Page 22 - Reliability and Maintainability of In service Pipelines

Introduction 11

In comparison to other types of piping, seamless pipes do not require any
welding or joints and are simply formed by solid round billets, which adds on to
its strength and other characteristics including corrosion resistance. According to
ASME, these pipes are also more effective in withstanding mechanical stress and
have a higher operating pressure than welded pipes which are known as nonseam-
less pipes (Ferrostaal, 2017).
In general, the application of seamless pipes depends on the thickness of the
pipe wall. Higher temperatures are required to produce pipes with thicker walls
which reduces deformation resistance resulting in a larger deflection (XINLIN,
2014).

1.3.2 NONMETALLIC PIPES

1.3.2.1 Plastic Pipes
These types of pipes are used in external and internal plumbing systems to carry
cold water. Specifically, rigid PVC pipes are used to carry water within tempera-
tures below 45 C as higher temperatures decrease the strength of these pipes.

Sunlight and frequent changes in temperature also reduces the life of PVC pipes.
The three common types of plastic pipes are outlined below:
Unplasticized PVC (UPVC) or rigid pipes, which are used in cold water
systems.
Plasticized PVC pipes, which include the addition of rubber, and have a lower
strength and carry water of lower temperatures than UPVC pipes.
Chlorinated PVC (CPVC) pipes, which are used in hot water systems, with
temperatures of up to 120 C.

These types of pipes are joined using solvent cementing and heat fusion. The
high durability as well as the capacity to function as insulation and resistance to
corrosion make these pipes very usable in plumbing systems. The downfall of
these pipes however are the temperature limitations, especially heat, as well as
their weight and cost. These types of pipes are heavy to handle and are expensive
to replace.
CPVC pipes are known to be widely used in hot and cold water systems.
However, the function of CPVC pipes is compromised if contamination were to
occur. A study conducted on the use of CPVC pipes in fire sprinkler systems
observed that the potential causes of failure were more than one, with the most
common cause of failure being contamination. The contamination was reported to
occur inside the pipes and fittings when exposed to chemicals that were not com-
patible with the use of these particular type of pipe. Although it was not the expo-
sure to harsh chemicals alone that caused failure, but rather the combined affect