Cathodic protection systems

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Cathodic Protection (CP)

The science of cathodic protection (CP) started in 1824, when Sir Humphry Davy made a presentation to the Royal Society of London: "The rapid decay of the copper sheeting on His Majesty's ships of war, and the uncertainty of the time of its duration, have long attracted the attention of those persons most concerned in the naval interest of the count. ... I entered into an experimental investigation upon copper. In pursuing this investigation, I have ascertained many facts ... to illustrate some obscure parts of electrochemical science... seem to offer important application." Davy succeeded in protecting copper against corrosion from seawater by the use of iron anodes.

From that beginning, CP has grown to have many uses in marine and underground structures, water storage tanks, gas pipelines, oil platform supports, and many other facilities exposed to a corrosive environment (see Corrosion Costs Study findings). Recently, it is proving to be an effective method for protecting reinforcing steel from chloride-induced corrosion. (reference)

History of Cathodic Protection

Cathodic protection has become a widely used method for controlling the corrosion deterioration of metallic structures in contact with most forms of electrolytically conducting environments, i.e. environments containing enough ions to conduct electricity such as soils, seawater and basically all natural waters. Cathodic protection basically reduces the corrosion rate of a metallic structure by reducing its corrosion potential, bringing the metal closer to an immune state.  From a thermodynamics point of view, the application of a CP current basically reduces the corrosion rate of a metallic structure by reducing its corrosion potential towards its immune state as shown here for iron and steel or here for aluminum and its alloys.

Cathodic Protection Basics

Corrosion Costs and Preventive Strategies Study

The cost of cathodic protection of metallic structures subject to corrosion can be divided into the cost of materials and the cost of installation and operation. Industry data have provided estimatesfor the 1998 salesof various hardware components totaling $146 million. The largest share of the cathodic protection market is taken up by sacrificial anodes at $60 million, of which magnesium has the greatest market share. Major markets for sacrificial anodes are the water heater market and the underground storage tank market.

The costs of installation of the various cathodic protection (CP) components for underground structures vary significantly depending on the location and the specific details of the construction. For 1998, the average total cost for installing CP systems was estimated at almost one billion(range: $0.73 billion to $1.22 billion). The total cost for replacing sacrificial anodes in water heaters and the cost for corrosion-related replacement of water heaters was estimated at $1.24 billionper year; therefore, the total estimated cost for cathodic and anodic protection is $2.22 billionper year. (reference)

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