JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 52

oil & gas / testing

potential profitability over the pipe's lifetime [3]. Greater demands have therefore
been placed on both metallic and nonmetallic materials' ability to withstand these
extreme new operating conditions and
increase the economic viability of projects.
Here, composite materials - especially in relation to their long-term performance capabilities and lightweight properties - present
a real opportunity, as well as a technology
gap that still needs to be addressed.

Deep and deeper: composites in
pipes operating at depth
Deep and ultra-deep offshore pipelines
are one of the greatest opportunities currently open to the oil & gas sector, with an
estimated 40% of future oil supply coming
from water depths of 1500 m to 3000 m.
Many of these new fields present more
extreme conditions relating to temperature,
salinity and the presence of carbon dioxide
(CO2) and hydrogen sulphide (H2S) than
environments explored for "easy" oil and
gas over the past 80-or-so years. The industry's understanding of the factors involved
in corrosion is limited in such environments, where even slight changes in CO2/
H2S content, temperature, flow velocity
and pressure can have a significant effect
on corrosion rates in pipelines, while high
salinity can affect the solubility of CO2 in
the corrosion solution [4].
This lack of understanding is characterised
by the difficulty of applying existing CO2/
H2S corrosion models. The effects of operating conditions in "normal" environments
on steel pipes would be predicted using key
variables including temperature (between
20-100°C), CO2 partial pressure (0-2 MPa),
organic acids (0-100 ppm), H2S traces (0-1
Pa), pH and brine chemistry (pH 3-7), steel

Fig. 2: Composite materials' lighter weight means
that pipelines can be carried and deployed from
smaller vessels and be deployed more easily

type, multiphase flow, and magnitude and
morphology of localised attack [5].
e parameters stated within these variables
can differ significantly within deep water
pipeline environments, including lower
external temperatures and higher CO2/
H2S pressure. These factors, along with
the introduction of composite materials in
pipelines, mean that corrosion rates cannot
be reliably predicted by extrapolating data
from existing models - despite significant
breakthroughs that have been made over
the past ten years.

Seeing the light: reducing the
weight of pipelines
Using composite materials would mean
removing substantial weight from pipes
running from the seabed to surface production systems, which would in turn reduce
topside counter-balancing weight and
buoyancy requirements. For example, if
alloy pipes can be replaced with lightweight
advanced composites, the reduced weight
of piping materials on the service deck of a
tension leg platform (TLP) would increase
the buoyancy of the TLP, reducing the
amount of structural steel needed below
water and, as a consequence, reduce costs
significantly [6].
To put this into perspective: Steel has a
weight density of 8 in air, whereas composites have a density of approximately 2.
In water, steel's density is reduced to 7 and
composites' to 1, representing a seven-fold
weight reduction.
Glass-reinforced epoxy and vinylester filament have already been used extensively in
pipes transporting water, crude oil and gases
in onshore environments; in the Arabian
Gulf, some lines have already been reliably
in place for over two decades. This is in contrast to conventional thermoset composites
tried in Norway during the 1990s, where reinforced epoxy pipes with an unreinforced
thermoplastic liner were proven to be a
poor alternative to steel pipelines [7].
This experience and knowledge of composite components used in various operating
conditions has seen an increase in demand
for their application and further testing in
offshore pipelines.

52 jec composites magazine / No97 May - June 2015

Fig. 3: Increasing demands are being placed on
both metallic and non-metallic materials' ability to
withstand extreme HPHT operating conditions

Testing new composites
The oil & gas industry has recently been
looking at new types of composite materials, moving on from glass-reinforced epoxies to carbon-reinforced thermoplastics that
offer high temperature capabilities, high
load capacities and stiffness, as well as lending themselves to continuous flow production, since consolidation and cure are not
such an issue as with thermosets.
Unreinforced plastics have long been used
in the sector, with PVDF, PEEK, polyamide
and others used widely for back-up rings
and barriers. But their use as composites
- that is to say, reinforced with continuous
glass or carbon fibres - calls for new testing
procedures looking at specific operating
conditions and identifying any macroeffects of exposure media and temperature.
Composite materials present a real, viable
alternative in sour conditions, although
many polymers have yet to be qualified for
sour gas service. However, with 25% of all
oil pipeline incidents reported as caused by
corrosion [8], and 1,600 repairs and cleanups to date for liquid product pipeline spills
[9], it is clear that testing of new materials
to combat pipeline corrosion is an industry
priority.

Stages of ageing
Operating environments can of course
cause irreversible changes to the original
properties of composites analogous to
corrosion. For long-term studies, therefore,
the various aspects of ageing (with "ageing" replacing the term "corrosion") and
their application to composite materials in
JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015
