Principles Of Cathodic Protection


 
 

Cathodic protection (CP) is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. CP was first described by Sir Humphry Davy in a series of papers presented to the Royal Society in London in 1824. After a series of tests, the first application was to the HMS Samarang in 1824. Sacrificial anodes made from iron were attached to the copper sheath of the hull below the waterline and dramatically reduced the corrosion rate of the copper.

The simplest method to apply CP is by connecting the metal to be protected with another more easily corroded "sacrificial metal" to act as the anode of the electrochemical cell. CP can also be apply by introducing an external power source, which provides the current. Cathodic protection systems are used to protect a wide range of metallic structures in various environments. CP is now a common international applications for: steel water or fuel pipelines and storage tanks; steel pier piles; ships and boats; offshore oil platforms and onshore oil well casings and metal reinforcement bars in concrete buildings and structures.


Cathodic Protection Methods
 
The Impressed Current Cathodic Protection (ICCP) systems use anodes connected to a DC power source, providing the CP current and achieve CP for the protected structure. Some common applications examples are as follow.
 
  • Ti MMO Anode System
  • Deep / Shallow Well Anode System
  • Titanium Mesh Anode
  • Conductive Coating System
  • Conductive Rubber Anode
  • Titanium Mesh Anode Embedded in Gunite
  • Titanium Mesh Anode  Encapsulated in Structural Jacket
  • Impressed Current CP Pile Jacket  System


Galvanic anodes are designed and selected to have a more "active" voltage than the metal of the protected structure. Through electrolyte (e.g. Sea), forms an electrochemical cell. The potential of the steel surface is polarized (pushed) more negative until the surface has a uniform potential. At that stage, the driving force for the corrosion reaction is removed. The galvanic anode continues to corrode, consuming the anode material until eventually it must be replaced. Some commonly used Galvanic anodes and protection methods are as follow.
 
  • Sacrificial anodes
  • Sprayed Sacrificial Zinc Metalizing System
  • Sacrificial Cathodic Protection Pile Jacket, Lifejacket System
  • Sprayed Sacrificial Zinc Metalizing System
  • Perforated Zinc Sheet System
  • Sacrificial Cathodic Protection Pile Jacket, Lifejacket System
  • Zinc-Hydrogel Anode

 

 
CP Protection selection

 Impressed Current Cathodic Protection (ICCP) Galvanic Anode Cathodic Protection
  •  High current output capable of protecting large structures
  • Capability of variable current output
  • Higher maintenance and operating costs
  • Frequent monitoring
  •  No external power supply required
  • Installation is relatively easy
  • Maintenance costs are minimal
  • Capital investment is low