DEEP7 2017 - Subsea 7 - page 18

Installation benefits
Since Pipeline Bundles are fabricated
onshore in a single, self-contained
length, there is no requirement for
offshore strength testing. The structure
also provides a low-stress environment
for the flowlines, with the carrier pipe
withstanding fatigue loadings, while the
on-bottom weight resists global lateral
buckling and generally requires no
trenching or rock stabilisation.
Subsea 7 has repeatedly demonstrated
the cost-effectiveness, versatility and
reliability of the Controlled Depth Tow
Method (CTDM) for the installation
of subsea Bundles and structures. This
technique has been successfully used on
Pipeline Bundles weighing over 10,000
tonnes, using only two conventional
anchor-handling tugs.
Since no specialist installation vessels
are required, fast, accurate offshore
installation is enabled with significantly
reduced marine operations.
The principle of the Pipeline Bundle
fabrication technology is simple: all
structures, valves, pipelines and controls
for field operations are fabricated,
assembled and function-tested onshore in
optimal controlled conditions.
The flowlines, together with control
umbilicals and injection lines, are packaged
within a large-diameter single carrier pipe
which terminates with a towhead structure
or manifold at both ends.
Pipeline Bundles have three significant
benefits over conventional pipelay and
subsea installation methods:
• Ability to incorporate a wide range
of pipeline materials to meet the most
challenging flow conditions
• Cost-effective and flexible towed
installation with no need for specialist
pipelay or heavy lift vessels
• An increased capability to incorporate
wide-ranging subsea process functions
within the system, either built-in during
fabrication or linked post-installation via
standardised connectors.
Our well-established Pipeline Bundle
concept is being further developed to
enhance its range and accommodate
advanced ancillary control, power,
communication and monitoring systems
within its carrier configuration.
Trials are advancing on using temperature
sensors and fibre-optic monitoring systems
for strain, temperature and hydrate
formation. These successful trials have
significance for future HP/HT Pipeline
Bundle applications and are moving
towards full field qualification.
We are successfully extending both the
depth and delivery ranges for Pipeline
Bundles. Having demonstrated our
capability to install Pipeline Bundles in
depths of around 1100m using additional
nitrogen in the carrier annulus, we are now
proposing increasing that range to around
1500m with the application of a low-cost
external buoyancy pipe.
To enable multiple Pipeline Bundle
structures in excess of 33km, we are in
the detailed design phase of a new multi-
bore connector system which will greatly
enhance the scalability of the product.
Along with other planned fabrication
developments, this extends the delivery
range of Bundle transportation to a
maximum of 2000km with no significant
increase in structural fatigue during the tow.
In anticipation of the use of Autonomous
Vehicles for long-term Life of Field
maintenance, Pipeline Bundles are now
pre-assembled with ready-fitted standard
USB connections for data transmission and
inductive power systems.
Flowline performance options
The large-diameter carrier pipes provide
a corrosion-free environment, which can
in itself reduce the need for individual
corrosion coating of flowlines.
To meet demanding flow assurance
and/or corrosion resistance specifications,
however, the rigid design of the Bundle
allows us to select from our market-leading
portfolio of flowline performance options:
• single or multiple flowlines
and umbilicals
• reduced wall thickness in internal
flowlines
• active electrical heating systems,
including hot water and EHTF
• circulated hot water heating systems
• high-performance insulation using
low-cost materials
• heat transfer between adjacent pipes
• corrosion-resistant alloys or cost-
effective mechanically lined BuBi® pipe
• polymer-lined pipe
• High Temperature and High Pressure
service to 220degC, 1400bar
18
deep7
Technology Magazine from Subsea 7
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