1. Introduction
Much of the existing pipeline infrastructure is constructed from
steel. Steel is strong, mechanically robust and relatively inexpensive.
However, large sums of money are spent in order to reduce
the exposure of steel pipelines to corrosive environments. One
way to overcome this problem is to use a material with good corrosion
resistance, such as Glass Fiber Reinforced Polymers (GFRPs),
instead of steel. GFRPs represent an attractive alternative for
pipelines subjected to severe internal or external environments
in onshore or offshore applications [1].
Composite material is a combination of two or more separate
materials in macroscopic state. Unlike metals, the building
constituents of composite materials, namely fiber and matrix, still
can be observed without magnification devices. Fibers in composite
material act as reinforcement of matrix because fibers are usually
stiffer than matrix. Matrix serves as a binder for fibers
arrangement and also protects fibers from environmental effect
and impact damage [2].
Matrix can be in the form of polymers, metals and ceramics.
Two types of polymers are usually used, namely thermoplastic
polymers and thermoset polymers. Epoxy, as one variant of thermoset
polymer, is commonly used to bind carbon or glass fibers
for its good dimensional stability [3].
Fibers act as structural materials to sustain loading since they
have higher stiffness than matrix. When they are mixed with
matrix, fibers are random in nature. A wide variety of fibers are
available. Most common fibers used as reinforcement are glass
(E-glass and S-Glass types), carbon (some forms of which are graphite)
and Kevlar fiber. Glass fiber in combination with polymeric
matrix (GFRP: glass fiber reinforced plastics) is commonly used for
storage tanks and pipeworks [4].
The connections between the various parts of the ducts are
made by quick lock bounded joints. In ship construction the need
to join different materials, such as the bonding of the hull/deck,
the sea chest, the portholes, the windshields, the panels of cabins,
etc., leads to choosing increasingly the adhesive joints [5].
Adhesive joining is defined as the process of joining parts using
a non-metallic substance (adhesive), which undergoes a physical
or chemical hardening reaction causing the parts to join together
through surface adherence (adhesion) and internal strength (cohesion).
The significance of adhesive bonding as structure-joining
technology is increasing because of its numerous advantages with
other joining methods [6].
The defects which are most often found in Glass Reinforced
Epoxy (GRE) pipe systems are lack of adhesive, disbonding and
delaminations in bonded joints, which can only be detected
through hydrostatic testing or in operational conditions due to
induced vibrations. Most of the service failures in composite
materials systems are due to mistakes made during the assembly
stage [1,5–7].
When the adhesive comes apart or loses its adhesion power,
pressure loss on the lines can occur, as well as oil leaks or oil