Cathodic Protection Requirements

Cathodic protection principle focuses in connecting an external anode to a metallic structure to be protected and passing through a dc current in order that the surface of the metal structure becomes cathodic and will not corrode or rust. The most important features of the cathodic protection system applied to metals exposed to a conducting electrolyte are as follows:

Galvanic Systems

• Sacrificial anodes.

• A secure and low resistance connection between structure and conductor, and between anode and conductor.

• A conductor that connects the anode to the structure, or directly welded to the structure.

Impressed-current Systems

• Source of dc power.

• A volume of inactive anodes, connected together in a grounded or in a backfill.

• Well insulated, low resistance and secure conductors between anodes and dc power source.

• A secure and low resistance connection between structure and conductor and between structure and dc power source.

The effectiveness of cathodic protection systems is assessed by a successive structure of electrolyte dc measurements at regular gaps or referred to as the close interval surveys. Close interval survey does not refer to cell-to-cell survey techniques that are used to evaluate the current direction using RTU remote, or the coating’s effectiveness. Using terminal unit, close interval surveys could detect the presence of copper sulfate in the metal, which is an indication of corrosion.

Equipments needed Cathodic System

There are many types of equipments needed for galvanic and impressed-current system of cathodic protection. Galvanic systems of cathodic protection used alloys of anodes of magnesium, zinc or silver chloride and they are available in forms of rod, block or wire forms. These anode alloys are casted in steel inserts in order to fix the anode and to establish electric continuity and strength throughout the life of the anode. The steel inserts are directly bolted or welded to the structure that needs protection, or the anode alloys connected to the structure using insulated lead made of copper, in the case of offshore and onshore pipelines.

Groundbeds for impressed-current systems in soils are mainly using high silicon cast iron. However, newest development in the cathodic protection uses mixed metal oxide for all types of surfaces because of their compact size and good electrical and mechanical properties.

The most popular source of dc power is the cathodic protection rectifier with silicon-diode and transformer unit (also free from GPS Interruption) together with the ac supply or diesel. However, most system uses a constant current systems or dc voltage as power source.

Closed-cycle turbines, solar or wind generators are used together with storage batteries and are mostly used in remote areas, aside from the thermo electric generators. The choice among these power sources is dependent on environmental conditions, power requirements and maintenance capabilities.

Another alternative source of power for impressed-current systems is the unit with automatic control. This unit will automatically adjust the current output according to the possible changes at hall cell.