The cathodic protection system design life is the period of time that the cathodic protection system is expected to offer protection to the structure. The CivilWeb Cathodic System Design Spreadsheet allows the designer to specify any design life for the cathodic protection system. It uses this design life to calculate the required mass of anodic material required.
Cathodic Protection System Design Life
The cathodic protection current density demand during the maintenance stage and the electrochemical capacity of the material are used to calculate the mass of anodic material which will be consumed for each year the structure is protected. The mass is simply the volume of anodic material multiplied by the anode density. The density is dependent on the precise composition of the anodes. This value is then simply multiplied by the system design life to produce a total mass of anodic material required.
Often the design life of a cathodic protection system will be the same as the design life of the structure, plus any time when the system will be active before the structure is in operation. This is particularly the case for offshore structures or pipelines where maintenance and replacement of cathodic protection systems during service would be very difficult, disruptive or expensive.
In other cases such as shore-side marine infrastructure it may be economically viable to replace cathodic protection systems rather than installing very large anodes initially. Also in cases where microbial induced corrosion (MIC) or accelerated low water corrosion (ALWC) are present, the cathodic protection system may be designed to offset the reduction in design life through these specific causes. So the design life in these cases will not be the full design life of the structure, but a percentage which it is estimated that the ALWC would take off the design life if left unchecked.
At the end of the cathodic protection system design life the anodes will slowly begin to reduce in effectiveness. The anodes will be depleted past their utilisation factor and will begin to offer uneven current output. Eventually the anodic material will be too small to be held in place by the anode insert and will fall away.