UFC 3-570-06
JANUARY 31 2003
2-2.3.2
Old-to-New Syndrome. This type of corrosion can also be rather severe.
Steel is unique among metals because of the high energy put into the process of
producing the steel (paragraph 2-2.1). New steel is more active, than corroded steel.
The potential difference between the high negative potential of the new steel and the
low negative potential of the old steel is the driving force, or voltage, of this
electrochemical corrosion cell. A severe and common example of this type of corrosion
is when an old bare steel pipeline fails, and a small section of the pipeline is replaced
with a coated section of new steel. The new section is the anode and corrodes to
protect the large cathode, resulting in failure of the new section.
Figure 2-9. Galvanic Corrosion Cell Caused by Old and New Steel
Anodic Area (New Pipe)
Cathodic Area (Old Pipe)
Cathodic Area (Old Pipe)
Current Flow in the Earth
2-2.3.3
different metal alloys. For example, there are over 200 different alloys of stainless steel.
Also, metals are not 100 percent pure. They normally contain small percentages of
other types of metals. Different batches of a metal vary in content of these other
metals. Different manufacturers may use different raw materials and even the same
manufacturer may use raw materials from different sources. Each batch of metal may
be slightly different in electrical potential. Even in the same batch of metal, the
concentration of these other materials may vary slightly throughout the finished product.
All these differences will produce the electromotive force for this type of corrosion to
occur.
2-2.3.4
may be mixed into the metal as it is produced or cooled. Impurities at the surface of the
metal may become part of the electrolyte causing concentration cell corrosion, or if
metallic, they may be anodic (corrodes and leaves a pit behind), or cathodic (corroding
surrounding metal).
2-2.3.5
Marred or Scratched Surface. A marred or scratched surface becomes
2-12
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