Page 83 - Reliability and Maintainability of In service Pipelines

72 Reliability and Maintainability of In-Service Pipelines

determines the frequency which the routine maintenance methodologies need to
occur; naturally the older the pipeline and the more brittle and easily corroded the
pipeline, the more dependent on maintenance.

2.4.1 COATINGS

Any pipeline that is buried or submerged is required by standard specifications to
have an external coating for external corrosion control. Many pipeline operators
use an epoxy coating to seal off the surface of the pipe. While epoxy coatings are
the most popular, the diverse terrain through which pipelines operate sometimes
require specialized coatings. For example, a pipeline operator might use a cement
coating for a pipeline crossing a river to help weigh it down and keep it in place.
There are different means of coatings specific to the original material in which
a pipe is made from as well as the purpose it serves. Coatings can be for the inner
or outer surface of the pipeline, and some are more specific to the pipeline joints.
There are variety of coatings commercially available to assist in the protection of
existing pipeline infrastructure from corrosion.
The coatings can come in spray forms, putties, tapes, and paints. Coating of
pipelines creates an additional barrier round the pipe to protect it from the sub-
stance running through the pipeline as well as the corrosive substances found
in the soil which the pipeline is surrounded by, thus adding to its functional
integrity.
Epoxy coating is one of the most commonly used maintenance techniques
used for pipelines. Epoxy coating shields the pipelines base material from the
substance which the pipeline is transporting as well as previous damage to the
pipe. Within a steel pipe, rust is almost inevitable especially when used in water
transportation. Rust isn’t desirable especially if the water being transferred is for
drinking; the rust can be harmful to humans. Once the pipe is assessed and
cleaned, the epoxy coating can be applied to prevent further rusting to occur, pre-
venting complete pipeline failure, and allowing the water to be much more sani-
tary. In the terms of a concrete pipe, epoxy coating is used to shield the pipe
from sulfide corrosion as well as fill in cracks which may cause pipeline failure.
Plastic coating on pipes (more specifically metal pipes) is also common. This
arrangement of coating prevents external damage to the pipe from the surrounding
environment. Ground water, salinity, and other minerals within the grounds’ sur-
face can be damaging to pipelines. The plastic coating creates a thin barrier
between the pipe material and corrosive substances thus preventing the pipeline
from deteriorating externally. This prolongs the pipeline’s life span as well as its
reliability.