Page 133 - Reliability and Maintainability of In service Pipelines

120 Reliability and Maintainability of In-Service Pipelines

5.3 Case Study 3-Cast Iron Water Mains in the UK 141
5.3.1 Problem Formulation 141
5.3.2 Results and Analysis 146
5.4 Case Study 4-Concrete Sewer Pipes in the UK 151
5.4.1 Individual Failure Mode Assessment 151
5.4.2 Multifailure Mode Assessment 161
Symbols 163
5.4.3 Corrosion Model 164
5.4.4 Calculation of Failure Probability 164
References 169
Further Reading 171

The use of theoretical methods for structural reliability analysis of in-service pipe-
lines explained in Chapter 4 is practiced in this chapter through case studies.
Different types of pipes including steel, cast iron, and concrete subject to different
type of corrosive environment (i.e., oil and gas, water, and wastewater) are ana-
lyzed. The steps used for the reliability analysis in each case study include:

Problem formulation: which introduces defining the limit state function(s),
establishing the corrosion model and presenting the method for calculation of
failure probability.
Analysis of the results: which illustrates variation of failure probability versus
time, verification of the results, and sensitivity analysis.

5.1 Case study 1-Oil and Gas Steel Pipes in USA

Oil and gas constitutes 60% of the world’s fuel usage. Although pipelines are a
very safe form of energy transportation, in the case of pipeline failures, the spilled
oil and gas can cause a considerable hazard to the surrounding environment and
population.
Deterioration and aging of pipeline infrastructure is one of the major problems
facing the pipeline industry. More than half of the US oil and gas pipeline net-
work is over 40 years old. 20% of Russia’s oil and gas system is almost at the
end of its design life and it is expected that in 15 years time 50% of their pipe-
lines will be at the end of its design life. Metal corrosion is a common threat to
the structural integrity of aging oil and gas pipelines. Corrosion as a time-
dependent process gradually reduces the pipe strength and eventually causes the
pipe failure. It has been shown (Sinha and Pandey, 2002; Anon, 2002; Thacker
et al., 2010; Mahmoodian and Li, 2016a,b) that corrosion is the predominant
cause for oil and gas pipe failures in many countries.