Page 274 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

252 CORROSION CONTROL AND PREVENTION

Plant and process design

Equipment fabrication
checks

Construction stage checks

Planned Corrosion monitoring
maintenance

Diagnostic
work

Remedial
action

Figure 4.10 The phases of corrosion control.

and permit continued operation of the pipeline. Severe and high density of the stress
corrosion cracks may necessitate pipe replacement from the economic point of view.
Some of the considerations that play a role in deciding on rehabilitation or replace-
ment of a pipeline are terrain conditions, expected or required life, excess capacity,
throughput requirements, and internal versus external corrosion (Table 4.23).
The location of a pipeline is critical to repair considerations. For instance, a pipe
in swampy clay would exclude recoating as a repair option. On the contrary, pipes
in prairies are conductive to recoating, with firm footing for the equipment and good
accessibility.
If the expected life of a section of pipe is short, the operator must decide whether
recoating and repair would extend the life of a pipe section to match the rest of the
pipeline. Otherwise, recoating is not a recommended solution. Replacing the pipeline
may be the best solution.
Alternatives other than rehabilitation and replacement such as abandonment of
the pipe section with a bypass loop increasing the frequency of ILI enables greater
accuracy in determining the point of failure for existing defects. Derating the pipe
may extend the life of the pipe provided throughput requirements are met. For the
replacement or repair option, it is generally necessary to have a loop system and
allow for pressure restrictions or interruptible service to facilitate repairs.
It is more difficult to combat internal corrosion than external corrosion. Internal
corrosion can be mitigated by having an internal coating or lining. For internal coating
repair, the pipeline will have to be completely out of service. The pipeline need not
be out of service for external recoating operations.