Cathodic protectionCP

A block of a more electrochemically active metal, commonly a zinc, aluminium or magnesium alloy, electrically connected to a structure so that it corrodes preferentially and protects the structure. Anodes are consumed in service and are inspected and replaced as part of planned maintenance.

Accelerated corrosion of the less noble material when two dissimilar conductors are electrically connected in an electrolyte such as seawater. Carbon fibre composites in contact with aluminium or steel can drive galvanic attack, so joints are isolated with sealants, coatings or an insulating glass ply.

A coating that protects primarily by impermeability, isolating the substrate from water, oxygen and dissolved ions rather than by galvanic or inhibitive action. High build epoxies and coatings pigmented with lamellar materials such as micaceous iron oxide or glass flake are typical examples.

A thermosetting epoxy powder coating applied electrostatically to preheated steel, on which it melts, flows and cures to form a continuous film. It is a standard factory applied coating for buried and subsea pipelines and for corrosion protected reinforcing bar.