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What is a Magnesium Anode?

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  • Written By: Paul Scott
  • Edited By: R. Halprin
  • Last Modified Date: 25 September 2016
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    Conjecture Corporation
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A magnesium anode is a galvanic or sacrificial corrosion prevention device connected to steel structures to prevent or slow down rusting. Magnesium anodes create an easier and more attractive source of oxidation than the steel structures they are connected to. In this way they are consumed by corrosion instead of the structure — hence the name sacrificial anode. A magnesium anode is typically made up of an alloy composite of magnesium and other metals. They are available in a selection of prefabricated designs and weights to suit a wide range of installation requirements.

The magnesium anode belongs to a group of corrosion protection devices known as galvanic or sacrificial anodes. These anodes are electrically connected to the surface of the steel work they protect by means of direct contact or a cable link. They are either left on the surface of the steel work or buried in the ground adjacent to the structure. They then offer corrosion protection by offering themselves up as a more attractive and direct source of oxidation than the steel structure and are slowly consumed or sacrificed in the process.

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Magnesium anodes are typically available in two alloy compositions. The first is typically a combination of 90% magnesium, 6% aluminum and 3% zinc. The second is 99% pure magnesium which is better suited to dry or resistant soil conditions or where the steel work is poorly coated with other corrosion barriers. The magnesium anode is most commonly used to protect propane tanks, ship hulls, submarine pipelines, piers, and heat exchangers.

Mangnesium anodes are available in a range of designs. Each type is specifically crafted to offer different conductive properties and connection options to suit particular types of structures or environments. Hull anodes, for instance, are designed to flush mount against the hulls of ships, dams, or tanks via built in steel straps. Drive-in anodes, on the other hand, are designed to be driven into the ground to protect buried propane tanks or steel pylons. Specialist anodes such as condenser and ribbon types may feature plastic coatings to increase anode life or offer higher than normal current carrying capacity.

Magnesium anodes are also available in a range of sizes and with several packaging options. The most popular magnesium anode size is the 17 pound (7.7 kg) anode although they are available in sizes ranging from a couple of ounces to over 200 pounds (90 kg). Magnesium anodes are also frequently presented in a ready-to-use backfill package which consists of a degradable bag filled with an electrically conductive filling of powdered gypsum, bentonite clay, and sodium sulphate. The whole package is buried intact where the bag disintegrates over time. The filling eventually creates a good conductive layer around the anode which can ensure excellent results in resistive soils.

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