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Fundamentals of Corrosion
11.3.6.3 Internal Corrosion
Although external corrosion is a problem throughout the length of any buried or submerged pipeline, internal corrosion is a problem only if the material being carried by the pipeline is of a corrosive nature. When the material
being carried by a pipeline is determined to be corrosive in nature, it may be
possible to treat the material to inhibit the corrosive properties. Where inhibitors are used, it is necessary to monitor the effectiveness of the corrosion
control method by, for example, using internal coupons that can be examined
at intervals in order to evaluate the effectiveness of the treatment method.
When treatment is not possible, the use of an internal coating system may
be resorted to. In petroleum or petroleum products, it is possible to apply
paint coatings in place on existing pipelines. Although any paint or coating system applied internally may not be 100% effective, it will nevertheless materially reduce the amount of internal pipeline surface that is directly
affected by the material being carried. In the case of water pipelines, good
experience has been obtained, where internal corrosion is a significant problem, by the use of linings of cement mortar that can be applied to pipelines
already in place. In other situations where conditions warrant it, good experience has been obtained with inserting plastic liners (of a type that is not
affected by the material being transported) inside the original metallic pipe
when it approaches the point of becoming unserviceable because of internal
corrosion. This approach is normally applicable to lower pressure pipelines.
In some instances it is possible to eliminate corrosion problems in the
design stage by selecting a material of construction that will be compatible
with the media being transported. Alternate materials other than an alternative metal may include one of the several plastic piping materials, many of
which are suitable for burial, providing pressure is not a limitation.
Where a substitute metal is suitable from the viewpoint of corrosion resistance and is competitive on an overall cost basis, this may be a suitable choice.
Materials other than metals suitable for use in the pipeline industry include
the following:
Asbestos cement
•
Reinforced concrete
•
Plastic
•
Filament-wound reinforced plastic pipe
•
11.3.7 Marine industry
One of the outstanding methods of protection for marine objects in seawater is cathodic protection. The combination of organic coatings and cathodic
protection has given military and merchant shipping plus offshore oil-well
towers much better corrosion control over corrosion problems than prior to
Fundamentals of Corrosion
11.3.6.3 Internal Corrosion
Although external corrosion is a problem throughout the length of any buried or submerged pipeline, internal corrosion is a problem only if the material being carried by the pipeline is of a corrosive nature. When the material
being carried by a pipeline is determined to be corrosive in nature, it may be
possible to treat the material to inhibit the corrosive properties. Where inhibitors are used, it is necessary to monitor the effectiveness of the corrosion
control method by, for example, using internal coupons that can be examined
at intervals in order to evaluate the effectiveness of the treatment method.
When treatment is not possible, the use of an internal coating system may
be resorted to. In petroleum or petroleum products, it is possible to apply
paint coatings in place on existing pipelines. Although any paint or coating system applied internally may not be 100% effective, it will nevertheless materially reduce the amount of internal pipeline surface that is directly
affected by the material being carried. In the case of water pipelines, good
experience has been obtained, where internal corrosion is a significant problem, by the use of linings of cement mortar that can be applied to pipelines
already in place. In other situations where conditions warrant it, good experience has been obtained with inserting plastic liners (of a type that is not
affected by the material being transported) inside the original metallic pipe
when it approaches the point of becoming unserviceable because of internal
corrosion. This approach is normally applicable to lower pressure pipelines.
In some instances it is possible to eliminate corrosion problems in the
design stage by selecting a material of construction that will be compatible
with the media being transported. Alternate materials other than an alternative metal may include one of the several plastic piping materials, many of
which are suitable for burial, providing pressure is not a limitation.
Where a substitute metal is suitable from the viewpoint of corrosion resistance and is competitive on an overall cost basis, this may be a suitable choice.
Materials other than metals suitable for use in the pipeline industry include
the following:
Asbestos cement
•
Reinforced concrete
•
Plastic
•
Filament-wound reinforced plastic pipe
•
11.3.7 Marine industry
One of the outstanding methods of protection for marine objects in seawater is cathodic protection. The combination of organic coatings and cathodic
protection has given military and merchant shipping plus offshore oil-well
towers much better corrosion control over corrosion problems than prior to