22
At the recent Renewable UK
Global Offshore Wind
conference and exhibition Terry
Griffiths, Director at Aurora
Offshore Engineering (and more
importantly, a founding member
of the SUT Perth Branch), talked
on the topic of "Thar be
Dragons", sharing lessons
learned from solving really
difficult design and integrity
problems for over 4000km and
22GW of subsea cable projects
across the globe.
In many ways, the rise of the wind
industry has built on the
inherited methods developed
over many decades by the
offshore oil and gas industry and
has been motivated as much by
environmental concerns about
the need to transition to
sustainable and renewable
sources of energy, as it is based
on energy security concerns. The
offshore industry has also been
transitioning as work
opportunities in the renewables
sector grow.
While the specifics and
economics between these
industries are different, it did not
take established offshore
companies long to exploit this
market. This has an added bonus
that there are to be considerably
more turbines than conventional
offshore oil installations. There
are very broad similarities.
Instead of production platform
jackets read offshore substation
jackets. Instead of oil pipelines,
read subsea cables. And this,
contends Terry, is a trap the
industry is sleepwalking into.
THAR BE DRAGONS
“We need to stop thinking about
subsea power cables as just small
oil and gas pipelines,” he said.
“A fundamental difference is that
because of the small diameter,
typically subsea cables have
Keulegan-Carpenter (KC)
numbers (a quantity describing
the relative importance of the
drag) that are in the range of 200
to 500. The typical oil and gas
pipelines, however, have a KC
number that's in the range of 30
to 50.
“Subsea cables also typically
have much smaller Reynolds
numbers, so the hydrodynamic
models that we've inherited from
the oil and gas industry are not
correct for subsea cables, and
using these engineering formulae
can result in fundamental errors
in the physics that is very relevant
to the design.”
“The reason the way pipeline
engineering has evolved because
of the hydrocarbon fluids they
Pipeline with rock bag
NEWS