Ánodo de Zinc

The zinc anode is a sacrificial anode used for cathodic protection of steel, cast iron, naval bronze, and other metals exposed to seawater or conductive brackish environments. It works because zinc has a more active potential than the protected structure: once electrically connected, the anode delivers current to the base metal and is consumed in a controlled way before the hull, tank, pile, sea chest, or heat exchanger.

In marine applications, high-purity zinc or alloy is normally specified per ASTM B418 and, where applicable, requirements such as MIL-DTL-18001 / MIL-A-18001. Its main advantage is not the highest capacity per kilogram, but its stable behavior in seawater, low risk of overprotection, and compatibility with naval equipment where a moderate, predictable current is required.

Chemical composition per ASTM B418

The values in this table are nominal reference data. Before using them in engineering decisions, review the technical notice at the end of this page and the raw-material certificate of your batch.

Type I (Zn-Al-Cd alloy) is the usual choice for seawater and conductive brackish water; Type II (high-purity zinc) is specified for soils and buried structures with backfill. The type required by the project is confirmed when quoting.

Zinc-focused comparison

The values in this table are nominal reference data. Before using them in engineering decisions, review the technical notice at the end of this page and the raw-material certificate of your batch.

Selection guide

• Use zinc when the electrolyte is seawater, typically with resistivity near 20-30 ohm·cm, or sufficiently conductive brackish water.
• In brackish water of 50-200 ohm·cm, zinc can work if chlorides and good electrical continuity are present; for large surfaces, compare against aluminum by weight and service life.
• Do not select zinc as the first option for fresh water or soils with resistivities above 1,000 ohm·cm; the available current may be low, and magnesium or impressed current should be evaluated.
• For buried or submerged steel, the protection criterion is verified in the field with structure-to-electrolyte measurements; for buried pipelines, the -850 mV vs Cu/CuSO4 criterion of NACE/AMPP SP0169 is used as technical reference, applied by competent personnel.
• Size by exposed area, coating condition, design life in years, required current, anode utilization factor, and Ah/kg capacity; do not choose by nominal weight alone.

Mounting and inspection

• The anode steel core or strap must have real metallic contact with the structure. On hulls, tanks, and heavy structures, strap welding is used; on removable equipment, bolting with washers and clean surfaces may be used.
• Do not paint the anode or cover its active face with coatings, greases, or sealants. If the structure is painted, leave the anode exposed and preserve electrical continuity.
• Avoid mounting the anode over paint, loose oxide, or insulating gaskets. Contact resistance must be low for current to flow.
• Inspect at haul-outs, maintenance, or scheduled shutdowns. As a practical rule, schedule replacement when the anode is 50-70 % consumed, or earlier if it has lost fixation, continuity, or effective mass.
• In mixed systems, do not combine metals without reviewing the design: zinc and aluminum do not always share current uniformly, and magnesium can overprotect in seawater.

Data for quoting

• Indicate whether you need a plate, bar, bracelet, disc, or pencil anode, or a design with a strap.
• Send dimensions, target weight or drawing, structure material, operating medium, and temperature.
• For vessels, report length, hull material, navigation area, propulsion type, and current number of anodes.
• For tanks, piles, or heat exchangers, send approximate exposed area, coating, expected service life, and mounting method.
• Attach photos of the current mounting, hole spacing, bolt diameter, or welding specification if a plant standard already exists.