Zinc galvanic anodes are used for cathodic protection both in the environment of salt and fresh water. They are used to protect marine onshore and offshore constructions, vessels (ships, yachts) and underwater pipelines.
Zinc anodes are made of alloys containing a small amount of alloy additives, mainly aluminum and cadmium, which improve the current efficiency of the anode. According to European standards DNVGL-RP-B401, EN 12496, NORSOK M-503 and the American standard NACE TM0190, zinc alloys should contain 0.10 – 0.50% aluminum and not more than 0.07% cadmium (American standard allows its quantity up to 0.15%). It is also acceptable to use high purity zinc anodes containing a minimum of 99.99% zinc, up to 0.005% aluminum and up to 0.003% cadmium.
The current capacity of zinc anodes according to all standards should not amount to less than 780 Ah/kg. The potential of the anodes during operation should not be more electropositive than -1030 mV vs. Ag/AgCl electrode, although the DNVGL-RP-B401 standard allows a potential up to -1000 mV.
Anode parameters for a given series of types
Series I: Alloys with regular zinc content
These anodes can be used in the sea water environment, sea mud and fresh water.
Anodic material meets the requirements of the following standards: DNVGL-RP-B401, NORSOK M-503, EN 12496 and NACE TM0190 regarding the alloy composition and electrochemical properties.
|
Alloy components |
Content |
Impurities |
|
Al |
0.20 – 0.45% |
Pb – max. 0.006% |
|
Cd |
0.030 – 0.070% |
Fe – max. 0.005% |
|
Zn |
remainder |
Cu – max. 0.005% |
|
other – max. 0.05% |
|
Electrochemical properties |
|
|
current efficiency in water (electrochemical capacity) |
minimum 800 Ah/kg |
|
current efficiency in sea mud |
minimum 750 Ah/kg |
|
closed circuit potential in water |
≤-1050 mV vs Ag/AgCl |
|
closed circuit potential in sea mud) |
≤-990 mV vs Ag/AgCl |
Series II: High purity zinc alloys
These anodes can be used in sea and fresh water. They are characterized by slightly lower current efficiency and a slightly more positive working potential compared to the anodes with more alloy additives.
Anodic material meets the requirements of EN 12496 standard regarding the alloy composition and electrochemical properties.
|
Alloy components |
Content |
Impurities |
|
Zn |
min. 99.99% |
Al – max. 0.05% |
|
Cd – max. 0.003% |
||
|
Pb – max. 0.003% |
||
|
Cu – max. 0.002% |
||
|
Fe – max. 0.0014% |
||
|
other – max. 0.05% |
|
Electrochemical properties |
|
|
current efficiency in water (electrochemical capacity) |
minimum 760 Ah/kg |
|
closed circuit potential |
≤-1000 mV vs Ag/AgCl |