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Impressed Current System

The components of an impressed current cathodic protection system are anodes, anode backfill, a power supply (transformer rectifier), structure, wiring and connections. Impressed current anodes are manufactured from material that are consumed at low rates, Impressed current CP system generally operate at higher current and driving voltage levels than sacrificial CP systems.
Below shown is a diagram for an Impressed current CP system

 Impressed Current
Impressed current anode, for the protection of buried structures have historically been made from higher silicon cast iron, which is low in cost and consumption rate. Graphite anodes are also used but are more brittle and requires careful handling. More recently mixed metal oxide anodes have proved cost effective in many instances, and is now the automatic choice of numerous end users. Several anodes are connected in parallel are grouped in a ground bed packed with low resistivity carbonaceous backfill, the purpose of the backfill is to reduce anode-to-earth resistance, enhance anode life and to provide an escape route for any gases generated by the anodic reactions.

Various ground bed configurations may be used, having anodes either horizontal or vertical according to the design requirements for the particular site conditions. Where surface soil resistivity are high, or interference could be a problem, deep vertical anodes are appropriate.

Direct current is fed to the ground bed from an external D.C source, usually a transformer-rectifier with adjustable output power. Where AC power is not available and current requirement are moderate, solar powered impressed current system are competitive in many locations. In these installations, solar panels are used to charge batteries during day light hours. The batteries then provide the direct current required by the cathodic protection system. Solar power system are simple to install and maintain and compared with sacrificial anode system can provide higher voltage and longer anode life.

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High Silicon Iron anodes

High Silicon Iron anodes are low cost impressed current anodes most frequently used in land based groundbeds. Alt6hough the anodes are suitable for use in a wide range of Onshore and Marine environments, carbonaceous backfill is frequently used to extend the life and reduce resistance to the anode. 
 High Silicon Iron anodes exhibit the following general characteristics: -

  • Wide range of application.

  • Low cost.

  • Low Consumption, generally less than 0.25 kg/amp year. (Dependent on the environment and operating current density.)

  • Limited current density 10-20 amps/m in backfill due to the possibility of gas blocking.  Higher current densities can be applied in fresh or seawater.    

  • Bulky, heavy and brittle. Careful handling during transportation and installation is  necessary.

There are two anode alloys available, NORMAL for general use and CHROME for use at elevated temperatures or in environments containing significant quantities of chloride ions.  Both alloys comply with the requirements of BS1591-1975 but due to the reasons mentioned above, it is accepted that only anodes of the CHROME alloy are used in Middle East environmental conditions.

The analysis for the CHROME anodes is :-




1.4 max.


14.25 - 15.25


0.5 max.


0.25 max.

0.1 max.


4.0 -5.0



High Silicon Iron anodes are available in many configurations but solid rod and tubular types are the most commonly used anodes.


Mixed Metal Oxide anodes (MMO)

Mixed Metal Oxide anodes (MMO) represent one of the most significant developments for the cathodic protection industry over recent years.  It was developed originally to produce chlorine from seawater and since then, the technology of using MMO in a wide range of cathodic protection applications has possibly made this anode the most popular impressed current anode as it offers several advantages.

  • Improved anode life and reliability. The consumption rate of this type of anode is so low that it is difficult to record unless current densities are very high.

  • Mechanical durability, extremely lightweight and portability reduces handling, shipping and installation costs.

  • Acid resistant.  Most cathodic protection systems operate in acidic environments.  The ability of MMO anodes to withstand acid corrosion sets them apart from all other cathodic protection anodes, which ultimately deteriorate because of acid attack.

These properties and advantages arise from the MMO anode because of its chemical nature and        method of production.  Basically the anode, in whichever form, consists of titanium substrate onto which are sintered very thin layers of metal oxides.  These oxides are chosen to operate in either chlorine evolving environments (sea water) or oxygen evolving environments (soil or fresh water). In this way, the electrochemical characteristics of the anode can be suited to its particular environment.


The fact that it is suitable for all types of cathodic protection systems, e.g. deep well groundbeds, horizontal groundbeds, offshore platforms, internal water tank protection, jetties, internal protection of plant cooling water pipelines, external tank base protection of tanks installed with a bottom plate membrane, reinforcing bars in concrete, and many other applications, makes its versatility unique.

Emirates Techno Casting - Cathodic Protection Division is a reliable supplier for all types of MMO Anodes.

Graphite anodes

Graphite anodes used as an anode material can be operated at a current density of 2.5 amps/m - 10 amps/m.  They are normally impregnated with wax or a synthetic resin to fill the pores and the consumption rate can then be substantially lower than that of iron and steel.  These anodes have a good track record when installed in dry environments.  However chlorine, which can be generated electrolytically in saline water is particularly aggressive towards graphite and there are known cases of premature failure of graphite anodes due to 'necking' of the anode in the area of the cable to anode connection.


Lead alloy anodes

Lead alloy of various compositions are utilised in seawater applications but are not suited for installations where there is a possibility where deposits may form.  The performance of lead alloy anodes rely on the formation of a lead dioxide surface film, which constitutes a conducting medium that does not deteriorate rapidly and is self repairing.  Thin platinum wires are often inserted into the lead alloy surface to form a bi-electrode, which can be beneficial in the initial formation of a film of lead dioxide.


Platinised anodes

Platinum and platinum alloys are excessively expensive to be considered as anodes except in some extreme applications.  However, these metals are used to form a thin layer of approximately 0.0025 mm thick on a titanium, niobium or tantalum substrate.  These metals are used as substrates as they are protected in anodic conditions by an adherent, inert, non-conducting surface oxide film and therefore resist corrosion at any gap in the coating.  The use of these type of anodes have to be carefully considered at the design stage as the oxide film on titanium may break down if the operating voltage exceeds 8 volts in electrolytes containing chlorides and with niobium and tantalum, 40 volts is permissible.



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