Cathodic protection, abbreviated as CP, is a method used to control corrosion on the surface of a metal which can be above or below ground pipes, tanks, vessels, etc. This process is accomplished by placing a sacrificial anode (material) connected to the protected metal.
Nomenclature & Symbols
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).
- 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 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 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 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
Cathodic Protection Glossary
- A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
- Abradable coating - It gives wear resistance to highly abrasive material when rubbed against, while leaving the underlying material damage free.
- Alternating current - An electric current that reverses its direction over and over.
- Anion - A negatively charged ion.
- Anode - The electrons flow away the anode (negative charge) at which corrosion or oxidation occures at the material.
- Anode Polarisation - The electrochemical state changing of an electrode's potential moving in a corroding positive direction.
- Back ionisation - A condition, which may occur during electrostatic application of powder coating where excessive build up of charged powder particles limits further powder to be deposited onto the substrate.
- Barrier coating - A protective layer of material that prevents the contact of corrosive elements.
- Base - A substance that releases hydroxyl ions when disolved in water.
- Blast cleaning - Removal of surface contamination and corrosion products by use of air and mechanical abrasives.
- Blistering bubbles - Formed under the cured powder film, usually caused by the expansion of trapped air, moisture or corrosion.
- Blooming - A hazy appearance on the surface of a coating.
- Cathode - The electrons flow toward the cathode reducing the corrosion or oxidation of the material.
- Cathodic Polarisation - The electrochemical state changing of an electrode's potential moving in a non-corroding negative direction.
- Corrosion - The thinning of a pipe wall that is typically caused by a chemical reaction from a corroding fluid or agent and is limited almost exclusively to metal products.
- Corrosion allowance - The amount of material in a pipe or vessel that is available for corrosion without affecting the pressure containing integrity.
- Corrosion coupon - Used to monitor the corrosion rate of a material in a process.
- Corrosion inhibitor - A substance that slows down the chemical reaction rate of corrosion on metal that is exposed to the environment.
- Corrosion mapping - An ultrasonic method that identifies and maps corroded areas in a pipelineby yhe varying material thickness.
- Crack - Cracks can come from fatigue, grith welds, or seam welds.
- Current - The rate of flow of electricity in a circuit, measured in amperes.
- Depolarization - When the CP cirrent stops flowing from athe anode to the structure being protected, the polarized structure will then begin to depolarize.
- Direct current - An electric current that flows in only one direction.
- Electrode - Refered to as the anode or cathode, whichever is approperate.
- Electrode potential - The potential of an electrode in an electrolyte as a measure against a reference electrode.
- Electrolyte - A chemical substance or mixture, liquid or solid, normally liquid, which conducts electric current.
- Etching - Removal of a layer of the base metal.
- External corrosion - When the outside of a pipe is decayed or eroded by chemical or electrochemical processes or any other environmental conditions.
- Flux - Chemicals used to protect metals from oxidation.
- Fretting corrosion - Takes place where there is friction between two metal surfaces.
- Impressed current anode - They are intended to discharge current when being powered by an external DC power source.
- Incomplete fusion - A weld break where complete fusion did not occur between the weld material and the faces or adjoining weld material.
- Interupter - A sophisticated switch that can be used to interrult the operation of a rectifier.
- Ion - An atom or molecular particle having a net charge. Positive charged ions are cations and negative charged are anions.
- Isolation gasket - Used to stop the current flow across metallic pipelines by separating two flanges.
- Ohm - A unit of resistance.
- Ohm's law - The relationships between power, voltage, current, and resistance.
- Oxidation - The loss of electrons in a chemical reaction in which an element combines with oxygen. Oxidation and reduction always occur at the same time in equal amounts.
- pH - Affects the corrosion rate by affecting the reaction rate of cathodes and anodes.
- Polarization - When CP current flows from the anode to the structure being protected, that structure's potential will shift more electrically negative. The shift is called polarization.
- Rectifier - A power supply that converts AC power to DC power.
- Rust - A corrosion product consisting primarily of hydrated iron oxide.
- Stray current - The flow of electric current into the ground by the leakage on industrial currents.
- Vent pipe - A small diameter pipe that has drilled holes or cut slots that allow gasses generated at the anode during the CP process to vent away from the anode.
- Volt - A unit of electrical pressure.
- Voltage - One volt is the amount of pressure that will cause one ampere of current in one ohm of resistance.
- Voltage coefficient of resistance - The change in resistance with applied voltage.
- Voltage drop - When the voltage at the end of the cable is less than the beginning of the cable.
- Voltage rating - The maximum voltage at which a cable or insulated conductor can be safetly maintained during continuous use in a normal manner.
- Well integrity - An operation of technical, operational, and organizational solutions to reduce fisk of controlled release of formation fluids throught the life cycle of a well.
Tags: Equations for Corrosion