effective pipe laying operations. For this, a motion reference
unit (MRU) is installed on the vessel close to the weld station
during pipelay. The aim is to acquire real
time data including heave acceleration,
heave velocity, pitch and roll, which are
used as an input for the client’s calculations
on weld station motion and induced stress.
Live plots of the weld station motions,
motion statistics over the last few hours,
displacement plots and the system statuses
are displayed on a PC. Such monitoring
systems have been deployed worldwide on
S-lay and J-lay vessels.
Fugro’s structural monitoring experts
have a role to play both during pipelay and
once the pipe is in operation, using sensors
to measure pipe motions in situ. Data from
metocean, geotechnical and geophysical
surveys will have determined the best route
for a pipeline, but sometimes these routes
may involve traversing depressions on the
seafloor. One problem for these freespan
sections of the pipe is ocean currents,
which can induce vibrations in the pipeline.
These vortex-induced vibrations (VIV) are
generally transverse to the flow of current and can be a major
cause of fatigue in subsea oil and gas pipelines. Accurate
measurements of the pipeline motions
caused by VIV allows for an understanding
of fatigue.
The motion caused by VIV can be
measured using Fugro’s DeepData pods,
proven subsea motion sensors that
have been used for numerous subsea
applications. The pods are put in position
by an ROV via a clamp arrangement (they
are removed in a similar way). When
the pods are fixed to pipes, they can
record data on acceleration, velocity and
displacement. Subsequent analysis of the
acceleration spectra enables identification
of the frequencies that have been excited
by VIV.
There are two DeepData pod variations;
one has high specification sensors and the
other has an improved battery life and has
been optimised for deployments of up
to a year. Where information needs to be
relayed to the surface during deployment,
hydroacoustic communications can also be
Figure 3.
DeepData pod with clamp for
ROV deployment.
p l a n t a n d m a c h i n e t e c h n i q u e s
ite-lifting.com
Schoenbeck GmbH & Co. KG
•
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•
Tel. +49 5721 99 44 39-26 • Fax +49 5721 99 44 39-23
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Coming Next Month
• Annual Offshore
Technology Review
• Leak Detection
• Offshore Coatings
• ROVs and Subsea Inspection
