OFFSHORE TOOLKIT · CALCULATOR 15

Cathodic Protection (Sacrificial Anode) Life Calculator

Estimates how long a sacrificial anode will last against a given current demand, or how many anodes are needed to cover a target design life — using the standard DNV-RP-B401 anode consumption methodology.

Structure / location name (optional, shown on the printed report)

Anode data

Anode net mass (kg)

Anode material

Utilization factor

Current demand

Current demand per anode (A)

From the structure's CP design calculation — typically protected area × design current density, divided among the anodes. Enter directly here, or use the helper below.

Helper: protected area (m²)

Helper: current density (mA/m²)

If both helper fields are filled, they override the current demand above (area × density, divided by 1000 for mA→A). Design current densities vary widely by zone and location — typical published ranges run roughly 50–180 mA/m², but always confirm against DNV-RP-B401 or your project's design basis rather than relying on this range.

ANODE LIFE

—

Total anode capacity—

Current demand used—

Structure / location name (optional, shown on the printed report)

Target

Target design life (years)

Total current demand for the structure (A)

Anode data (per anode)

Anode net mass (kg)

Anode material

Utilization factor

ANODES REQUIRED

—

Total Ah needed—

Ah per anode—

Actual life at this count—

Quick reference

The formula

Anode life (years) = (Mass × Utilization factor × Electrochemical capacity) ÷ (Current demand × 8760)
Per DNV-RP-B401 methodology — the standard reference for offshore sacrificial anode CP design
8760 converts ampere-hours to ampere-years (hours in a year)

Typical design values

Material	Design capacity	Typical use
Aluminum alloy (Al-Zn-In)	2000 Ah/kg	Most common offshore choice
Zinc alloy	780 Ah/kg	Lower driving voltage, some subsea uses
Magnesium	1230 Ah/kg	Higher driving voltage, mainly buried/soil

Utilization factor

Accounts for anode material that becomes ineffective before full consumption due to shape change and loss of electrical contact
Stand-off/bracelet anodes: typically 0.80
Flush-mounted anodes: typically 0.75, since more material is left unusable against the structure

Where current demand comes from

Current demand = protected surface area × design current density, from a full CP design calculation
Design current density depends on water depth zone (splash/submerged/buried), location, water temperature, and design life phase (initial/mean/final)
This tool's area × density helper is illustrative only — always use the project's actual design current density from DNV-RP-B401 or the design basis, not a generic assumption