Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
FLOATING BARRIERS FOR CONTAINING OIL SPILLS
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Br~ckground
Different types of barriers have been specifically adapted to
particular applications. Nave-Boom barriers have a light
structure, but they have only slight resi~tance to longitudinal
s stress and to the corrosive action of water. Oil-Fence barriers,
given their thick weave, are substantially resistant to the
corrosive action of water (tested in Haracaibo Lake) and to stress
by wind, waves, currents and solid waste. They have orientable
floats, are reversible, and occupy little storage space since they
are foldable, but they are unstable and unrecoverable. Globe-Boom
barriers, also resistant to the corrosive action of water (tested
in Maracaibo Lake) and to stress by wind, waves, currents and solid
waste, and easy to store, are too heavy and, although easily
connectable, they have a coupling that is not universal.
In accordance with U.S. Patent No. 4,543,012, barriers
referred to therein possess a relief pocket for the pollutant, but
they are effective only in still water. The barrier of U.S. Patent
No. 4,300,857 is adjusted to the seabed, thus retaining the water,
but it i8 rigid and can be used only in still and not too deep
waters.
Summary of the Invention
With regard to existing barriers in the market, Barriers I,
II, and III solve several of the most critical problems faced in
this technology. Because of the weave of twisted nylon thread, the
containment means provides higher resistance to longitudinal
stresses, which means higher versatility in its application. By
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providing fixing means basically made out of aluminum, stabillty
is increased, on the one hand, to face the environment's corrosive
action and, on the other hand, with regard to the pressure exerted
by current against the barrier. With lower rigidity in structure,
it is thus possible to control oil spills efficiently.
The barriers have a number of distinct aspects which,
individually and in different combinations, contribute
substantially to the subject invention.
a) their essential components are containment means,
floating means, fixing means and ballast means,
b) the containment means (when floated in water) consist of
a screen or curtain having an above-water zone
(freeboard) and a submerged zone (skirt or flap),
c) the floating means keep the containment means afloat when
the latter is placed in water,
d) the fixing means secure the floating means to the screen
or curtain and impart stability to the containment means,
e) the ballast means maintain the screen or curtain
substantially vertically disposed when the containment
means is floated in water,
f) the screen or curtain is of woven twisted nylon thread,
g) the screen or curtain is coated on both sides with water-
resistant polymer,
h) the water-resistant polymer is PVC,
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1) the floating means have a density of from 70 to 170 g/l,
~) the fixing means comprise aluminum ~traps,
k) the ballast means comprise a ballast chain secured to the
skirt or flap, and
l) steel wire rope tensioning means are provided along and
secured to the freeboard.
Brief Description of Figures
Figure 1 is a perspective view of Barrier I.
Figure 2 is a perspective view of Barrier II.
Figure 3 is a perspective view of Barrier III.
Figures 4, 5 and 6 are transverse sections of float supports
of Barriers I, II and III, respectively.
Figure 7 is a side and front view of the support for the
ballast chain.
Figure 8 is a front view of the coupling for Barriers I and
II.
Figure 9 is a front view of the coupling for Barrier III.
Det~ls
Tensioning Means
The tensioning means (l) of Barrier I i8 located in the upper
part of said barrier (Fig. l). It consists, e.g., of a steel wire
rope that has been twisted from four to seven times with from 15
to 56 threads, thus obtaininq a thickness of from 0.45 to 2.0 cm.
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A preferred tensor element wlre rope is one of 7 turns and 19
threads (e.g. NSR, 7 x 19) with a dia~eter between the values of
3/16 inch and 1/4 inch (0.476 cm and 0.635 cm). This kind of wire
rope combines flexibility with fatigue resistance and corrossion
s resistance ("Handbook or Ocean and Underwater Engineering", by J.J.
Meyers, C.H. Holm and R.F. McAllister). Alternative tensioning
means with similar properties are known and available. The wire
rope is coated with a rubber hose, not shown in the figure, to
avoid wear of the support plate ~7) (Fig. 1). Barrier II does not
have tensioning means (1) since it includes a thicker ballast chain
that allows it to absorb longitudinal stresses. Barrier III has
a ballast chain that is able to exert a double function as a
stabilizing and a tensioning means (given its size), and its use
is recommended in places where water currents are not too strong.
Floating Mean~
The floating means 12) (Figs. 1, 2 and 3) are identical for
the three barriers and consist of cylindrical devices, having,
e.g., a diameter between 20 and 22 cm and a length from 49 to 51
cm, spaced about each 35 to 45 cm and preferably throughout the
barrier. Said arrangement, together with the float size,
eliminates the relative rigidity that creates fragility when known
barriers receive an impact.
The devices are preferably made from rigid aromatic polyether
polymer (e.g. SINTHENAD-90) with a model density in the range of
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from 130 g/l to 170 g/l conferring resistance~bouyancy
characteristics. The water absorption of such polymer is low,
6ince it has a hiqh percentage of closed cells and a compact
surface skin that stronqly resists water absorption.
s Said cylinders consist of two symmetrical convex covers fixed
to the barrier's skirt (6) (Figs. 1, 2 and 3) by means of a pair
of aluminum straps. The cylinders are made out of a polyurethane
having a molded density between 70 and 90 kg/m', which gives them
a buoyancy that is from four to five times the barrier's weight.
With this excellent flotation capability, said material also
increases their useful life and durability since they undergo wear
"by layers" and not by breaking or cracking when faced with
saltpeter, sunlight, meteorological conditions, etc.
Floats are preferably made of a low density polyurethane
(e.g. that manufactured by the MONOMEROS COLOMB0-VENEZOLANOS
industry). Said polyurethane has the following advantages with
regard to polyurethane of commercial barriers: first, its
molecular structure avoids easy water nsoaking" and is responsible
for floats wearing "by layers" with no channel formation, which
greatly reduces float cracking probabilities; second, it features
better fire-resistance.
Containment Mean~
~his consists of a screen or a curtain ~6) (Figs. 1, 2 and 3)
which maintains a zone above the water surface, that is to say the
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freeboard, and a submerged zone called skirt or flap. Said curtain
is ~pproximately from 14 to 16 m long and from 0.75 to 0.85 m wide
for Barriers I and II, and from 14 to 16 m long and from 0.35 to
0.45 m wide for Barrier III.
The length of each barrier section is about 15m for each of
the three types (models). With the indicated materials, the
dimensions that succeed best in joining flexiblity and stability
are found in a length range of from 14 to 15 m per barrier section.
The width of barriers I and II i~; preferably in the range of from
0.70 m to 1.00 m and that for barrier III if from 0.35m to 0.45 m.
The weave said flap is made out of consists of a twisted nylon
thread. The nylon (preferably Nylon-6) is reinforced with from 5
to lOS fiberglass and an ultraviolet-ray-resistant additive
(TINU~,'INrff). The thread is twisted to increase its resistance.
Then, warping and winding of the twisted thread takes place, and
the required weave is conventionally manufactured in a loom.
Immediately thereafter, scouring of the weave is performed. A
plastisoi is prepared, as well-known in the art, from a polyvinyl
chloride (e.g. PVC-360) to coat the weave on both sides. Said
polyvinyl chloride (PVCI coating is made in two rolling furnaces,
both at a temperature of about 170-C.
PVC-360 polymer has the following characteristics:
K Value 80 + 2
Immediate Brooksfield (min.) (max.)
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Viscosity 3,000- 10,000 cps
Brooksfield viscosity
after 24 hours 10,000- 30,000 cps
Moisture 0.15%
Apparent Density 0.25 - 0.32 gr/mm3
In the case of Barrier II, the weave is double-coated on each side,
thus increasing thickness and, consequently, rigidity. The ob~ect
of this variant with regard to the other two types is that it is
intended for permanent use in sites with strong current and wave
action.
Traction tests were conducted on wave samples from said flap
having dimensions of about 2.5 cm wide and 1 to 1.5 mm thick. The
following breaking stress values were obtained: 507 Kg/cm2 for
Barriers I and III, and 737 Kg/cm2 for Barrier II, the weave high
stress-resistance being thus demonstrated.
A traction test carried out on the threads of Barriers I, II
and III yielded the following results:
Threads of Barriers I and II
For 0.45 cm wide strips per 0.1 cm thick
Average breaking load, 200 lb.
Average breaking stress, 7,200 lb/sq.inch
For 0.54 cm x 0.15 cm strips
Average breaking load, 515 lbs.
Average breaking stress, 10,400 lbs/sq. inch.
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Fixing an~ ~upport ~eans
A couple of aluminum plates (7) tFigs. 1 to 6) are
provided as fixing or support means of floats. Said plates are
riveted to the skirt body. In the case of Barrier I, the plates
extend over the freeboard, as a horseshoe, which permits lining up
the tensioning means with the containment means.
In the case of Barriers I and II, said plates increase
stability since they maintain the containment means vertically.
Square aluminum rings riveted to the skirt work as support
means (4) (Figs. 1, 3 and 7) and are used to line up the ballast
chain (3) all along the barrier. In Barrier II, they have been
replaced by a cover or a pocket (8) made out of the same material
as the skirt and hermetically sewn to it also with nylon, covering
the chain longitudinally. The variant's intention is to distribute
the chain's weight uniformly all along the skirt's length, since
the latter is thicker and, therefore, heavier than the other two
models (I and III).
Ballast Means
The ballast means consists of a galvanized steel chain (3)
(Figs. 1 to 3) from 14 to 15 m (preferably 14.5 m) long and from
0.82 to 0.88 cm thick in models I and III, and a similar length and
from 1.24 to 1.30 cm thick in Barrier II.
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Such means function as an additional tensioning means in order to
support longitudinal stresses better.
Connecting Means
These consist of male-female couplings (5) (Figs. 1, 2 and 3)
that link the barrier sections or portions. Said couplings are
aluminum (e.g. A3334 series, manufactured by the Venezuelan
industry ALCANVEN) planar bars that have grooves and holes on the
end opposed to the connection serving as the flap's clamping area.
The male-female coupling means are universally known. Couplings
used in the present invention are displayed in two different
designs, both showing the same efficiency. Figure 8 shows coupling
means useful in Barriers I, II and III. This figure shows holes
made in the aluminum bar: a) to clamp the cloth (holes 8 of
approximately 7 mm in diameter), b) to clamp the ballast chain
(holes 9 of approximately 7 mm in diameter), and c) to clamp the
tensioning wire (holes 10 of approximately 7 mm in diameter).
The cloth width (or flap) is trapped in said coupling's
longitudinal groove and additional fixed with bolts that go through
a fold made in that very end of the cloth, a plate that also has
grooves and that has been wrapped in said fold, and the coupling
itself.
Specific Aspects of Each Type of Barrier
Barrier I is appropriate for bays and ports and/or wherever a
long stay is not required. It has been designed for a rapid
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deployment from a medium-size craft. The combined effort of the
ten~ioning wire rope and the ballast chain make it particularly
resistant to longitudinal stresses.
This barrier can be vertically thrown into the water at a
place of interest, and deployed according to any of U, V, J or 0
configurations, allowing for effective containment due to the
flexibility of the weave it is made of. It can be handled from
medium-size crafts. Also, it is possible to achieve rapid
deployment with a maximum of four men by holding the barrier by its
tensioning means, which can be readily done due to its light
weight. When used offshore, sections are previously coupled to two
crafts, and stored in a zig-zag arrangement in order to save
storage space, while avoiding overlapping floats. Both the
freeboard (app_oximately 35 cm) and flap (approximately 45 cm)
dimensions account for an ideal relationship that allows a
combination of stability and containment capability resulting in
higher barrier efficiency.
Barrier II i8 adequate for places with winds up to 70 Km/h and
currents up to 1.5 knots. It can keep operating for more than a
year. The weave's thickness guarantees optimum penetration in
water and increased capacity in containing crude oil.
This barrier i8 similar to model I barriers with respect to
deployment. As it is heavier, up to siX men are required for
handling it. Since it is not provided with any tensioning means
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on the upper part, it must be held by the flap itself to be thrown
into the water, with no risk of tearing because the weave in this
model i6 thick enough so as to stand such stress.
Barrier III is suitable for spills requiring easy handling and
occupation of a reduced area.
Only two men are required for deployment for it is lighter and
smaller than Barriers I and II. It proves particularly useful as
a deviation barrier.
The male-female coupling means in the three models of barriers
has an approximate weight of 8 Kg regardless of the design, and it
is heavier than coupling means in barriers already known. In this
way, barrier stability is increased.
The invention and its advantages are readily understood and
appreciated from the foregoing description. Various changes may
be made in individual components without departing from the spirt
and scope of the invention or sacrificing its material advantages.
The described barriers are merely illustrative of preferred
embodiments of the invention.
