1. Why robust cargo containment
system is a must for FLNG
Running a successful FLNG
project entails a whole host of
factors that include determining
risks and preparing mitigating
strategies to reduce, if not, totally
avoid those risks. IQPC’s Darwin
Jayson Mariano recently spoke to
Okada Tetsuo, Structural
Engineering General Manager at
Japan Marine United Corporation
(JMU), a leading company in the
shipbuilding industry, to get some
insights with regard to this issue.
The discussion also touched on
interesting technologies in FLNG
as well as Asia’s role in the future
development of the industry.
What are the most common
risks associated with FLNG
projects? Pls share some
details.
There are varieties of risks
associated with the operation of
FLNG projects, but what we see
as most important from the point
of view of engineering on cargo
containment system are the risks
in association with cargo liquid
sloshing and collision by other
ships.
Sloshing is, as you know, is a
phenomenon where the fluid
movement in the tank resonates
with the ship motion and creates
an impact force between the free
surface of the fluid and the tank
structure. This is a very
dangerous phenomenon, and to
date, many damages due to
sloshing have been reported for
LNG membrane cargo
containment systems, but what
was most devastating may be the
explosion and fire accident of onshore oil tanks, caused by the
Tokachi-oki Earthquake that hit
northern Japan in 2003. In that
case, large-amplitude long-period
ground motion of the earthquake
generated severe sloshing of oil
in the tank, and then caused the
sinking of floating roofs and fires.
In case of LNG carriers, such
dangerous situation can be
controlled to some extent by
limiting the liquid filling level to
nearly full or nearly empty,
prohibiting intermediate level.
However, in case of FLNG
operation, intermediate liquid
level is inevitable, thus sloshing is
more important than for LNG
carriers.
It is known that as long as the
resonance can be avoided, the
liquid motion in the tank can be
well controlled, and that small
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2. “
tanks have small natural period of
the internal liquid, sufficiently
apart from that of ship motion. I
consider that it is essential to
apply sufficiently small tanks both
in longitudinal and athwartship
direction, or to divide the tank by
swash bulkhead internally so that
each compartment is small
enough. This is a very natural
engineering solution,
conventional and established way
against sloshing in marine field so
far, applied to almost all ships
carrying bulk liquids including oil
tankers.
Another risk associated with
FLNG operation is collision by
other ships. In the worst case, it
may lead to the flooding of hold
space. Subsequent to such an
undesirable event, it is quite
important to avoid secondary
disaster, such as total loss of
LNG, fires, cryogenic brittle
fracture of the hull structure, and
so on. Key words to realize this
would be sufficiently robust cargo
containment system and
emergency cargo transfer.
Knowing these risks, what
other risk mitigation strategies
do you employ? How effective
are they in your opinion?
I have almost answered this
question in the previous question,
but I would like to stress that as
long as IHI-SPB cargo
containment system is employed,
it can effectively avoid sloshing
problems by arrangement of
internal structures, and the cargo
tank structures can be designed
robust enough to withstand
external loads from cargo hold
flooding, giving chance for the
LNG in the flooded compartment
to be safely transferred into other
tanks.
What we see as most important from
the point of view of engineering on
cargo containment system are the risks
associated with cargo liquid sloshing
and collision by other ships.
What interesting technologies
or innovations do you see
lately in the FLNG field? How
will it affect the industry?
One of the areas that I am
interested in is the fabrication
technology of aluminum
structures. In recent years, many
research and development
activities and even investments to
actual construction lines are
observed, including friction stir
welding and many varieties of
welding robots. I think that these
activities and investments will
contribute to supply more costeffective aluminum tanks of better
quality.
What are the yet to be explored
opportunities in the FLNG
sector?
As you know, LNG is becoming
more and more important,
because of worldwide trend to
reduce emission and keep
environment, skyrocketing of
energy prices, and so on, leading
to development of smaller, deep
water and far offshore gas field,
which did not pay to the
investment formerly.
Development of FLNG capable of
efficient operation in many
varieties of harsh environment will
open new opportunities.
”
What role will Asia be playing
in the future development of
the industry?
Asia is now one of the most
active areas in the world in
various aspects such as LNG
consumption, engineering and
construction of FLNG projects
and gas production. Asian
demand for LNG will double
within a decade. To absorb such
strong demand, faster
development of FLNG is
expected, and Asian countries will
be able to contribute to this
supply, using engineering and
construction capability in Japan,
Korea and China.
Learn more about the
latest progress from
ongoing and upcoming
floating LNG projects at
the 10th Annual FLNG
Asia Pacific Summit | 2526 June 2013 | Singapore
To find out more, visit
www.flngsummit.com
www.flngsummit.com