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Coastal Erosion Calculator

Design cathodic protection systems for submerged steel structures using sacrificial anodes. Calculate current demand, anode mass, count, and resistance per DNV-RP-B401.

Inputs

Results

Total current demand (A)

60

Total anode mass required (kg)

8,212.5

Number of anodes

33

Actual mass installed (kg)8,250
Single anode resistance (Ω)0.14
Total circuit resistance (Ω)0
Current capacity ratio1.01
How to Use This Calculator
  1. Enter bare steel area (m2) requiring cathodic protection.
  2. Enter design current density (mA/m2) for the environment: tropical ~150, temperate ~100, arctic ~80.
  3. Enter design life (years), anode capacity (Ah/kg), and mass per anode (kg).
  4. Read total current required (A), number of anodes needed, and total anode mass (kg).
  5. Verify anode spacing and coverage meets DNV-RP-B401 or project specification requirements.

How the result changes with Bare steel area (m²)

Bare steel area (m²)Total current demand (A)Total anode mass required (kg)Number of anodes
10,0011,200.12164,266.4658
35,0014,200.12574,891.42,300
65,0007,8001,067,6254,271
90,00010,8001,478,2505,913

What each input means

Bare steel area (m²)
Total exposed (uncoated) steel surface area requiring protection.
Current density (mA/m²)
Design mean current density. Tropical ~150, temperate ~100, arctic ~80 mA/m².
Design life (years)
Required cathodic protection design life.
Anode capacity (Ah/kg)
Electrochemical capacity. Al-Zn-In ~2000, Zn ~780 Ah/kg.
Mass per anode (kg)
Net mass of a single sacrificial anode.
Utilization factor
Anode utilization factor u (typically 0.8-0.9).
Anode length (m)
Length of anode for resistance calculation (Dwight formula).
Anode effective radius (m)
Effective radius of anode cross-section.
Seawater resistivity (Ω·m)
Electrical resistivity of seawater. Typical 0.2-0.35 Ω·m.

What each result means

Total current demand (A)
Required protection current for the entire structure.
Total anode mass required (kg)
Minimum anode material mass to last the design life.
Number of anodes
Minimum number of anodes (rounded up).
Actual mass installed (kg)
Total mass of whole anodes as installed.
Single anode resistance (Ω)
Electrical resistance of one anode in seawater (Dwight formula).
Total circuit resistance (Ω)
Parallel resistance of all anodes.
Current capacity ratio
Ratio of available current to required current. Must exceed 1.0 for adequate protection.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Bare steel area (m²) = 500, Current density (mA/m²) = 120, Design life (years) = 25, Anode capacity (Ah/kg) = 2000 = 9 input(s) provided
  2. Calculate Total current demand
    Total current demand = (surfaceArea * currentDensity) / 1000
    60 = 60
  3. Calculate Total anode mass required
    Total anode mass required = totalCharge / (utilFactor * anodeCapacity)
    8212.5 = 8212.5
  4. Calculate Number of anodes
    Number of anodes = ceil(totalAnodeMass / anodeMassEach)
    33 = 33
  5. Calculate Actual mass installed
    Actual mass installed = numAnodes * anodeMassEach
    8250 = 8250
  6. Calculate Single anode resistance
    Single anode resistance = (rhoSW / (2 * π * L)) * (ln((4 * L) / r) - 1)
    0.1361 = 0.1361

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