Cathodic Protection/Impressed current cathodic protection: Corrosion Control

Describes the mechanism of Impressed current cathodic protection/Cathodic Protection. Mentions the advantages and disadvantages of this method. Compares this method with sacrificial anodic protection method.
Impressed current cathodic protection (ICCP)/Cathodic protection
You will be able to define cathodic protection.
You will be able explain the mechanism of impressed current cathodic protection method.
You will be able to enumerate the advantages and limitations of this method.
You will be able to compare the impressed current cathodic protection with the sacrificial anodic protection.
Galvanic corrosion
Definition
When two dissimilar metals are in contact with each other in the presence of a corrosive medium (electrolyte), the more active metal acts as an anode and undergoes corrosion.
The metal with low standard reduction potential (high std. oxidation potential), acts as anode and undergoes corrosion and the metal with high standard reduction potential acts as cathode and is protected. (electrochemical series)
Electrochemical series
Arrangement of the standard reduction potential or standard oxidation potential of all metals on hydrogen scale in an increasing or decreasing order is known as electrochemical series.
Cathodic protection
The metal to be protected is forced to act as cathode so that corrosion does not occur.
Impressed current cathodic Protection
The metal to be protected (undergoing corrosion) is connected to an insoluble anode and current is passed using DC power source (or AC powered transformer rectifier) opposite to the corrosion current, so that the corroding metal gets converted from anode to cathode and is protected from corrosion.
Insoluble Anode /Inert anode (conducting materials which is not consumed): Platinum, graphite, stainless steel, mixed metal oxides, lead alloys, platinised titanium etc.
How Does Impressed current cathodic Protection Work?
The metal to be protected can be iron or steel pipe or storage tanks buried under the ground.
Applications of Impressed current cathodic protection
Hull of a ship - Rusts at the stern (steel) which is closer to
Mn-Bronze propellers and sea water acts as the electrolyte
on-shore pipelines
sea vessels such as ships and boats
boat propellers and rudders
mobile or fixed offshore pipelines
production platforms
water heaters
oil casings
hull of ship and boats
concrete bridges in sea water
storage tanks under the soil /sea water
Advantages of Impressed current cathodic protection
automatically controls the corrosion protection by continuously monitoring and varying the power required
long term protection (even for about 20 years)
need not replace the anodes
single installation required
no welding requirements
Limitations of Impressed current cathodic protection
sensitive components
requires highly regulated control systems
maintenance required
expensive