Page 91 - Reliability and Maintainability of In service Pipelines

80 Reliability and Maintainability of In-Service Pipelines

3.3 Generalization of a Basic Reliability Problem 84
3.4 Reliability of Structural Systems 86
3.5 Sensitivity Analysis 88
3.5.1 Relative Contribution 88
3.5.2 Sensitivity Ratio 89
3.5.3 Omission Sensitivity Factor 89
3.6 Background and Methods for Reliability Analysis of Pipes 90
3.6.1 Deterministic Models 91
3.6.2 Probabilistic Modes 92
3.6.3 Other Models 96
References 99
Further Reading 101

3.1 Background

Reliability analysis and the prediction of the service life of pipelines is one of the
major challenges for infrastructure managers and maintenance engineers.
Historically, reliability theory has most often been introduced in the military, aero-
space, and electronics fields (Cheung and Kyle 1996). Over the past decades, the
significance of reliability theory has been increasingly realized in the area of pipe-
line engineering. The structural reliability began as a subject for academic research
about 50 years ago (Freudenthal 1956). The topic has grown rapidly during the
last three decades and has evolved from being a topic for academic research to a
set of well-developed or developing methodologies with a wide range of practical
applications.
Structural reliability can be defined as the probability that the structure under
consideration has a sufficient performance throughout its service life. Reliability
methods are used to estimate the service life of structures.
In addition to the prediction of initial service life, reliability methods are
effective tools to evaluate the efficiency of repair and replacement. The impact of
any repair and maintenance option upon the future performance of the structure
can be evaluated by decision makers using reliability analysis methods.
Furthermore, reliability analysis of a pipe or a pipeline network can be used at
the conceptual design stage to evaluate various design choices and to determine
the impact that their implementation could have upon their service lives.
The uncertain nature of the loadings and the performance aspects of pipelines
could have led the planners to probabilistic approaches for service life
assessment. In probabilistic methods for dealing with uncertainties, the safety and