U.S. patent number 3,877,238 [Application Number 05/413,378] was granted by the patent office on 1975-04-15 for sea sled for entrenching and pipe burying operations.
This patent grant is currently assigned to Santa Fe International Corporation. Invention is credited to Nuke Ming Chang, Elmer R. Remkes.
United States Patent |
3,877,238 |
Chang , et al. |
April 15, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
SEA SLED FOR ENTRENCHING AND PIPE BURYING OPERATIONS
Abstract
The sea sled includes a pair of pontoons mounting depending
rollers for straddling a pipeline disposed on the sea bottom. Water
jets fluidize the sea bottom to form a trench in which the pipeline
settles. The slurry formed by the water jets is removed from the
trench by the eductor system which includes a pair of conduits each
having a suction inlet at its lower end for location within the
trench, a discharge at its upper end, a pair of pump nozzles each
having an inlet external to the associated conduit and an outlet
within the conduit directed toward the corresponding discharge, and
a pair of primary nozzles respectively spaced from the inlet ends
of the pump nozzles. A high pressure, low volume, fluid is pumped
from the surface through the jet nozzles. The fluid emanating from
the jet nozzles entrains ambient fluid and delivers low pressure,
high volume, fluid through the respective pump nozzles to their
corresponding discharges. The action of the pump nozzles in the
conduits creates a suction whereby the slurry from the trench is
pumped from the trench through the conduits and discharged to
opposite sides of the trench.
Inventors: |
Chang; Nuke Ming (Orange,
CA), Remkes; Elmer R. (Orange, CA) |
Assignee: |
Santa Fe International
Corporation (Orange, CA)
|
Family
ID: |
23636997 |
Appl.
No.: |
05/413,378 |
Filed: |
November 6, 1973 |
Current U.S.
Class: |
405/162; 37/335;
405/163; 417/183; 37/322; 417/158 |
Current CPC
Class: |
F16L
1/16 (20130101); E02F 5/108 (20130101); E02F
5/107 (20130101); E02F 5/104 (20130101) |
Current International
Class: |
F16L
1/12 (20060101); E02F 5/10 (20060101); F16L
1/16 (20060101); E02f 005/02 (); E02f 003/88 ();
F04f 005/00 () |
Field of
Search: |
;61/72.4,72.3,72.1
;417/183,153 ;37/81,62 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Shapiro; Jacob
Attorney, Agent or Firm: Le Blanc & Shur
Claims
What is claimed and desired to be secured by U.S. Letters Patent
is:
1. A sea sled for use in excavating a trench below a pipeline laid
along the sea bottom and for removing the slurry formed by the
excavation comprising:
a base structure, means carried by said base structure for
excavating the trench and including a plurality of jet nozzles
directed to flow high pressure fluid below the pipeline to fluidize
the sea bottom and form a slurry, means and carried by said base
structure for removing the slurry including a conduit having an
inlet disposed below said base structure and a discharge, a pump
nozzle having an inlet external to said conduit and exposed to the
ambient fluid, said pump nozzle having an outlet within said
conduit for delivery of fluid to said conduit intermediate said
inlet and discharge, a primary nozzle external to said conduit and
spaced a predetermined distance from said pump nozzle inlet, and
means for supplying fluid under pressure to said primary nozzle,
said primary nozzle being disposed to flow the supply fluid toward
said pump nozzle inlet across the space therebetween to entrain
ambient fluid and deliver the entrained fluid and at least a
portion of the supply fluid through the pump nozzle into said
conduit whereby the combined flow through said pump nozzle causes
slurry to flow through said conduit inlet into said conduit and
delivery of the slurry, the supply fluid portion, and entrained
fluid to the conduit discharge.
2. A sea sled according to claim 1 including means for adjusting
the elevation of said excavating means and said conduit inlet
relative to said base structure.
3. A sea sled according to claim 1 including guide means depending
from said base structure for maintaining said sled in alignment
with the pipeline as the trench is excavated, said guide means
including rollers for straddling the pipeline.
4. A sea sled according to claim 3 including a frame for supporting
said excavating means, said slurry removal means and said guide
means, and means for adjusting the elevation of said frame relative
to said base structure thereby to adjust the elevation of said jet
nozzles, said conduit and said rollers, relative to said base
structure.
5. A sea sled according to claim 1 wherein said slurry removal
means includes a second conduit having an inlet disposed below said
base structure and a discharge, a second pump nozzle carried by
said base structure, said second pump nozzle having an inlet
external to said second conduit and exposed to the ambient fluid,
said second pump nozzle having an outlet within said conduit for
delivery of fluid to said second conduit intermediate the inlet and
discharge of said second conduit, a second primary nozzle carried
by said base structure external to said second conduit and spaced a
predetermined distance from said second pump nozzle inlet, means
for supplying fluid under pressure to said second primary nozzle,
said second primary nozzle being disposed to flow the supply fluid
toward said second pump nozzle inlet across the space therebetween
to entrain ambient fluid and deliver the entrained fluid and at
least a portion of the supply fluid through said second pump nozzle
into said second conduit whereby the combined flow through said
second pump nozzle causes slurry to flow through said second
conduit inlet into said second conduit and delivery of the slurry,
the supply fluid portion, and entrained fluid to the second conduit
discharge, said first mentioned and said second conduits being
carried by said frame for disposition on respective opposite sides
of the pipeline, said conduit discharges having outlet conduit
portions directed laterally of said sled for disposing the slurry
removed from the trench and flowing through said conduits on
opposite sides of said trench.
6. A sea sled according to claim 5 wherein said base structure
includes a pair of laterally spaced pontoons, and means for
ballasting and deballasting said pontoons.
7. A sea sled according to claim 5 including guide means carried by
said base structure for maintaining said sled in alignment with the
pipeline as the trench is excavated and including rollers for
straddling the pipeline, a frame for supporting said excavating
means, said slurry removal means and said guide means, and means
for adjusting the elevation of said frame relative to said base
structure thereby to adjust the elevation of said nozzles, said
conduit inlets and said rollers relative to said base
structure.
8. A sea sled according to claim 7 wherein each of said conduit
inlets has an aperture opening in a lateral inward direction with
said apertures lying in substantial lateral registry one with the
other.
9. A sea sled according to claim 5 including guide means carried by
said base structure for maintaining said sled in alignment with the
pipeline as the trench is excavated and including at least a roller
each carried by said conduits for straddling the pipeline, each of
said rollers lying inwardly of the conduit carrying said roller for
engagement with said pipeline, said conduit inlets being comprised
of inwardly directed openings in substantial lateral opposition to
one another.
10. A sea sled according to claim 5 wherein said base structure
includes a pair of pontoons spaced laterally one from the other,
guide means carried by said base structure for maintaining said
sled in alignment with the pipeline as the trench is excavated and
including rollers for straddling the pipeline, a frame for
supporting said excavating means, said slurry removal means, and
said rollers between said pontoons, and means for ballasting and
deballasting said pontoons.
11. A sea sled according to claim 5 wherein each of said primary
nozzles is spaced from the corresponding pump nozzle inlet a
distance within a range of about 2 to 30 inches.
12. A sea sled according to claim 11 including means mounting each
of said primary nozzles for movement into selected positions
relative to the corresponding pump nozzle inlets whereby the
spacing therebetween is adjustable.
13. A sea sled according to claim 1 wherein said primary nozzle is
spaced from the pump nozzle inlet a distance within a range of
about 2 to 30 inches.
14. A sea sled according to claim 4 wherein said primary nozzle is
spaced from the pump nozzle inlet a distance within a range of
about 2 to 30 inches.
Description
The present invention relates to a sea sled for entrenching and
burying undersea pipeline and particularly relates to an eductor
system for removing slurry from the trench whereby pipeline laid
along the sea bottom settles into the trench.
Various systems for laying pipelines along the sea bottom have been
proposed and utilized in the past, (for example, see U.S. Pat. No.
3,751,927). Certain of these systems provide a sea sled having jet
nozzles directed to fluidize the sea bottom and form a trench for
receiving the pipeline. Air jet type eductor systems have also been
provided for removing the cuttings or slurry formed by the jet
nozzles from the trench. Such air jet eductor systems usually
comprise a nozzle disposed in the inlet end of a discharge conduit
with air being supplied under pressure from a surface floating
tender. Air jet eductor systems are very efficient and will lift
significant quantities of slurry. However, with the increasing
necessity to lay pipelines in deeper water, for example in water
depths exceeding 150-200 feet, an air jet eductor system becomes
uneconomical. That is, as the water depth increases, the horse
power requirements to supply compressed air from the surface
increase quite rapidly.
The present invention provides a novel and improved sea sled and
eductor system for forming a trench for and burying underwater
pipelines, particularly in depths beyond the feasible or practical
limits of presently available equipment which minimizes or
eliminates problems associated with prior sea sled and eductor
systems and provides a novel and improved sea sled and eductor
system having various advantages in construction, mode of operation
and use in comparison with such prior sea sleds and eductor
systems. In considering the problem of entrenching and burying
pipelines in deeper water, for example, in water depths beyond 200
feet, a water jet eductor system was proposed to overcome the
problems associated with prior air jet systems and also in order to
utilize an available low volume high pressure supply for the
eductor. Upon further consideration, however, it was found that
utilization of a high pressure water jet would give rise to severe
cavitation problems in the throat and mixing region of the eductor
conduit. In short, while a high pressure water jet could be
utilized, the eductor system per se would have an extremely short
life as cavitation effects would destroy the efficiency of the
system as well as the equipment itself. Reduced flow rates and
pressures from the high pressure water jet were rejected as
solutions to the cavitation problem for a number of reasons
including the desirability of obtaining a significant predetermined
flow rate of slurry removal from the trench.
In accordance with the present invention, the problems of
economically removing the slurry from a trench in water depths
exceeding about 200 feet and the cavitation problems associated
with utilization of a high pressure water jet nozzle are overcome
by providing an eductor system having a double nozzle arrangement.
Particularly, the present eductor system provides a pair of suction
conduits each having an inlet at its lower end for receiving the
slurry from the trench and a discharge at its upper end for
discharging the slurry into the ambient water astride the trench. A
pump nozzle is disposed in each conduit and has an inlet external
to the conduit, the inlet being exposed to the ambient water. The
outlet of each pump nozzle is disposed within the eductor conduit
in a direction toward the conduit discharge. A pair of primary jet
nozzles are carried by the sea sled and each is located a
predetermined distance from the inlet to a corresponding pump
nozzle. Each jet nozzle is provided with high pressure, low volume
fluid from the surface floating tender and which fluid flows
outwardly from the jet nozzle through the ambient fluid toward the
inlet of the corresponding pump nozzle. This high pressure jet
expands freely in the ambient fluid and entrains the ambient fluid
for delivery through the pump nozzle at low pressure, high volume,
into the eductor conduit. This low pressure, high volume, fluid
delivery to each eductor conduit creates a suction at the inlets of
the conduits whereby slurry from the trench is sucked into the
conduit, the entrained fluid and slurry being discharged at the
discharges for the conduits. By permitting the high pressure, low
volume, jet to expand in the ambient fluid, the high energy
available in the jet is reduced with consequent reduction in the
tendency of the eductor conduit to pit as a result of cavitation
pressures. Consequently, it has been found that by utilizing a high
pressure, low volume, fluid source pumped from a surface floating
tender through each jet nozzle, a low pressure, high volume,
condition occurs through the corresponding pump nozzle which, in
turn, creates a satisfactory magnitude of suction at the eductor
inlets for removal of the slurry. It will be appreciated that the
gap between each primary jet nozzle and the inlet to the
corresponding pump nozzle must be chosen such that desired flow
rates of slurry removal are provided. Generally, the larger the
gap, the lower the volume of slurry removed and the probability of
encountering cavitation problems. The smaller the gap the greater
the volume of slurry removed but the greater the probability of
cavitation. Consequently, gap distance is a significant factor in
the configuration of the eductor.
Accordingly, it is a primary object of the present invention to
provide a novel and improved sea sled and eductor system for
entrenching and burying underwater pipelines.
It is another object of the present invention to provide a novel
and improved sea sled and eductor system for entrenching and
burying underwater pipelines in deep water, for example, on the
order of 200 feet or more.
It is still another object of the present invention to provide a
novel and improved eductor system for burying subsea pipelines.
It is a further object of the present invention to provide a novel
and improved sea sled and eductor system for entrenching and
burying subsea pipelines utilizing a double nozzle configuration
for suctioning the slurry from the trench in which the pipeline is
to be laid.
These and further objects and advantages of the present invention
will become more apparent upon reference to the following
specification, appended claims and drawings wherein:
FIG. 1 is a schematic illustration of a tender barge for handling
the sea sled and eductor system of the present invention and
illustrating the latter in use on the sea bottom;
FIG. 1a is a view similar to FIG. 1 illustrating the tender barge
and sea sled positioned for deepwater pipeline entrenching and
burying operations with both illustrated under tow from a tug;
FIG. 2 is a perspective view of the sea sled and eductor system
constructed in accordance with the present invention;
FIG. 3 is an enlarged top plan view thereof;
FIG. 4 is an enlarged fragmentary cross-sectional view taken
generally about on line 4--4 in FIG. 3;
FIG. 5 is an enlarged end elevational view thereof;
FIG. 6 is an enlarged fragmentary cross-sectional view thereof
taken generally about on line 6--6 in FIG. 2;
FIG. 7 is an enlarged side elevational view of a portion of the
eductor system with parts broken out and in cross section for ease
of illustration;
FIG. 8 is a cross-section view thereof taken generally about on
line 8--8 in FIG. 7; and
FIG. 9 is a graphical illustration of the flow rates achieved with
a preferred embodiment of the present invention.
Referring now to the drawings, particularly to FIG. 1, there is
illustrated a tender barge generally designated 10, carrying a sea
sled and an eductor system generally designated 12 by means of an A
frame 14 and a gantry 16. The A frame 14 also supports an extension
18 pivotally connected at 20 to the stern of tender barge 10 and
movable between the full line and dashed line positions illustrated
in FIG. 1. The extension 18 is adapted to support the fluid lines
connecting between the tender barge and sea sled when the latter is
employed along the sea bottom. The tender barge 10 also carries a
crane 22 for use in locating the sea sled 12 from a position on the
deck of tender barge 10 and in the water and also for removing the
sea sled 12 from the water for positioning on the deck of the
tender barge. A boom 13 is carried on the bow of barge 10 and tow
cables 15 depend from bottom 13 for connection with the sea sled
and for towing the latter. Further details of the tender barge 10
are not believed necessary since the tender barge per se forms no
part of the present invention. It is believed sufficient to note
that the tender barge 10 serves to transport the sea sled to and
from the work site, to tow the sea sled 12 along the sea bottom
designated SB in FIG. 1 during entrenching and pipeline burying
operations, and to provide a surface floating carrier for personnel
and equipment necessary to the operation of the sea sled and
eductor system as described hereinafter.
Referring now particularly to FIGS. 2-5, sea sled 12 comprises a
pair of generally cylindrical, laterally spaced, pontoons 24
structurally interconnected one to the other by a plurality of
longitudinally spaced transversely extending trusses 26. Each truss
26 is comprised of vertical and diagonally upstanding members 28
and 30 respectively and transversely extending member 32 connecting
between the upper ends of the vertical and diagonal members 28 and
30. Forwardly inclined struts 34 also support the forwardmost pair
of trusses 26 while rearwardly inclined struts 36 support the aft
truss 26. It will be appreciated that the foregoing described
structure of the sled provides a clear area between the pontoons 24
whereby the pontoons are adapted to straddle a pipeline disposed on
the sea bottom for reasons which will be appreciated from the
ensuing description. The pontoons are compartmented and suitable
valves are provided whereby the pontoons can be ballasted and
deballasted.
A pair of transversely spaced, vertically extending, risers 40
upstand from each of the transverse members 32 of the aft and
intermediate trusses 26 for supporting the entrenching and eductor
apparatus, generally designated 41, carried by sled 12. A
cross-over brace 42 interconnects the upper ends of the risers 40
carried by the intermediate truss 26. Additional bracing for the
aft risers 42 is provided by diagonally extending struts 44.
The entrenching and eductor apparatus 41 are carried by risers 40
for location at selected elevations relative to the shed. To
accomplish this, the support for entrenching and eductor apparatus
41 is provided by a generally rectangular frame (FIG. 3) comprised
of a pair of longitudinally extending frame members 46 and
transversely extending frame members 48 interconnecting the
opposite ends of members 46. A pair of lugs 50 project forwardly
from the opposite ends of forward cross member 48 and a similar
pair of lugs 52 project rearwardly from the opposite ends of aft
cross member 48. Along the aft side of each forward riser 40 and
along the forward side of each aft riser 40 there is provided a
pair of laterally spaced, vertically extending plates 60 having
laterally registering vertically spaced openings 62 therealong.
Gusset plates 64 are disposed between each pair of openings 62 to
reinforce plates 60 and risers 40. The lugs 50 and 52 are disposed
within the slots formed by the pairs of plates 60 in the forward
and aft pairs of risers 40 respectively and lugs 50 and 52 have
openings which register with the openings 62. A pair of laterally
spaced longitudinally extending support tubes 68 are secured at
opposite ends to members 48. Support tubes 68 are secured to
transversely extending members 48 by clamps 74 which permit support
tubes 68 to be positioned at selected transversely adjusted
positions along members 48 for purposes as will become apparent
from the ensuing description. Accordingly, the frame comprised of
members 46, 48, and 68 and which frame rigidly supports the
entrenching and eductor apparatus 41, may be selectively positioned
along risers 40 at desired elevations by inserting bolts or pins 63
through the openings 62 of plates 60 and the registering openings
of the lugs 50 and 52 as applicable.
The entrenching and eductor apparatus 41 is comprised of parts, for
example jet tube pipes 70 and suction tubes 72 and other equipment,
which are duplicated on opposite sides of sea sled 12 (excepted as
otherwise noted) and therefore a description of the apparatus on
one side of the sled will suffice as a description of both.
Referring now particularly to FIGS. 4 and 6, the upper end of each
jet tube 70 inclines upwardly and in an aft direction for
connection with fluid lines connected at their opposite end to the
tender barge 10 whereby fluid under pressure from tender barge 10
is pumped through tubes 70. Each jet tube 70 is structurally
interconnected with the suction tube 72 on the like side of the
sled by cross-bracing 80 and carries along its forward edge a
plurality of jet nozzles 82 for ejecting the high pressure fluid
flowing into tube 70 from tender barge 10 forwardly of the sled.
The jet tubes 70 extend below pontoons 24 a distance approximating
the depth of the trench to be dug for the pipeline. The nozzles 82
are spaced vertically along the tubes 70 such that they lie at
elevations coincident with and below pontoons 24. Nozzles 82 are
also spaced circumferentially about the tubes 70 and incline
downwardly such that high pressure fluid flows in a downward
direction both forwardly and inwardly to fluidize the sea bottom
ahead of the tubes 70 and thereby form a trench between the jet
tubes.
The eductor apparatus includes the generally circular suction tube
72 which passes through a transition section 84 to form a slurry
inlet pipe 86 substantially oblong in cross-section. The lower end
of inlet pipe 86 is provided with an inlet 88 opening along the
inner side thereof and through which opening large quantities of
the slurry produced by the fluidization of the sea bottom enters
for transmission through the suction pipe 72. Carried by each
oblong inlet pipe section 86 is a roller assemblage 90 comprised of
a roller 92 on each of the fore and aft sides of inlet pipe section
86. Opposite ends of each vertically disposed roller are carried by
links 94 which in turn are pivotally carried by a shaft 95
previously mounted to a pivot housing 96. Housing 96 is secured to
the inlet tube 86. A plurality of gusset plates 98 are also secured
to inlet tube 86 and project in fore and aft directions on opposite
sides thereof. The ends of the forward gusset plate 98 are also
secured to the jet tube 70 to provide further support therefor. The
forward and aft gusset plates carry load cells which interact with
the pivotally mounted rollers 92 whereby the load exerted on either
side of the sled by the pipeline can be determined.
Referring now to FIGS. 7 and 8, the jet nozzle and jet pump for the
eductor system on one side of the sled are illustrated in detail.
Particularly, the eductor system includes a jet nozzle generally
indicated 100, and a jet pump, generally indicated 102, the latter
being disposed within an elbow section 104 of the outlet pipe
72.
The jet nozzle 100 is supported by a bracket 106 extending upwardly
and inwardly from transition section 84 and also by horizontally
inwardly extending bracket 108 secured to pipe 72. Bracket 106
supports a water supply pipe 112 for jet nozzle 100. Particularly,
the outer end of bracket 106 terminates in a pair of flanges 110 on
opposite sides of the water supply pipe 112.
An arcuate bracket 114 having lateral flanges 116 on opposite sides
thereof overlies the water supply pipe 112 and bolts 188 cooperate
with flanges 110 and 116 to secure supply pipe 112 to the support
bracket 106. The forward end of the supply pipe 112 terminates in a
nozzle holder 120 which, in turn, supports a jet nozzle 122.
Jet pump 102 is comprised of an eductor entry pipe 124 carrying, at
its forward end, an eductor nozzle 126. A nozzle attachment 128
encompasses the lower end of the eductor entry pipe 124 and
terminates in a flange 130. An annular support 132 is secured about
the lower end of the re-entry pipe 124. From a review of FIG. 7, it
will be seen that pump 102 is axially aligned with nozzle 100 and
that the nozzle attachment 128 is secured to the wall of elbow
section 104 of outlet tube 72 with the re-entry pipe 124 and nozzle
126 oriented to flow fluid axially through a venturi cone 134, an
outlet pipe section 136, an eductor outlet cone 138 and a pipe
outlet 140. Also, from a review of FIG. 3, it will be appreciated
that the nozzle 100 and pump 102 on each side of the sled are
oriented to discharge fluid from outlet 140 to a like side of the
sled on which the corresponding pump and nozzle are associated.
Pipe 124 has a plurality of elongated bars 142 disposed
longitudinally along its outer surface and at circumferentially
spaced positions thereabout whereby pipe 124 is slidably received
in nozzle attachment 128. A plurality of spindles 144 threaded at
opposite ends interconnect the annular support 132 carried by
slidable entry pipe 124 and an annular flange 146 secured to
bracket 114 whereby pipe 124 is slidable in opposite directions
within nozzle attachment 128 axially toward and away from nozzle
100 to selected axial distances relative thereto. Thus the gap
between the nozzle 100 and pump 102 can be adjusted and this gap
spacing bears on the power requirements and resulting suction as
hereinbelow amplified.
It will be appreciated that the sea sled and eductor system hereof
are utilized after the pipeline has been laid along the sea bottom
and that it is desirable to locate the pipeline within a trench and
cover the trench. To accomplish this, the sea sled 12 is ballasted
and lowered from the tender barge 10 such that the rollers 92 on
the port and starboard eductor assemblies straddle the pipeline P
as illustrated in FIG. 6. High pressure fluid, i.e., sea water, is
then supplied to the jet tubes 70 from the tender barge 10 through
fluid lines 150 (FIG. 1) supported by extension 18. The high
pressure fluid issuing from jets 82 tends to fluidize the sea
bottom directly below the pipeline and in front of sled 12. The
sled thus sinks to a depth wherein pontoons 24 rest on the sea
bottom on opposite sides of the pipeline. The sled is thus ready to
be towed by line 15 connected to the bow of the tender barge. As
the barge is towed, high pressure fluid, i.e., sea water, is also
supplied jet nozzles 100 via suitable conduits from the tender
barge 10. Each of nozzles 122 supplies a high pressure low volume
fluid flow across the gap or space between it and the inlet to the
jet pump 102. That is, the high pressure energy of the fluid
flowing through nozzle 100 is dissipated to some extent in the
ambient medium while also entraining ambient fluid as the fluid
flows from nozzle 122 to jet pump 102. Thus, the jet nozzle flow
and the entrained fluid pass through pump 102 and pump nozzle 126.
This results in a high volume low pressure flow through nozzle 126
into the venturi cone 134 and the eductor outlet. The flow issuing
from the jet pump 102 causes a suction at the inlet opening 86 of
pipe 72 whereby slurry produced by the fluidization of the sea
bottom by jet nozzles 82 enters inlet 88 and flows upwardly through
pipe sections 86 and 72 for delivery from the outlet pipe 140 on
one side of the trench.
A preferred embodiment of the present invention provides a jet
nozzle having a throat diameter of 1 inch, a jet pump inlet having
a diameter of 53/4 inches and a jet pump throat having a diameter
of 31/2 inches. The eductor pipe 72 is 20 inches in diameter, the
elbow 104 is 24 inches in diameter with a 45.degree. bend, the
venturi cone 134 is 16 inches long and provides a transition from a
24 to a 14 inch diamter, the outlet pipe section 136 is 7 feet
long, the eductor outlet cone 138 is 3 feet 10 inches long and
forms a transition from 14 to 24 inches in diameter, and the outlet
pipe 140 is 2 feet long with a 24 inch diameter forming the eductor
pipe. Preferably, the jet pump nozzle exit lies axially at a
location intermediate the venturi cone.
Since prior airlift systems for removal of slurries are not
satisfactory for use in depths beyond 150-200 feet and low volume
high pressure water systems are presently available to supply an
eductor from a tender barge, the present invention utilizes and
arranges the aforedescribed novel jet nozzle and pump in a manner
to advantageously fully utilize such available low volume high
pressure water to remove a predetermined quantity of slurry from
the trench. As noted previously, a high pressure water jet is
necessry to generate the required lifting or suction capacity.
However, utilization of a high pressure water jet to accomplish the
desired flow rate would cause severe cavitation problems. The jet
nozzle and pump arrangement disclosed herein solves these problems
while maintaining desired flow rates and pressures. Particularly,
by permitting the fluid from the high pressure jet to expand in the
surrounding ambient fluid or sea water whereby the high energy
available is reduced and by properly spacing the jet nozzle from
the inlet of the jet pump, the desired removal rates can be
obtained with the cavitation problem minimized or eliminated. For
example, the sea sled and eductor system hereof is adapted for use
with available equipment which provides 200 gallons per minute and
2500 pounds pressure at the operating depth. With this available
power, the sea sled can remove over 20,000 gallons per minute of
slurry from the trench at a depth of 280 feet.
With the foregoing parameters, the desired discharge flow rates are
achieved. This is illustrated in FIG. 9 wherein the flow rates
through the pump, the eductor pipes and the discharge of the
eductor pipes are indicated as a function of the gap distance,
i.e., the distance between the jet nozzles and the inlets to the
jet pumps. The lower curve designated Q.sub.P indicates the rate of
flow of the entrained water through the jet pumps 102, i.e., the
combined flow from the jet nozzles and the entrained flow derived
therefrom, as a function of gap distance. The intermediate curve
designated Q.sub.s indicates the rate of flow of the slurry through
the eductor pipes as a function of gap distance. The uppermost
curve Q.sub.P indicates the total discharge from the outlet pipes
as a function of gap distance. Note the sharp increase in the flow
rate illustrated by each curve and particularly the total flow rate
as the jet nozzle is moved away from the jet pump inlet. Once
spaced several inches from the jet pump inlet substantially
insignificant changes occur in the flow rates as the gap is
increased to about 20- 25 inches whereupon the flow rate falls off
upon further increase in gap distance. As noted previously,
however, close spacing of the jet nozzle and the jet pump inlet
causes cavitation problems in the jet pump. Since the jet nozzle
can be spaced a considerable distance from the jet pump inlet
without significant change in the flow rates, the gap between the
jet nozzle and the jet pump inlet is preferably located at 12
inches and preferably within a range of 2 to 30 inches depending
upon other parameters, i.e., depth of water, nozzle configuration,
etc.
It will be appreciated that certain of the prior pipe burying
systems require two sets of pumps on the lay barge. One set of high
pressure fluid pumps is utilized for the jetting nozzles while
another set is utilized for use with the eductor system. The
present invention, however, utilizes high pressure fluid emanating
from a single pump source for both the jetting and eductor systems.
The configuration of the eductor hereof is such that the pump
requirements therefor are altered to the same as required for the
jetting action. That is, the high pressure fluid delivered to the
eductor system is transformed to the necessary low pressure through
the foregoing described nozzle arrangement.
The foregoing described sea sled has been utilized in actual pipe
entrenching and burying operations in the North Sea. During initial
operations, the sea sled has entrenched and buried in 360 feet of
water 18,000 feet of 34 inch pipeline with a 2 inch concrete
coating in a 24 hour period. For operation at this depth, the sea
sled is preferably towed from the bow of the tender barge 10 by a
tow line 15 connected to the bow of the sea sled. The fluid lines
150 provide the high pressure fluid from the tender barge to the
jets and to the eductor system.
In particularly deep water pipe entrenching and burying operations,
the sea sled is towed from a tug which in turn also tows the bury
barge. This operation is illustrated in FIG. 1A wherein the tug
designated T tows sea sled 12 by a towline 200 while simultaneously
towing the bury barge by tow line 202. The tug is thus necessarily
in advance of the sea sled and enables the sea sled to be drawn
along the sea bottom without significant lifting motion. Preferably
the tow line 15 or 200 as the case may be for either relatively
shallow depth or deep water pipe entrenching and burying operations
is formed of a chain weighted to prevent the blow of the sea sled
from rising. Preferably, cable depends from the tender barge or tug
as the case may be and heavy chain is attached to the end of the
cable adjacent the sea sled. This chain weights the bow of the sea
sled and maintains it on the sea bottom.
The invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. The
present embodiment is therefore to be considered in all respects as
illustrative and not restrictive, the scope of the invention being
indicated by the appended claims rather than by the foregoing
description, and all charges which come within the meaning and
range of equivalency of the claims are therefore intended to be
embraced therein.
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