UFC 3-570-06
JANUARY 31 2003
Figure 2-19. Distributed Sacrificial (Galvanic) Cathodic Protection System
Metallic connection
Test Lead
TANK
Anode
Anode
(Cathode)
Current Flow in the Earth
Current Flow in the Earth
Metallic Anode Selected from Galvanic Series (Usually Magnesium or Zinc)
2-6.1
Galvanic Anode Types. There are three materials that are commonly used
as galvanic anodes: magnesium, aluminum alloy, and zinc. Each material has different
grades or types available. Each type is available in a multitude of sizes and shapes.
For specific information on design, and information on types, sizes and shapes, consult
MIL-HDBK-1004/10.
2-6.1.1
Magnesium Anodes. Magnesium is the most commonly used sacrificial
anode material for the protection of buried structures. Magnesium anodes are also used
for the protection of the interiors of water tanks and heaters, heat exchangers and
condensers, and waterfront structures. Magnesium anodes are available as castings
and extrusions weighing from 0.45 kilograms to over 90.72 kilograms (1 to over 200
pounds) and in a wide variety of shapes as shown in MIL-HDBK-1004/10 (Table 2-10).
In addition, magnesium alloy anode material is available as a "ribbon" anode that
consists of a 10 gauge steel wire surrounded by standard alloy magnesium 9.5
millimeters by 19 millimeters (3/8-inch by 3/4-inch).
Two different anode compositions are commonly used. They are the
standard alloy and a commercially pure or "high potential" alloy. The high purity alloy
has the highest electrical potential available for any sacrificial anode, approximately -
1.75 volts DC to copper/copper sulfate in soil. The standard alloy has the next highest
electrical potential available, approximately -1.55 volts to copper/copper sulfate in soil.
The composition of each alloy is given in Table 2-5. The consumption rate for
magnesium is 4 kilograms (8.8 pounds) per amp year. The efficiency for providing
cathodic protection, considering the self-consumption rate, is higher for the standard
alloy than the high purity alloy. For design purposes, the efficiency of both types is 50
2-30
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