Extruded magnesium anodes are available with plain ends or the core rod exposed.  Anodes may also be furnished with steel fittings for ease of mounting in water tanks.

 

Exothermal™ Extruded Magnesium Anodes find widespread use, where conventional cast magnesium or zinc anodes are impractical.  In some cases extruded anodes are advantageous over cast magnesium or zinc anodes.

  • Water Heaters – Extruded magnesium anodes offer an important advantage, since the geometry of water tanks necessitates the use of a long small diameter anode.  Magnesium is innocuous to humans, therefore poses minimal risk when used in potable water systems, the same is not true for aluminum.  Zinc anodes also can not be used in hot water systems, since zinc suffers a potential drop above 60˚C, which would compromise its ability to protect the tank.

  • Gas meters and services – These anodes need to be driven into the ground, thus a small diameter extruded anode would provide a cost advantage in the installation of the anode.  

Above is shown a consumed magnesium anode from a hot water heater that has failed, superimposed on a new magnesium anode.  Notice that on the after portion of the anode, we can see that there is no visible magnesium left on the core wire, but only corrosion products.  During the lifetime of a magnesium anode the magnesium should be consumed equally around the circumference of the anode. 

 


  Standard Extruded Anode Sizes
 

Nominal diameter, inches

Core centering, inches

Core wire diameter, inches

Approx. weight, lbs/in

0.500

.040

0.135

0.015

0.675

.050

0.135

0.025

0.700

1/16

0.135

0.027

0.750

1/16

0.135

0.031

0.800

1/16

0.135

0.035

0.840

1/16

0.135

0.038

0.900

1/16

0.135

0.043

1.050

1/16

0.135

0.057

1.315

1/16

0.135

0.089

Anode rods are available in standard potential, also known as Type AZ31 alloy, and high potential, Type M1 alloy.   

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Chemical Composition for Extruded Anodes
 

Material

Mg %

Al %

Mn %

Zn %

Si %
max

Cu %
max

Ni %
max

Fe %
max

Other imp.
% max

each

total

ASTM B843 Type AZ31

Bal.

2.5-
3.5

0.20
min

0.7-
1.3

0.05

0.01

0.001

0.002

0.05

0.30

ASTM B843 Type M1

Bal.

0.010
max

0.50-
1.3

-

-

0.02

0.001

0.03

0.05

0.30

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Some of the more important features of the two alloy systems are listed below:  

 

AZ31 (standard potential) alloy

M1 (high potential) alloy

Voltage Potential (with respect to Cu/CuSO4)

1.4 – 1.5 V

1.6 – 1.7 V

Current Capacity

450 – 550 Ah/lb

400 – 500 Ah/lb

Current Efficiency

45 – 55 %

40 – 50 %

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