Page 15 - Reliability and Maintainability of In service Pipelines

4 Reliability and Maintainability of In-Service Pipelines

enormous disruption of daily life, massive costs for repair, widespread flooding,
and then pollution. This warrants a thorough assessment of the likelihood of pipe-
line failures and their remaining safe life, which is the topic of this book.

1.2 Scopes of Pipeline Reliability Analysis

Accurate prediction of the service life of pipelines is essential to optimize strate-
gies for maintenance and rehabilitation in the management of pipeline assets.
Service life (of building component or material) is the period of time after instal-
lation during which all the properties exceed the minimum acceptable values
when routinely maintained (ASTM E632-82, 1996).
The basis for making quantitative predictions of the service life of structures
is to understand the mechanisms and kinetics of many degradation processes of
the material whether it is steel, concrete or other materials. Material corrosion in
pipeline networks is a matter of concern for both strength and serviceability func-
tions. Loss of wall thickness through general corrosion affects the strength of the
pipeline. To that effect, incorporating the effect of corrosion into the structural
analysis of a pipeline is of paramount importance. There are several parameters
which may affect corrosion rate and hence the reliability of pipelines. To consider
uncertainties and data scarcity associated with these parameters, various
researches on probabilistic assessment of buried pipes have been undertaken
(De Belie et al., 2004; Sadiq et al., 2004; Davis et al., 2005; Salman and Salem,
2012; Mahmoodian and Alani, 2014; Mahmoodian and Li, 2017).
Since the deterioration of buried pipelines is uncertain over time, it should ide-
ally be represented as a stochastic process. A stochastic process can be defined as
a random function of time in which for any given point in time the value of the
stochastic process is a random variable depending on some basic random vari-
ables. Therefore a robust method for reliability analysis and service life prediction
of corrosion affected pipes should be a time-dependent probabilistic (i.e., stochas-
tic) method which considers randomness of variables to involve uncertainties in a
period of time.
In most of the literature, failure and reliability assessment of pipelines has
been carried out by considering one failure mode (Davis et al., 2005; De Silva
et al., 2006; Moglia et al., 2008; Yamini and Lence, 2009; Zhou, 2011). However
in reality, even in simple cases composed of just one element, various failure
modes, such as flexural failure, shear failure, buckling, deflection, etc., may exist.
To have a more accurate reliability analysis and failure assessment, multifailure
mode of pipelines is also explained in Chapter 3 as system reliability analysis.
For a comprehensive reliability analysis, evaluation of the contributions of
various uncertain parameters associated with pipeline reliability can be carried