Examples of actual and possible uses

Pure magnesium is used in private and apartment steel reservoirs of hot water. Their service life duration for domestic water reservoirs can exceed 10 years but checking is necessary since accelerated corrosion rates are functions of water composition. Domestic tanks are of two kinds either they 

74 Bracelet anodes for subsea pipe lines (Morgan, 1993). 

Mg anodes can deliver sufficient current density 21.5 to 32.28 mA/nF to protect the inner wall of a galvanized steel hot water tank. It is reported that galvanized hot water tanks either corrode within few years or, if they last longer than this, remain sound for 15 to 20 years. This is supported by the fact that scale formation has a preservative or corrosion preventive effect of galvanized steel in hard water. Soft water can prevent the formation of this scale due to localized galvanic corrosion that can lead to perforation. It is suggested that if a tank is cathodically protected for the first year or 

15 Cathodically protected hot water tank with Mg anode (Uhlig and Revie, 1985). 

The most important factor in whether a water heater fails is the condition of its sacrificial anode. Generally, a 6 year warranty residential tank will have one, while a 12 year warranty tank will have two or an extra-large primary anode. Commercial tanks have from one to five. Special Al/Zn sacrificial anodes or powered anodes may be used to resolve odor problems caused by bacteria in some water. Magnesium is frequently preferred to aluminum for several reasons principally because aluminum produces less driving current between anode and cathode and shows less protection especially in soft water. Also, aluminum produces about a thousand times its original volume in corrosion by-product, most of which falls into the bottom of the tank as a sort of jelly or chunk, and adds to sediment buildup there, or can occasionally float out the hot water port (http //www.waterheaterrescue, 1995-2009). 

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