Over the past
two decades, the pipe-in-pipe (PiP) product has become an essential part of the
subsea field development engineer's "tool box." Due to its high
insulation performance it minimizes heat losses from the transported fluid to
the environment that more traditional subsea coatings cannot provide. This is
achieved using thermal insulation of very low thermal conductivity, such as
aerogel, encased in dry atmospheric conditions between the inner pipe or
"flowline," which transports the fluid, and the outer pipe or
"carrier," which provides the mechanical protection from the subsea
environment.
Sumber: http://www.brederoshaw.com/solutions/offshore/pipe-in-pipe.html
Other benefits
of the PiP solution include compatibility with high temperatures (in terms of
material and enhanced compliance with large axial loading), stability on the
seabed, and protection by the outer pipe against external loads. In some cases
this may obviate the need for burial.
In 2014,
Technip installed its 50th PiP via the reel-lay method; the first project was
in Australia in 1989. Along the way, the company has advanced the technology at
various points. For example, the company's third PiP project in 1997 on
Statoil's Gullfaks field in the Norwegian North Sea. This represented the first
implementation of a corrosion resistant alloy (CRA) flowline, but more
importantly, the un-bonded design was to become the essential DNA of the
product for the projects that followed.
During
manufacture, flowline and carrier pipeline stalks are first welded and
inspected. Then the flowline stalk is progressively sleeved into the carrier
pipe stalk, while thermal insulation panels and nylon rings are hand-applied at
regular intervals. The function of the nylon rings, known as centralizers, is
to maintain the two pipelines concentric and to mechanically protect the
thermal insulation during each phase of the PiP assembly, installation, and
operational life. Once full PiP stalks are completed, they are spooled onto the
reel-lay vessel following intermediate tie-in connections.
The next major
milestone was the first implementation of a reeled PiP on a deepwater project,
BP's Nile field in the Gulf of Mexico (GoM) in 2001. Novel features introduced
for this installation included microporous insulation, designed to meet the
field's challenging thermal demands, and the implementation of qualified buckle
arrestors and waterstop features. The aim was to limit the potential
consequences of a (very unlikely) wet buckle event. Experience gained on this
deepwater project proved important for future projects in the GoM, West Africa,
and Brazil.
In 2002,
Technip installed the first reeled PiP steel catenary risers on Shell's Nakika
field in the GoM in water depths of more than 2,100 m (6,890 ft). Four years
later, Total's Dalia field development offshore Angola featured the first
qualification and industrialization of superior aerogel insulation to achieve
exceptionally high thermal performance.
But there have
also been technical advances in the shallower environment of the North Sea. In
2011, the first implementation of a fully reelable bulkhead on BP's Devenick
project in the UK central North Sea was a breakthrough for the reeled PiP
product. It enabled tight separation of a PiP in independent sections, permitted
the first implementation of a fully reeled T-piece, and led to major
enhancements in pipelay schedule efficiency.
In January
2012, the first electrically trace heated (ETH) PiP was deployed on Total's
Islay field in the UK northern North Sea. This transformed the technology from
a simply passive flowline to an active system. The ETH-PiP technology allows
active control of the temperature of the transported fluid, including
monitoring in real time of the pipeline temperature profile, using fiber-optic
technology.
Subsequent
offshore testing campaigns on the installed system demonstrated the efficiency
of this active heating technology, which exceeded expectations in terms of
reactivity and accuracy. The results also enabled the calibration of comprehensive
and sophisticated computational fluid dynamics (CFD) models to accurately
predict the ETH-PiP performance in service and underlined the benefits of the
technology for addressing complex flow assurance issues.
In parallel,
Technip has been performing a comprehensive full-scale hydrate plug
dissociation test
program. This is designed to demonstrate the capability of
the ETH-PiP technology to identify, characterize, and melt hydrate plugs in a
safe and fully controlled manner by turning on and then carefully adjusting the
external heating power provided by the ETH cables, as monitored by the optical
fiber system. This three-year R&D initiative will be completed during the
current quarter, and has been supported by several majors in the framework of a
joint industry project.
As a result,
loops for flowline preservation purposes can be eliminated and field lay-outs
can be simplified by considering single line architectures for all the
production flowlines.
Furthermore,
since the Islay project, a second generation of electrical trace heating cables
has been developed and qualified to enable the heating of much longer
flowlines. Long tiebacks of satellite fields to existing facilities more than
40-50 km (25-31 mi) with minimum electrical power requirements (i.e. only 1 MW
typically) are now feasible.
Finally, the
ETH-PiP technology is now reaching a maturity level which should help operators
to develop increasingly complex and challenging offshore fields in the future
while optimizing the SURF-related capex by minimizing the number of flowlines
and risers.
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