MME Sacrificial Anodes booklet

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Transcript of MME Sacrificial Anodes booklet

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    A Longer Life

    SACRIFICIAL ANODES

    www.mme-group.com

    Hull Anodes

    Bolt-on Anodes / Disc Anodes

    Tank Anodes

    Pitguard Anodes

    Pencil / Rod Anodes

    Mounting Material

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    Page: CONTENTS: 2 Alloy specification of standard sacrificial anodes 3 Choosing zinc or aluminium anodes 4 Anode recommendations 5 Choosing tank anodes

    WELD-ON HULL ANODES 7 - 28 Aluminium weld on hull anodes30 - 48 Zinc weld on hull anodes50 - 55 Magnesium weld on hull anodes

    BOLT-ON HULL ANODES57 - 68 Aluminium bolt on hull anodes (with 2 bolting holes)70 - 81 Zinc bolt on hull anodes (with 2 bolting holes)83 - 86 Magnesium bolt on hull anodes (with 2 bolting holes)

    BOLT-ON DISC ANODES88 - 93 Aluminium bolt-on disc anodes (with 1 bolting hole)95 - 102 Zinc bolt-on disc anodes (with 1 bolting hole)104 Magnesium bolt-on disc anodes (with 1 bolting hole)

    TANK ANODES106 - 121 Aluminium tank anodes123 - 136 Zinc tank anodes

    PITGUARD ANODES138 - 141 Aluminium pitguard anodes (including 1 clamp per anode)143 - 147 Zinc pitguard anodes (including 1 clamp per anode)

    PENCIL / ROD ANODES149 Zinc pencil anodes + brass plugs for pencil anodes151 Zinc rod anodes (solid / massive zinc anode bar, excl. holes, excl. insert)

    MOUNTING MATERIAL153 - 154 Stud assembly for bolt-on anodes155 M-clamp installation for tank anodes in general156 M-clamps for tank anodes (2 clamps per anode required)

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    GENERALThe 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) 3.50 - 5.00Titanium (Ti) 0.01 - 0.05Silicon (Si) 0.05 - 0.20Bismuth (Bi) 0.05 - 0.15Indium (In) 0.02 - 0.05Copper (Cu) 0.01 maxIron (Fe) 0.15 maxOthers each 0.10 maxAluminium Balance

    Nominal electrical capacity: 2700 AmpHr/KgNominal open circuit potential: -1100 mV vs Ag/AgCl (seawater) reference cell

    Element Range (%)Aluminium (Al) 0.10 - 0.5Cadmium (Cd) 0.025 - 0.07Copper (Cu) 0.005 maxIron (Fe) 0.005 maxLead (Pb) 0.006 maxOthers total 0.10 maxZinc (Zn) BalanceNominal electrical capacity: 780 AmpHr/KgNominal open circuit potential: -1050 mV vs Ag/AgCl (seawater) reference cell

    The copper, iron and lead contents of our normal zinc alloys are usually less then 0.003% each.

    ZINC ALLOY acc. US MIL Spec. A-18001K

    ALLOY SPECIFICATIONS OF STANDARD SACRIFICIAL ANODES

    A LONGER LIFE

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    GENERALTraditionally 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) the 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 InstallationAs 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 EffectiveIn brackish water aluminium anodes work more effectively than zinc, due to the higher driving voltage of aluminium.

    4. Environmental PollutionCompared to aluminium alloys, zinc is considered to be less neutral to the environment.

    For anodes used in water ballast and other tanks see chapter Choosing tank anodes (page 5).

    CHOOSING ZINC OR ALUMINIUM AS ALLOY FOR SACRIFICIAL ANODES

    A LONGER LIFE

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    Saltwater

    Brackish Water

    Fresh Water

    Zn Al Mg

    Zn Al Mg

    Zn Al Mg

    In saltwater, both Zinc and Aluminium are suitable, but aluminium has a better re-activation performance.

    Aluminium is the recommended material for brackish water.

    On pure fresh water magnesium is the best performing anode material.With polluted water or when a boat is temporary in brackish water, aluminium is the preferred anode.

    The recommendations apply to steel structures. For more detailed information, please consult your local distributor.

    ANODE RECOMMENDATIONS

    A LONGER LIFE

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    GENERALTraditionally 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 societies 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 anodesFor a good operation of the anodes it is vital to have a good electrical conductivity 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 (see page 134).

    For the pros and cons of the use of zinc or aluminium alloys for sacrificial anodes used see chapter Choosing zinc or aluminium as alloy for sacrificial anodes (page 3).

    CHOOSING TANK ANODES

    A LONGER LIFE

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    ALUMINIUM WELD-ON HULL ANODES

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    ZINC WELD-ON HULL ANODES

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    MAGNESIUM WELD-ON HULL ANODES

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    ALUMINIUM BOLT-ON HULL ANODES

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