Page 16 - Reliability and Maintainability of In service Pipelines

Introduction 5

out by using sensitivity analysis techniques. Sensitivity analysis is conducted as a
main part of reliability analysis from which the effect of different variables on
service life of pipelines can be investigated. Sensitivity analysis is the study of
how the variation in the output of a model (numerical or otherwise) can be appor-
tioned, qualitatively or quantitatively, to different sources of variation (Saltelli
et al., 2004; Mahmoodian and Alani, 2016). Among the reasons for using sensitiv-
ity analysis are:
To identify the factors that have the most influence on reliability of the
pipeline.
To identify factors that may need more research to improve confidence in the
analysis.
To identify factors that are insignificant to the reliability analysis and can be
eliminated from further analysis.
To identify which, if any, factors or groups of factors interact with each other.
With a focus on “structural reliability”, factors affecting both the structure and
function of pipelines are analyzed and these are predicated on material type,
design methods, and uses. As structural reliability is defined as a multifaceted
term which considers factors that either have a direct or partial impact, deteriora-
tion mechanisms are also analyzed to illustrate the degree of impact on pipelines
under various conditions.
Because corrosion is an ongoing issue, assessment of structural reliability of
pipelines can also help to gain an insight into corrosion prevention mechanisms,
by altering the unfavorable factors that contribute to this type of deterioration and
consequently the service life of pipelines can be prolonged.

1.3 Types of Pipelines

Pipelines are tubular structures, typically underground and constructed from
metals, plastics, and/or concrete for the purpose of carrying flow, including
liquids and gasses.
The various types of pipelines are determined by the type of materials used to
manufacture each pipeline based on its different applications (Table 1.1), the
different functions it carries out, and the type of matter it is exposed to.
The engineering materials which can be used for pipe manufacturing are pre-
sented in Table 1.2. The commonly used pipe types are generally split into two
categories: metals and nonmetals, with its subclassification: nonferrous/ferrous,
plastics, ceramics, and composites.
Typically, metallic piping is derived from steel or iron, including unfinished
black steel, carbon steel, stainless steel, galvanized steel, brass, and ductile iron.