EP2268887B1 - Inertia transition pipe element in particular for fixing a rigid submarine pipe - Google Patents

Description

The present invention relates to an inertial transition pipe element, more particularly intended to be assembled at the end of an underwater rigid pipe, in particular a rigid riser vertical riser type pipe.

The present invention relates more particularly to an installation of production risers for the underwater extraction of oil, gas or other soluble or fusible material or a suspension of mineral material from submerged wellheads. up to a floating support, for the development of production fields installed offshore at sea. The main and immediate application of the invention being in the field of oil production.

The floating support generally comprises anchoring means to remain in position despite the effects of currents, winds and waves. It also generally includes oil storage and processing means as well as means of unloading to removal tankers, the latter occurring at regular intervals to carry out the removal of the production. The common name of these floating supports is the Anglo-Saxon term "Floating Production Storage Offloading" (meaning "floating medium of storage, production and unloading") which we use the abbreviated term "FPSO" in the whole of the following description.

• un riser vertical constitué d'une conduite rigide en acier, dont l'extrémité inférieure est ancrée au fond de la mer par le biais d'une articulation flexible, et relié à une dite conduite reposant au fond de la mer, et l'extrémité supérieure est tendue par un flotteur immergé en subsurface auquel elle est reliée, et
• une conduite de liaison, en général une conduite de liaison flexible, entre l'extrémité supérieure dudit riser et un support flottant en surface, ladite conduite de liaison flexible prenant, le cas échéant, de par son propre poids la forme d'une courbe en chaînette plongeante, c'est-à-dire descendant largement en dessous du flotteur pour remonter ensuite jusqu'audit support flottant.

Background-to-surface bonds of an underwater pipe resting at the bottom of the sea are known, a tour-hybrid link comprising:

• a vertical riser consisting of a rigid steel pipe, whose lower end is anchored to the seabed by means of a flexible hinge, and connected to a said pipe resting at the bottom of the sea, and the end upper is stretched by a float immersed in subsurface to which it is connected, and
• a connecting pipe, generally a flexible connecting pipe, between the upper end of said riser and a floating support surface, said flexible connecting pipe taking, if appropriate, by its own weight in the form of a curve in plunging chain, that is to say, descending widely below the float and then up to said floating support.

Also known are bottom-surface connections made by going up continuously to the subsurface of the resistant and rigid conduits consisting of tubular elements of thick steel welded or screwed together, in a chain configuration with a curvature continuously variable throughout their length in suspension, commonly called "Steel Catenary Riser" (SCRs) meaning "steel riser chain" and also commonly called "catenary type rigid pipe" or "SCR type riser". Such a catenary duct may go up to the floating support surface or only to a subsurface float that tensions its upper end, which upper end is then connected to a floating support by a plunger flexible connecting pipe. Reinforced catenary risers are described in WO 03/102350 of the plaintiff.

In WO 00/49267 as a connection line between the riser, the top of which is tensioned by a float immersed on the surface and the floating support, rigid pipes of the SCR type have been proposed and the float at the top of the riser is installed at a greater distance from the surface. in particular at least 300 m from the surface, preferably at least 500 m.

In WO 00/49267 of the Applicant, there is described a multiple hybrid tower having an anchoring system with a vertical tendon consisting of either a cable or a metal bar, or a pipe stretched at its upper end by a float. The lower end of the tendon is attached to a base resting at the bottom. Said tendon comprises guiding means distributed over its entire length through which passes a plurality of said risers vertical. Said base can be placed simply on the seabed and stay in place by its own weight, or remain anchored by means of batteries or any other device to keep it in place. In WO 00/49267 , the lower end of the riser vertical is adapted to be connected to the end of a bend, movable cuff, between a high position and a low position, relative to said base, to which this cuff is suspended and associated with a means of return bringing it back up in the absence of the riser. This mobility of the bent sleeve makes it possible to absorb the length variations of the riser under the effects of temperature and pressure. At the top of the vertical riser, a stop device, integral with it, comes to rest on the support guide installed at the head of the float and thus maintains the entire riser in suspension.

The connection with the submarine pipe resting on the seabed is generally effected by a pig-shaped or S-shaped pipe portion, said S being then made in a vertical or horizontal plane, the connection with said underwater pipe being generally carried out via an automatic connector.

This embodiment comprising a plurality of risers held by a central structure comprising guide means is relatively expensive and complex to install. On the other hand, the installation must be prefabricated on the ground before being towed at sea, then once on site, cabane to be put in place. In addition, its maintenance also requires relatively high operating costs.

In addition, since crude oil travels a great distance for several kilometers, it must be provided with an extremely expensive level of insulation to, on the one hand, minimize the increase in viscosity would lead to a reduction in the hourly production of wells, and secondly to avoid the blockage of the flow by paraffin deposition, or formation of hydrates when the temperature drops to around 30-40 ° C. These last phenomena are all the more critical, especially in West Africa, that the temperature of the seabed is of the order of 4 ° C and that the crude oils are of the paraffinic type.

It is therefore desirable for the bottom-surface links to be of short lengths and thus for the bulk of the different links connected to the same floating support to be limited.

This is why it is sought to provide facilities capable of operating from the same floating support a plurality of bottom-surface links tower-hybrid compact size and simpler to install and can be manufactured at sea from a laying ship driving.

In WO 02/066786 and WO 2003/095788 Hybrid tower installations requiring the use of flexible joints between the vertical riser and the base have been described because the angular variations generated by the movements of the FPSO and by the action of the swell and the current on the pipes and the float tensioning the vertical portion of pipe, are important, reaching 5 to 10 ° and these variations prevent the use of rigid connection embedded in said base. Such flexible joints are very delicate and expensive to manufacture because they consist of stacks of elastomer layers and steel reinforcements and must withstand fatigue throughout the life of the facilities that exceeds 20-25 years or more. In addition, the presence of the float creates a voltage discontinuity at the gooseneck piece, at the interface between the substantially vertical rigid pipe and the flexible pipe in a chain configuration, which is detrimental to the overall stability at level of said interface and affects the mechanical strength of the installation.

In WO 02/103153 it has been sought to provide an installation which can be manufactured entirely on land, in particular as regards the assembly of the rigid pipes resting at the bottom of the sea and the vertical risers ensuring the bottom-surface connection. On the other hand, in WO 02/103153 , it was sought to implement an installation whose establishment at the bottom of the sea requires no flexible joint ball joint in the lower part of the tower. To do this, the underwater pipe resting at the bottom of the sea is connected to said vertical riser by a flexible pipe element held by a base resting at the bottom of the sea. The assembly of the lower end of the vertical riser and the the end of the pipe resting at the bottom of the sea, via said element of flexible pipe secured and held by said base, is pre-assembled on the ground before being towed at sea and deposited at the bottom of the sea where said base is , then, anchored. However, this embodiment has certain drawbacks because this anchoring system requires, for the towing and cabanage phase, considerable buoyancy elements to balance the weight of said base structure, and the flexible connecting elements are subjected to significant fatigue throughout the life of the facilities that reaches and exceeds 25-30 years.

In addition, in all the installations described in the prior art mentioned above, the vertical riser is tensioned by a subsurface float and the connection between the vertical riser and the floating support is done by a flexible pipe in a plunging chain configuration. whose end is connected to the upper end of said vertical riser by a gooseneck device. This mode of connection of the upper end of the vertical riser with the floating support has certain disadvantages in terms of mechanical strength, at the level of the voltage discontinuity created by the gooseneck connecting piece and, because of the tensioning of the riser vertical by a float of very large volume, the latter is subjected to the action of currents and the swell, which generates, for this type of connection, angular variations of the top of the riser, very important, these last ones reverberating at the foot of the riser, at the level of the flexible joint thus strongly solicited.

When flexible pipes are connected to rigid structures, such as an FPSO plating or a drilling platform, the flexible pipe being free to move in all directions, requires reinforcement at its connection on said rigid support. For this purpose, a variable stiffness reinforcement generally made of thermoplastic or thermosetting material is generally installed over a length of 2 to 6 m in order to improve the transition of inertia between the current portion of the flexible pipe and its embedding on said rigid support.

By "inertia" is meant here the moment of inertia of said inertial transition line element with respect to an axis perpendicular to the axis of said inertial transition conductor element, which reflects the bending stiffness in each planes perpendicular to the axis XX 'of symmetry of said pipe element, this moment of inertia being proportional to the product of the section of material by the square of its distance from said axis of the pipe element.

In the same way, when a rigid pipe suspended in the sea is connected to a fixed support, either via a flexible elastomer hinge or a flexible pipe, the rigid pipe is equipped with general of a connection flange. The end of the rigid pipe is then generally reinforced over 1-2 m or more by increasing its thickness, for example by doubling said thickness, and realizing over a length of a few meters a transition zone of shape inertia conical. Such cylindro-conical parts can be machined without difficulty on conventional lathes, but of great capacity.

• à l'extrémité la plus mince un diamètre intérieur de préférence égal à celui de ladite conduite et une épaisseur sensiblement égale à celle de ladite conduite, et
• à l'autre extrémité, un diamètre intérieur de préférence égal à celui de ladite conduite et une épaisseur 2 à 10 fois supérieure à celle de ladite conduite.

It is possible to make a recessed connection of a pipe by implementing at its end a pipe element of variable thickness forming a cylindro-conical transition piece, said part having:

• at the thinner end an inner diameter preferably equal to that of said pipe and a thickness substantially equal to that of said pipe, and
• at the other end, an inner diameter preferably equal to that of said pipe and a thickness 2 to 10 times greater than that of said pipe.

Such pieces can measure from 15 to 30m in length, the cylindrical portion extending over a length of 3-5m. These parts are however very expensive to manufacture, because they must be made using very thick pipes, but variable thicknesses, assembled together, and then machined on a very large lathe to obtain the conical shape. Such parts are very expensive to achieve, because to obtain a good result, it is necessary that the pipe assembled by welding before machining is perfectly rectilinear, and moreover the turns capable of precisely machining parts of 20 to 30m in length are difficult to find and at a very high operational cost.

In some extreme cases, the cylindro-conical transition pieces can not be made of steel, and require the use of titanium, which further increases the cost and complexity.

On the other hand, if one seeks to achieve a perfect embedding in a structure of extreme rigidity, the bending moments to be transmitted at the actual embedding are considerable and require extremely large cylindro-conical transition pieces, both in thickness in the reinforced part and in total length.

In EP-0 911482 there is described an inertial transition piece constituted by a plurality of pipe members of increasing lengths and decreasing diameters, the annular space between the various pipe elements being filled with a solid filler material.

In EP-0 911482 , the annular spaces between the different adjacent coaxial pipe elements are closed by welded steel bushings or ferrules.

This results in discontinuities in the variation of inertia of the transition piece at each upper orifice of the annular spaces closed by said bushings or ferrules made of steel, insofar as the filling material inside said annular spaces consists of another material, namely in this case cement.

In use, this inertial transition piece does not have a reliable mechanical reliability of embedding due in particular to a discontinuous variation of inertia along the part, because said part is not a cylindro-conical transition piece.

Specifically, the transition piece of EP-0 911 482 at the level of said sleeves or ferrules considerable variations in inertia, thus leading to phenomena of accelerated fatigue when said zone is subjected to repeated angular deflections throughout the life of the installations, which reaches and exceeds 20 years in Difficult conditions. In addition, the entire device as it is presented is not protected against external aggression, mainly seawater.

In the present application, "cylindro-conical" is understood to mean a part whose variation in cross-sectional diameter along its axial longitudinal direction is progressive and continuous, that is to say without discontinuity by increasing continuous from the smaller diameter end to the larger diameter end.

An object of the present invention is to provide a new type of cylindro-conical inertia transition piece capable of rigidly embedding the end of a rigid pipe, in particular on an anchoring device at the bottom of the sea. and more particularly to provide an installation that does not require the implementation flexible hinges, especially at the base of a rigid pipe rising from the seabed or riser vertical.

Another object of the invention is to provide a bottom-surface connection system with hybrid towers, compact, simple to install and can be manufactured at sea from a pipe laying vessel, but the system of anchoring is of great strength and low cost, and whose manufacturing processes and implementation of the various constituent elements are simplified and also low cost, and can be carried out at sea, also, from a ship deposit.

To do this, the present invention provides an inertia transition conduit member according to claim 1.

According to the invention, said annular space is entirely filled with the same solid filler material, preferably comprising an elastomer material, more preferably based on polyurethane, having a Shore hardness greater than or equal to A50, preferably A50 to D70, and said inertial transition element is covered with a corrosion-resistant elastomeric cover material, preferably of polyurethane type, said inertia transition terminal member having a substantially cylindrical shape. conical by its coating by said cover material.

According to the present invention, because the annular space is completely filled with the same filling material and the covering material imparts a cylindro-conical shape to the transition piece, a continuous variation of the cross-sectional diameter of the same is obtained. the piece and with the same filling material over the entire height of the transition piece, which results in a gradual and continuous variation of inertia, that is to say without discontinuity of inertia. In addition, the implementation of an elastomeric cover material provides a corrosion protection guaranteeing greater longevity to said transition piece, which is subjected to a high mechanical stress and without this protection would have reduced longevity.

It is understood that said solid filler material must have a compressive strength so as to transfer the shear forces to the higher order reinforcing element "i + 1" in a manner proportional to the deformation of a said coaxial element that it contains order "i" under the effect of a bending effort. In practice, the solid filler material must have a Poisson's ratio of 0.3 to 0.49, preferably 0.4 to 0.45.

It is understood that this type of inertial transition pipe element according to the invention is advantageous in its simplicity of manufacture and therefore much less expensive than pipe elements having a cylindro-conical transition piece of inertia constituted by a single pipe element with walls of varying thicknesses as known in the prior art.

As will be seen below, this new type of inertial transition terminal pipe element makes it possible to implement bottom-surface connection installations with the anchoring of a rigid pipe rising by rigid embedding on a base stationed at the bottom of the sea, that is to say without recourse to a flexible joint, in particular of the spherical flexible ball type.

This elastomer may be polyurethane or rubber alone or in combination with a mineral filler such as sand.

In an alternative embodiment, the solid filler material is in the form of a hydraulic binder such as cement, optionally filled with particulate material, preferably sand.

Preferably, for practical reasons of manufacture and cost, but also to increase the flexibility of the transition piece and therefore its longevity, said cover material and said filler material comprise the same elastomer material, preferably based on polyurethane .

More preferably, said solid filler material comprises a polyurethane of shore hardness A90 or A95.

In another alternative embodiment, the solid filler material comprises an elastomer loaded with particulate material, preferably sand.

• la différence entre le diamètre interne d₁ dudit élément de conduite principal et le diamètre externe D₄ dudit élément de conduite de renfort de plus grand diamètre est égale à 3 à 10 fois l'épaisseur dudit élément de conduite principale, et le nombre desdits éléments de renfort coaxiaux est n = 2 à 4, et
• la différence de longueur entre les différents éléments de conduite de renfort coaxiaux h_i-h_i+1 est sensiblement constante et égale à ${\mathrm{h}}_{\mathrm{i}}\times \frac{\mathrm{1}}{\mathrm{n}},$
  
  et
• l'espace annulaire entre deux desdits éléments de conduite D_i+1-d_i est supérieur ou égal à l'épaisseur dudit élément de conduite de plus petite épaisseur et inférieur ou égal à deux fois l'épaisseur dudit élément de conduite de plus grande épaisseur délimitant ledit espace annulaire, et
• la longueur dudit élément de conduite principale est de 10 à 50 m de préférence de 20 à 30 m et il comprend 2 ou 3 desdits éléments de renfort coaxiaux.

According to other more particular features of an inertial transition conductor element according to the present invention:

• the difference between the inner diameter d _{1 of} said main pipe element and the outer diameter D _{4 of} said larger diameter pipe element is 3 to 10 times the thickness of said main pipe element, and the number of said pipe elements coaxial reinforcement is n = 2 to 4, and
• the difference in length between the various coaxial reinforcing pipe elements h _i -h _{i + 1} is substantially constant and equal to ${\mathrm{h}}_{\mathrm{i}}\times \frac{\mathrm{1}}{\mathrm{not}},$
  
  and
• the annular space between two of said pipe elements D _{i + 1} -d _i is greater than or equal to the thickness of said pipe element of smaller thickness and less than or equal to twice the thickness of said pipe element of larger thickness delimiting said annular space, and
• the length of said main pipe element is 10 to 50 m, preferably 20 to 30 m, and it comprises 2 or 3 of said coaxial reinforcing elements.

In other words, it is understood that the difference in step height of a coaxial pipe element to the other that it contains or that it covers is substantially constant.

In a particular embodiment, the various elements of coaxial main pipe and reinforcing pipe are fixed to the same bottom plate consisting of a first fastening flange able to allow its leaktight connection to a second fastening flange at the end of the pipe. a terminal rigid pipe element of another rigid pipe.

Preferably, said main pipe elements and coaxial reinforcing pipe elements each consist of all or part of a standard unitary element of standard pipe, in particular underwater pipe made of steel, or each consist of several unitary driving elements. standard assembled end to end and preferably, held coaxially by centering wedges 18 regularly distributed along their longitudinal direction and on their circular section in their annular spaces.

The present invention also provides an underwater rigid pipe, preferably a bottom-to-surface bond line, having at one of its ends an inertia transition pipe member, said main pipe member preferably having a thickness greater than or equal to that of said underwater rigid pipe, and a substantially identical inner diameter.

More particularly, the pipe according to the invention, for its connection to equipment of stiffness greater than that of said rigid pipe.

More particularly, said upper stiffness equipment consists of a pipe connection element preferably comprising a fixing flange, said equipment being located at a base resting at the bottom of the sea, or the side of a floating support or buoy on the surface or subsurface.

1. a) au moins une conduite rigide comprenant à une extrémité un élément de conduite de transition d'inertie selon l'invention, ladite conduite rigide étant une conduite montante, sensiblement verticale, dénommée riser vertical, fixée à son extrémité inférieure à un dispositif d'ancrage au fond de mer, et
2. b) au moins une conduite de liaison flexible (assurant la liaison entre un support flottant et l'extrémité supérieure dudit riser vertical, caractérisée en ce que :
   1. 1/ une extrémité de ladite conduite flexible est directement raccordée, de préférence par un système de brides, à l'extrémité supérieure dudit riser vertical, une partie terminale de la conduite flexible, du coté de sa jonction à l'extrémité supérieure dudit riser, présentant une flottabilité positive, et au moins la partie supérieure dudit riser vertical présentant également une flottabilité positive, de sorte que les flottabilités positives de ladite partie terminale de la conduite flexible et de ladite partie supérieure dudit riser vertical permettent le tensionnement dudit riser en position sensiblement verticale et l'alignement ou la continuité de courbure entre l'extrémité de ladite partie terminale de la conduite flexible et la partie supérieure dudit riser vertical au niveau de leur raccordement, et
   2. 2/ l'extrémité inférieure dudit riser vertical comprend un dit élément de conduite terminal selon l'invention formant une pièce de transition d'inertie dont la variation de l'inertie est telle que l'inertie dudit élément de conduite terminal, à son extrémité supérieure, soit sensiblement identique à celle de l'élément de conduite de la partie courante du riser vertical auquel elle est reliée, ladite inertie de l'élément de conduite terminal augmentant progressivement jusqu'à l'extrémité inférieure de ladite pièce de transition d'inertie, comprenant une première bride de fixation permettant l'encastrement de l'extrémité inférieure dudit riser vertical au niveau dudit dispositif d'ancrage au fond de la mer.

The present invention also provides a bottom-surface bonding facility, particularly at a greater depth of more than 1000 m, comprising:

1. a) at least one rigid pipe comprising at one end an inertial transition pipe element according to the invention, said rigid pipe being a rising pipe, substantially vertical, called riser vertical, fixed at its lower end to a device of anchorage to the seabed, and
2. b) at least one flexible connection line (connecting a floating support to the upper end of said vertical riser, characterized in that:
   1. 1 / an end of said flexible pipe is directly connected, preferably by a system of flanges, to the upper end of said vertical riser, an end portion of the flexible pipe, on the side of its junction at the upper end of said riser, having a positive buoyancy, and at least the upper part said vertical riser also having a positive buoyancy, so that the positive buoyancy of said end portion of the flexible pipe and said upper portion of said vertical riser allow the tensioning of said riser in a substantially vertical position and the alignment or continuity of curvature between the end of said end portion of the flexible pipe and the upper portion of said vertical riser at their connection, and
   2. 2 / the lower end of said vertical riser comprises a said terminal pipe element according to the invention forming an inertial transition piece whose variation of inertia is such that the inertia of said terminal pipe element at its end higher, that is substantially identical to that of the pipe element of the running part of the riser to which it is connected, said inertia of the terminal pipe element gradually increasing to the lower end of said transition piece of inertia, comprising a first fixing flange for embedding the lower end of said vertical riser at said anchoring device at the bottom of the sea.

The term "vertical riser" is used here to account for the theoretical position of the riser when the riser is at rest, provided that the riser axis can know angular movements with respect to the vertical and move in a cone. angle α whose apex corresponds to the point of attachment of the lower end of the riser on said base.

"Continuity of curvature" between the upper end of the vertical riser and the hose having a positive buoyancy, means that said curvature does not present any singular point, such as a sudden variation of angle of inclination of its tangent or a point inflection.

Preferably, the slope of the curve formed by the flexible pipe is such that the inclination of its tangent with respect to the axis Z ₁ Z ' ₁ of the upper portion of said vertical riser increases continuously and progressively from the point of connection between the upper end of the vertical riser and the end of said end portion of flexible pipe of positive buoyancy, without point of inflection and without inversion point of curvature.

The installation according to the present invention therefore makes it possible to prevent the tensioning of the vertical riser by a surface or subsurface float, at which its upper end would be suspended, on the one hand, and, on the other hand, to avoid the connection to said plunging flexible pipe via a gooseneck device, as used in the prior art. This not only results in greater intrinsic reliability in terms of mechanical strength over time of the connection between the vertical riser and the flexible pipe, because the gooseneck devices are fragile. But above all, this type of installation confers increased stability in terms of angular variation (γ) of the angle of excursion of the upper end of the vertical riser with respect to a theoretical position of vertical rest, because this angular variation is reduced in practice to a maximum angle not exceeding 5 °, in practice of the order of 1 to 4 ° with the installation according to the invention, whereas, in the embodiments of the prior art, the angular excursion could reach 5 to 10 ° or more.

Another advantage of the present invention is that, because of this small angular variation of the upper end of the vertical riser, it is possible to implement, at its lower end, a rigid recess on a base resting at the bottom of the sea, without having recourse to a part of transition of inertia of dimension too important and thus too expensive. It is therefore possible to avoid the implementation of a flexible hinge, in particular of the spherical flexible ball type, as long as the junction between the lower end of the riser and said recess comprises an inertia transition piece.

The positive buoyancy of the riser and the flexible pipe can be made in known manner by coaxial peripheral floats surrounding said pipes, or, preferably, as regards the rigid pipe of the vertical riser, a positive buoyancy material coating. , preferably also constituting an insulating material, such as syntactic foam, in the form of a shell enclosing said pipe. Such buoyancy elements resistant to very high pressures, that is to say at pressures of about 10 MPa per 1000 m of water are known to those skilled in the art and are available from the Company. BALMORAL (UK).

More particularly, said flexible pipe has a positive buoyancy over a length corresponding to 30 to 60%, of its total length, preferably about half of the total length of the flexible pipe, so that the flexible pipe has an S configuration, with a first flexible pipe portion on the side of said floating support having a concave warp of plunging chain-shaped chain and the remaining terminal portion of said flexible pipe having a convex chain curvature inverted by its positive buoyancy, the end of said end portion of flexible pipe, at the upper end of said riser being located above and substantially in alignment with the axis Z ₁ Z ' _{1 of} said riser at its upper end.

The portion of plunging flexible pipe, that is to say, negative buoyancy may be even shorter than the anchoring of the floating support surface is steep.

• ledit riser vertical est relié à son extrémité inférieure à au moins une conduite reposant au fond de la mer, et
• ledit dispositif d'ancrage comprend un dispositif de support et de raccordement fixé sur une embase posée et ancrée au fond de la mer, et
• ladite conduite reposant au fond de la mer comprend un premier élément de conduite rigide terminal solidaire de ladite embase reposant au fond de la mer et ledit premier élément de conduite terminal est maintenu fixement par rapport à ladite embase, avec, à son extrémité, une première partie d'élément de raccordement, de préférence un élément mâle ou femelle d'un connecteur automatique, et
• ladite première bride de fixation à l'extrémité inférieure de ladite pièce de transition d'inertie est fixée à une deuxième bride de fixation à l'extrémité d'un deuxième élément de conduite rigide coudé, solidaire dudit dispositif de support et de raccordement fixé sur ladite embase et supportant, de façon fixe et rigide, ledit deuxième élément de conduite rigide coudé, dont l'autre extrémité comprend une deuxième partie d'élément de raccordement complémentaire de ladite première partie d'élément de raccordement et raccordée à celle-ci lorsque ledit élément de support et de raccordement est fixé à ladite embase.

In a preferred embodiment of a bottom-surface connection plant, the latter comprises the following features, according to which:

• said vertical riser is connected at its lower end to at least one pipe resting at the bottom of the sea, and
• said anchoring device comprises a support and connection device fixed on a base stationed and anchored to the bottom of the sea, and
• said pipe lying at the bottom of the sea comprises a first terminal rigid pipe element integral with said base resting at the bottom of the sea and said first terminal pipe element is held fixed relative to said base, with at its end a first connecting element part, preferably a male or female element of an automatic connector, and
• said first fastening flange at the lower end of said inertial transition piece is attached to a second fastening flange at the end of a second bent rigid pipe member secured to said support and connecting device attached to said base and rigidly and rigidly supporting said second bent rigid pipe element, the other end of which comprises a second connecting element part complementary to and connected to said first connecting element part when said support and connection member is attached to said base.

It will be understood that the static geometry of said first rigid pipe element terminating said pipe lying at the bottom of the sea, with respect to said base, and the static geometry of said second rigid pipe element bent, with respect to said support and connection device. fixed to said base, allow to position the respective ends of said first and second rigid pipe members, so as to facilitate the connection of the complementary parts of automatic connectors once the support device is connected is fixed to said base.

• ladite embase est ancrée au fond de la mer par un premier pieu tubulaire passant à travers un orifice traversant de ladite embase, ledit premier pieu étant enfoncé dans le sol au fond de la mer, et sa partie supérieure coopérant avec l'embase de manière à permettre l'ancrage de ladite embase, et
• ledit dispositif de support et raccordement supportant ledit deuxième d'élément de conduite rigide coudé comporte un deuxième pieu tubulaire, dénommé insert tubulaire d'ancrage, inséré à l'intérieur dudit premier pieu tubulaire d'ancrage de ladite embase, ladite embase comprenant un dispositif de blocage retenant ledit insert tubulaire d'ancrage à l'intérieur dudit premier pieu tubulaire en cas de traction dudit deuxième pieu tubulaire vers le haut.

More preferably, the bottom-surface bonding plant has the characteristics that:

• said base is anchored to the sea floor by a first tubular pile passing through a through orifice of said base, said first pile being driven into the ground at the bottom of the sea, and its upper part cooperating with the base so as to allow the anchoring of said base, and
• said support and connection device supporting said second bent rigid pipe element comprises a second tubular pile, called tubular anchoring insert, inserted inside said first tubular anchoring pile of said base, said base comprising a device locking member retaining said tubular anchoring insert inside said first tubular pile in case of pulling said second tubular pile upwards.

Preferably, said first and second piles are assemblies of standard unitary elements of rigid pipes or unitary unit portions of rigid pipes, said second pile being shorter than said first pile.

This anchoring system of the base and fixing said support device and connection, at the lower end of said inertial transition piece on said base, is particularly advantageous for the following reasons.

Firstly, the combination of the first pile and the tubular anchoring insert constitutes a guide system, which makes it possible to make said first connecting element parts and the second end connecting element part coincide with each other. on the one hand, the terminal pipe element of the sea-bottom pipe which is fixedly positioned with respect to said base, and, on the other hand, the end of said rigid pipe element fixedly positioned relative to said support device.

The transverse forces or shear forces resulting from the bending moment occurring at the seabed, at the level of the recess of the lower end of the vertical riser at said base, resulting from the angular variations of the riser at its end superior, are not transmitted to said base but first anchor pile, which extends deep to the seabed over a length of 30 to 70 m. Thus it is possible to implement a said base of relatively small volume and weight, which can be lowered relatively easily from the surface, integral with said first end pipe element of the pipe resting at the bottom of the sea.

More particularly, said tubular anchoring insert is positioned in the axis of said inertia transition piece and said second rigid pipe member supported by said support and connecting device is curved or bent so that said first automatic connector-type connection member portion is laterally disengaged from the remainder of said support and connection device, and said second connector-type connector element automatically at the end of said first rigid terminal conduit element of said pipe resting at the bottom of the sea, integral with said base, is also disengaged with respect to the orifice of said base and with respect to said support device and connection of which said anchoring insert is inserted inside said first anchor pile.

In this embodiment, said first end pipe element of said pipe resting at the bottom of the sea may preferably also be bent or bent to coincide with the end of said second bent rigid pipe member and allow a connection easy by a submarine robot type ROV at the bottom of the sea

1. 1/- on descend, au fond de la mer, un dit dispositif d'ancrage, et
2. 2/- on descend une conduite rigide formant un riser vertical, directement fixée, à son extrémité supérieure, à une extrémité de ladite conduite flexible présentant une portion terminale de flottabilité positive, l'autre extrémité de ladite conduite flexible étant suspendue à un flotteur en subsurface, et
3. 3/- on fixe l'extrémité inférieure de ladite pièce de transition par encastrement au niveau dudit dispositif d'ancrage, et
4. 4/- on déplace l'extrémité de ladite conduite flexible suspendue audit flotteur et on la fixe ou relie à un dit support flottant.

The present invention therefore also provides a process for placing at the bottom of the sea a bottom-surface connection installation according to the invention, comprising the following successive stages in which:

1. 1 / - one descends, at the bottom of the sea, a said anchoring device, and
2. 2 / - down a rigid pipe forming a vertical riser, directly fixed, at its upper end, to one end of said flexible pipe having a positive buoyancy end portion, the other end of said flexible pipe being suspended from a float in subsurface, and
3. 3 / - the lower end of said transition piece is fixed by embedding at said anchoring device, and
4. 4 / - the end of said flexible pipe suspended from said float is moved and fixed or connected to a said floating support.

1. 1/- on descend, au fond de la mer, une dite embase solidaire d'un dit premier élément de conduite rigide, ladite embase comprenant un orifice traversant, et
2. 2/- on descend au fond de la mer un dit premier pieu tubulaire d'ancrage que l'on enfonce au fond de la mer à travers ledit orifice de l'embase, pour ancrer ladite embase au fond de la mer, et
3. 3/- on descend au fond de la mer, depuis un navire de surface, ladite conduite rigide constituant ledit riser vertical, directement fixée à son extrémité supérieure à une dite conduite flexible, ladite pièce de transition à l'extrémité inférieure dudit riser étant fixée à un dit dispositif de support et de raccordement, supportant un dit deuxième élément de conduite rigide coudé ainsi qu'un dit insert d'ancrage, et
4. 4/- on fixe ledit dispositif de support et de raccordement sur ladite embase en insérant ledit insert d'ancrage à l'intérieur dudit premier pieu tubulaire, et
5. 5/- de préférence, on verrouille ledit insert d'ancrage à l'intérieur dudit premier pieu tubulaire à l'aide d'un dispositif de blocage, et
6. 6/- on réalise le raccordement desdits premier élément de conduite rigide coudé et deuxième élément de conduite rigide coudé, et
7. 7/- on finit de descendre ladite conduite flexible présentant une portion terminale de flottabilité positive, avec l'autre extrémité de ladite conduite flexible suspendue à un flotteur en subsurface, et
8. 8/- on déplace puis on fixe ou relie l'autre extrémité de ladite conduite flexible à un dit support flottant.

Preferably, a method of setting up a bottom-surface connection installation according to the invention comprises the following successive stages in which:

1. 1 / - descends, at the bottom of the sea, a said base integral with a said first rigid pipe element, said base comprising a through orifice, and
2. 2 / - it descends to the bottom of the sea said first tubular anchoring stake that is pressed to the bottom of the sea through said orifice of the base, to anchor said base to the bottom of the sea, and
3. 3 / - it descends to the bottom of the sea, from a surface vessel, said rigid pipe constituting said vertical riser, directly fixed at its upper end to a said flexible pipe, said transition piece at the lower end of said riser being fixed a said support and connection device, supporting a said second bent rigid pipe element and a said anchoring insert, and
4. 4 / - fixing said support device and connection to said base by inserting said anchoring insert inside said first tubular pile, and
5. 5 / - preferably, said anchoring insert is locked inside said first tubular pile with the aid of a locking device, and
6. 6 / - the connection of said first rigid elbow pipe element and second rigid elbow pipe element, and
7. 7 / - one ends up down said flexible pipe having a terminal portion of positive buoyancy, with the other end of said flexible pipe suspended from a subsurface float, and
8. 8 / - it moves and then fixes or connects the other end of said flexible pipe to a said floating support.

This process according to the invention is particularly simple and therefore advantageous to set up. This simplicity results from the fact that the anchoring function on said base is filled by said anchoring insert, on the underside of said support and connection device, and that the bending moments experienced by the inertia transition piece are taken by the first anchoring pile driven to the bottom of the sea and not by said base, so that it is possible to implement a relatively low weight and low volume base.

• la figure 1 est une vue de côté d'une installation de liaison fond-surface 1 selon l'invention comportant une conduite rigide 9 de type Riser encastrée en partie basse dans un premier pieu 6 traversant une embase 4 et reliée à son extrémité supérieure 9b à une conduite flexible 10 flottante sur une partie terminale 10a de sa longueur, l'autre extrémité de la conduite étant reliée à un FPSO ("Floating Production Storage Offloading") 12,
• la figure 2A est une vue de côté de l'installation de la liaison fond-surface dans son embase en cours de mise en place à partir d'un navire de travail 20,
• la figure 2B est une vue de côté de la mise en place d'un dit premier pieu d'ancrage 6 dans une embase supportant l'extrémité d'un conduite sous-marine reposant sur le fond de la mer,
• la figure 2C est une vue de côté de l'extrémité inférieure du riser 9 avec une pièce de transition d'inertie 8 au niveau de son raccordement avec un dispositif de support et de raccordement 5 comprenant un insert tubulaire d'ancrage 5e à l'intérieur dudit pieu d'ancrage 6,
• la figure 3 est une vue de côté de l'installation de la liaison fond-surface, en cours de mise en place, après engagement de l'insert d'ancrage 5e dans le pieu d'ancrage 6,
• les figures 3A et 3B représentent en vue de côté et en coupe deux variantes d'embase du raccordement à une conduite reposant au fond de la mer d'une installation de liaison fond-surface selon l'invention,
• la figure 4 est une vue en coupe et en vue de côté d'une pièce de transition 8 massive en acier, de forme conique, installée à l'extrémité inférieure du riser 9,
• les figures 5A-5B-5C sont des vues en coupe et en vue de côté, d'une version préférée de réalisation d'une pièce de transition constituée d'empilements de conduites acier coaxiales, les interstices étant remplis de matériaux élastomères sur les figures 5B et 5C,
• la figure 6 est un diagramme illustrant la variation de l'inertie des pièces de transition selon la figure 5C.
• la figure 7 est une vue de côté d'une liaison en sub-surface en configuration de W entre un FPSO et une bouée de déchargement, comportant à chacune de ses extrémités une pièce de transition selon l'invention.

Other features and advantages of the present invention will become more apparent in the light of the detailed description which follows, given in an illustrative and nonlimiting manner, with reference to the drawings in which:

• the figure 1 is a side view of a bottom-surface connection installation 1 according to the invention comprising a rigid pipe 9 Riser type recessed at the bottom in a first pile 6 through a base 4 and connected at its upper end 9b to a pipe floating hose 10a on an end portion 10a of its length, the other end of the pipe being connected to a FPSO (Floating Production Storage Offloading) 12,
• the Figure 2A is a side view of the installation of the bottom-surface connection in its base being set up from a work vessel 20,
• the Figure 2B is a side view of the establishment of a said first anchoring pile 6 in a base supporting the end of an underwater pipe resting on the seabed,
• the Figure 2C is a side view of the lower end of the riser 9 with an inertia transition piece 8 at its connection with a support and connection device 5 comprising a tubular anchoring insert 5e inside said pile anchor 6,
• the figure 3 is a side view of the installation of the bottom-surface connection, in the course of being put in place, after engagement of the anchoring insert 5e in the anchoring pile 6,
• the Figures 3A and 3B show in side view and in section two base variants of the connection to a pipe resting at the bottom of the sea of a bottom-surface connection installation according to the invention,
• the figure 4 is a sectional and side view of a solid conical steel transition piece 8 installed at the lower end of the riser 9,
• the Figures 5A-5B-5C are views in section and in side view, of a preferred embodiment of a transition piece consisting of stacks of coaxial steel pipes, the interstices being filled with elastomeric materials on the Figures 5B and 5C ,
• the figure 6 is a diagram illustrating the variation of the inertia of the transition pieces according to the Figure 5C .
• the figure 7 is a side view of a sub-surface connection in W configuration between an FPSO and an unloading buoy, having at each of its ends a transition piece according to the invention.

On the figure 7 there is shown in side view an FPSO 12 connected to an unloading buoy 12b by a crude oil export pipe 12c consisting of a rigid steel pipe of large diameter, said steel pipe being equipped with each of its ends of a transition piece 8 according to the invention. Such transition pieces 8 are advantageously used at the ends of the rigid pipes 12c when they are secured to a pipe connection element 13, preferably having a fastening flange or any other equipment of stiffness greater than that of the pipe. rigid 12c.

In the figure 1 there is shown a bottom-surface connection facility 1 connecting an underwater line 2 resting on the seabed 3 to a floating support type FPSO 12 surface moored by anchor lines 12a.

1. a) une conduite flexible 10 comprenant une première partie 10b concave qui s'étend depuis l'extrémité 10e de la conduite flexible fixée au support flottant 12 jusqu'à environ la moitié de la conduite flexible sous forme d'une configuration en chaînette plongeante de par sa flottabilité négative jusqu'à un point d'inflexion en 10d sensiblement à la moitié de longueur de la conduite flexible, la partie terminale 10a s'étendant depuis le point central d'inflexion 10d jusqu'à l'extrémité 10c de la conduite flexible présentant une flottabilité positive de par une pluralité de flotteurs 10f de préférence régulièrement espacés le long et autour de ladite portion terminale 10a de conduite flexible, et
2. b) une conduite rigide montante en acier 9 ou « riser vertical » équipée de moyens de flottabilité, non représentés, tels des demi-coquilles de mousse syntactique réparties de préférence de manière uniforme sur tout ou partie de la longueur de ladite conduite rigide, et comprenant à son extrémité inférieure une pièce de transition d'inertie 8 équipé d'une première bride de fixation 9a à son extrémité inférieure. La première bride de fixation 9a est fixée sur une deuxième bride de fixation 5a constituant la partie supérieure d'un dispositif de support et de raccordement 5, lui-même ancré sur le premier pieu 6 solidaire de l'embase 4 reposant au fond de la mer, ledit dispositif de support et raccordement 5 permettant le raccordement de l'extrémité inférieure du riser 9 à une conduite 2 reposant au fond de la mer, comme explicité ci-après.

An installation according to the invention comprises from the support 12 on the surface to a base 4 at the bottom of the sea, the following elements:

1. a) a flexible pipe 10 comprising a first concave portion 10b which extends from the end 10e of the flexible pipe attached to the floating support 12 to about half of the flexible pipe in the form of a plunging chain configuration of by its negative buoyancy up to a point of inflection at 10d substantially at half the length of the flexible pipe, the end portion 10a extending from the central point of inflection 10d to the end 10c of the pipe hose having a positive buoyancy from a plurality of floats 10f preferably evenly spaced along and around said end portion 10a of flexible pipe, and
2. b) a rigid steel riser pipe 9 or "riser vertical" equipped with buoyancy means, not shown, such half-shells of syntactic foam preferably distributed uniformly over all or part of the length of said rigid pipe, and comprising at its lower end an inertia transition piece 8 equipped with a first fastening flange 9a at its lower end. The first fastening flange 9a is fixed on a second fastening flange 5a constituting the upper part of a support device and connection 5, itself anchored on the first pile 6 secured to the base 4 resting at the bottom of the sea, said support device and connection 5 for connecting the lower end of the riser 9 to a pipe 2 resting at bottom of the sea, as explained below.

The flexible pipe has a variation of continuous curvature, first concave in the plunge chain configuration portion 10b, and then convex in the positive buoyancy end portion 10a with an inflection point 10d between the two, thereby forming an S disposed in a substantially vertical plane.

In operation, as shown on the figure 1 when the upper part of the rigid pipe 9 is inclined at an inclination γ relative to the vertical ZZ ', the end 10c of the end portion of the positive buoyancy 10a of the flexible pipe remains substantially in the axial alignment Z' ₁ Z 'of the upper end 9b of the rigid pipe 9, and in any case in continuity of curvature therewith. This confers a better mechanical strength to the sealed fastener 11 between the two pipes and avoids the implementation of a gooseneck device as implemented in the prior art.

The advantage of this flexible pipe is to allow its initial portion 10b plunging to dampen the excursions of the floating supports 12 so as to stabilize the end 10c of the flexible pipe connected to a rigid rising vertical riser pipe 1.

The end of the portion of the floating end portion 10c of the flexible pipe carries a first fastening flange member 11 with the upper end of a rigid pipe extending from the seabed recessed at a base 4 resting at the bottom of the sea.

The vertical riser 9 is "tensioned" on the one hand by the buoyancy of the end portion 10a of the flexible pipe, but on the other hand and especially by floats regularly distributed at least on the part 9b, preferably, all along the rigid pipe, particularly in the form of syntactic foam advantageously acting as both an insulation and buoyancy system. These floats and this syntactic foam can be distributed along and around the rigid pipe over its entire length or, preferably, only on a portion of its upper part.

Thus, if the base 4 is at a depth of 2500 meters, it can be limited to coating the rigid pipe 1 of syntactic foam over a length of 1000 m from its upper end, which allows to implement a syntactic foam that must withstand less pressure than if it had to withstand pressures up to 2500 m, and therefore a radically reduced cost compared to a syntactic foam to withstand said depth of 2500 m.

The rigid pipe 1 according to the invention is therefore "tensioned" without implementation of a float surface or sub-surface as in the prior art, which limits the effects of the current and the swell, and thus drastically reduces the excursion of the upper part of the vertical riser and therefore the efforts in the foot of riser at the level of the embedding.

The fastening flange system 11 between the upper end of the vertical riser 9 and the flexible pipe 10, and the connection of the fastening flanges 9a, 5a between the lower end to the inertia transition piece 8 and the device of FIG. connection support 5, provide sealed connections between the relevant conduits.

The base 4 resting at the bottom of the sea supports a first terminal conductor element 2a angled or curved of said pipe resting at the bottom of the sea 2. This first curved or curved terminal conductor element 2a has at its end a first male part or female of an automatic connector 7b, which is disengaged laterally with respect to a through-orifice 4a of said base, but positioned in a fixed manner and determined with respect to the axis ZZ 'of said orifice.

The support and connection device 5 supports a second rigid elbow pipe element 5b having at its upper end said second attachment flange 5a and at its lower end a second female or male part of an automatic connector 7a, complementary to Part 7b.

A first tubular anchoring pile 6 is lowered from an installation vessel 20 on the surface, then depressed, preferably beaten in known manner, through an orifice 4a vertically traversing from one end to the base 4 until a peripheral protuberance 6a at the upper end of said first pile 6 comes to cooperate with a complementary shape 4c in the upper part of said orifice 4a of the base. The orifice 4a is slightly larger than the first pile 6 to let it slide freely. And when the threshing of said first pile is completed, the base 4 is thus nailed to the ground without being able to move laterally or pivot around any horizontal axis.

Optionally, a plurality of orifices and said first piles 6 are provided.

In the method of setting up a bottom-surface connection installation according to the invention, the first step consists in descending to the bottom of the sea from the surface, said base equipped with said first terminal pipe element 2a of the resting pipe. at the bottom of the sea. After anchoring said base by a said first pile 6, anchoring of the transition piece 8 is carried out at the lower end of the vertical riser by attachment to the support and connection device 5, which is even anchored on said base, thus forming a rigid recess of the lower end of the vertical riser.

The support and connecting device 5 consists of elements of rigid and stiffening structure 5c supporting said second fastening flange 5a and said second rigid bent pipe element 5b, said rigid structure elements 5c assuring also the connection between said second fastening flange 5a and a lower plate 5d supporting on the underside a second tubular pile 5e called tubular anchoring insert.

When the base 4 is anchored to the bottom of the sea 3 as shown on the Figure 2A the various surface-to-surface connection elements are manufactured on board the surface vessel 20, in particular assembling the rakes consisting of a plurality of standard pipe elements, which are progressively lowered. First of all, said device 5 is connected in a sealed manner to the lower end of the vertical riser 9 via the conical transition piece 8, then the entire vertical riser equipped with its buoyancy elements, and finally the flexible connecting pipe equipped with its buoyancy elements fixed in direct continuity with the upper end of the vertical riser 9.

The assembly and the laying of the rigid pipe 9 are conventionally made from the ship 20 by assembling unit pipe elements or reams of unitary elements stored on the surface vessel 20, and descended as and when a technique known to those skilled in the art and described in particular in previous patent applications in the name of the applicant, from a laying ship in J.

When all of the rigid pipe 9 has been manufactured and lowered to the seabed, is connected in known manner, for example by means of flanges 11 the upper end of the pipe 9 at the end of a flexible pipe 10, which as it deviates from the laying ship 20 is first in vertical form as shown in FIG. Figure 2A in that it is made floating at least in its end portion 10a by the buoyancy elements 10f evenly distributed over the end portion 10a.

It will also be noted that the rigid steel pipe 9 may be in a known manner a Pipe-in-Pipe type pipe comprising a insulation system in the annular space between the two coaxial pipes constituting the riser 9 and further an insulation system such as syntactic foam acting as buoyancy system as described above.

When the lower end of the tubular anchoring insert 5e, preferably having a slightly conical shape 5f is positioned close to and in line with the orifice 4a of the base 4, it is advantageous to direct said tubular insert anchoring 5th, more precisely thanks to an automatic submarine or "ROV" 20a piloted from the surface. Said tubular insert 5e of length 10 to 15 m then returns naturally by its own weight in said first tubular anchoring pile driven to the bottom of the sea to a depth of 30 to 70 m.

The external diameter of the tubular anchoring insert 5e may be slightly smaller than the internal diameter of the first pile 6, for example less than 5 cm, which facilitates guiding the tubular insert 5 inside said first pile 6 , while preventing transverse movements in a horizontal plane once the tubular insert 5 is fully inserted as shown in FIG. figure 3 .

At this moment, a latch 4b shown in the retracted position on the Figure 2A is moved to the engaged position as on the figures 1 and 3 so as to block the upper plate 5d of the tubular insert 5e, inside said first pile 6, thus preventing any upward movement of the bottom-surface connection assembly 1 which is recessed via of the connecting support device 5 in the first pile 6 integral with said base 4.

After engaging the latch 4b, the turning of the flexible pipe is terminated as shown in FIG. figure 3 and connecting the upper end of the flexible pipe to a sub-surface temporary buoy 21, itself connected to a dead body 21b resting at the bottom of the sea by a cable 21a.

By doing so, it is advantageous to pre-install the entire bottom-surface connection 1 before the introduction of the FPSO 12, which greatly facilitates operations.

Once the floating support 12 is positioned on the surface, the end 10e of the flexible pipe 10 is recovered which is then connected to said floating support FPSO 12 as shown in FIG. figure 1 , and the provisional buoy 21 is recovered as well as its dead body 21b and its anchoring cable 21a.

The tubular insert 5e transmits to said first tubular pile 6, the bending moments due to the cutting and transverse forces experienced at the recess of the part 8 on the device 5.

The fixing system of the upper end of the rigid pipe 9 with the flexible pipe 10 and the tensioning of said pipes gives greater stability to the upper end of the rigid pipe 9 with an angular variation γ not exceeding in operation the 5 ° C.

Thus, it has been possible according to the present invention to achieve a rigid embedding of the lower end of the rigid steel pipe 9 on the base 4 with the connecting support device 5. To do this, the lower end pipe element of the rigid pipe 9 comprises a conical transition piece 8 whose inertia in cross section increases progressively from a value substantially identical to the inertia of the pipe element of the riser 9 to which it is connected, in the tapered upper part of the transition piece 8, to a value 3 to 10 times greater than the level of its lower part connected to said first attachment flange 9a. The coefficient of variation of inertia essentially depends on the bending moment that the vertical riser must bear at said transition piece, said moment being a function of the maximum excursion of the upper part of the rigid steel pipe 9, thus of the angle γ. To make this transition piece 8, high-grade steels are used. elastic limit and in extreme cases of stress, it may be necessary to manufacture titanium transition parts 8.

On the figure 4 , there is shown a cylindro-conical transition piece 8 having a variable thickness gradually increasing from the tapered upper part 81 to the thicker lower part 82 with a constant internal diameter corresponding to the internal diameter of a standard rigid pipe and In any event, at the internal diameter of the second rigid pipe element 6.

In a preferred version of the invention, shown in section and in side view on the Figures 5A-5B-5C , the transition piece 8 consists of a main steel pipe element 8a, preferably of internal diameter d ₁ identical to that of the current portion of the pipe 9, and preferably of thickness equal to or slightly greater than that of the of said current portion of said duct 9, and of a thickness equal to that of said second elbow pipe element 5b. To obtain an increase in inertia as one approaches the flange 9a, one has a succession of coaxial pipe elements (8b-8d) of heights (h ₂ , h ₃ , h ₄ ) each of said coaxial pipe elements having an internal diameter (d ₂ -d ₄ ) greater than the external diameter D ₁ -D ₃ of the preceding coaxial pipe element and a length or height less than the length of the previous pipe element, that is to say the pipe element that it contains or that it covers, and a thickness depending on the desired increase in stiffness.

So, on the Figure 5A there is shown a transition piece 8 comprising a first inner pipe element 8a and three coaxial reinforcement pipe element 8b-8c-8d of increasing diameters d ₂ -d ₃ -d ₄ and lengths h ₂ -h ₃ - h ₄ decreasing, each of said coaxial pipe elements being secured at its lower end of the same said first flange 9a. To ensure a substantially continuous variation of the inertia between the high part of low inertia of the transition piece 8, and the low part of high inertia located at connection with the flange 9a is advantageously injected into the annular spaces between said coaxial pipe elements, an elastomeric material 8 ^e , such as a polyurethane, whose shore hardness is adjusted to obtain the desired variation in stiffness, especially a shore hardness of A50 at D70.

It is sufficient to inject said rigid material 8e only in the annular gaps between the coaxial pipe elements, as shown in FIG. Figure 5C . However, according to the invention, a mold is installed in such a way as to obtain a cylindro-conical piece as shown in FIG. Figure 5B , which makes it possible to perform in a single operation the reinforcement of the transition piece and its protection vis-à-vis the aggression of the external environment by an outer coating thus conferring a cylindro-conical shape with a transition of steady and continuous inertia. Care should be taken not to cover the upper part of the transition piece with thermosetting resin over a length of 20 to 50 cm so as to be able to assemble it on board the installation vessel 20, by welding at the lower end of the the rigid pipe 9.

• on soude l'extrémité inférieure du premier élément de conduite principale 8a de plus grande longueur sur la bride 9a, et
• on insère autour dudit premier élément de conduite principal 8a un premier élément de conduite de renfort 8b coaxial dont on soude l'extrémité inférieure sur la même bride 9a, et
• on insère la deuxième conduite de renfort 8c autour du premier élément de conduite de renfort 8b, et on soude son extrémité inférieure sur la bride 9a, et
• on insère un troisième élément de conduite de renfort 8d de plus petite hauteur autour du deuxième élément de conduite de renfort 8c, et on soude son extrémité inférieure sur la bride 9a, et
• on injecte un matériau thermoplastique ou thermodurcissable entre les divers éléments de conduites, et le cas échéant on revêt leur surface externe à l'aide d'un un moule cylindro-conique pour obtenir la rigidité et variation d'inertie et protection contre la corrosion recherchées.

It will be understood that in order to manufacture the transition piece 8 according to the invention, the procedure is as follows:

• the lower end of the first main pipe element 8a of greater length is welded to the flange 9a, and
• a coaxial first reinforcing pipe element 8b is inserted around said first main pipe element 8a, the lower end of which is welded to the same flange 9a, and
• the second reinforcing pipe 8c is inserted around the first reinforcing pipe element 8b, and its lower end is welded to the flange 9a, and
• inserting a third reinforcing conduit member 8d of smaller height around the second reinforcing conduit member 8c, and welding its lower end to the flange 9a, and
• a thermoplastic or thermosetting material is injected between the various pipe elements, and, if necessary, their external surface is coated with a cylindro-conical mold in order to obtain the desired rigidity and variation in inertia and protection against corrosion. .

On the figure 6 , the variation diagram of the inertia I is plotted on the ordinate between the flange 9 and the upper end of the transition piece 8 of the Figures 5B and 5C . The dashed staircase 30 represents the variation of the steel section in the absence of roofing and filling material at each of the reinforcing pipe members. The curves 31-32-33 represent the variation of the inertia (ΣEI) of the transition piece 8 of the figures 4 and 5C depending on its length, depending on the type of filler material. Curve 33, of parabolic shape is obtained with a polyurethane filling material of shore hardness A90 or A95, and is a preferred version of the invention. The curve 31 is obtained with a much stiffer material, such as a cement with very high performance, alone or in combination with a powdery load, such as sand.

For example, a transition piece of 18m in length h ₁ is produced using a flange 9a of 200 mm thick on which is welded a main pipe element 8a of external diameter d ₁ = 323.85 mm, of thickness 20.6mm and length h ₁ = 18m, of a first coaxial reinforcement 8b of external diameter d ₂ = 457.20mm, thickness 12.7mm and length h ₂ = 12m, of a second coaxial reinforcement 8c of external diameter d ₃ = 609.6mm, thickness 6mm and length h ₃ = 6m. Then it overmould all, either in vertical position, or in an oblique position with a slope of 5 to 30% to facilitate filling and avoid voids, using a polyurethane resin 8th hardness shore A90 or A95. The space between the first pipe 8a and the first reinforcement 8b is 53.98mm, and the space between the second reinforcement and the first reinforcement is 70.2mm. The increase of the inertia is substantially of a factor k = 3 at the level of the first reinforcement 8b, and of a factor k = 5 at the second reinforcement 8c. During casting, vacuum cycles are advantageously carried out in the mold during filling so as to eliminate as much unwanted air bubbles as possible. Indeed, because the purpose of the transition piece is to be installed at a very great depth, the hydrostatic pressure can have detrimental effects on the overall mechanical operation following a collapse on itself of said bubbles due to said pressure which is substantially 10MPa per 1000m of water.

On the figure 3A , the invention has been described with a base 4 placed at the same time as the submarine pipe resting on the bottom, said base being stabilized by a first pile 6 therethrough. But we remain in the spirit of the invention considering as on the figure 3B a base 4 constituted by a suction anchor, having an orifice, preferably circular integrated with said suction anchor and acting as a pile 6 and capable of receiving the anchoring insert 5e. Thus, the support and connecting device 5 at the lower end of the bottom-surface connection is directly embedded in the suction anchor whose weight reaches 25 to 50 tons for a diameter of 3 to 5 m and a height of 20-25m. In this configuration, the underwater pipe 2 is placed independently and therefore requires a junction pipe 7 manufactured on demand after installation of the bottom-surface connection and the underwater pipe 2. Said pipe junction 7 then requires two automatic connectors 7a-7a ₁ , 7b ₁ -7b, one at each of its ends, while the version described with reference to the figure 3A only requires one 7a-7b automatic connector.

The invention has been described in a preferred version manufactured and simultaneously installed on site from a laying ship 20, but it remains in the spirit of the invention with a prefabrication of the complete set on a shipyard on land , the assembly is then towed substantially horizontally to the site, then finally cabane to inserting the anchoring insert 5e into the first tubular pile 6.

Claims (14)

1. An inertia transition terminal pipe element (8) comprising a main rigid pipe element (8a) including at one of its ends an inertia transition piece that is constituted by at least one and preferably a plurality (n) of coaxial reinforcing pipe elements (8b-8d) placed coaxially around said main pipe element (8a), each said reinforcing pipe element (8b-8d) presenting an inside diameter (d_i+1) greater than the outside diameter (D₁, D_i) of the main pipe element and where appropriate of the other reinforcing pipe element(s) it contains, the various main and reinforcing pipe elements (8a-8d) each being positioned with one end situated at the same level along the axis of symmetry (Z₁Z'₁) of said pipe elements, and each said reinforcing pipe element (8b-8d) presenting a length (h_i with i = 2 to n), that is less than the height (h₁) of the main pipe element (8a), and where appropriate the heights (h_i-1) of the other reinforcing pipe elements that it contains, the annular gap (D_i - d_i+1) between the various pipe elements being filled with a solid filler material (8e);
   the element being characterized in that:

   - said annular gap is completely filled over the entire height thereof with a common solid filler material preferably comprising an elastomer material, more preferably a material based on polyurethane, presenting hardness that is greater than or equal to A50 on the Shore scale, and more preferably that lies in the range A50 to D70 on the Shore scale; and

   - said inertia transition element is covered in a corrosion-resistant elastomer covering material, preferably of the polyurethane type, said inertia transition terminal pipe element presenting a substantially cylindrical-and-conical shape as a result of it being covered in said covering material, said cylindrical-and-conical shape consisting in a variation in diameter in cross-section along its axial longitudinal direction increasing in continuous manner from its smaller-diameter end to its larger-diameter end.
2. An inertia transition pipe element according to claim 1, characterized in that said covering material and said filler material comprise the same elastomer material, preferably based on polyurethane.
3. An inertia transition pipe element according to claim 1, characterized in that said solid filler material comprises polyurethane having hardness of A90 or A95 on the Shore scale.
4. An inertia transition pipe element according to any one of claims 1 to 3, characterized in that said filler material comprises an elastomer filled with a particulate material, preferably sand.
5. An inertia transition pipe element according to claim 1, characterized in that said solid filler material is in the form of a hydraulic binder such as cement.
6. An inertia transition pipe element according to any one of claims 1 to 5, characterized in that the difference in length between the various coaxial reinforcing pipe elements (h_i - h_i+1) is substantially constant and equal to $\left({\mathrm{h}}_1\times \frac{\mathrm{1}}{\mathrm{n}}\right)\mathrm{.}$

   
7. An inertia transition pipe element according to any one of claims 1 to 6, characterized in that the annular gap between two of said pipe elements (D_i+1 - d_i) is greater than or equal to the thickness of said thinner pipe element and less than or equal to twice the thickness of said thicker pipe element defining said annular gap.
8. An inertia transition pipe element according to any one of claims 1 to 7, characterized in that the length of said main pipe element (8a) is 10 m to 50 m, preferably 20 m to 30 m, and in that it comprises two or three of said coaxial reinforcing elements (8b-8d).
9. An inertia transition pipe element according to any one of claims 1 to 8, characterized in that the various main and coaxial reinforcing pipe elements (8a-8d) are fastened to a common bottom plate (5d) constituted by a first fastener flange (9a) suitable for enabling leaktight connection with a second fastener flange (5a) at the end of a terminal rigid pipe element (2a) of another rigid pipe (2).
10. An inertia transition pipe element according to any one of claims 1 to 9, characterized in that each of said main and coaxial reinforcing pipe elements (8a-8d) is constituted in full or in part by a standard unit pipe element, in particular of steel undersea pipe, or is constituted by a plurality of standard unit pipe elements assembled together end-to-end and preferably held coaxially by centering spacers (18) distributed regularly along their longitudinal direction and around their circular section in their annular gaps.
11. A pipe element according to any one of claims 1 to 10, characterized in that said annular gap is completely filled with a common filler material thereby giving rise to variation in inertia that is progressive and continuous along said transition piece and over its entire height.
12. A rigid undersea pipe, preferably a bottom-to-surface connection pipe, including at at least one of its ends a said inertia transition pipe element (8) according to any one of claims 1 to 11, said main pipe element (8a) preferably presenting thickness (D₁- d₁) greater than or equal to the thickness of said rigid undersea pipe (9, 12c), and an inside diameter (d₄) that is substantially identical.
13. A method of rigidly restraining the end of a rigid pipe according to claim 12 that, for coupling, has equipment of stiffness greater than that of said rigid pipe.
14. A method according to claim 13, characterized in that said equipment of greater stiffness is constituted by a pipe coupling element (13, 5a-5b) preferably including a fastener flange, said element being situated at the level of a base (4) resting on the sea bottom, or at the side of a floating support (12) or of a buoy (12b) on the surface or at sub-surface.

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