Cathodic Protection (CP) Accessories
Sacrificial anodes and CP system components protect buried and submerged pipelines from external corrosion. Used in conjunction with external coatings.
3.1 Sacrificial Anodes
Galvanic anodes corrode preferentially to protect the steel pipeline. Selection depends on soil resistivity (onshore) or water salinity (offshore).
Magnesium Anodes (Onshore / Soil)
Parameter Detail
Alloy High-potential Mg alloy (ASTM B843 AZ63B or M1C)
Application Buried pipelines in soil resistivity > 2,000 ohm-cm
Typical Shapes Packaged anode (Mg ingot cast around steel core, backfilled with gypsum/bentonite/clay in cloth bag)
Weight Range 7.7 kg (17 lb) to 32 kg (70 lb)
Connection Insulated copper cable with thermite weld or pin brazing to pipe
Standards ASTM B843, NACE SP0169
Zinc Anodes (Seawater / Marine)
Parameter Detail
Alloy ASTM B418 Type I or Type II (Special High Grade Zinc)
Application Subsea pipelines, offshore structures, river crossings
Typical Shapes Bracelet (split ring clamp-on), stand-off, sled anodes
Weight Range 10 kg to 500+ kg
Standards ASTM B418, DNV-RP-B401
Aluminum Anodes (Offshore / Seawater)
Parameter Detail
Alloy Al-Zn-In (ASTM B418 Type III)
Application Offshore pipelines, subsea templates (superior capacity-to-weight ratio vs. zinc)
Capacity ≥ 2,500 A·h/kg (high efficiency)
Typical Shapes Bracelet, stand-off, hull anodes
Standards ASTM B418, DNV-RP-B401
Anode Selection Guide:
Environment Recommended Anode Reason
High-resistivity soil (>5,000 ohm-cm) Magnesium Higher driving voltage
Low-resistivity soil (<3,000 ohm-cm) Zinc or Magnesium Zinc for permanent; Mg for temporary Seawater immersion Aluminum or Zinc Aluminum preferred for weight savings Brackish water (estuaries) Zinc or Aluminum Dependent on salinity Hot buried pipelines (>60°C) Zinc Mg passivation at elevated temperature
3.2 CP Test Stations & Monitoring
· Test Station Posts: Above-ground terminals for pipe-to-soil potential measurement
· Cable Connection Kits: Thermite weld kits, pin brazing kits, cable-to-pipe connections
· Permanent Reference Electrodes: Cu/CuSO4 or Ag/AgCl electrodes for permanent monitoring installations
· Junction Boxes: Buried junction boxes for CP cable routing
3.3 Electrical Isolation Components
· Monolithic Insulation Joints / Flanges: Electrically isolate pipeline sections
· Isolation Gaskets & Sleeves: For bolted flange isolation
· Surge Protection: Lightning arrestors and AC mitigation for pipelines near power lines