Subsea pipelay is accomplished by flying the pipestring underwater with the use of wings which provide sufficient lift to maintain the pipestring off bottom as it is towed.

BACKGROUND OF THE INVENTION 
Offshore submerged pipelines are installed usually either by dragging the 
pipeline along the seabottom, pulling the pipeline while maintaining it in 
buoyant condition, or deploying the pipeline from a conventional lay 
barge. Pipe laying procedures involving moving contact between the 
pipeline and either the seabed or handling equipment may be damaging to 
the pipeline, particularly if the pipeline is coated with a material 
sensitive to abrasion, or in cases where existing pipelines need to be 
crossed and contact with them needs to be avoided. 
A principal purpose of the present invention is to provide a system for 
installing offshore submerged pipelines by pulling them through the water 
while providing means for supporting the pipeline during the pull so that 
the pipeline does not touch the seabed and avoids abrasive contact with 
the seabed and other obstructions or existing pipelines. 
Applicants are not aware of any prior art references which, in their 
judgment as those skilled in the pipeline art, would anticipate or render 
obvious the novel pipelay system of this invention; however, for the 
purposes of fully developing the background of the invention and 
establishing the state of the requisite art, the following are set forth: 
U.S. Pat. Nos. 3,849,997; 4,107,933; 4,191,494; 4,326,821; 4,474,507. 
SUMMARY OF THE INVENTION 
In accordance with the invention there is provided a system for installing 
offshore submerged pipelines comprising wing means operable to permit a 
submerged pipeline to be pulled above seabottom. More preferably, the 
invention comprises means for gripping at least one pipeline at 
longitudinally spaced intervals, and detachable wing means secured to the 
gripping means and operable to permit the pipeline to be pulled above the 
seabottom. Means may also be provided for detaching and retrieving the 
wing means after the pipeline has been pulled to a predetermined location. 
Optionally, the gripping means may be functional to support the pipeline 
above the shore or seabottom when the pipeline is not being pulled. 
Other purposes, features and advantages of the invention will be apparent 
to one skilled in the art from the following detailed description of a 
preferred embodiment thereof taken in conjunction with the accompanying 
drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
"Flying" pipelines to avoid contact with the seabed, is not a new concept, 
but previous applications have used means other than the present invention 
to lift the pipe off the seabed. As shown in the above cited U.S. Pat. No. 
4,474,507, the pipe is being installed by the so-called "off-bottom tow" 
method wherein the pipe itself (with or without additional buoyancy tanks 
attached) is kept at a predetermined height above the seabed by attaching 
chains at certain intervals. This method also has received the name 
"controlled depth tow method" and requires making up a pipeline or pipe 
bundle at an onshore location. The pipe has a slightly positive buoyant 
submerged weight when empty. Chains are attached to give the total 
assembly a slightly negative submerged weight. The pipe ends are attached 
with tow cables to a leading and trailing tug. If the assembly is not 
moving the pipe will float at some height above the seafloor. The weight 
of the chain hanging from the pipe, but not resting on the seabed, is 
equal in magnitude to the positive buoyancy of the pipe itself, and the 
remainder of the chain on the seafloor provides resistance against 
hydrodynamic forces from lateral currents. When the tow starts, the chains 
will start to deviate from their vertical position and the pipe will start 
to lift off from the bottom. The reason for this phenomenon is that the 
hydrodynamic drag force on the chains splits into two components: an 
upwards force which reduces the total system submerged weight and a 
horizontal force. Thus, the pipeline configuration will take the shape of 
a catenary. When the tow speed increases, the inclination of the chains, 
measured from the vertical, increases also, and thus provides a greater 
upwards force. To some extent this upwards force would also be present 
without the use of chains, due to the hydrodynamic drag on the pipeline 
itself. It is, of course, possible to lift the pipe totally off the 
bottom, without towing it, but the required tension in the tow cables 
would be very large. 
The chains are not an optimum means to provide this upwards force, because 
they also create a drag force along the pipe axis, and they have a large 
weight to start with. In comparison, attaching wings to the pipeline in 
accordance with the present invention has the following main advantages: 
1. Wings are much more efficient in providing lift force, with little 
additional drag. The latter reduces tow horsepower requirements. 
2. Instead of requiring the pipe itself to have a positive buoyancy, the 
pipe now can have a negative buoyancy. This is in particular of importance 
in deep water applications: the requirement to withstand external pressure 
in the empty condition leads to low diameter/thickness ratios, and thus 
high negative buoyancy, unless the pipe is pressurized to balance the 
external pressure. The only way to make a pipe or bundle positively 
buoyant, is to add buoyancy tanks, or to pressurize the line during 
tow-out. In fact, depending on the material, the wings themselves may be 
buoyant and thus provide additional lift force. 
The functional requirements of the wings are summarized below: 
1. The wings provide predictable lift force under varying conditions 
(change in tow speed, change in pipe configuration). 
2. The wing assembly does not damage the pipeline. 
3. The wings are detachable without the use of divers. 
4. The wing assembly provides stability to the pipe, i.e., it does not 
cause the pipe to roll around its longitudinal axis. 
5. The wing assembly withstands and transfers different forces, the largest 
usually being wave impact forces during launch of the pipe through the 
surf zone. 
Principles of airfoil theory known in the ar: are applicable to determine 
the magnitude of the lift force as a function of tow speed, wing geometry, 
and wing inclination relative to the direction of the fluid flow, even 
though operation is in relatively low Reynolds numbers. Airfoils have seen 
extensive use for trimming purposes, for example, on submarines and on 
seismic floats. 
A key parameter is the angle of the wing to the direction of the fluid flow 
(which is for simplicity assumed to be parallel to the longitudinal axis 
of the pipe). The pipe configuration will change from an essentially 
straight position to a catenary during the course of increasing tow speed 
from zero to the desired level. Each point along the pipeline, therefore, 
undergoes a change in inclination. Having the wings 1 rigidly attached 
along the axis of pipe 2 towed between tugs 3 and 4 will not be efficient 
(FIG. 1), because the trailing end of the pipe experiences a downward 
directed force 5 on the wings while the forward end of pipe 2 experiences 
an upward force 6. In some cases, it is desirable to move the pipe back in 
the direction it came from, using the trailing tug 4 as the leading tug 
instead. It is therefore preferred to have some means to adjust the 
inclination of the wing. 
The wings can comprise one or two sections (FIGS. 2 and 7). If the wing 7 
comprises one section, it can pivot around a hinge 13 (FIG. 3) with tails 
8 (FIG. 2) providing lateral strength. Preferably, the wings 7 are not 
left on the pipe 2 after installation of the pipe because (1) they may 
have a negative effect on hydrodynamic stability of the pipe, and (2) 
using wings may not be economically viable if they are not re-used. 
Detachment of the wings 7 may be achieved remotely or with use of a 
remotely operated vehicle (not shown). 
A long pipe string which is towed without buoys or chains, will roll around 
its longitudinal axis. Wing design is such that this roll is avoided. This 
is achieved by constructing the wing assembly such that, if the assembly 
is positively buoyant, its center of gravity is above the center of 
gravity of the pipe string, and if the wing assembly is negatively 
buoyant, its center of gravity is below the center of gravity of the pipe 
string. This is also important during start-up of the tow procedure, when 
the pipe is close to the seabed: the wings are not allowed to dig into the 
seabed or hook behind an obstruction. 
It is likely, as above stated, that the largest forces on the wing 7 will 
be due to wave impact forces during pipe launch from shore (aside from 
accidental loads). Vertical forces on the wing 7 (downwards and upwards) 
can be orders of magnitude higher than those encountered during tow. Other 
forces are hydrodynamic forces during tow, impact forces with the seabed, 
hydrostatic forces, and handling forces during installation on the pipe 
and launch from the beach. 
Based on the foregoing requirements, the wing components are: (1) the wing 
itself, (2) wing inclination adjustment mechanism, (3) wing rotation 
mechanism, (4) wing attachment to pipe, (5) wing release mechanism, and 
(6) pipe slides. 
It is probably more advantageous to have relatively small wings at close 
intervals, say one every joint or two joints, than larger wings, further 
apart. The smaller the wing area, the easier the handling becomes. Chances 
of damage or inadvertently hitting an obstruction decrease also. In 
addition, "mass production" may become attractive, especially if the wings 
are made from moldable materials (high density foams, plastics). The wings 
preferably are light and they preferably have a solid cross section, to 
withstand the hydrostatic pressure. The low density of foams (about 20 
lb/ft.sup.3) results in positively buoyant wings, which increases the roll 
stability in the configurations shown. Wings preferably are placed 
symmetrically and comprise one or two sections (FIGS. 2 and 8), depending 
on primarily economic considerations. 
The wings 7 are preferably made using syntactic foam, a high-density 
polyurethane, fiber reinforced polyester or epoxy. Manufacturing costs for 
the wing are low, especially if the cost of molds, etc. are spread out 
over several hundred units. 
As above mentioned, it is preferred to have the capability to adjust the 
inclination of the wings 7. This inclination may be set prior to launch of 
the pipe 2, but this may not result in the desired lift force distribution 
during varying conditions under tow. It is unlikely that the inclination 
of the wings will be adjusted while towing (in which case the required 
torque to rotate the wing 7 would be high), so a simple, low torque 
mechanism is employed (FIGS. 3 and 4). This mechanism comprises screw bolt 
9 extending through threaded holder 10 and activating rotating arm 11 
which moves along slide 12 to swivel wing 7 about hinge 13. Torque to 
activate bolt 9 can be provided by a pre-loaded spring, a remotely 
operated vehicle equipped with an hydraulic arm, or by a small hydraulic 
cylinder (energy provided by an accumulator) which is activated by the 
remotely operated vehicle. Alternatively, inclinometers can be placed at 
regular intervals, with a system of transponders placed along the line, to 
automatically actuate the wing inclination mechanism. The rotating arm 11 
and the hinge 13 may include hinge bolts (not shown) which will fail at a 
predetermined shear force. This will ensue that, if the wing accidentally 
gets caught behind an obstruction, the wing will shear off without damage 
to the pipe. 
The wing assembly may experience the largest forces when being pulled 
through the surf zone. To minimize the exposure to on-rolling waves 
passing from surf zone 14 to beach 15, the wings 7 may be rotated 90 
degrees (FIG. 5). A simple spring loaded system (not shown) may be 
activated by divers or a remotely operated vehicle, to rotate the wings 7 
back into their proper position for tow (FIG. 6). 
It is suitable in accordance with the invention to attach the wings 7 to 
the pipe Z or pipe bundle in several ways. Main considerations are given 
to ease of assembly, compatibility with movements between individual 
pipes, avoidance of damage to the pipeline, and ease of release. If launch 
forces can remain low, then clamps 38 do not have to transfer significant 
forces. The weight of the clamp preferably is kept low, and various 
materials other than steel, such as molded clamps made of a hard plastic, 
may be more economical. An emergency release preferably is incorporated, 
which releases the wing if it gets stuck, or hangs behind an obstruction. 
Various different release mechanisms are suitable for use with the 
invention. It can be a chain reaction type trigger mechanism, with a 
trigger rope or cutting cable along the pipe, or the clamps may be 
released individually. The mechanism shown in FIGS. 8 and 9 is a typical 
example of the latter. 
The purpose of slides 16 and 17 as shown in FIGS. 7-9 is to prevent contact 
of the pipe with the beach 15 when the pipe is being launched, or when the 
tow speed is still too low for "lift-off". For the slides 16 and 17 to be 
successful, it is necessary to have a fairly close wing spacing (to avoid 
mid span contact between pipe and seabed) and to have a hard, and fairly 
smooth seabed surface, for example, a sandy soil. In soft mud, more 
commonly found in deeper waters, the slides sink into the seabottom and 
restarting a tow requires high tow forces. Some contact of coating and 
seabed over short distances may not be detrimental, while continuous 
contact over a long tow would be, so slides are not always necessary. 
In FIG. 7, pipe bundle 18 is shown being pulled from the shore 15 into the 
surf zone 14 by a suitable towing means, while sliding on spaced pairs of 
slides 16 and 17 on the shore. Once the pipe bundle 18 is in the water, 
and the tow speed has increased sufficiently, wings 19 and 20 lift the 
pipe bundle 18 off the seabottom and cause it to fly in the water, 
whereupon the pipe bundle may be pulled to a desired location before 
depositing it on bottom. Thus, the pipe bundle 18 is kept out of contact 
with the seabed and may be moved eventually to a final location where the 
wing assemblies may be detached and retrieved. The ends of the pipes 
comprising pipe bundle 18 are sealed by closures (not shown) and are 
attached to or are an integrated part of a pull assembly (not shown) 
permitting attachment of tow cable 37. 
The construction of the wing assembly is made clear from FIG. 8. At 
intervals of about 40 to 120 feet centers along the pipestrings, 
combination wing and clamping assemblies are provided for gripping the 
pipe bundle 18 and supporting it both above the land while being pulled 
into the sea and above the seabottom when the pipe bundle is under water, 
so that the pipe bundle will not touch the ground on the shore or the 
seabed during the placement. Details of one combination clamping and wing 
assembly appear in FIGS. 8 and 9. Each member of a pair of cross ties 21 
and 22 is suitably grooved to receive and clamp between the ties the pipe 
bundle 18. This clamping assembly may be used with one, two or many 
pipestrings or pipe bundles which can be arranged not only side-by-side 
but also above each other, either aligned or staggered, but preferably 
parallel. The bottom tie 21 is notched on the top side to receive the pipe 
bundle 18 and the top tie 22 is notched on the bottom side to nestle the 
pipe bundle 18 therebetween. The upper tie is then bolted or otherwise 
fastened to the lower tie by means not shown and also to the sleds or 
skids 16 and 17, thereby forming a structure which firmly binds the pipe 
bundle to the clamping assembly and also the sleds or skids as well. The 
ties may also be attached by releasable means to permit burying the 
pipelines. Attachable to the tie 22 is an axle 23 and wings 19 and 20 
which form parts of the wing assembly. Preferably, the wings 19 and 20 are 
rotatably attached to the clamping assembly. Active means (not shown) may 
be utilized to provide rotation of the wings. Flanges 24 and 25 extend 
from the front and back faces of the axle 23, respectively, and have 
apertures which match with the apertures shown in lugs 26 and 27. Buoys 28 
and 29 are attached via lines 30 and 31 to eyebolts 32 on one face of the 
axle 23 and another eyebolt (not shown) on the opposite face of axle 23 to 
a shear pin 33 at the end of eyebolt 32 and also at the end of line 30 
(not shown) which are insertable into :he matching holes in flanges 24 and 
25 and lugs 26 and 27. Manifestly, a single buoy could be employed instead 
of the double buoys 28 and 29. 
As more clearly shown in FIG. 9, the line 31 passes through a ring 34 which 
is, in turn, attached to a ring 35 which is affixed to flange 36. Line 31 
then attaches to the eyebolt 32 which passes through the holes in the 
flanges 24 and at the opposite end thereof, is attached to a shear pin 33. 
When it is desired to release the eyebolt from flanges 24 and 25, and lugs 
26 and 27, respectively located between the flanges, so that the wings 19 
and 20 may be retrieved at the surface, a suitable force is exerted upon 
buoys 28 and 29 and lines 30 and 31 to break the shear pin 33 and the 
similar shear pin on the opposite side of axle 23 whereupon the wings 19 
and 20 may be retrieved at the surface. This is, of course, after the pipe 
bundle 18 has been towed to a desired on-bottom location. When the force 
is exerted to break the shear pins and release the wing assemblies from 
the gripping assembly, the eyebolt 32 preferably does not pass through the 
ring 34 but catches thereat and permits retrieval of the wing assembly by 
means of the lines 30 and 31. 
The foregoing description of the invention is merely intended to be 
explanatory thereof. Various changes in the details of the described 
method and apparatus of the invention may be made within the scope of the 
appended claims without departing from the spirit of the invention.