GB2049094A

GB2049094A - Apparatus for Burying Pipes or Cables in the Sea Bed

Info

Publication number: GB2049094A
Application number: GB8013695A
Authority: GB
Original assignee: Coflexip SA
Current assignee: Technip France SAS
Priority date: 1979-04-27
Filing date: 1980-04-25
Publication date: 1980-12-17
Also published as: NO153619C; FR2455235B1; NL187653B; NO801220L; NL8002436A; NO153619B; GB2049094B; NL187653C; FR2455235A1; BR8002556A

Abstract

An apparatus for burying flexible pipelines or cables in the sea bed and which has on a trolley movable on the sea bed and connected to a surface ship from which the trolley is controlled and from which the pipelines to be laid are submerged, an articulated plough 8 which can be raised having a front part 11 constituting a mechanical cutting member and a rear part 12 for receiving from the top the pipeline to be laid and for guiding it to the bottom of the trench dug out by the front part during the controlled advance of the trolley, wherein a plurality of nozzles 16 permitting the injection of a pressurized fluid and in particular water is provided on the front surface 15 of the front part of the plough which serves as a mechanical cutting member <IMAGE>

Description

SPECIFICATION Apparatus for Burying Flexible Pipelines or Cables in the Sea Bed The present invention relates to an apparatus for burying flexible pipelines or cables in the soil forming the bottom of a volume of water and in particular the sea bed. Although the invention is also applicable to other volumes of water, such as rivers or lakes, to simplify the description reference is made hereinafter to the sea bed. In the same way, the article to be buried will be called a pipeline without this term being in any way limitative.

Already, numerous apparatuses are known for submerging a pipeline and in particular a flexible pipeline as from the surface and then burying it in the sea bed, i.e. it is placed in a trench dug out for this purpose on the said bed.

In a first category of known apparatus, called jetting apparatuses, a trench is made on the sea bed by means of a movable trolley connected to a surface ship. The latter controls the trolley and the pipelines to be laid are submerged from the ship.

The trolley is equipped with arms having pressurized fluid injection nozzles, the fluid being in particular water. As a result, the soil can be dug out and the debris can be removed to the sides of the trollery.

Such apparatuses have not proved satisfactory, particularly when the sea bed is hard, being for example rock. Moreover, with such apparatuses it is not possible or is at least very difficult to control the depth of the trench and ensure that it is covered after laying the pipeline.

Another problem associated with this type of apparatus is that very high power levels are required for ensuring satisfactory cutting under the action of pressurized fluid injection. These power levels often exceed 20,000 kW.

A second category of apparatuses is known called cutting apparatuses. Such a cutting apparatus comprises a trolly which moves on the sea bed and is connected to a surface ship. An articulated plough, which can be raised has its forward part shaped so as to form a mechanical cutting member and a rear part which receives from the top the pipeline to be laid. This rear part generally also has means for internally guiding the pipeline to be laid when the latter is flexible, pressing it against the bottom of the trench dug out by the front part during the controlled advance of the trolley.

However, such apparatuses are not always satisfactory for certain types of sea bed and also cause problems in connection with the propulsion or pulling of the trolley and the control of the latter.

The object of the present invention is to provide an improved apparatus for the latter type which makes it possible to bury, with relatively low energy costs, flexible piplines and similar products, no matter what the nature of the sea bed. In addition, this can be carried out when the water is very deep, i.e. several dozen and even several hundred metres.

The apparatus according to the invention also makes it possible to simultaneously lay and bury a plurality of pipelines from a single ship. These piplines can be laid in the sea bed at depths exceeding one metre. The trench tends to become covered over as soon as burying has taken place, so that the laid piplines do not remain exposed.

The apparatus according to the invention comprises on the front face of the front part of the plough which acts as a mechanical cutting member, a plurality of nozzles making it possible to inject a pressurized fluid and in particular water.

According to a specific embodiment, the front part of the plough substantially has the shape of a prism and which has, starting from the forwardly directed edge, a substantially horizontal and planar base surface, two parallel planar lateral surfaces and a substantially planar upper frontal surface inclined by an angle of approximately 220 relative to the lower surface.

According to the invention, preferably two spaced rows of nozzles parallel to the lateral edges of the upper surface are arranged symmetrical to its longitudinal axis.

At least certain of the nozzles are arranged in such a way that the pressurized fluid jets are oriented slightly upwards by an angle of approximately 1 50 relative to the horizontal.

Advantageously, the front part of the plough has, in the extension of the inclined upper surface, a substantially vertical upper portion which has for example two nozzles, arranged substantially in accordance with the longitudinal axis of the front part of the plough. These nozzles are positioned inusuch a way that they direct the pressurized fluid jets in a substantially horizontal manner.

According to a preferred embodiment, the upper inclined surface has, at least on one part of its length in the longitudinal axis thereof, a rib with inlined side faces, on either side of which are arranged the rows of nozzles.

According to another particularly advantageous feature of the invention, in the rear part of the plough in which is ensured the' guidance and fitting of the pipeline, there is a preferably hydraulically controlled access door, laterally articulated to the top of said rear part and gives access to the pipeline when the need arises.

For this purpose, the plough is preferably raised by pivoting around its pivot pin on the trolley.

Advantageously on the upper part of the trolley, and above the rear part of the plough, a guidance chassis is provided which facilitates the introduction of the pipeline into said rear part.

According to yet another feature of the invention, pressurized fluid passage orifices are made on the lateral faces of the plough, which are able to upwardly direct the pressurized fluid away from the wall, so as to aid the release of the plough, particularly after it has been immobilised in position such that it is embedded in the ground.

The apparatus according to the invention has proved particularly suitable for laying flexible piplines or cables, such as for example flexible hydrocarbon-conveying pipelines of the type marketed in very considerable lengths by the Applicant Company, control lines, power transmission cables and telecommunications cables.

The invention is described in greater detail hereinafter relative to non-limitative embodiments and the attached drawings, wherein show: Fig. 1 diagrammatically, the burying apparatus according to the invention connected to the surface vessel.

Fig. 2 a perspective view of an apparatus according to the invention.

Fig. 3 in longitudinal elevation the apparatus according to the invention, the plough being indicated in two operating positions Fig. 4 a front elevation of the apparatus according to the invention.

Fig. 5 plan view of the apparatus.

The apparatus according to the invention, designated by the reference numeral 1 in Fig. 1 and which will be described in greater detail hereinafter, is connected to a surface ship 2 which is preferably equipped with dynamic positioning means.

The apparatus 1 according to the invention is pulled by the ship 2 by means of a towing cable 3 and is connected to the ship by at least one umbilical line 4. The latter can, for example, be of the electrohydraulic type manufactured in considerable lengths by the Applicant Company.

It is able to convey from the surface all the control fluids necessary to the operation of the apparatus and in particular the pressurized fluid to be supplied to the -nozzles of the plough, in the manner to be described hereinafter.

Ship 2 is also equipped with means, such as hoists for unreeling from the surface the pipeline 5, which is to be buried in the sea bed 6.

Although not shown in the drawing, it is to be understood that the invention makes it possible to simultaneously bury a plurality of pipelines 5 from ship 2 via the burying apparatus 1.

When the burying apparatus 1 is pulled in the direction of arrow A it makes, in the manner to be described hereinafter, a trench in the sea bed in which is placed the pipeline 5.

Reference will now be made to Figs. 2 to 5, which show in a more detailed manner the apparatus according to the invention.

This apparatus essentially comprises a trolley which can be towed and which is constituted by a metal chassis supported by two profiled hollow lateral blocks 7, preferably having a circular crosssection.

In order to adapt to the different submarine soil conditions, the blocks can be wholly or partly filled beforehand with ballasting water.

The apparatus according to the invention comprises a plough which can be raised and which is designated by the reference numeral 8, articulated relative to the trolley at 9. The pivoting movement of the plough performed by a jack 10 permits the raising thereof from a position shown by continuous lines in Fig. 3 to a position shown by broken line therein.

The plough essentially comprises a front part 11 which forms a mechanical cutting member and a rear part 12,which receives the pipeline to be laid and guides it to the bottom of the trench made by the front part 11 during the forward movement of the trolley.

As can best be seen from Figs. 2 to 4, the front part of the plough has the general shape of a prism with a substantially horizontal planar lower surface 13, two lateral surfaces 14 and an upper surface 1 5, which is inclined relative to the lower surface 13 by an angle of approximately 25 .

As can best be seen in Fig. 4, the upper inclined surface 1 5 has two parallel rows of nozzles 16, which are supplied with fluid and in particular water under a pressure which can be approximately 100 to 1 50 bars. The water supply path from line 4 is indicated by the arrows in Fig.

2. In the same way, Figs. 2 and 3 indicate the orientation of the jets from nozzles 1 6.

According to the invention, it is advantageous that the jets leaving these nozzles are inclined slightly upwards at an angle of approximately 1 50 relative to the horizontal.

The upper surface 1 5 also carries a central edge 1 7 with inclined sides arranged in the longitudinal axis of the front part 11 of the plough 8.

In accordance with the invention, nozzles and in particular two nozzles 1 8 are arranged in the longitudinal axis of an upper substantially vertical portion of front part 11 of the plough. They are supplied with pressurized fluid and arranged in such a way that the fluid jets are substantially horizontal.

According to the invention, pressurized fluid passage orifices 1 9 are provided on the lateral surfaces of plough 8, as can be seen in Fig. 3.

These orifices are positioned in such a way that the pressurized fluid jets are directed upwards and away from the corresponding walls.

According to the invention, plough 8, has in its rear part 12, a door 20, which is laterally articulated to said rear part 1 2 and above the latter in order to give access to the pipeline introduced into rear part 12.

In Fig. 5, door 20 is shown in the open position by broken lines. Hydraulic control means are provided for pivoting the door and locking it in the closed position.

According to the invention, the upper part of the trolley carries a chassis comprising a plurality of components 21, which aid the guidance and introduction of the pipline into the upper part of the plough by means of an upper shaped chute 22.

In order to permit the remote front control of the apparatus according to the invention, its operation is advantageously monitored from the surface ship by means of a television circuit.

The articulated plough 8 of the apparatus according to the invention is obviously interchangeable and its characteristics and dimensions are adapted to the conditions of use.

Experience has shown that by means of the apparatus according to the invention, it is possible to bury piplines with a speed greater than 5 m/minute. The special configuration of the front part 11 of plough 8, its special shape and the arrangement of the pressurized fluid injection nozzles 1 6 and 18 make it possible to dig a trench having a rectangular cross-section and with vertical sides ensuring a perfect laying of the pipeline, whilst the trench is rapidly covered after laying the latter.

According to the embodiment shown, the trolley has two lateral blocks and is pulled by cables. For the purposes of the invention, it is obviously possible to use other types of trolleys, such as for example those having caterpillars and those which are selfpropelling.

Although'the invention has been described and represented hereinbefore relative to specific embodiments, numerous variants are possible thereto without passing beyond the scope of the invention.

Claims

1. An apparatus for burying flexible pipelines or cables in the sea bed and which has on a trolley movable on the sea bed and connected to a surface ship from which the trolley is controlled and from which the pipelines to be laid are submerged, an articulated plough which can be raised having a front part constituting a mechanical cutting member and a rear part for receiving from the top the pipeline to be laid and for guiding it to the bottom of the trench dug out by the front part during the controlled advance of the trolley, wherein a plurality of nozzles permitting the injection of a pressurized fluid and in particular water is provided on the front surface of the front part of the plough which serves as a mechanical cutting member.

2. An apparatus according to claim 1, wherein the front part of the plough substantially has the shape of a prism and which has, starting from the forwardly directed edge, a substantially horizontal and planar base surface, two parallel planar lateral surfaces and a substantially planar upper frontal surface inclined by an angle of approximately 250 relative to the lower surface.

3. An apparatus according to claim 2, wherein it has two spaced rows of nozzles parallel to the sides of the upper surface and symmetrical with respect to its longitudinal axis.

4. An apparatus according to claim 3, wherein at least some of the nozzles are arranged in such a way that the pressurized fluid jets are directed upwards at an angle of approximately 15 relative to the horizontal.

5. An apparatus according to any one of the claims 2 to 4, wherein the front part of the plough has in the extension of its inclined upper surface a substantially vertical upper portion having nozzles, and in particular two nozzles, arranged substantially in accordance with the longitudinal axis of the front part of the plough and positioned so as to direct the pressurized fluid jets in a substantially horizontal direction.

6. An apparatus according to any one of the claims 2 to 5, wherein the inclined upper surface has over at least part of its length and in its longitudinal axis, a rib with inclined sides, on either side of which are positioned the rows of nozzles.

7. An apparatus according to any one of the preceding claims, wherein in its rear part the plough has an access door, which is preferably hydraulically controlled and laterally articulated to the top of said rear part.

8. An apparatus according to any one of the preceding claims, wherein it has a guidance chassis facilitating the introduction of the pipeline into the rear part in the upper portion of the trolley and above the rear part of the plough.

9. An apparatus according to any one of the preceding claims, wherein it has a plurality of pressurized fluid passage orifices on the side faces of the plough, said orifices being positioned in such a way that the pressurized fluid is directed upwards and away from the wall.

9.An apparatus according to any one of the preceding claims, wherein it has a guidance chassis facilitating the introduction of the pipeline into the rear part in the upper portion of the trolley and above the rear part of the plough.