Page 23 - Reliability and Maintainability of In service Pipelines

12 Reliability and Maintainability of In-Service Pipelines

of stresses with incompatible chemicals. This action resulted in environmental
stress cracking (ESC) and it is understood that due to the sprinkler system being
static, the contaminants were sucked into the CPVC piping system due to pressur-
ization and accumulated there.
Common issues that contribute to failure in these types of pipes are poor
installation methods and manufacturing processes. Before installation, the pipe
walls remain in a “frozen” state with a low level of stress, and during usage stres-
ses within these pipes increase resulting in a requirement to release the stress.
Exposure to heat, organic matter, and other chemicals including hydrocarbons
allow the structural composition of the pipe to relax, by absorbing these materials,
and causing softening of the pipe surface. This results in the overall softening of
the pipe and can lead to longitudinal hairline cracking.
Causing additional stress on the pipe during installation can increase sensitiv-
ity towards ESC. Furthermore, temperature variances occurring inside these pipes
can also contribute to ESC, by causing changes in pressure, therefore increasing
the likelihood of more contaminants that can cause cracking and ultimately failure
within CPVC pipes.

Thermoplastic pipes
Propylene random copolymer (PRP) pipes: The PRP pipe is one of the latest
pipes and is used in cold and hot water systems. These pipes function both in san-
itary and pure water pipelines as well as underground heating systems and hot
water recycling systems. They are also useful in carrying compressed air, indus-
trial water, and chemical materials. PRP pipes are considered to be the optimal
pipe material for hot and cold water systems due to their high functionality,
safety, cost-effectiveness, and high lifetime of up to 50 years. This type of pipe
does not follow the aging process of most pipes and time-based leakage is almost
nonexistent once installed and pressure tests have proven sufficient. The smooth
inner wall and structural stability, as well as the capacity to function as heat insu-
lation make this type of pipe reliable in supporting materials of various chemical
compositions, pressures, and temperatures.
The disadvantages of these particular pipes, include the increased need for
higher technical requirements, including the usage of special tools and profes-
sionals in the installation process to ensure safety of the systems involved.
Another factor is that companies involved in construction do not fully rely on
these pipes, therefore they are not widely used as they are not as popular as other
materials used in pipeline industry.
High Density Polyethylene (HDPE) pipes: HDPE pipes are made from poly-
ethylene thermoplastics derived from petroleum through a heating process, where
petroleum is exposed to high temperatures to form ethylene gas. These gas