Simple flexible joint for high pressure and high temperature

Abstract

A flexible joint for providing a hinged connection with an underwater transport line or “riser” for transporting an oil or gas fluid and that is subjected to a traction force. The joint comprises a substantially cylindrical housing containing: a second tubular portion fixed to one end of said housing; a first tubular portion fixed to said underwater transport line and secured to a laminated hinge abutment fixed to another end of said housing and against which the traction force of said transport line is exerted; and tubular isolation means interconnecting said first and second tubular portions in such a manner as to confine the fluid passing through the flexible joint.

Description

TECHNICAL FIELD

[0001] The present invention relates to the offshore oil industry, and more particularly it relates to a simple flexible joint for use with high pressure and high temperature and designed to be fitted to connection systems for risers (underwater lines carrying fluid).

PRIOR ART

[0002] FIG. 3 shows an example of a simple flexible joint 10 of the prior art as used in the offshore oil industry and designed to have its bottom portion connected (in general via a weld 12) to an underwater tubular structure 14 or “riser” connected to a well head (not shown) in a gas or oil field that is to be worked, with its top portion connected (in general by means of a plurality of bolts 16) to the head 18 of a pipe-line 20 for carrying the extracted gas or oil fluid.

[0003] That conventional assembly includes a laminated spherical hinge abutment 30 made up of rigid layers, e.g. of metal, alternating with elastomer layers, the various layers being bonded to one another. The abutment is housed between a strength member 32 in the form of a spherical cap and forming an integral portion of a first tubular portion 34 of said assembly that is designed to be fixed to the extraction line 14, and a strength member 36 constituted by a ring which is fixedly connected, e.g. by a plurality of bolts 38, to a second tubular portion 40 of said assembly and presenting in the example shown the general external shape of a bell surmounted by a flange 42 for receiving the line head 18. The faces of the layers of the abutment and the faces of the cap and of the ring between which the abutments are disposed are concentric spherical surfaces centered on a common point O situated on the flexible hinge axis (which coincides with the axis of the transport line). Internally, this tubular portion has a spherical emerging end portion 44 which is designed to come into contact with and cooperate with the spherical cap 32 so as to avoid putting the laminated abutment 30 under tension while the riser 14 is being installed.

[0004] That conventional structure gives complete satisfaction under most circumstances of offshore use, in particular when the pressures involved do not exceed 400 bars and the temperatures do not exceed 100 degrees Celsius (° C.). Nevertheless, as liquid or gas hydrocarbon reserves become rarer, more and more fields are being worked in deep water. Unfortunately, at very great depths (greater than 1500 meters (m)), the pressure and the temperature of the extracted fluid are both very high (greater than or equal to 600 bars and 120° C., respectively) and conventional assemblies of the kind described above cannot withstand them, in particular because the laminated hinge is not protected from the fluid.

OBJECT AND DEFINITION OF THE INVENTION

[0005] An object of the present invention is to mitigate the above-described drawbacks by proposing a simple flexible joint which can be guaranteed to operate under extreme conditions of pressure and temperature. Another object of the invention is to provide an assembly that is particularly reliable and that also presents a long lifetime. Yet another object of the invention is to protect the laminated hinge effectively against chemical attack by the fluid.

[0006] These objects are achieved by a flexible joint for providing a hinged connection with an underwater transport line or “riser” for transporting an oil or gas fluid and that is subjected to a traction force, the joint comprising a substantially cylindrical housing containing: a second tubular portion fixed to one end of said housing; a first tubular portion fixed to said underwater transport line and secured to a laminated hinge abutment fixed to another end of said housing and against which the traction force of said transport line is exerted; and tubular isolation means interconnecting said first and second tubular portions in such a manner as to confine the fluid passing through the flexible joint.

[0007] With this particular structure for a flexible joint, the fluid remains confined within the housing in a central channel that is defined in succession by the first tubular portion, the tubular isolation means, and the second tubular portion, thereby isolating the laminated hinge abutment from attack by the fluid.

[0008] The tubular isolation means comprise a spherical laminated abutment which is preferably mounted between a first strength member secured to said first tubular portion and a second strength member secured to said second tubular portion, the strength members advantageously including sealing means of the O-ring type.

[0009] In an embodiment, the second spherical laminated abutment has a center of rotation O in common with the center of rotation of said first laminated hinge abutment.

[0010] Advantageously, the housing has a plurality of slots for allowing seawater to flow through as a cooling fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Other characteristics and advantages of the present invention will appear more clearly from the following description given by way of non-limiting indication and made with reference to the accompanying drawings, in which:

[0012] FIG. 1 is a longitudinal section view through a simple flexible joint of the invention for use with high pressure and high temperature;

[0013] FIG. 2 is an external perspective view of the simple flexible joint of FIG. 1; and

[0014] FIG. 3 is a longitudinal section view through a simple flexible joint of the prior art.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0015] FIGS. 1 and 2 are respectively a longitudinal section and an outer perspective view of a simple flexible joint of the invention for use in extracting hydrocarbons from very deep waters (depths in excess of 1500 m) where pressure and temperature conditions are extreme, i.e. greater than or equal to 600 bars and 120° C. The joint itself is commonly located a little below the surface.

[0016] Like a conventional assembly, this assembly comprises a single laminated spherical hinge abutment 50 comprising rigid layers, e.g. of metal, alternating with layers of elastomer, the various layers being bonded to one another. This abutment is also received between a first strength member 52 in the form of a spherical cap on which there comes to rest a first tubular portion 54 of said assembly, which portion is shaped like a golf tee and is for welding (via a weld 56) to a fluid extraction line 14, and a second strength member 58 constituted by a ring forming the bottom of this assembly and securely connected, e.g. by means of a first set of stud bolts 60 disposed circumferentially to a second annular portion of the assembly. The connection between the cap and the tee is advantageously a pressed connection (the abutment 50 being precompressed during assembly) with mechanical cone-on-cone contact.

[0017] To make the assembly easier to assemble, the second tubular portion is advantageously made up of two parts (but it would naturally be possible for it to comprise a one-part structure as in the prior art) comprising a cylindrical housing body 62 and a cover plate 64 covering its top portion and surmounted by a flange 66 for receiving the line head (not shown). The plate 64 is fixed to the cylindrical housing in the same manner as the bottom 58 is fixed to the bottom portion of the housing, by means of a second set of stud bolts 68 that are likewise disposed circumferentially. The faces of the abutment layers and the faces of the cap and of the ring between which the abutment is disposed are concentric spherical surfaces centered on a common point O situated on the flexible hinge axis (which coincides with the axis of the extraction line).

[0018] As in a conventional assembly, the traction force exerted by the riser 14 is transmitted to the first tubular portion 54 of the cylindrical housing 62 by the laminated abutment 50 which also accommodates angular variations of the riser 14 in all directions.

[0019] According to the invention, the laminated hinge abutment 50 is isolated from attack from the transported fluid by tubular isolation means 70 disposed between and in line with the first and second tubular portions to which they are connected to form a confinement channel 72 for the fluid under pressure and at high temperature. For this purpose, the first tubular portion 54 is secured rigidly by first connection means 74 (although a simple force-fit would also be possible) to a hemispherically-shaped first strength member 76 of a second laminated abutment 78 whose ring-shaped second strength member 80 is securely fixed by second connection means 82 to the plate 64 of the second tubular portion. This second laminated abutment is likewise of a structure that is concentric about a center of rotation O in common with that of the hinge abutment 50.

[0020] The confinement channel is frustoconical in shape, being of smaller section level with the first tubular portion and isolation of the fluid is reinforced by sealing means of the O-ring type 84, 86 mounted firstly between the first strength member and the first tubular portion, and secondly between the second strength member and the cover plate, and preventing fluid from flowing towards the laminated hinge abutment 50. In addition, in order to ensure that heat is removed effectively, the cylindrical housing includes a plurality of slots 88 that are regularly distributed around its periphery and that allow seawater to flow inside the housing, thereby ensuring that it is at the same pressure as the surrounding ocean. The particularly high internal pressure flowing in the transport line and passing through the joint therefore does not act on this housing and thus does not act either on the laminated hinge abutment 50.

[0021] With this particular structure, the laminated hinge abutment 50 which takes up both tension from the line and angle variations due to the riser 14 (i.e. which takes up mechanical forces), is completely protected from chemical attack, and also from the pressure and the temperature of the fluid, by the second laminated abutment 78 which performs this separation function (confinement barrier) between the fluid and the hinge abutment 50. This second abutment which takes up the pressure of the fluid and which accompanies the variations of angle (because of its secure connection to the tee 54 fixed to the riser) can, in contrast, accommodate a certain amount of damage due to the fluid since it has little influence on the overall mechanical strength of the assembly.

Claims

1/ A flexible joint for providing a hinged connection with an underwater transport line or “riser” for transporting an oil or gas fluid and that is subjected to a traction force, the joint comprising a substantially cylindrical housing containing: a second tubular portion fixed to one end of said housing; a first tubular portion fixed to said underwater transport line and secured to a laminated hinge abutment fixed to another end of said housing and against which the traction force of said transport line is exerted; and tubular isolation means interconnecting said first and second tubular portions in such a manner as to confine the fluid passing through the flexible joint.

2/ A flexible joint according to claim 1, wherein said tubular isolation means include a spherical laminated abutment.

3/ A flexible joint according to claim 2, wherein said spherical laminated abutment is mounted between a first strength member secured to said first tubular portion and a second strength member secured to said second tubular portion.

4/ A flexible joint according to claim 3, wherein said first and second strength members include O-ring type sealing means.

5/ A flexible joint according to claim 1, wherein said second spherical laminated abutment has a center of rotation O in common with that of said first laminated hinge abutment.

6/ A flexible joint according to claim 1, wherein said housing includes a plurality of slots to allow seawater to flow through as a cooling fluid.