Page 24 - Reliability and Maintainability of In service Pipelines

Introduction 13

molecules then link together, forming a polymer chain, referred to as polyethylene
(Kumar et al., 2011).
These types of pipes function as underground pipelines, carrying fresh drink-
ing water, gases, corrosive substances, and sewerage. The easy installation pro-
cess of these pipes, ensures that they do not require connectors to form a pipeline
network compared to metal piping installation methods. The pipes are simply
fused together, creating a monolithic system, resulting in an antileak HDPE
pipeline.
Due to their strength, durability, flexibility, and light weight characteristics,
HDPE pipes are ideally used as water and gas pipes. Their ability to resist high
stresses, pressure, leakage, tearing, and corrosion makes HDPE pipes very useful
both as buried and on-ground pipes. These pipes are also environmentally sustain-
able, as they are nontoxic, and chemical-resistant, therefore they are ideal for
water application, energy, and industrial usage.
Because the surfaces of HDPE pipes are smoother than ferrous and concrete
pipes, it ensures there is less drag in terms of flow, therefore these pipes hold
great hydraulic characteristics, ensuring good volumetric flow rate, and less turbu-
lence with higher flows. The chemical resistance of these pipes also eliminates
any sticking of chemicals, bacteria, fungi, and other organic substances to the
pipe surfaces thereby ensuring prolonged service life.
In terms of weather resistance and long service life, HDPE pipes have the
capacity to withstand freezing water more efficiently than metal pipes and mini-
mal heat transfer, making them excellent insulators. Even at temperatures exceed-
ing 35 C, HDPE pipes do not become brittle and show lower friction loss rates

than metal pipes. Furthermore, these pipes can also resist UV, if carbon black is
added to the HDPE.

1.3.2.2 Composite Pipes

Concrete Pipes: Concrete pipes are used for drainage purposes, including storm
water, road culverts, and sewers. Manufactured but not limited to 2.44 m lengths
as well as being custom made, with specific pipe fittings, these types of pipes are
usually buried under roads of urban cities, therefore it is important to ensure the
structural safety and durability of these types of pipes. As concrete pipes are usu-
ally difficult to repair and replace, it is important to ensure that certain measures
are taken to preserve their life span. These particular types of pipes are suscepti-
ble to sulfide-based corrosion, and their design must ensure adequate structural
safety.
When considering storm water pipes and sewerage pipes, providing a high
axial load transfer capacity and a flexible high watertight joint is critical to ensure
safe installation and proper function.