Cathodic Protection

cathodic protection banner 8Cathodic protection, abbreviated as CP, is a technique used to prevent corrosion of metal structures and equipment by making them the cathode of an electrochemical cell.  Corrosion occurs when metal is exposed to an electrolyte, such as water or soil, and a flow of electrons occurs between the metal and the electrolyte, resulting in the metal corroding.  By making the metal structure the cathode of an electrochemical cell, the flow of electrons is reversed, and corrosion is prevented.  CP is typically achieved by connecting a sacrificial anode made of a more active metal, such as zinc or magnesium, to the metal structure being protected.  The sacrificial anode corrodes instead of the metal structure, providing cathodic protection.  Another method of cathodic protection is impressed current cathodic protection, which involves using a direct current power source to provide the required current flow to the structure being protected.

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Cathodic Protection Index

CP is commonly used in a variety of industries, including oil and gas, marine, and transportation, to protect metal structures such as pipelines, tanks, and ships from corrosion.  It is a highly effective technique for preventing corrosion, and can extend the life of metal structures significantly.  CP systems require regular monitoring and maintenance to ensure that they continue to function properly over time.  Corrosion engineers and technicians are responsible for designing, installing, and maintaining cathodic protection systems to ensure that metal structures remain protected from corrosion.


Cathodic Protection Types

  • Galvanic anode CP (GACP)  -  Also called sacrifical CP.  Uses a sacrifical anode that corrodes before the material being protected does by an electrochemical reaction (no power source needed).
    • Galvanic anode material  -  aluminum, magnesium, and zinc
    • Galvanic anode pro
      • Easy installation
      • No external power source
      • Require virtually no monitoring or maintenance
    • Galvanic anode con
      • Limited current, low driving voltage
      • Limited life
      • Limited control, no power source to adjust the power output
  • Impressed current CP (ICCP)  -  Uses a sacrificial anode connected to an external DC power source.  DC flows from source to anode, to protected material, to source.
    • Impressed current anode material  -  graphite, high silicon cast iron, and mixed metal oxide
    • Impressed current anode pro
      • Current can be controlled, with no limit of driving voltage
      • Can be remotely controlled
      • Can replace anodes when needed
    • Impressed current anode con
      • Require regularly monitoring or maintenance
      • Requires power source
      • More monitoring or maintenance means more likely the breakdowns.


Cathodic Protection Advantages and Disadvantages

  • Cathodic protection effectiveness in preventing corrosion of metal structures.  By imposing a negative potential on the metal surface, the corrosion process is inhibited. 
  • Cathodic protection can provide long term protection, often extending the lifespan of structures and equipment.  This can result in significant cost savings over time, as the need for frequent repairs or replacements is reduced.
  • Cathodic protection is particularly useful for buried or submerged structures, such as underground pipelines and ship hulls, where direct access for maintenance and inspection is challenging.
  • In many cases, cathodic protection can be a cost-effective solution compared to alternatives such as coating systems or frequent maintenance.  It helps to avoid the costs associated with corrosion related failures.
  • Once installed, cathodic protection systems are generally passive and require minimal maintenance.  This makes them suitable for remote or hard to reach locations.
  • Cathodic protection can be used in conjunction with coating systems to provide dual layer protection, enhancing overall corrosion resistance.
  • Designing an effective cathodic protection system requires a thorough understanding of the structure, the surrounding environment, and the corrosive factors involved.  This complexity can lead to challenges in system design and implementation.
  • While cathodic protection can be cost effective in the long run, the initial installation cost can be relatively high.  This may be a deterrent for some projects with budget constraints.
  • Cathodic protection systems often require a power source, which can be an external power supply or sacrificial anodes. Dependence on power sources may be a limitation, especially in remote or off grid locations.
  • While cathodic protection systems are generally low maintenance, periodic monitoring and maintenance are still necessary to ensure their continued effectiveness.  This may involve testing the electrical potential, inspecting anodes, and addressing any issues that arise.
  • The use of sacrificial anodes in some cathodic protection systems involves the consumption of metals like zinc or aluminum, which can have environmental implications.  Proper disposal and recycling practices are essential to minimize environmental impact.


Cathodic Protection standards

ASME Standards

  • ASME B16.5 - Pipe Flanges and Flanged Fittings: NPS 1/2 through NPS 24 Metric/Inch Standard
  • ASME B16.9 - Factory-Made Wrought Buttwelding Fittings
  • ASME B16.47 - Large Diameter Steel Flanges, NPS 26 Through NPS 60
  • ASME B16.36 - Orifice Flanges
  • ASME B31.4 - Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids
  • ASME B31.8 - Gas Transmission and Distribution Piping Systems
  • ASME G8 - Standard Test Methods for Cathodic Disbonding of Pipeline Coatings
  • ASME G14 - Testing Method for Impact Resistance of Pipeline Coatings (Falling Weight Test)
  • ASME G95 - Testing Method for Cathodic Disbonding of Pipeline Coatings (Attached Cell Method)

AWWA Standards

  • AWWA C209 - Cold-Applied Tape Coating for the Exterior of Special Sections, Connections, and Fittings for Steel Water Pipelinss
  • AWWA C214 - Tape Coating Systems for the Exterior of Steel Water Pipelines
  • AWWA C216 - Heat-Shrinkable Cross-Linked Polyolefin Coatings for the Exterior of Special Sections, Connections, and Fittings for Steel Water Pipelinss
  • AWWA C222 - Polyurethane Coatings for the Interior and Exterior of Steel Water Pipe and Fittings

NACE Standards

  • NACE RP0186 - Application of Cathodic Protection for External Structures of Steel Well Casings
  • NACE SP0102 - In-Line Inspection of Pipelines
  • NACE SP0104 - The Use of Coupons for Cathodic Protection Monitoring Applications
  • NACE SP0106 - Control of Internal Corrosion in Steel Pipelines and Piping Systems
  • NACE SP0169 - Control of External Corrosion on Underground or Submerged Metallic Piping Systems
  • NACE SP0188 - Discontinuity (Holiday) Testing of Protective Coating
  • NACE SP0193 - External Cathodic Protection of On-Grade Carbon Steel Storage Tank Bottoms
  • NACE SP0216 - Steel-Cased Pipeline Practices
  • NACE SP0205 - External Corrosion Control of Underground Storage Tank Systems by Cathodic Protection
  • NACE SP0207 - Close-Internal Potential Surveys on Buried or Submerged Metalic Pipelines
  • NACE SP0216 - Sacrificial Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Concrete Structures
  • NACE SP0290 - Impressed Current Protection of Reinforcing Steel in Atmospherically Exposed Concrete Structures
  • NACE SP0502 - Pipeline External Corrosion Direct Assessment Methodology
  • NACE SP0607 - Petroleum and Natural Gas Industries-Cathodic Protection of Pipeline
  • NACE SP21434 - Cathodic Protection Systems for the Mitigation of External Corrosion of Buried and Submerged Metallic Piping Systems at Nuclear Power Plants
  • NACE Publication 1E100 - Engineering Symbols Related to Cathodic Protection
  • NACE TR01105 - Sacrificial Cathodic Protection of Reinforced Concrete Elements
  • NACE TR21447 - Consequences of Coating Failures as Related to Interaction with Cathodic Protection
  • NACE TR21463 - Criteria for Evaluation of Cathodic Protection Methods for Steel in Existing Concrete Structures

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