1 Alloy specification of standard sacrificial anodes BOLT-ON ANODES / DISC ANODES

Transcription

1 Page: CONTENTS: 1 Alloy specification of standard sacrificial anodes 2 Use of zinc or aluminium anodes 3 Use of sacrificial anodes in tanks HULL ANODES 4 23 Aluminium hull anodes Zinc hull anodes BOLT-ON ANODES / DISC ANODES Aluminium hull bolt-on anodes (with 2 bolting holes) Zinc hull bolt-on anodes (with 2 bolting holes) Aluminium bolt-on disc anodes (with 1 bolting hole) Zinc bolt-on disc anodes (with 1 bolting hole) TANK ANODES Aluminium tank anodes Zinc tank anodes PITGUARD ANODES Aluminium pitguard anodes (including 1 clamp per anode) Zinc pitguard anodes (including 1 clamp per anode) PENCIL / ROD ANODES 109 Zinc pencil anodes + brass plugs for pencil anodes 110 Zinc rod anodes (solid / massive zinc anode bar, excl. holes, excl. insert) MOUNTING MATERIAL 111 M -clamps for tank anodes (2 clamps per anode required) 112 Stud assembly for bolt-on anodes

2 MATERIAAL METINGEN EUROPE B.V. P.O. Box GE Ridderkerk (the Netherlands) ALLOY SPECIFICATIONS OF STANDARD SACRIFICIAL ANODES GENERAL The below mentioned alloys have been chosen with great care to ensure an even corrosion pattern, reliable electrical capacity and a long working life. These alloys are used for standard sacrificial anodes. On request Materiaal Metingen Europe can cast anodes with different alloy specifications. ALUMINIUM ALLOY Element Range (%) Zinc (Zn) Titanium (Ti) Silicon (Si) Bismuth (Bi) Indium (In) Copper (Cu) 0.01 max Iron (Fe) 0.15 max Magnesium (Mg) - Lead (Pb) - Cadmium (Cd) - Others each 0.10 max Aluminium Balance Nominal electrical capacity: 2700 AmpHr/Kg Nominal open circuit potential: mv vs Ag/AgCl (seawater) reference cell ZINC ALLOY acc. US MIL Spec. A-18001K Element Range (%) Aluminium (Al) Cadmium (Cd) Copper (Cu) max Iron (Fe) max Lead (Pb) Silicon (Si) - Titanium (Ti) - Bismuth (Bi) - Indium (In) - Magnesium (Mg) max Others total 0.10 max Zinc (Zn) Balance Nominal electrical capacity: 780 AmpHr/Kg Nominal open circuit potential: mv vs Ag/AgCl (seawater) reference cell The copper, iron and lead contents of our normal production alloy are usually less then 0.003% each. Page 1 van 2 of

3 MATERIAAL METINGEN EUROPE B.V. P.O. Box GE Ridderkerk (the Netherlands) ZINC VERSUS ALUMINIUM AS ALLOY FOR SACRIFICIAL ANODES GENERAL Traditionally many companies prefer to use zinc instead of aluminium. MME advices the use of aluminium instead of zinc for the following reasons: 1. Price of anode material Due to the fact that the capacity of aluminium (2700 A hr/kg) is almost 3.5 times higher than zinc (780 A hr /Kg) tot total amount of required anode material (Kg) is less. This results in a cheaper Cathodic Protection System to that given by zinc with an equal level of protection. 2. Price of Installation As the total weight of anode material for a system using aluminium is less compared to a system using zinc anodes the installation costs for a system using aluminium anodes will also be less. 3. Multi Effective In brackish water aluminium anodes work more effectively than zinc, due to the higher driving voltage of aluminium. 4. Environmental Pollution Compared to aluminium alloys, zinc alloys contain more elements which are detrimental for the environment. For anodes used in water ballast and other tanks see chapter The use of sacrificial anodes in tanks Page 2 van 3 of

4 MATERIAAL METINGEN EUROPE B.V. P.O. Box GE Ridderkerk (the Netherlands) THE USE OF SACRIFICIAL ANODES IN TANKS GENERAL Traditionally many vessels are fitted with sacrificial anodes for external protection (hull). For achieving the same protection of the internal construction of the vessel (mainly water ballast tanks) sacrificial anodes can also be used. However due to the fact that tanks are inherently complex structures as well as being confined spaces the use of anodes has to be well engineered and the following rules adhered to. 1. Effect of ballast tank anodes The ballast tank anodes will be without effect when the ballast tanks are empty. It will take some time to obtain full effect (polarisation) of submerged steel surfaces after filling with seawater. In the ullage space or under deck area on top of tanks the anodes will not be effective unless the tank is completely filled. 2. The use of zinc / aluminium or magnesium alloy anodes Anode alloy materials based on zinc or aluminium are acceptable, magnesium alloy is not allowed. Ballast tanks adjacent to tanks for liquid cargo with a flash point < 60 C are to be considered as dangerous areas. Aluminium alloy anodes are to be located in such way that the kinetic energy which is developed in case of loosening and falling down will be < 275 J. This means that in these areas the maximum height (in mtr) of an aluminium anode above tank bottom, deck or stringer may not exceed the value obtained by "28 / W", where "W" is the gross weight of the anode. Furthermore classification society may require structures to be installed to protect the aluminium anodes from being hit by falling objects. Please consult your local surveyor / classification society branch office for full details. 3. Welding or bolting type anodes For a good operation of the anodes it is vital to have a good electrical continuity between the ship structure and the anodes. This can be obtained either by welding (preferably) or bolting the anodes to the ship structure. In case bolting type anodes are requested the optional "M" clamps can be used. For the pros and cons of the use of zinc or aluminium alloys for sacrificial anodes used see chapter Zinc versus aluminium as alloy for sacrificial anodes Page 3 van 4 of

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