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.
