes the cathode).

In practice, zinc blocks are typically fitted to the stern and to the parts of the hull below the waterline to prevent corrosion of the hull. Beyond ship hulls, electrochemical protection is also widely used for protecting submarine cables, oil pipelines, buried equipment and chemical plant structures in seawater or brackish environments.

Suitability and Typical Use Conditions

Marine zinc anodes are especially suitable for low-resistivity, relatively moist environments. Their key advantages include high current efficiency, low self-corrosion rate, long service life, and a degree of self-regulation in current output. When zinc anodes come into contact with other steel structures, they do not produce sparks and they rarely cause “over-protection” problems.

Note: Typical galvanic systems operate with a driving voltage generally below 0.7 V, which limits the cathodic protection current output. If a storage tank or another structure becomes electrically shorted to connected elements, the tank may become difficult to protect and the sacrificial anode system may be rapidly consumed.

Common Marine Applications

Zinc anodes (and zinc-alloy anodes) are used extensively in marine and coastal applications, including:

• Ship hull protection and external underwater surfaces

• Ballast tanks and sea chests

• Offshore platforms and subsea valves / pressure housings

• Subsea pipelines laid in seawater (often used in ring or distributed arrangements)

• Heat exchangers and condensers in seawater service, seawater pumps

• Pipelines, cables and other metallic structures in low-resistivity soils and coastal installations

Performance Characteristics of Marine Zinc Anodes

The principal performance attributes of shipboard zinc anodes are:

• Low self-dissolution (low self-corrosion) and high current efficiency.

• Good self-regulating behavior of the generated protection current.

• Long protection life—typical service lives can range broadly and under favorable conditions reach 20–30 years.

• Minimal risk of inducing sparks on mechanical contact and low likelihood of “over-protection.”

Typical Alloy and Product Notes

Marine zinc anode products are often produced as zinc-aluminum-cadmium (ZAC) type alloys. These ZAC sacrificial anodes are cast from high-purity zinc together with controlled additions of aluminum and cadmium to achieve the desired electrochemical performance and consumption rate.

Summary

Marine zinc sacrificial anodes remain a widely adopted, economical and effective method for protecting ships and offshore steel structures from seawater corrosion. When selected and installed correctly—and when the system design accounts for environmental resistivity and potential shortcutting—the zinc anode system provides reliable long-term protection for a broad range of marine engineering applications.