Note: Descriptions are shown in the official language in which they were submitted.
1055Z61
The present invention relates to the laying
of submerged pipelines such as submarine pipelines, which
are provided for instance for transporting liquid or gaseous
hydrocarbons.
This invention is an improvement in a known
process for laying submarine pipelines, which consists in
hauling from the shore seawards a part of a pipeline of a
gradually increasing length; this part is made of a series
of sections which are successively added together at the rear
end, still on the strand, of the already submerged pipeline
length.
Each section is itself obtained by the assem-
bly of a rather large number of unitary tubes of short length
(for example of the order of 12 or 24 meters) which are
welded end to end together. Such a section may have then an
appreciable length (of the order of 1 km or even more) with-
out any other limit than the availability of a sufficient space
for prefabricating and storing pipelines in the vicinity of
the shore. The sections are prefabricated ashore, for in-
stance during winter, when bad weather does not allow a work-
ing at sea and they are launched when meteorological condi-
tions are propitious.
For the laying of pipelines, each new section is
welded to the rear end of the already submerged pipeline part
which still rests on the shore. The assembly made of this
part and the new section is then hauled seawards over a dis-
tance, which is equal to that of a section, by means of haul-
ing contrivances carried by floating devices. Hauling is
then suspended, the following section is welded and this oper-
ation is repeated as many times as sections are to be added
A and laid.
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1055Z61
With respect to another process for layingsubmarine pipelines - which consists in submerging from the
water surface, by means of a floating device which is
specially arranged, pipeline sections assembled on this float-
ing device - the above-mentioned hauling process has in par-
ticular the following advantages:
- the pipeline is protected over its full
length, during all the laying operations,
against storms and cross sea;
- the pipeline is not subjected to distor-
tions difficult to be controlled such as
those which occur in the course of immer-
sion during the aforesaid process;
- the critical phases, which include the exe-
cution and the checking of all the welds,
are carried out ashore in much easier con-
ditions than afloat;
- the number of welds to execute and check dur-
ing the laying proper of the pipeline is
quite small by reason of the great length of
the prefabricated sections. Thus this lay-
ing proceeds in a very short time.
There is however a problem which is to be faced
in the hauling process for laying submarine pipelines of a
great length which have to be submerged in places where cross
currents predominate.
In order to prevent a submarine pipeline from
drifting under the action of a cross current it is weighted
with known means in such manner that the pipeline will rest
on the sea bed with such a weight that the resulting friction
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force is great enough for resisting the current. As an
alternative, the pipeline will float under water and it
may be arranged that there are only weighting anti-drift
elements, attached to the pipeline, which are frictionally
engaged with the sea-bed.
A drawback thereof results from the consid-
erable increase of the hauling force to be applied for lay-
ing the pipeline, which creates in the latter very high
tensile stresses.
Because of such stresses the manufacturer is
constrained to take particular precautions and avoid for
instance the use of traditional unitary tubes of the "rolled-
welded" type which show heterogeneous mechanical properties
(owing to the presence of a continuous seam along a genera-
trix) with the possibility of failures. Instead it is
necessary to use seamless tubes which are more costly than
the ordinary tubes of the "rolled-welded" type and which
possess greater dimensional tolerances, so that the supply-
ing of the yard becomes complicated. Besides, said tubes
have to be made of a special steel of a better quality than
the ordinary steels for pipelines, which makes them more
costly (for this reason also) and moreover it is more dif-
ficult to weld them together than is the case with the
ordinary steel tubes.
It is an object of the present invention to
provide an improved method of laying an under-water pipeline
while forming the pipeline from a plurality of pipe sections
stored ashore so that tensile stresses in the pipeline are
minimised.
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It is also an object of the invention to pro-
vide apparatus for carrying out the improved method.
Accordingly in one of its aspects the invention
provides a method of positioning an under-water pipeline while
forming the pipeline with a plurality of pipe sections ini-
tially stored ashore. The method comprises the steps of
advancing à first one of said pipe sections towards the body
of water, connecting a forward end of a second one of said
pipe sections to a rear end of said first pipe section, fur-
ther advancing said first and second pipe sections towards the
water body connecting a forward end of a third one of said
pipe sections to a rear end of said second pipe sections, and
so on, each advancing step comprising hauling a pipeling por-
tion of substantial length towards the body of water while
maintaining the pipeline so formed buoyant, each advancing
step comprising applying a traction force to a forward end
of said first pipe section, and contemporaneously applying
a plurality of further traction forces to a plurality of
points spaced along said pipeline portion.
According to another of its aspects, the
invention provides apparatus for positioning an under-water
pipeline having positive buoyancy while forming the pipeline
with a plurality of pipe sections initially stored ashore,
the apparatus generally having a negative buoyancy and com-
prising means for advancing towards the body of water a
pipeline portion of substantial length, the advancing means
comprising a hauling cable attached to a forward end of the
pipeline portion, elongated force distribution means adapted
to be positioned below and in generally parallel spaced
relationship from the buoyant pipeline and extending over
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lOSS261
the full length of the pipeline portion, means attaching
the force distribution means to a plurality of points
spaced along the pipeline portion, means applying a first
traction force to the hauling cable, and means applying a
second traction force to the force distribution means.
Reference is next made to the drawings, in
which:
Fig. 1 is an illustrative diagram for explain-
ing the principle of the laying of a submarine pipeline by
hauling;
Fig. 2 is a schematic, longitudinal elevation
view of a preferred embodiment of apparatus used in the dis-
tribution of the traction forces and using a distributing
cable which is connected to the pipeline by intermediate
hangers;
Fig. 3 is a schematic view showing the way a
hanger is attached to a pipeline and to a distribution cable;
Fig. 4 is a view similar to Fig. 3, showing
the position of the distribution cable on an irregular bottom
ground;
Figs. 5 and 6 are schematic, longitudinal
elevation views, showing the weighting of buoyant pipelines
by means of weighty elements fixed to the distribution cable,
while Fig. 6 also shows inverted catenary systems which can
be used to complete the hangers;
Figs. 7 to 11 are schematic, longitudinal
elevation views which show the weighting of the pipeline
by means of guideropes;
Fig. 12 is a schematic view in the form of a
cross-section, taken along XII-XII, of the weighted pipeline
shown in Fig. 10;
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~055Z61
Fig. 13 is a schematie, longitudinal ele-
vation view for illustrating the pipeline fitted with
anti-drift slackening elements;
Figs. 14 and 15 are schematie, cross-
section views, in two working positions, of an anehoring
block whieh is used as an anti-drift, slaekening element;
Figs. 16 and 17 are similar to Figs. 14 and
15 and show a modification of the embodiment of the anchor-
ing block;
Fig. 18 (adjaeent to Figs. 5 and 6) is a
schematic, perspective view, showing another possible em-
bodiment of the anchoring block;
Figs. 19 to 21 (adjacent to Figs. 5 and 6)
are schematie, cross-section views, illustrating several
working positions of the anchoring block shown on Fig. 18;
Fig. 22 is a schematic, perspective view of a
traveller which acts as an anti-drift slackening element;
Fig. 23 is a partial plane view of the tra-
veller shown on Fig. 22;
Fig. 24 is similar to Fig. 23 for illustrat-
ing a modification of embodiment of the traveller; and
Fig. 25 (adjacent Figs. 2 to 4) illustrates
an alternative embodiment of the`apparatus shown in Fig. 1.
In all the Figs. the reference letter T
designates the pipeline section in the process of being laid
by hauling. This pipeline has itself or in association with
floating means (not shown) a positive buoyancy. To this end
spaeed or continuous (extending over all the pipeline length)
floats are used, which are filled with a gaseous or liquid
fluid, having a specifie weight less than water (atmospherie
or pressurized air, hydrocarbon, ammoniac or liquid carbonic
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1055Z61
dioxide, fluidized compound made of a suspension of plastic
microballs in water, etc.). Said floats may be releasable
or filled with water at the end of the operations for laying
the pipeline. The floating means are associated with weight-
ing means that will be described further on.
The pipeline T may comprise in fact either
one single useful tube or a system of useful, parallel tubes,
integral with each other.
In. Fig. 1 are schematically illustrated sev-
eral successive phases for laying in position a submarinepipeline by the hauling process, when starting from an initial
shore R.
The pipeline is formed with sections Tl, T2,
T3...T 1' Tn; each of them may be made of a rather great
number of unitary short tubes (for instance 12 or 24 m. long)
which are welded together end to end. The sections, having
an eventual length of 1 klm. or even more, are prefabricated
and stored ashore in the vicinity of the shore R.
Laying of the pipeline is obtained by means of
a floating device 1, which is anchored in the offing by means
of dead weights 2 and equipped with a hauling device such as
a winch 3 (see Fig. 2) around which a pulling cable 4 is
wound.
When the floating device 1 is in a first work-
ing position (I) remote from the shore R, the cable 4 is
attached to the head section Tl and by means of the hauling
device 3 a traction is exerted on this cable for advancing
seawards the section Tl weighted in an appropriate manner.
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10552~
As long as it is still on the land, the
section Tl is carried on lorries or glides over tyres.
When the rear end of this section arrives at the border
line of the shore, hauling is suspended. The floating
device 1, freed from its anchors, is removed further
away from the shore (the cable 4 belng allowed to unwind)
over a distance equal to the length of a section, so that
it comes to its second working position (II). During this
time the front end of the second section T2 is welded to
the rear end of the head section T2.
The floating device being in its position II,
the pipeline part T, made of the first two sections Tl and
T2 weighted in an appropriate manner is hauled towards the
open sea by means of the hauling device 3 as far as the rear
end of section T2 arrives to the border line of the shore.
Hauling is then suspended anew; the floating device 1 is
removed further away unto its new working position (III).
The third section T3 is welded to the first two ones and so
forth until all sections are assembled and the head section
Tl has arrived at its destination, for instance to the shore
opposite.
Fig. 2 illustrates the principle of the dis-
tribution of the pulling forces according to a preferred
embodiment of the invention.
An essential element for putting said principle
into practice is a distribution cable 5 arr'anged in prolonga-
tion of the hauling cable 4, which extends over the full length
of the pipeline T (with all the already welded sections) and
which is attached to the latter at a plurality of points
spaced all along this pipeline part.
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1055Z~l
The pipeline T being in a configuration
of positive buoyancy, the distribution cable 5 is situated
under this pipeline to which it is connected by a plurality
of spaced hangers 6. This cable may be shaped as a metal
cable comprising stranded or parallel wires, or a chain or
a metal rod or bar having the necessary length, or a suc-
cession of metal rods or bars which are connected together
by cable or chain parts. The hangers 6 may be made of metal
cables or chains or preferably of plastic material. The
hangers may be shorter or longer according to the height of
the sheet of water. The interval between two successive
hangers will depend from the buoyancy conferred to the
pipeline, the bending strength of the pipeline and the
eventual existence of cross currents. This interval is
normally of the order of a few tens of meters, for example
between 15 and 100 meters.
Another portion of cable 30 is attached to
the head of the pipeline for transmitting directly to the
latter a part of the haulage force exerted by the cable 4.
To this effect, this portion of cable 30 is connected to
the cable 5 at a certain distance in front of the head of
the pipeline so as to divide the hau]age force F exerted
by the tug on the cable 4 into two forces F' and F" applied
to the cable 5 and the pipeline respectively.
One can in this way ensure that the elastic
extensions of the cable 5 and the pipeline are substantially
the same whereas if one hauls on the cable alone, the latter
assumes an extension capable of causing difficulties in the
operation of the suspenders 6. This difficulty could be
avoided by using suspenders of increasing length towards the
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1055261
head of the pipeline to compensate for the displacements
of the points of attachment of the suspenders to the
cable 5, but this arrangement would be complicated.
The division of the force F between the
cable 5 and the cable 30 should be made as a function of
the moduli of elasticity of the cable 5 and the pipeline,
the division being equal if these moduli are equal. For
example, if the cable 5 is formed of parallel steel wires
and has a modulus of elasticity substantially equal to
that of a steel pipeline, a twisted cable having like
steel wires will have a modulus of the order of a half.
An interesting solution consists in attach-
ing the cables 5 and 30 to a weight 31 sufficiently heavy
to rest on the bottom and harnessed to the haulage cable
4. This arrangement also has the advantage that the weight
31, in sliding on the bottom, prepares a path for the
trailing cable 5.
Fig. 3 shows by way of example a possible
way for attaching a hanger 6 to the distribution cable 5
and the pipeline T in case the hanger is a cable. At every
end the hanger forms a welded loop which is passed through
an eye integral with a sleeve 20 welded to the distribution
cable 5 or carries by a collar 21 that is welded to the pipe-
line T. As an alternative one could also use a catching
system by means of hooks, in particular for hangers made
of chains.
The system "pipeline T - distribution cable
5 - hangers 6" has itself or in association with weighting
means (which will be described further on) a slightly neg-
ative buoyancy so that the pipeline floats under water.
A
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1055261
In the pipeline part which is still ashore (consisting ofthe last welded section) the cable 5 and the hangers 6 are
momentarily laid against the pipeline and are released
after entering the water preferably beyond a certain depth.
As it may be seen, the pulling force exerted
by the hauling cable 4 is substantially supported by the
distribution cable 5 which transmits every time but a
small fraction of the force to the pipeline T. The stresses
which result in the pipeline are thus extremely reduced.
In the example of Fig. 3, weighting is en-
sured by the weight of cable 5 and hangers 6. The latter
are taut and the cable 5 lies with its central portion,
between two successive hangers, on the bed 7.
The pipeline T, being subjected (because of
its positive buoyancy) to an uplifting force, but being
maintained by the hangers 6, behaves as a deck girder with
inverted loads. If the buoyancy of the pipeline is great,
the number of hangers is consequently increased so as to
reduce the interval between two hangers. As an alternative
it is possible to resort to catenary inverted systems in-
cluding holding cables 8 so as to form a catenary curve and
auxiliary hangers 9.
The distribution cable 5 and the hangers 6
are shown in a pulling configuration in Fig. 3 and in a rest
configuration in Fig. 4. In the latter Fig. it is admitted
that the surface of the seabed, lakebed or the like, 7 is
rather rugged. If the hangers 6 have all the same length the
cable 5 will be raised in certain zones, which may produce
"free spans" for pipeline T that will be larger than an
ordinary interval between two successive hangers. Thus the
pipeline will take an average position with respect to the
profile of the seabed.
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1055261 ll
If necessary a supplemental weighting may
be formed by means of weighty elements 10 which are fixed
at places to the distribution cable 5, for instance between
two hangers 6 or plumb with each hanger, as the Figs. 5
and 6 show respectively. Such weighty elements may be
executed in the form of steel or cement blocks through
which the distribution cable passes; at the same time they
may be used, as will be seen further on, as anti-drift ele-
ments for the pipeline.
Figs. 7 to 11 illustrate other arrangements
according to the invention. The weighting of the system
"pipeline T - distribution cable 5 - hangers 6" is comple-
mented with supple or articulate, relatively heavy links,
such as hanging chains 11, disposed at places along the
pipeline, which drag partly on the seabed and work like
guideropes for balloons. Said guideropes may be fixed to
the hangers 6, as Fig. 7 shows, or even confounded with the
latter as in Fig. 8. As an alternative, the guideropes 11
may be directly fixed to the pipeline T as in Figs. 9 to 12.
They are heavy-enough for retaining the pipeline in a cal-
culated equilibrium condition.
Apart from their weighting function, the
guidèropes 11 develop because of their bulk laying on the
seabed (see Fig. 12) an appreciable friction force which
contributes to prevent the pipeline T from drifting under
the influence of cross currents V.
In Figs. 7 to 9, the length of the hangers
6 is so chosen that the distribution cable 5 remains per-
manently raised above the bed. This disposition however
is not obligatory. In the case of cross currents in par-
ticular it may be contemplated to have the cable dragging
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1055Z61
along the sea bed as shown in Figs. 10 and 12. In this
case, the current V produces a transverse shifting, de-
fined by an angle a, between the pipeline T and the
cable 5. sesides the guideropes 11 ensure then stability
in the vertical equilibrium of the pipeline. Effectively
if the angle ~ varies (for instance because of a variation
of the thrust Fx exerted by the cross current on the pipe-
line) the resulting vertical displacement of the pipeline
is converted into a variation of the free length of the
guideropes and thus with production of a vertical force
Fz which will have the effect of bringing the pipeline back
to its initial level.
When the pipeline T is definitely in the
wanted position the distribution cable S is of no great use.
After a time and without inconvenience it may be severed by
the displacements of the guideropes, if there are inversions
of direction of the cross currents. As shown in Fig. 11,
the cuts thus produced may even be beneficial if they are
executed at points a, b, c, which are above hollows in the
sea bed. The cable being dropped on the sea bed, a supple-
mental anchoring of the pipeline and relaxation of the
vertical strains imparted to the pipeline by the hangers
is obtained.
Eigs. 13 to 24 relate to slackening means
acting as drags on the sea bed 7, which are more especially
used in case laying of pipeline T has to be executed in
zones traversed by appreciable cross currents.
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A first embodiment of these slackening means
is shown in Figs. 13 to 15 in the form of anchor blocks
12 fixed at places to the distribution cable. They are
pivotally mounted about this cable, every one of them hav-
ing on top a rigid rod 13 (normally vertical) which is con-
nected to the pipeline T by a hanger 6.
In a zone deprived of cross-currents, the
anchor block 12 stands upright (see Fig. 14) because of the
uplifting vertical force of pipeline T, which is amplified
by the lever arm formed by rod 13, and glides over the bed
on an under face 12_ having a small friction coefficient with
respect to the bed. In this configuration thus, because of
the friction against the bed the block opposes only a rela-
tively small resistance against the advance of cable 5 in
its longitudinal direction.
When an important cross-current is present,
it exerts a thrust on the pipeline, which causes the pivot-
ing aside of the anchor block around cable 5 (see Fig. 15)
through the intermediary of hanger 6 and rod 13. The block
is then anchored on the sea bed by a lateral face 12b, or
12c having a much greater friction coefficient than the
friction coefficient of the under face 12a. With this
configuration, the anchor block offers then a very high
resistance against the drifting of cable 5 (and consequently
of the pipeline) in its transverse direction. If pivoting
occurs in the course of the laying of the pipeline, pulling
on the cable 5 assists in releasing the anchor-blocks there-
after.
1055Z61
As it is seen in Fig. 15, every side face of
the anchor block is provided with projections 14 which form
as many anchoring noses. Similar teeth 15 may also be pro-
vided on the upper face 12d of said block.
Figs. 16-17 show a modification in which the
anchor block 12 takes its bearing on the bed 7 with the
intermediary of a large footing 17, instead of standing
upright on a narrow under face. This structure is to be
preferred in the case of a loose bottom ground, for avoiding
that the standing anchor block would penetrate deeply the
sea bed. Besides such a footing will improve anchoring of
the block when it swings as is shown in Fig. 17.
Figs. 18 to 20 show another possible embodi-
ment in which the anchor-block 12 is deprived from its upper
rigid rod 13 and is pivotally mounted about the distribution
cable 5 in such manner that its center of gravity G is
situated lower than the cable.
The upper face 12d of this block has a con-
cave configuration delimited by two cutting, longitudinal
ridges 7, either of which being provided for engagement with
the bed after pivoting of the block. As Fig. 18 shows, said
ridges may have a scalloped profile with points or tips 17x
which function as anchoring noses. From this Fig. there is
also to be noticed that the fore end 12_ of the block is
shaped as a stem or prow so as to facilitate the advance of
the block in the longitudinal direction. Figs. 20 and 21
show this anchoring block during and at the end of its pivot-
ing due to an initial drift of the distribution cable 5.
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1055Z61
The slackening means shown in Figs. 13-21
are particularly efficient on a relatively loose ground.
For more consistent or harder grounds it is preferable to
resort to means of another type, shcwn in Figs. 22 to 24.
In Fig. 22, reference number 20 designates
a "traveller" formed by a frame 21 which receives the
distribution cable 5. Said cable extends across the
traveller and is fixed to the frame 21 at the front and
back thereof by clamping members 22. The frame 21 may also
be connected to the pipeline T by a hanger 6. On the frame
there are fitted horizontal revolving axes 24, perpendicu-
lar to the cable, which carry some rolling members 23 which
rest on the sea-bed. The travellers 20 have a fixed orien-
tation with respect to the cable 5, thus they can only run
in the longitudinal direction of this cable, that is to say
when hauling is performed. If there are any cross-currents,
they are solicited in a direction parallel to the axes 24,
so that the members 23 rub against the bed and their side
faces act as abutments.
In the example shown in Figs. 22 and 23,
the rolling members 23 are rollers or balls made of con-
crete, which are equipped on their outer surface with a
number of hard steel points 23a, capable of producing
disintegration of a ground composed of such crumbly rocks
(schistose shoals, soft limestones) as are often found in
sea beds. Moreover said points assist in anchoring the
travellers 20 against transverse drifting.
In the example shown in Fig. 24, the rolling
members 23 are made of relatively thin wheels or disks hav-
ing side flanges which play the part of abutments against
transverse drifting.
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105526~
When the hauling-laying operations are ended,
that is to say when the front end of the pipeline has reached
its destination, it is possible to cancel or not-according
to case the positive buoyancy of the pipeline.
If the initial buoyancy of the pipeline were
relatively small, this cancellation may be automatically
obtained by putting the pipeline in service, in particular
if the latter is provided for transporting a liquid hydro-
carbon. In other cases, it will be possible to suppress the
positive buoyancy of the pipeline by releasing the floats or
filling them with water. This operation is particularly easy
to carry out in the case of such a pipeline as shown in Fig.
2, equipped with a continuous float that is initially filled
with a fluid of small specific weight which may be replaced
by water when wanted.
For choosing the definitive configuration
of the pipeline one will have to take into account such
factors as the depth of the sea bottom, the nature and
irregularities of this bottom the dangers of seisms, the
existence of cross currents and the danger of constituting
a possible obstacle against submarine navigation. In cer-
tain cases, especially for relatively shallow regions, it
will be recommended to lay firmly the pipeline on the sea
bed with a definitive configuration. This solution pre-
sents the advantage of improving pipeline anchorage against
cross currents and to suppress the dangers of collisions
in submarine navigation at the same time.
On the contrary, for deeper situated bottoms
it may be contemplated to maintain permanently the pipeline
under water at a sufficient height for avoiding any risk of
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1055Z61
the pipeline being squeezed by the surrounding water and
also for it being outside the routes followed by modern
submarines. The manifested configuration will be such
as the one illustrated for instance in Fig. 6 or 13.
By the way it will be remarked that the process of the
invention permits easily of obtaining such a configuration,
for it is quite convenient to use hangers 6 of very great
length which extend from a distribution cable 5 situated
near the bottom, when laying the pipeline. I
With a definitive conformation, the anti- ¦
drift anchor blocks 12 which are shown in Fig. 13 continue
to work efficiently even in the long run, that is to say
even if the distribution cable 5 is destroyed by corrosion.
As a matter of fact, said blocks are fixed not only to
cable 5 (which is important when laying the pipeline) but
also to the hangers 6 which may be made with practically
non-deteriorating plastic material.
Alternatively, as shown in Fig. 25, one need
not connect together the cables 5 and 30 but form them part
of two independent haulage winches provided on the tug or
at the haulage station, which will enable the distribution
of the forces F' and F" between~the two cables to be regu-
lated.
It is to be understood that the embodiments
described are only examples and it would be possible to
modify them, particularly by the substitution of technical
equivalents, without departing from the scope of the inven-
tion.
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