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HIGHLIGHTS
ABBREVIATIONS
D, DICL
Ductile iron clay-lined
G, GRP
Glass reinforced plastic
M, MSCL
Mild steel clay-lined
C-H
Site C to Hussainia pipeline
H-M
Hussainia to Muntashar pipeline
M-B&T
Muntashar to Habuna and Thar pipeline
INTRODUCTION
With the ever-increasing cost of pipelines and pipe network projects, it has become increasingly important to make every possible effort to optimize the cost of such projects. Under-design issues can result in undesirable and costly pipe failures, and over-design can result in wasted resources (Kanakoudis 2004a). Both over-design and under-design issues can be avoided by incorporating an efficient search for an optimum design with the lowest lifecycle cost.
Transient events can result in above- and below-normal pressures at certain points in a pipe network or a pipeline system (Kanakoudis 2004a). Without proper protection devices installed at appropriate locations, high surge pressures can lead to catastrophic failures. Subatmospheric pressure conditions resulting from these transients can cause leaky joints and introduce contaminants into the pipe system from the environment surrounding the pipes (Jung et al. 2007; Kanakoudis & Tsitsifli 2017; Tsitsifli & Kanakoudis 2018). Water hammer protection devices are mandatory, but they usually represent a small fraction of the pipe network costs. In some of the literature, pipe networks have been designed for steady-state flow conditions, but it has been proven that this approach is not accurate (Jung & Karney 2006).
Pipe network optimization has been discussed in the literature to varying degrees. Most studies have considered certain objectives or aspects of decision variables and ignored other important factors. Some studies have addressed pipe network optimization using the pipe diameter as the only decision variable. Both steady-state and unsteady flow conditions have been considered but without the use of surge pressure protection devices (Djebedjian et al. 2005; Afshar 2006). The optimization of surge protection devices has been discussed in some studies. For instance, if there is a high point along a pipeline, a simple surge vessel can be used for protection. This approach can reduce the overall cost of the pipeline. If, however, the design requires an impractically large surge tank, a small surge tank and air valves can be combined (Matringe 2004). It is possible to replace a surge tank connecting the apex of a pipe with an air...