Anode Formulae (+3)

Anode Formulae

Equations for anode mass, current output, resistance, and utilisation.

Detection heuristics:

• Keywords: "anode mass", "current capacity", "utilisation factor", "anode resistance"
• Symbols: M_a, C_a, u, R_a, I_a
• Units: kg, Ah/kg, ohm, ampere
• Geometric terms: "length", "radius", "cross-section"

Key extraction fields:

- content_type: equations
  domain: cathodic_protection
  sub_type: anode_formula
  data:
    name: "Anode current output"
    expression: "I_a = (E_c - E_a) / R_a"
    variables:
      - {symbol: I_a, name: "anode current output", units: A}
      - {symbol: E_c, name: "structure protection potential", units: V}
      - {symbol: E_a, name: "anode closed-circuit potential", units: V}
      - {symbol: R_a, name: "anode resistance", units: ohm}
    source: "DNV-RP-B401 Section 4.3"

Anode resistance formulae (by geometry):

• Flush-mounted: McCoy's formula — R = ρ / (2π × S) where S = shape factor
• Stand-off: Dwight's formula — depends on length/radius ratio
• Bracelet: Peterson's formula — for cylindrical anodes on pipelines

Coating Breakdown Factors

Linear degradation model: f_c(t) = f_ci + k × t, clamped at 1.0.

Detection heuristics:

• Keywords: "coating breakdown", "breakdown factor", "coating category"
• Symbols: f_c, f_ci, k, t
• Pattern: table with Category I/II/III rows, f_ci and k columns
• Section reference: typically Section 3.4 in B401

Key extraction fields:

- content_type: constants
  domain: cathodic_protection
  sub_type: coating_breakdown
  data:
    name: "Coating Category I breakdown parameters"
    values:
      f_ci: {value: 0.05, units: dimensionless, description: "Initial breakdown factor"}
      k: {value: 0.020, units: "1/year", description: "Degradation rate"}
    applicability:
      category: "I"
      description: "High quality >= 300 um epoxy"
    source: "DNV-RP-B401 Section 3.4.6"

Category definitions (B401-2021):

Design Life Tables

Design life parameters for CP system sizing.

Detection heuristics:

• Keywords: "design life", "service life", "lifetime", "years"
• Pattern: table with years in one column, other parameters varying
• Often cross-referenced with temperature and environmental severity
• Section reference: typically early sections of B401/F103

Key extraction fields:

- content_type: tables
  domain: cathodic_protection
  sub_type: design_life
  data:
    title: "CP design life parameters"
    columns: [design_life_years, mean_current_density, final_current_density]
    applicability:
      temperature_band: ">12-17°C"
      environment: "seawater"
    source: "DNV-RP-B401 Table 3-2"

Current Density Values

Design current densities by zone and environmental condition.

Detection heuristics:

• Keywords: "current density", "mean current density", "initial current density", "final current density"
• Units: mA/m², A/m²
• Pattern: table indexed by zone (submerged/splash/atmospheric) and temperature
• Distinction between coated and bare steel values

Key extraction fields:

- content_type: constants
  domain: cathodic_protection
  sub_type: current_density
  data:
    name: "Mean design current density — submerged, coated"
    current_density_type: mean   # mean | initial | final
    value: 0.060
    units: "A/m²"
    applicability:
      zone: submerged
      temperature_range: ">12-17°C"
      surface_condition: coated
    source: "DNV-RP-B401 Table 3-1"

Structured discriminator: Always include current_density_type (one of mean, initial, final) — do not encode the type only in the name field.

Zone classification: