ICCP or sacrificial anodes for buried tanks?
Cathodic protection of buried tanks can be arranged with either sacrificial anodes (SACP) or impressed current cathodic protection (ICCP) systems. Both systems have their benefits and disadvantages.
ICCP is the preferred cathodic protection system for buried storage tanks.
Underground steel tanks corrode due to an electrochemical reaction between the tank and the surrounding soil. Small voltage differences on the steel surface result in the flow of DC current from one location on the steel surface to another. Where the current flows from the tank surface into the soil corrosion occurs (anodic area). Where the current flows from the soil into the tank surface no corrosion will occur. Yoy may learn more about corrosion.
Protecting underground tanks from corrosion is easily achieved by establishing a cathodic protection system. The two general types of cathodic protection systems are sacrificial anodes and impressed current systems.
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The most commonly used anode material for external protection of buried tanks is magnesium, and the voltage difference between steel and a magnesium anode is 1.2 to 1.8 V (depending of type of magnesium alloy used).
Magnesium anodes can protect underground tanks in most soil conditions, however, most suitable for use in ground with moderate resistivities. As the magnesium anode has a relatively high self-corrosion rate, the lifetime of the anodes is limited. The presence of signiﬁcant amounts of chloride can reduce the utilisation further due to increased self-corrosion.
Advantages: Economical solution, simple installation.
Disadvantages: Short lifetime, limited capacity, not controllable.
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Impressed current system
An impressed current system for buried tanks is established by either a continuous cable-like anode (installed around the tank, or parallel with the tank’s long sides) or by one or more FeSi anodes installed aside the tank. The anodes are energised by a controllable DC current source, control panel. An impressed current system can be automatically regulated to obtain optimum cathodic protection. This system has high capacity, long lifetime, and will work in high resistivity soil.
Advantages: Adjustable/controllable current output (optimum corrosion protection effect), long lifetime, high capacity.
Disadvantages: Expensive, extensive installation.