Alloys used for sacrificial anodes are based on magnesium, zinc or aluminium. The performance, and hence the suitability of a particular alloy for a specific application, will depend on the composition of both the alloy and electrolyte, temperature of operation and anode current density.
At our foundry in Fredrikstad, Norway, the main activities are related to production of the following high quality anode alloys:
CORAL® ‘A’ High Grade
Pure aluminium corrodes to form an oxide film which is tightly adherent and causes rapid polarization when the pure metal is used as an anode. In chloride-containing electrolytes this film breaks down to give very non-uniform attack by pitting.
The addition of indium as an alloying element imply breakdown of the oxide film and is necessary to make aluminium useful as a sacrificial anode.
Chemical composition of CORAL® ‘A’ High Grade anode alloy is according to NORSOK standard M-503 and ISO 15589-2, and certified according to DNV Type Approval Programme.
CORAL® ‘A’ Special Grade
CORAL® ‘A’ Special Grade is an aluminium alloy with the preferred chemical composition of the major oil and offshore operator companies for deep and cold water use. Content of Fe is limited to 0.06% by weight and for other elements such as Zn, In and Si more narrow ranges are specified compared to the more conventional offshore anode alloys.
CORAL® ‘A’ Special Grade anode alloy is certified according to DNV Type Approval Programme
Zinc is particularly useful in sea-water applications, e.g. for the protection of ships`hulls, where its low driving potential against steel is insufficient to cause damage to most paints and enables the current output to vary with demand; thus, it is to some extent self-controlling. Zinc anodes do not normally evolve hydrogen nor is there a risk of thermite sparking.
CORAL® ‘Z’ anodes are made to US Mil Spec. MIL-A-18001.
NORANODE® (High Temperature Zinc Alloy) is a special zinc alloy developed to meet the demand of a sacrificial anode for use at elevated temperatures. NORANODE® is practically cadmium free, and should be recommended for enviromental reasons.
Magnesium anodes are used extensively where a high driving potential is desirable, in soils, and fresh and brackish waters.