2
Cathodic Protection
2.1I ntroduction
Atremendous investmentexists world-wide in undergroundmetallic structures such as pipelines, storage facilities, wellc asings, structure supports,
communication cables, etc. When these members are in direct contactw ith
the soil and unprotected, they are subject to corrosion.
Attempts have been made to overcome this problem by the use of various
types of coatings appliedt ot he surface. Although suchc oatings can be
effective,i nvariably smallh oles or holidays are usually present. These
holidays provide access to the uncovered basem etal and permit corrosion.
Subsequent repairs can be extremely costly. In addition, undetected failure
(or leakage) can cause accidents or lead to safety hazards, such as causing
roadways to collapsea saresulto fa nu ndergroundw ater leak, or to
environmental hazards resulting from oil leaks.
By cathodic protection, bare metals and holidays in coated metals can be
protected from corrosion.
2.2B ackground
Cathodic protection is am ajorf actor in metals’ corrosion control. When an
external electric current is applied, the corrosionr ate can be reduced to
practically zero. Under theseconditions, the metal can indefinitely remain in
ac orrosive environment without deterioration.
In practice, cathodic protection can be utilized with suchm etalsa ss teel,
copper,b rass,l ead, and aluminuma gainst corrosion in all soils and almost
all aqueous media. Although it cannot be used abovethe waterline (because
the impressed electric current cannotreach areas outside of the electrolyte),
CAT8247—CHAPTER 2—6/10/2006—12:05—SRIDHAR—XML MODEL B–pp. 43–54
43
Cathodic Protection
2.1I ntroduction
Atremendous investmentexists world-wide in undergroundmetallic structures such as pipelines, storage facilities, wellc asings, structure supports,
communication cables, etc. When these members are in direct contactw ith
the soil and unprotected, they are subject to corrosion.
Attempts have been made to overcome this problem by the use of various
types of coatings appliedt ot he surface. Although suchc oatings can be
effective,i nvariably smallh oles or holidays are usually present. These
holidays provide access to the uncovered basem etal and permit corrosion.
Subsequent repairs can be extremely costly. In addition, undetected failure
(or leakage) can cause accidents or lead to safety hazards, such as causing
roadways to collapsea saresulto fa nu ndergroundw ater leak, or to
environmental hazards resulting from oil leaks.
By cathodic protection, bare metals and holidays in coated metals can be
protected from corrosion.
2.2B ackground
Cathodic protection is am ajorf actor in metals’ corrosion control. When an
external electric current is applied, the corrosionr ate can be reduced to
practically zero. Under theseconditions, the metal can indefinitely remain in
ac orrosive environment without deterioration.
In practice, cathodic protection can be utilized with suchm etalsa ss teel,
copper,b rass,l ead, and aluminuma gainst corrosion in all soils and almost
all aqueous media. Although it cannot be used abovethe waterline (because
the impressed electric current cannotreach areas outside of the electrolyte),
CAT8247—CHAPTER 2—6/10/2006—12:05—SRIDHAR—XML MODEL B–pp. 43–54
43