Cathodic Protection Calculator

Professional Article

1) Cathodic protection in construction assets

Cathodic protection (CP) is a corrosion control method used on buried or submerged metallic structures such as pipelines, tanks, piles, and sheet piling. It reduces metal loss by shifting the structure’s electrochemical potential so corrosion reactions are suppressed. Projects typically combine coatings for barrier performance and CP to protect coating holidays and aging defects.

2) Key inputs and where the numbers come from

The calculator uses surface area, a coating breakdown factor, a design current density, and a design life. Surface area can be measured from drawings, takeoffs, or as-built records. Breakdown factors may be derived from coating quality, inspection history, and expected damage rates during installation and service.

3) Coating breakdown drives current demand

Required current is proportional to exposed area. For example, 250 m² with 20 mA/m² at a 0.05 breakdown factor yields 0.25 A. If breakdown increases to 0.15, current triples to 0.75 A. For risk management, evaluate best-case, expected, and conservative scenarios.

4) Selecting current density with practical ranges

Current density reflects environment severity and coating performance. Lower values are common for well-coated, low-resistivity soils, while higher values can apply in marine splash zones, aggressive soils, or poorly coated surfaces. Use site tests, experience, and standards-based guidance to justify the chosen density.

5) Translating demand into anode mass

Total charge demand is calculated in amp-hours over the design life (8760 hours per year). Anode mass is then estimated from capacity (Ah/kg) and utilization. If demand is 43,800 Ah, with 1200 Ah/kg and utilization 0.85, required mass is about 43.0 kg.

6) Galvanic versus impressed-current planning

Galvanic systems are simpler and self-powered but limited in output. Impressed-current systems can deliver higher current and better control. For impressed-current planning, the tool estimates rectifier voltage using circuit resistance and a polarization allowance, then reports DC power.

7) Installation, verification, and documentation

Good results depend on installation quality. Confirm continuity bonds, insulation joints, test stations, and cable connections. Perform commissioning checks such as current output, potentials, and depolarization where applicable. Record soil or water conditions, coating repairs, and test readings for lifecycle traceability.

8) Using exports to support decisions

The CSV and PDF exports help compare scenarios, communicate assumptions, and archive calculation packages. Attach exports to method statements, inspection plans, and handover documentation. When values change (area, breakdown, or current density), rerun the tool to keep procurement quantities and power estimates aligned.

FAQs

1) What does coating breakdown factor represent?

It is the estimated fraction of surface area exposed through coating defects, damage, or aging. Higher breakdown increases required current and anode mass, so it strongly affects sizing and cost.

2) How do I choose a current density value?

Use project experience, standards-based guidance, and site conditions like soil resistivity, moisture, and chloride exposure. Run multiple values to bracket uncertainty and document the basis for the selected design density.

3) Why does design life change anode mass so much?

Total charge demand scales with operating hours. Doubling design life roughly doubles amp-hours, which increases required anode mass or the rectifier duty needed to deliver protection for the full period.

4) Is the rectifier voltage result accurate for field use?

It is a planning estimate based on a simplified circuit resistance and an allowance. Real voltage depends on groundbed design, soil resistivity, wiring, contact quality, and operating potential criteria.

5) What does utilization factor mean in practice?

Not all anode material can be consumed effectively. Utilization accounts for anode core, uneven wear, and end-of-life limits. Use manufacturer or standard values appropriate for the selected anode type.

6) Should I size anodes using average or peak current?

Many designs use a higher initial current and a lower maintenance current. This calculator assumes constant current; for advanced designs, evaluate stages or use conservative current to ensure life requirements are met.

7) What checks confirm the system is working?

Verify output current, continuity, and protection criteria using potential measurements at test stations. Document commissioning readings and repeat surveys periodically to confirm performance as coating condition and environment evolve.