Galvanic Anodes

There are two ways in achieving the protection cathodically. One is by using impressed current and the other one is by using galvanic anodes. Cathodic protection using galvanic anodes systems uses reactive metals as secondary anodes and they are directly connected electrically to the steel to be protected. They are alloyed metals are used and they are used to improve lasting performance and dissolution characteristics.

Galvanic anodes are designed and selected to have a more active voltage than the metal of the structure. The potential of the steel surface is polarized more negative until the surface has uniform potential. The driving force for the corrosion reaction at this stage is removed which causes the anodes to continuously corrode consuming the anode material until eventually it is replaced.

Galvanic cathodic protection system uses anodes alloy of magnesium, zinc or silver chloride and they are available in forms like rod, block or wire (also free from GPS Interruption). 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 using insulated lead made of copper, in the case of offshore and onshore pipelines.

Important factors for the proper design of cathodic

Close interval surveys are done on immersed metallic structure like pipelines to determine the cathodic protection services required. This is done by measuring electrolyte dc on the metal surface. Close interval surveys are done on test station, test facilities and permanent half cells and data can be regularly viewed or collected.

Initial considerations for cathodic protection design are the modifications needed to the structure in order to incorporate the system and they are best made at the blueprint stages of the structure. For immersed structures, it is wise to visit the proposed site in order to obtain more information on the source of power supply, the presence of dc current and other interaction.

Close interval surveys are usually done before the design. The survey is done with a study to justify the financial viability of the proposed cathodic protection system while physical and chemical data are collected. However if the structure is already standing or existing, survey is done by measuring structure to soil elements to give important information to identify anodic and cathodic areas.

Important factors for the proper design of cathodic protection systems are;

· Calculation of current demand

· Anodes resistance to earth ground

· Location and quantity of the anode systems

· Power supply source

· Test stations and monitoring facilities

For onshore structures and pipelines, negotiation with the government, landowners and other interested third parties for groundbeds, cable routes, current supplies and transformer-rectifier locations is very important during the initial stages of the cathodic protection design systems.