Sacrificial anodes: designed in or added later
Cathodic protection can be planned at construction, or added once corrosion is already active. In both cases the diagnosis comes first.
Once a corrosion diagnosis is in place, protection can be specified. Sacrificial anodes, and other forms of cathodic protection, may be curative, on a structure already in service, or designed in from the start, with electrodes for later monitoring.
Where corrosion is already active, sacrificial anodes can be added to protect the reinforcement that remains. The extent of the system follows the map of activity, the chloride profile and the condition of the cover. MAREX method sheet MX-COR-10 places cathodic protection among the preventive or electrochemical treatments that may follow a corrosion diagnosis.
On new tanks, rafts and marine structures, anodes and reference electrodes can be provided in the pour. The electrodes support later half-cell surveys to ASTM C876 and long-term monitoring, without waiting for rust staining or leaks to appear.
For the operator, the practical point is this: anodes are not a substitute for a diagnosis. A half-cell map, cover, carbonation, chlorides, resistivity and, where useful, corrosion rate are what decide whether protection is justified, and over what area. The same methods later show whether the system is doing its work.
MAREX specifies protection from the inspection findings. It acts as an independent expert: it only carries out repairs with the agreement of all parties, with no conflict of interest. The sheets cited here are method references and are not offered as a public download on this site at this stage.