Why Cathodic Protection Is Essential for Marine Steel
Steel structures exposed to seawater face corrosion rates of 0.1-0.5 mm per year. Cathodic protection (CP) is the most reliable method for preventing corrosion of submerged marine steel structures.
Fundamentals
CP converts the entire steel structure into a cathode, eliminating anodic dissolution. Protection criteria: -0.80V or more negative vs Ag/AgCl reference electrode. Design target: -0.85V to -1.00V.
Sacrificial Anode CP (SACP)
Anode Materials
Zinc: 780 Ah/kg, 0.20V driving voltage. Aluminum: 2,600-2,800 Ah/kg (3x zinc), 0.25-0.30V, standard for new vessels. Magnesium: 0.7V, for soil/freshwater.
Design Methodology
Current demand: bare steel 100-150 mA/m2, coated 5-30 mA/m2. Anode mass: W = (I x t x 8760) / (U x utilization factor).
Impressed Current CP (ICCP)
Anode Types
MMO (Mixed Metal Oxide): Titanium substrate, 2,000-6,000 Ah/kg capacity. Platinum-Niobium: For space-limited applications. Flexible MMO ribbon: Internal tank protection.
Design
Rectifier with 25% margin. Anode placement by computer modeling. Current: hundreds of amps for ships, thousands for offshore platforms.
Standards
DNV-RP-F107, NACE SP0169, NACE SP0387, ISO 15589-2. Classification society rules (ABS, DNV, Lloyd’s, BV).
CoreMetal Steel supplies ABS/DNV/Lloyd’s certified marine steel optimized for CP compatibility with pre-welded anode brackets available.