Description

This Standard specifies requirements for the cathodic protection of external surfaces of fixed immersed structures, including offshore platforms, wharves, jetties, pontoons, sewage treatment plants, water treatment plants, lock gates, dam gates, pump station piles in rivers, weirs, mooring buoys, piling, foundations and water inlet/outlet structures.

Scope

Whilst fixed immersed structures are rarely affected by stray direct traction currents, there are some significant examples where this does occur and where mitigation is required. Examples of affected fixed immersed structures are underwater tunnels and electrically continuous sheet piling along water-ways and harbours.

This Standard does not apply to steel in concrete structures, see AS 2832.5.

The Standard specifically covers the following subjects which relate to cathodic protection: 

• (a) The design of structures requiring cathodic protection.
• (b) Coatings for use on immersed metal structures.
• (c) Criteria for the choice of cathodic protection potential.
• (d) The design of cathodic protection systems.
• (e) The installation of cathodic protection systems.
• (f) The control of interference currents on foreign structures.
• (g) The cathodic protection of structures subject to stray direct current.
• (h) The operation and maintenance of cathodic protection systems.

This Standard employs conventional (positive) current flow, for consistency with accepted practice, and uses the potential sign conventions specified in AS 1852. In order to understand the various electrochemical reactions that occur at electrodes during cathodic protection, it should be recognized that electron flow occurs in the opposite direction to conventional current flow.

Notes:

1. Guidance on the general use and design of cathodic protection systems and factors affecting the corrosion of immersed metallic structures are given in Appendix A.
2. This Standard employs positive current flow. The international convention is that the potential of an electrode is measured with respect to the potential of an electrode situated in the electrolyte. In the absence of cathodic protection, positive current in a corroding system flows through the electrolyte from the more negative to the more positive portion of the circuit. The aim of cathodic protection is to move the potential of the structure in the negative direction so that positive current flows on to it.