UFC 3-570-06
JANUARY 31 2003
When corrosion is noted, or when a corrosion leak occurs, it is essential that
the cause of the corrosion be identified so that corrective action can be taken. Once the
type of corrosion is understood, the method of repairing the cause of the corrosion can
be easily determined and future leaks can be prevented. In many cases, the location of
the anodic area can be predicted by understanding the process of corrosion. These
anodic areas tend to be in the worst possible places. Examples are pipeline river or
swamp crossings, pipelines entering pits or foundations, pipelines under stress and
pipelines at elevated temperatures.
In a majority of leak situations, the primary concern is to patch the hole in the
pipeline or tank. Without an understanding of corrosion and corrosion control, a bad
situation can be made even worse. Even considering the criticality of stopping a
gushing leak, it is imperative to fix the cause of the leak. This means taking action to
identify and mitigate the cause of the leak. In some situations it may be a failed
insulator or broken bond wire which actually caused the leak. Probably the most
common cause of corrosion leaks are the methods or materials used from previous leak
repairs, breaking or shorting the continuity. An example of many types of corrosion at
work simultaneously can be demonstrated by the following figure, which shows most of
the different types of corrosion discussed.
Figure 2-11. Combination of Many Different Corrosion Cells at Work
Different Environment
Different Metal
Stress
Different Metal
Moist/Dry
Oxygen Concentration
Different Metal
Scratched/Marred Surface
2-2.4
Stray Current Corrosion. This type of electrochemical corrosion cell is
caused by an electromotive force from an external source affecting the structure by
developing a potential gradient in the electrolyte or by inducing a current in the metal,
which forces part of the structure to become an anode and another part a cathode. This
pickup and discharge of current occurs when a metallic structure offers a path of lower
resistance for current flowing in the electrolyte. This type of corrosion can be extremely
severe because of very high voltages that can be forced into the earth by various sources.
The potential gradient in the electrolyte forces one part of the structure to pick up current
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