JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 53

service need to be identified. To this end,
testing looks at gradual ageing, starting
from surfaces exposed to corrosive media.
For composites, ageing can occur through
primary mechanisms that are physical,
chemical or mechanical - all of which are,
inevitably, highly dependent on material
characteristics such as thickness and density
as well as application, environment and
length of exposure.
The long-term ageing of composite materials has several identifiable stages: Stage 1,
where the diffusion of hostile fluids into the
material and inner surface causes physical
changes; Stage 2, where further diffusion
causes chemical ageing; and Stage 3, where
the ageing is such that it causes mechanical
damage to the inner surface.
To evaluate the service life of composite
materials for use in oil & gas pipelines, reliable predictions need to be made as to the
effects of ageing on a pipe on a ply-by-ply
basis, knowing the condition of each ply
at any point in time and the effect the ageing has on the overall performance of the
pipe. Approaches used extensively in the
aerospace sector, such as A- and B-basis allowables along with limit-load approaches,
could of course serve as a useful starting
point for the oil & gas industry.

Reality checks: laboratory
limitations and full-scale testing
These tests are all under ongoing development, and inevitably it is also crucial to
validate any models with realistic testing, up
to and including full-scale testing.
Many laboratory-based ageing tests immerse samples in the relevant fluids and
temperature for different periods of time,
but this approach is considered less than
realistic because all of the sample's surfaces
are exposed, whereas in a pipe only the inner surface would be exposed. This problem
led to investigations into the development
of laboratory-based tests for singled-sided
exposures while protecting the edges.
In addition, test programmes have tended
to assume that exposure environments
are consistent throughout the life of the
composite material component, where in
reality this is very seldom the case. In fact,

there are often multiple changes to the fluid
being carried and/or to the operating temperature and pressure, and these may have
a cumulative or synergistic effect on the ageing process. A good example of this is when
composite liners are used in water alternating gas (WAG) processes for enhanced
oil recovery, with both sea water and CO2
potentially causing ageing of the liner, with
potential synergistic effects. Ideally, then,
any major changes in use should also be
evaluated.
A more appropriate evaluation and validation method would be to include a section
of the pipeline in an installation that can
be removed from service without affecting
production. This can then be thoroughly examined using destructive methods to compare with predictive levels of degradation
throughout the component's twenty- to
thirty-year lifespan. As the use of embedded
sensors to measure material properties and
the presence through the thickness of harmful fluids develops, then real-time evaluation
will be realized.
Such methods are being pioneered at testing laboratories such as Element Materials
Technology's facilities in Hitchin, UK, and
Houston, TX in the USA, where a new
polymers facility has been developed to
this end.

Fig. 4: Long-term ageing (corrosion) testing
methods of composite materials are being pioneered at Element's flagship O&G technology centre
in Houston, TX

Enabling the sector: the place of
composites in oil & gas
In the oil & gas sector, composite materials
are becoming a highly enabling material
allowing the industry to solve some of its
major technical challenges, especially in

accessing hard-to-reach oil and gas reserves
with priority on deepwater production.
In particular, highly-specific strengths and
stiffnesses are paramount to achieving
required performance levels, for example in
deepwater fields.
The increasing pursuit of composite
materials use in oil & gas will have a major
impact in that these materials do not
corrode - aside from long-term degradation in hostile environments, whose rate
needs to be measured and understood.
As we have seen, this evaluation of longterm degradation or ageing in oil & gas
environments requires new technologies
to be developed and new knowledge to be
gained about the service life of compositebased components in the sector. n
More information:
www.element.com/hitchin
References
[1] R.H. Martin, A Technology Gap Review
of Composites in the UK Oil & Gas Industry,
MERL Technical Report C1889,
1 March 2007, Hitchin, UK
[2] G. Marsh, Thermoplastic Composite
Solutions for Deep Oil & Gas Reserves,
Reinforced Plastics, 9 July 2013,
Kidlington, UK
[3] ...
[4] G. Jaiyeola, Hidden Beneath the Surface,
World Pipelines Corrosion Supplement,
December 2014
[5] S. Nesic, S. Wang, H. Fang, W. Sun, and
J.K.L. Lee, A New Updated Model of CO2/
H2S Corrosion in Multiphase Flow (2008),
Ohio University, NACE International
[6] R. Lea, Composite Piping Systems to
Improve Oil and Gas Production,
EDO Speciality Plastics, October 2002,
Los Angeles, USA
[7] G. Marsh, Thermoplastic Composite
Solutions for Deep Oil & Gas Reserves,
Reinforced Plastics, 9 July 2013,
Kidlington, UK
[8] US Department of Transportation,
Pipeline and Hazardous Materials Safety
Administration, 2000
[9] Pipeline Research International Council,
1996

No97 May - June 2015 /

jec composites magazine 53

http://www.element.com/hitchin

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

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