liminfoCathodic Protection Calculator
Free web tool: Cathodic Protection Calculator
Typically 85%
Calculation Details
Design Formula
About Cathodic Protection Calculator
The Cathodic Protection Calculator is a free, browser-based engineering tool that designs galvanic (sacrificial anode) cathodic protection (CP) systems for steel structures in soil or seawater environments. Cathodic protection is an electrochemical corrosion prevention technique in which a sacrificial anode — a metal with a more negative electrochemical potential than steel — is electrically connected to the structure to be protected. The anode preferentially corrodes, releasing electrons that flow to the steel structure and suppress the oxidation reaction that causes rust.
To use the calculator, you specify the protected surface area (in m²), the structure type (bare steel in soil, coated steel with good/average/poor coating, bare or coated steel in seawater, or submerged concrete), the anode material (zinc, standard magnesium, high-potential magnesium, or aluminum), the design life in years, the anode utilization factor (typically 85%), and the individual anode weight. The tool calculates the required protection current using the appropriate current density for the structure type, determines the total charge (in ampere-hours) needed over the design life, computes each anode's effective capacity based on its electrochemical output, efficiency, and utilization, then divides total charge by capacity per anode to determine the minimum number of anodes required.
Corrosion engineers, pipeline engineers, offshore structure designers, and infrastructure maintenance professionals rely on cathodic protection calculations to comply with standards such as NACE SP0169 and ISO 15589. The tool displays detailed calculation steps — structure type, protected area, current density, total current required, total charge, anode type and capacity, current per anode, and total current output — so engineers can verify every step. A warning is displayed if total anode output may be insufficient over the full design life. All calculations run locally in your browser.
Key Features
- Supports 4 anode materials: zinc (Zn), standard magnesium (Mg), high-potential magnesium, and aluminum (Al)
- Covers 7 structure types with pre-set current densities from bare steel (10.8 mA/m²) to seawater (65 mA/m²)
- Calculates required anode count using: I_total = Current Density × Area, then N = Total Charge / (Anode Weight × Utilization × Capacity × Efficiency)
- Total anode weight output for material procurement and cost estimation
- Full calculation details panel: current density, total current, charge, anode capacity, current per anode
- Warning alert when total anode output may not meet requirements throughout design life
- 100% client-side processing — engineering data never leaves your browser
- Dark mode support and clean layout for professional use
Frequently Asked Questions
What is cathodic protection and why is it needed?
Cathodic protection (CP) is an electrochemical method to prevent corrosion of metal structures. When a structure is buried in soil or submerged in water, the electrochemical potential difference between different areas drives corrosion. CP works by applying a more negative electrochemical potential to the entire structure surface, either through sacrificial anodes (galvanic CP) or an impressed current system (ICCP). Without CP, buried pipelines and offshore structures can corrode rapidly.
What is a sacrificial anode?
A sacrificial anode is a piece of reactive metal (typically zinc, magnesium, or aluminum) that is more electrochemically active than the steel structure it protects. When electrically connected to the steel, the anode preferentially oxidizes (corrodes) instead of the steel, releasing electrons that flow through the metal to suppress corrosion on the protected structure. The anode gradually "sacrifices" itself — hence the name.
How does the calculator determine the number of anodes needed?
The calculation follows standard galvanic anode design: (1) Calculate total protection current: I = Current Density × Protected Area. (2) Calculate total charge over design life: Q = I × Life × 8,766 hours/year. (3) Calculate effective capacity per anode: C = Anode Weight × Utilization Factor × Electrochemical Capacity × Efficiency. (4) Number of anodes: N = Q / C, rounded up to the nearest whole number.
What anode material should I choose?
Zinc anodes are standard for seawater and moist soil applications, offering reliable performance at moderate cost. Magnesium anodes are preferred for high-resistivity soils because their more negative potential (-1.55V or -1.75V) drives higher current in resistive environments. Aluminum anodes are used primarily in seawater and offshore applications — they offer the highest electrochemical capacity (2,700 A·h/kg) and are lightweight.
What is the utilization factor and why is it typically 85%?
The utilization factor accounts for the fact that a sacrificial anode cannot be fully consumed before it loses effectiveness. As an anode corrodes, it may become too small to maintain good electrical contact or the remaining material becomes less active. Using 85% (0.85) means only 85% of the anode mass is counted as usable for protection. This is a standard conservative design factor used in industry guidelines.
What are typical current densities for different structure types?
Current densities used in this tool: Bare steel in soil: 10.8 mA/m² (high, no coating protection). Coated steel with good coating: 0.1 mA/m² (excellent coating provides most protection). Coated steel with average coating: 1.0 mA/m². Coated steel with poor coating: 5.0 mA/m². Bare steel in seawater: 65 mA/m² (seawater is highly conductive and aggressive). Coated steel in seawater: 5.4 mA/m². Submerged concrete: 2.0 mA/m².
What standards does cathodic protection design follow?
Common standards include NACE SP0169 (Control of External Corrosion on Underground or Submerged Metallic Piping Systems), ISO 15589-1 (Petroleum industries — Cathodic protection of pipeline transportation systems), and DNV-RP-B401 (Cathodic Protection Design for offshore structures). This calculator implements the fundamental current and charge calculations that underpin all these standards.
Is this calculator free to use?
Yes, the Cathodic Protection Calculator is completely free with no usage limits and no account required. All anode calculations run locally in your browser, so your structural dimensions and design parameters are never sent to any server.