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Cathodic Protection

Pivotrom is a total solutions provider for all aspects of cathodic protection to enhance the service life of assets.

Pivotrom’s team of experts, in association with Anode Engineering Pty Ltd, design, install, monitor and maintain cathodic protection systems for new and existing installations.  Along with a full range of impressed current, sacrificial and hybrid anode systems, Pivotrom is a supplier of related equipment such as corrosion inhibitor wraps and monitoring equipment.

Principles of Cathodic Protection

“Rusting” of steel is a form of metallic corrosion due to electrochemical reactions.

All metals have a tendency to “rust” or oxidise over time albeit at very different rates.

In the case of steel rusting, the metal has a lower electrical potential compared to its surroundings which is often water. In technical jargon, the steel forms the anode and the water is the cathode in the electrochemical reaction.

In the case of two dissimilar metals in contact with each other, the metal with the lowest potential will become the anode and the metal with the higher potential will become the cathode.

The galvanic series of metals shows where various well-known metals fit on the scale.

  • Platinum - Least active, highest potential.   Cathodic
  • Gold
  • Graphite
  • Titanium
  • 316/304 Stainless Steel (passive)*
  • Monel metal (70% Nickel, 30% Copper)
  • Silver
  • Nickel
  • Lead
  • Bronze, Copper, Brass
  • Tin
  • Lead/Tin (solder)
  • 316/304 Stainless Steel (active)
  • Cast Iron/ Mild Steel
  • Cadmium
  • Aluminium
  • Zinc
  • Magnesium - Most active, lowest potential.    Anodic

* Passive stainless arises when a Chromium rich oxide film is present on the surface of the steel.

The whole aim of cathodic protection systems is to offset or marginally reverse this natural electrical potential.

There are two main ways to achieve this

Sacrificial Anodes: In this case, a metal such as zinc is attached (electrically connected) to the metal to be protected such as the steel of a ship’s hull.
There is a preference for the galvanic reaction to be set up between the zinc and the water rather than the steel and the water because the former has a higher potential difference. The important point here is that the zinc is consumed in the process and has to be replaced periodically.

Impressed Current Cathodic Protection:  (ICCP) This is a technique where an electrical potential is set up between the metal to be protected and the corroding environment that negates the natural potential thus stopping the electrochemical reaction process.

There are three main conditions that must exist before electrochemical corrosion occurs:

  1. The metal must be in contact with the electrolyte.
  2. Dissolved or mobile ions must be available. I.e. oxygen or hydroxide ions.
  3. The creation of a “corrosion cell” where any part of the metal is acting as an anode to be oxidized and any part of the dissolved or mobile ions are able to act as a cathode and be reduced.

Interference with any one of these conditions will impede the electrochemical corrosion process.

ICCP is the most often used in conjunction with other surface protection systems such as painting. Such coatings substantially reduce the actual electrical energy consumption required to maintain the ICCP.