Zdjęcie Anody cynkowe

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; drawings and dimensions of anodes

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

Al

0.20 – 0.45 %

Cd

0.030 – 0.070%

Zn

rest

Fe

max. 0.005 %

Cu

max. 0.005 %

Pb

max. 0.006 %

other

max. 0.010 %

Electrochemical properties

current efficiency (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

Al

max. 0.005 %

Cd

max 0.003 %

Zn

minimum 99,99 %

Fe

max. 0.0014 %

Cu

max. 0.002 %

Pb

max. 0.003 %

other

max. 0.005 %

Electrochemical properties

current efficiency in water (electrochemical capacity)

minimum 760 Ah/kg

closed circuit potential

 

≤- 1000 mV  vs Ag/AgCl

Series III: Al-Zn-In-Mg alloys

These anodes can be used in the sea water environment and in sea mud.

They are characterized by the addition of magnesium, a reduced content of zinc and an increased content of indium in comparison to Al-Zn-In type anodes.

The current efficiency of the anodes is lower in comparison to the Al-Zn-In type anodes, but they have a more negative potential during operation.

Anodic material meets the requirements of the NACE TM0190 standard regarding alloy composition and electrochemical properties.

Alloy components

Zn

1.5 – 3.0 %

In

0.20 %

Mg

0.6 – 1.0 %

Al

rest

Cu

max. 0.010 %

Fe

max. 0.100 %

Impurities – every component

max. 0.020 %

Impurities – total

max. 0.050 %

Electrochemical properties

current efficiency (electrochemical capacity)

minimum 2400 Ah/kg

closed circuit potential

≤- 1100 mV  vs calomel electrode
( ≤- 1146 mV  vs Ag/AgCl electrode)