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.

 

 

 

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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 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

 

Cathodic Protection Glossary

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A

• 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 Corrosion  -  The dissolution of a metal acting as an anode.

• Anode Corrosion Efficiency  -  The ratio of actual to theoretical corrosion based on the total current flow calculated by Faraday's law from the quantity of electricity that has passed.

• Anodic Coating  -  A film on a metal surface resulting from an electrolytic treatment at the anode.

• Anodic Inhibitor  -  A chemical substance or combination of substances that prevent or reruce the rate of the anodic or oxidation reaction by a physical, physico-chemical or chemical action.

• Anodic Polarisation  -  The electrochemical state changing of an electrode's potential moving in a corroding positive direction.

• Anodic Potential  -  An appreciable reduction in corrosion by making a metal an anode and maintaining this highly ploarized condition with very little current flow.

• Atmospheric Corrosion  -  A gradual degradation of alteration of a material by contact with substances present in the atmosphere, such as oxygen, carbon dioxide, water vapor, sulfur and chlorine compounds.

• Auxiliary Anode  -  A supplementary anode positioned so as to raise the current density on a certain area of the catnode and thus obtain distribution of plating.

• Auxiliary Electrode  -  An electrode commonly used in polorization studies to pass current to or from a test electrode, usually made of noncorroding material.

B

• Backfill  -  Material placed in a drilled hole to fill space around anodes amd buried components.

• 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.

C

• Cathode  -  The electrons flow toward the cathode reducing the corrosion or oxidation of the material.

• Cathode Cleaning  -  Electrolytic cleaning in which the work is the cathode.

• Cathode Corrosion  -  Corrosion resulting from a cathodic condition of a structure usually caused by the reaction of an amphoteric metal with the alkaline products of electrolysis.

• Cathode Disbondment  -  The destruction of adhesion between a coating and its substrate by products of a cathodic reaction.

• Cathode Efficiency  -  Current efficiency at the cathode.

• Cathode Film  -  The portion of solution in immediate contact with the cathode during electrolysis.

• Cathodic Pickling  -  Electrolytic pickling in which the work is the cathode.

• Cathodic Polarisation  -  The electrochemical state changing of an electrode's potential moving in a non-corroding negative direction.

• Cathodic Reaction  -  Electrode reaction equipment to a transfer of negative charge from the electrode to the ionic conductor.
  

• Catholyte  -  The electrolyte adjustment to the cathode of an electrolytic cell.

• Catholyte  -  A positively charged ion that migrates through the electrolyte toward the cathode under the influence of a potential gradient.

• 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 pipeline by the 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.

• Current Density  -  The measure of current per unit of cross section.

• Current Efficiency  -  The ratio of the electrochemical equivalent current density for a specific reaction to the total applied current density.

D

• Depolarization  -  When the CP cirrent stops flowing from athe anode to the structure being protected, the polarized structure will then begin to depolarize.

• Descaling  -  Removing the thick layer of oxides formed on some metals at elevated temperatures.

• Dezincification  -  Corrosion at which zinc is selectively leached from zinc-containing alloys.

• Diffusion  -  The spread of gases, liquids, or solids from areas of high concentration to areas of low concentration.

• Diffusion Coefficient  -  Expresses the transfer rate of a substance by random molecular motion.

• Direct Current  -  An electric current that flows in only one direction.

• Dummy Cathode  -  A substitute cathode that is used during adjustment of operating conditions.

E

• Electric Conductivity  -  The amount of current that a material can conduct.

• Electric Current Density  -  The measure of current per unit of cross section.

• Electrochemical Cell  -  A system consisting of an anode and a cathode in metallic contacts and immersed in an electrolyte.

• Electrochemical Corrosion  -  Corrosion that is accompanied by a flow of electrons between cathodic and anodic areas on metallic surfaces. 

• 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.

F

• Faraday's Law of Induction  -  States that whenever a conductor is placed in a varying magnetic field, an electromotive force is introduced.

• Flux  -  Chemicals used to protect metals from oxidation.

• Fretting Corrosion  -  Takes place where there is friction between two metal surfaces.

G

H

• Hot Corrosion  -  An accelerated corrosion of metal surfaces that results from the combined effect of oxidation and reactions with sulfur compounds and other contaminants.

• Hot Cracking  -  Caused by the segregation at grain boundaries of low-melting constituents in the weld metal.

• Hot Dip Coating  -  A metallic coating obtained by dipping the base metal into a molten metal.

• Hot Working  -  Deforming metal physically at such a temperature and strain rate that recrystallization takes place simultaneously with the deformation, thus avoiding any strain hardening.

• Hydrogen Disintegration  -  Deep internal cracks caused by hydrogen.

• Hydrogen Embrittlement  -  A process resulting in a decrease of the toughness or ductility of a metal due to the presence of atomic hydrogen.

• Hydrogen Overvoltage  -  Overvoltage associated with the liberation of hydrogen gas.

I

• 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.

J

K

L

• Localized Corrosion  -  Corrosion at discrete sites, stress-corrosion cracking.

M

N

O

• 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.

P

• 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.

Q

R

• Rectifier  -  A power supply that converts AC power to DC power.

• Rust  -  A corrosion product consisting primarily of hydrated iron oxide.

S

• Stray Current  -  The flow of electric current into the ground by the leakage on industrial currents.

T

U

V

• 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.

W

• 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.

• Wetting Agent  -  A substance that reduces the surface tension of a liquid causing it to spread more readily on a solid.

X

Y

Z

 

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