UFC 3-570-06
JANUARY 31 2003
graphite anodes. The anodes exhibit superior conductivity and experience very little
change in resistance with time, unless the anode is damaged. The high tensile strength
of the metal is an asset in some circumstances, except that their very low elongation
makes them brittle and subject to fracture from severe mechanical and thermal shock.
Cast iron anodes are manufactured in a wide variety of dimensions, shapes,
and weights. Refer to Table 2-13 for a description of the various sizes. A proprietary
type of cast iron anode, originally manufactured from "off-specification" corrosion
resistance piping, is called a tubular anode. This uses the ASTM 518 Grade 2
chromium alloy and has demonstrated since 1971 to have superior resistance to "end
effect," common to anodes with poor connection resistance values.
Table 2-12. Cast Iron Composition
ASTM 518
Element
Grade 1
Grade 2
Silicon
14.2 - 14.75%
14.2 - 14.75%
1.5% max.
1.5% max.
-
3.25 - 5.0%
Carbon
0.75 - 1.15%
0.75 1.15%
Copper
0.50% max.
0.50% max.
Iron
Balance
Balance
Consumption
Soil
0.45 kg (1 lb)/amp-year
0.34 kg (0.75 lb)/amp-year
Rate
Seawater
8.4 kg (18.5 lb)/amp-year
0.11 kg (0.25 lb)/amp-year
2-46
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