FR2728598A1 - Process for protecting submarine cables, pipes on the sea-bed from anchors and other equipment - Google Patents

Abstract

The cables, pipes or any other constructions (1) follow an axis YY and run along this line on the seabed (5). Piles (7) are inserted in the seabed on either side of the construction at a minimum distance (l) from it, forming two lines (12) running parallel to the axis YY. The piles are regularly spaced and a metal cable with tensile strength (81) is attached between the piles. Cylindrical pipes or tubes being laid by a boat are protected by joining two halves of a casing around the pipe and allowing the casing to drop until it rests against the previous casing. A metal grid is tight between the respective piles in both parallel lines forming a coverage on top of the pipe.

Description

METHOD AND DEVICE FOR PROTECTING SUBMARINE WORKS
EXTENDED AND POSITIONED AT THE BOTTOM OF THE SEA
The present invention relates to a method and device for the protection of underwater works of elongated shape, and positinnnbs at the bottom of the sea.
The technical sector of the invention is the field of protection of pipes, cables or objects of similar shape against the external damage which they could suffer.

 The main application of the invention is in fact the protection, essentially of cables or conduits which can be rigid or flexible pipes or tubes, and which are not buried or which are only sufficiently tainted, which can then be 'object of shocks, tears, friction or other external damage on the one hand by anchors or other equipment trainsée towards the structure and which are partially, totally or not at all buried in or on the bottom and on the other hand by those able to look vertically, from the surface for example.

 I1 is known in fact that at sea, this term being taken in the broad sense of an expanse of water which can of course also be an ocean, a lake, a strait etc ..., near any installation of maritime exploitation such as an oil platform, also leaving a place of loading of a ship or a port, or simply a sheltered area, ships can anchor and thus remain at anchor: gold, towards or from these same sites, because of the activity which takes place there, there are often connections by cables or submerged conduits which are deposited at the bottom of the sea to connect a point of said site to another point, of the same site or of another more distant site.

 Even if the location of these connections is generally identified on nautical charts, this is often only approximately, because because during the installation there could have been course offsets and all the lines thus deposited are not not necessarily repositioned with precision; in any event, even if this were the case, ships which are at anchor often do not control their own movements, either by an involuntary wrongful maneuver, or by navigation error, or by negligence, by bad weather or any other voluntary or involuntary cause: thus, their anchor can hunt on the bottom and be dragged on it towards the said works in which it then risks knocking, rubbing and being hung up, and by its ploughshare shape being able to then provoke until the line breaks. Such risks also exist with fishing activities by trawling, anchoring of nets or others, because such zones and sites are often also favorable to the arrival of essentially light fleets of fishing boats, especially of artisanal type.

 If the attachment causes a tearing, the consequences can be catastrophic, especially for example if it is petroleum or gas pipes which will then pollute the environment and whose interruption of supply for a long period may create significant financial losses; even if it's a cable. its rupture can also greatly disrupt the operation of the installations that this cable supplied and also cause breaks in the production or operation of the site concerned.

 Even if there is no tearing and rupture, the damage caused may in any case require immediate repair or risks of subsequent rupture also requiring short-term repair. In addition, these structures can also be damaged due to falling objects vertically.

especially if this work is flexible, coite an electric cable or a flexible pipe, which can then be crushed or cut by the fall of this object.

To mitigate these risks of deterioration, the most commonly used protection to date is burial below sea level of these structures, but
- on the one hand it must be deep enough to put the latter below the maximum depth of insertion of the plowshare, which may require burial at several urethers under the sea floor, therefore costing quite expensive and difficult to guarantee in the long term, due to the displacement of the sediments
- And secondly, depending on the soil conditions of this seabed, this burial may be impossible or difficult and in any case uneconomical.

 If their burial is not or ial carried out, such works then remain unprotected or insufficiently protected.

 Various other solutions which could overcome this lack of protection could then be developed, some of which were the subject of patent applications, such as French application FR 2367243 published on May 5, 1978 on "a device for the protection of pipe- non-buried submarine lines "comprising on either side of the longitudinal axis of the pipeline, plates parallel to its axis.

fixed and articulated on a profiled sole in the form of a longitudinal gallery enveloping the pipeline; the external field of said plates resting on the seabed when the plate is in the rest position and lifting by pivoting about its axis in the event of an anchor slipping towards the pipeline, which is thus protected.

 Mention may also be made of application FR 2,595,386 published on September 11, 1987 on "a device and method for ensuring the protection of structures, in particular submerged reinforcements", which consists in surrounding the part of said structure to be protected a sheet of flexible and waterproof material to conform a hermetic envelope into which a liquid material is injected which is hardened on site and which thus provides protection of the structure.

 There is also the patent application EP 165659 published December 27, 1985 on a flexible cover consisting of an envelope comprising a plurality of segments arranged in one or more layers such that according to a plan view the structure thus produced, either in shape honeycomb and forms a protective mattress on the work.

We could cite other types of protection which have been the subject of patent applications for some but in all cases, all of these additional protections are cumbersome to implement and are placed directly on the structure and integral with it. , be very close to him. In fact, the stopping of the equipment which can attack the structure, and which must therefore take place before the displacement and / or the damage thereof, is in fact only ensured by the weight of the protective structures and their friction on the ground these therefore have a very unfavorable relationship between the amount of material used and their capacity to oppose a lateral force. They are in any case quite expensive, even if their effectiveness which is especially valid against the lateral hydrodynamic forces or the shocks of objects looking vertically vertically can be valid and moreover in case of damage, even if the structure has not been damaged in itself. this protection must nevertheless be repaired, which in general is quite difficult and costly, especially when the protection device is linked or integrated into the structure. because you also have to change it
In addition, some of these protections can only be implemented on the seabed directly during the installation of the structure or immediately after it, which makes subsequent protective installations and actions difficult. repair at a reasonable price.

 The problem posed is therefore to be able to protect such works, of elongated shape and positioned on the sea bottom against attacks by anchors or other equipment dragged on the bottom, but also for non-rigid works against the risks of crushing by shock of material that may fall vertically from these structures, and said protections must be easy to implement; moreover, even when the structure is already in place, the protection, at least against damage to equipment dragged along the bottom, must be able to be implemented, and this without having to intervene directly or to position itself exactly on 1 he structure and in all cases, the protections concerned must be of a reasonable cost and can also be repaired and maintained in a fairly easy state.

A solution to the problem posed is a method of protecting underwater works of elongated shape along a longitudinal axis
YY 'and positioned along this axis at the bottom of the sea, placed on it and / or completely or partially buried, such that
- Piles are driven into said bottom on either side and at a given minimum distance 1 from said structure, piles forming at least two lines almost parallel to the axis YY ′ of this structure and at given intervals d
- One connects, fixes and stretches at least between the piles, constituting each of the two said lines, a structural element resistant to traction.

Another objective of the present invention for the protection of flexible underwater works, of elongated and cylindrical shape, against the falling of objects vertically thereof, and which are deposited at the bottom from a ship, is achieved by a method according to the present invention, such as
- Hollow protective half-shells are assembled around said structure and before its immersion, the internal diameter of which is substantially greater than the external diameter of the structure
- said shells thus assembled are allowed to descend, along the part of the structure not laid, from the ship towards the bottom until it comes to bear against shells already lowered
- We continue the installation of said structure by unrolling it from the surface while advancing the ship and depositing on the bottom along its axis YY 'the assembly consisting of the structure and the protective shells.

 When the structure is already in place, whether rigid or flexible, its protection against falling objects vertically. can be achieved according to the present invention by a device comprising at least one trellis of cables stretched between the respective piles of the two almost parallel lines which they form and arranged above said structure already ais in place.

 The result is new methods and devices for protecting submarine structures of elongated shape and positioned at the bottom of the sea, without the drawbacks mentioned previously with regard to the protection devices existing to date, and responding to the problem posed.

 Indeed, the structural elements resistant to traction.

arranged on either side of the structure, and which can be either metallic or textile cables, or bars or tubes of steel or synthetic materials thus constitute two protective barriers which can thus stop the anchors or other equipment dragged on the bottom of the sea, such as in particular according to the example described in Figure 5 below.

 This protection can be put in place, either after the installation of the structure on the seabed, or before the installation thereof, thus avoiding any risk of damage to this structure during installation for any object lying on the bottom, since its lateral protection is then immediately effective. The implementation of this protection by piles or tie rods anchored in the bottom, can be easily carried out with known surface means and suitable for this and at a very reasonable cost, by particular directly from existing ships for burying works, which can then implement the method, the device and the means of the present invention complementary to burial when this is difficult or even impossible, and therefore without having to re-engage a ship thereafter.

 In the event of subsequent intervention on said protective devices, such as after damage caused by an anchor which is caught in the device. without of course damaging the work. it is possible to reposition other piles next to those previously fixed to consolidate the line and rest one or more structural element (s) between the piles thus added in a fairly quick and easy way, doubling and / or replacing those which would then have lost their effectiveness.But this possibility should not normally occur, because the protective device according to the invention, by its design, its resistance and its implementation, dreams if it deforms at the time of its stress, returns to its original state after it has stopped, unlike existing gravity barriers, which, once moved, no longer provide the desired protection: the devices according to the present invention can indeed be stressed several times during same place, without being redeveloped or reinforced.

 The prior tensioning of the cables or bars fixed between said piles forming the two almost parallel protective lines or barriers 9 structure, on either side of it, allows, on the one hand an almost immediate reaction efficiency of these structural elements in the event of attachment by an anchor for example, with then a very small displacement of the latter towards the structure, and on the other hand the distribution of the tensile force transmitted by said anchor to any a group of piles or tie rods.

then working simultaneously and allowing better resistance to this traction of the anchor which has thus slipped.

 With regard to the protection of cables or any flexible structure laid from the surface along a "J" curve, as shown in FIG. 5 attached, the method and the device according to the invention allow its protection against falls of possible objects from the surface, without underwater intervention, thus reducing of course the cost of the installation of this protection, while allowing an intervention afterwards in the event of repair by plunger for example, thanks to the possibility to dismantle the half-shells without intervening on the structure thus protected, other than by lifting it, for example.

One could cite other advantages of the present invention, but those mentioned above already show it sufficiently to prove its novelty and its interest.
The description and the figures below represent exemplary embodiments of the invention but are in no way limiting. Other embodiments are possible within the scope and scope of the invention, in particular for example by changing the arrangement of the connecting devices between the piles and the resistant structural elements of the protective barriers.

 Figure 1 is a perspective view of a minimum protection device of a structure according to the invention.

Figure 2 illustrates the operating principle of the device according to Figure 1
Figures 3 and 4 show other protective devices according to the invention, in addition to that of Figure 1
Figure 5 is a side view of the implementation of a device according to the invention for the protection of flexible structures against falling objects vertically.

An underwater structure 1 of elongated shape along a longitudinal axis YY ′ and which can therefore be a pipeline, a cable, a hose, etc., is positioned, either laid only, or partially or completely buried along this axis. at the bottom 5 of the sea. Its protection device according to the invention comprises at least piles or tie rods 7 forming at least two lines 12 almost parallel to the axis YY 'of said structure 1 and at given intervals d, which piles are driven into said bottom 5, and at least two lines of elements, tensile-resistant, of structure 8 each connecting at least said piles 7 constituting one of said lines 12 almost parallel, and on which said structural elements 8 are fixed and tensioned This xininu embodiment is shown in Figure 1
The insertion of said tie rods or piles 7 into the ground, as well as their dimensions and their spacing between them, are designed to resist tensile forces, such as those generated for example by a situation as shown in Figure 2. due therefore to anchors or equipment dragged on the bottom: these dimensions of the piles or tie rods are also a function of the size and geometry of these anchors or equipment, the conditions and the nature of the ground 5 itself, acceptable displacements of the barriers 81 thus formed with respect to the initial minimum distance 1 thereof relative to the structure 1 as well as the desired service life of the entire device.

These calculation criteria are also of course valid for the dimensioning and the tension or pretension of the longitudinal structural elements 81 connecting said piles 7. Such dimensions are perfectly calculable by any person skilled in the art knowing the strength of the materials from hypotheses tensile forces
T data and characteristics of the environment of the given site, which can be measured and provided elsewhere in a known manner.

The establishment in the ground by jacking, vibration, threshing, drilling, etc., of such tie rods or piles 7, then of said longitudinal structural elements 81, is also possible by any known process and implementation of installations and underwater operations.

 The connections 11 between said structural elements 81 and said piles 7, which preferably will be as level as possible with respect to the level of the seabed 5, are also preferably positioned close to this bottom, in order to lininize the bending stresses on the piles and / or tie rods 7 during traction on said protection lines 81, as shown in FIG. 2.

 Indeed, an anchor 10 thus dragged on the bottom 5 in the direction of the structure 1, meets and grips the barrier 81, located upstream thereof relative to the direction of drag 13 of the anchor, and formed by said elements 81 of longitudinal structure which then deform under the effect of the traction T, correct the force which they undergo thus by their connecting fasteners 11 to the first piles 71 situated on either side of the point of hooking these then deform under the effect of this tensile force and also communicate part of it to the following piles 72 by the continuous link 81 which connect them all together and so on the anchor 10 is thus stopped by the tensioning of the whole of the barrier, fixed to the piles or tie rods, and the device is designed so that this tensioning is immediate with a very small displacement of the anchor 10 towards 1 1 structure 1, and that 1 effort is transmitted to a group of pi them 7 or tie rods then working simultaneously.

In FIG. 2, the resistant structural elements 81 are represented inside the lines 12 formed by the piles or tie rods 7, therefore between these and the structure 1 to be protected, left in other embodiments, said structural elements 81 could be located outside the piles, also positioned at sea level 5. but also as shown in the
Figure 1 or 3, at the top of the piles or tie rods and therefore, as the case may be, slightly offset above said bottom 5. Said fasteners 11 may consist of any known element of connection between a cable and a metal structure or two metal structure elements etc ...

 On all the attached figures, the lines of layout 9 represented are only virtual lines appearing a certain mesh of spacing d between the piles along their lines 12 of establishment parallel or almost parallel to the longitudinal axis Yy ' of the structure 1 and at more or less constant distances from it but of a minimal value 1; ltaxe XX 'shown in Figure 2 9 each pile or tie is that of their establishment and anchoring in the seabed 5, as close as possible to the vertical.

According to Figure 3, the protective device according to the invention may also include at least one resistant structural element 84, stretched between two piles 7 each taken in one of the two said lines 12 almost parallel and thus forming a line crossing above of said structure 1 the 'YY axis' thereof and by multiplying such crossed lines, a couplet mesh is obtained
In another embodiment or in addition to that described in FIG. 3, the protection device can also comprise at least one trellis 82 of cables stretched between the respective piles 7 of the two almost parallel lines 12 which they drill and au- above said work 1.

 Said resistant structural elements 8 can be either.

metallic cables, either textile cables, or also bars made of rigid or semi-rigid material, such as synthetic material.

 When the structure 1 is a flexible structure of elongated shape along a longitudinal axis YY 'such as a cable or a flexible pipe, this is generally deposited in a known den on the bottom 5 of the sea 4 or in a trench made before or simultaneously, from a surface vessel 2, for example by means of a deflection pulley 6, integral with said vessel 2, making it possible to unwind said cable or flexible while advancing vessel 2 and thus allowing the laying of the cable or flexible 11 on the bottom 5.

Such a cable or flexible thus laid on the bottom. is then quite vulnerable and even with the devices described in Figures 1 to 4 above, remains exposed to falling objects possibly falling vertically thereof; in order to complete its protection against such falls, around said structure 1 and before its immersion, from said vessel 2, are assembled hollow protective half-shells 3, the internal diameter of which is substantially greater than the external diameter of the structure 1
- One lets down said shells 31 thus assembled. along the part of the structure not laid from the ship 2 towards the bottom 5 until it comes to bear against shells already lowered 32 and remaining above the bottom 5, carried by the structure around which they slide
the laying of said structure 1 is continued by unrolling it from the surface while advancing the ship 2 and the assembly consisting of the structure and the protective shells 32 is deposited on the bottom 5 along its axis YY '.

Claims (9)

 1. Method for protecting underwater works (1) of elongated shape along a longitudinal axis W 'and positioned along an axis at the bottom (5) of the sea, characterized in that  - It is driven into said bottom (5) on either side and at a given minimum distance 1 from said structure (1), piles (7) forming at least two lines (12) almost parallel to the 'YY' axis of this one and following given intervals d  - One connects, fixes and stretches at least between the piles (7) constituting each of the two said lines (12), at least one element (8) of structure resistant to traction.  2. Method for protecting flexible underwater structures (1) of elongated and cylindrical shape, according to claim 1, and such that said structure is placed on the bottom (5) from a ship (2), characterized in what  - Hollow protective shells (3) are assembled around said structure (1) and before it is immersed, whose internal diameter is substantially greater than the external diameter of the structure (1)  - Said shells (31) thus assembled are allowed to descend, along the part of the structure not laid from the ship (2) towards the bottom (5) until it comes to bear against shells already lowered (32)  - the laying of said structure (1) is continued by unrolling it from the surface while advancing the ship (2) and depositing on the bottom (5) along its axis YY 'the assembly constituted by the structure and the shells of protection (32).  3. Device for protecting sub-arine structures (1) of elongated shape along a longitudinal axis YY ', characterized in that it comprises at least piles (7) forming at least two lines (12) almost parallel to the axis YY 'of said structure (1) and at given intervals d, which piles are driven into said bottom (5), and at least two lines of elements, tensile-resistant, of structure (8) each connecting to the minus said piles (7) constituting one of said lines (12) almost parallel, and on which said structural elements (8) are fixed and tensioned.  4. Device for protecting structures under arins (1) flexible of elongate and cylindrical shape, and according to claim 3, characterized in that it comprises hollow half-shells (3) of protective ase assembled around said structure (1) and whose internal diameter is substantially greater than the external diameter of this work, which shells thus assembled are arranged one after the other along said work.  5. Protective device according to any one of claims 3 or 4, characterized in that it comprises at least one resistant structural element (84), stretched between two piles (7) each taken in one of the two said lines ( 12) almost parallel and thus forming a line crossing around said structure (1) the axis thereof.  6. Protection device according to any one of claims 3 to 5, characterized in that it comprises at least one trellis (82) of cables stretched between the piles (7) respective of the two almost parallel lines (12) which they form. and above said structure (1).  7. Protection device according to any one of claims 3 to 6, characterized in that said resistant structural elements (8) are metallic cables  8. Protection device according to any one of claims 3 to 7. characterized in that said resistant structural elements (8) are textile cables.  9. Protective device according to any one of claims 3 to 7, characterized in that said resistant structural elements (8) are bars of rigid or semi-rigid material.