Page 62 - Reliability and Maintainability of In service Pipelines

Pipeline Inspection and Maintenance 51

design lifetimes and pose a potential risk for structural failure due to defective
problems such as corrosion and deterioration. The continuous monitoring, assess-
ment, and evaluation of these pipelines is essential to ensure the networks are
safe and have no serious problems.
Much of the current available literature acknowledge that manual inspection
methods are extremely time-consuming and are also error-prone in detecting
defects in the pipelines and therefore are not very reliable or accurate. However,
developments in the inspection techniques are constantly growing and as a result,
automated inspection and evaluation systems are replacing the manual inspection
procedures to resolve this concern.
Pipeline inspection can be very expensive to carry out and it is crucial to fol-
low reliable methods to maintain the pipes’ safety and prevent defects from
occurring in the future and reduce the total costs of pipeline maintenance.
Common methods for maintenance of pipelines such as coatings and cathodic
protection will be discussed in more detail in Section 2.4.

2.2 Pipelines Integrity

Pipeline operators and regulators need to carefully consider the integrity manage-
ment of pipelines. Integrity management plans include emergency protocols but
most importantly include maintenance and preventative measures. Operators take
measures to defend pipelines against specific risks. Considering the potential for
costly public and environmental damages given a pipeline failure, these measures
are generally mandated by government. Through proper maintenance and inspec-
tion, operators can manage the integrity of their pipelines and mitigate the risk of
failure.
Pipelines might lose their integrity often due to corrosion, manufacturing pro-
blems, construction errors, environmental incidents, and/or human interference.
The consequence can be either serviceability failure or ultimate strength failure.
A serviceability failure occurs when a pipe does not collapse, but rather fails to
meet the required specifications. For example, pipeline leakage can be considered
as serviceability failure, because the pipe does not operate well but it is still in
place. In ultimate strength limit state cases, a pipe completely loses its structural
integrity and ends up in ultimate collapse. While cracking and leakage can be in
the category of pipeline serviceability failure, flexural failure, and shear failure
are involved in the category of ultimate strength failure.
Among the causes of pipe failure, corrosion is often the most significant. A
study over the period of 1999 2001 of the percentage distribution of all failures
in the Unified gas supply system showed more than 44% of failures are related to
pipeline corrosion (Litvin and Alikin, 2003), see Fig. 2.1.