GB2520749A

GB2520749A - Fluid flow

Info

Publication number: GB2520749A
Application number: GB1321116.4A
Authority: GB
Inventors: Sui Wang
Original assignee: GE Oil and Gas UK Ltd
Current assignee: Baker Hughes Energy Technology UK Ltd
Priority date: 2013-11-29
Filing date: 2013-11-29
Publication date: 2015-06-03
Also published as: GB201321116D0

Abstract

The invention relates to means of suppressing pressure pulsation in fluid flow through a flexible pipe. It features a rigid enclosure 300 which is secured in an in-line configuration to an end fitting 305 of a flexible pipe 310 via a connector 335, and aligns the bores of the housing with that of the flexible pipe. The bore 370 of the housing comprises a cylindrical wall which features a plurality of openings and an attenuation region, which can contain absorber material, such as rock wool, fibreglass or steel wool, or a reactive attenuator which alters the phase of the fluid exiting the attenuator to cancel the pulsations. The cylindrical wall can further comprises a foraminous cylindrical inner wall of an insert 360 which has an outer wall coaxial with the inner wall, and is aligned with the through bore 370. The insert can comprise a plurality of spacer members.

Description

FLUID FLOW

The present invention relates to a method and apparatus for attenuating pressure pulsation in a fluid flow associated with a fluid flow through a flexible pipe. In particular, but not exclusively, the present invention relates to a rigid enclosure which is securable in an in-line configuration to an end fitting of a flexible pipe and which includes a region that attenuates an amplitude of pressure waves of fluid flowing from the flexible pipe through the enclosure.

Traditionally, flexible pipe has been utilised to transport production fluids, such as oil and/or gas and/or water from one location to another. Flexible pipe has been found to be useful in connecting a subsea location to a sea-level location. Flexible pipe has generally been formed as an assembly of flexible pipe body and one or more end fittings. The pipe body is conventionally formed as a combination of layered materials that form a pressure-containing conduit. The pipe structure allows large deflections in use without causing bending stresses that impair the pipe's functionality over its lifetime. The pipe body is generally built up as a combined structure including tubular metallic and polymer layers which are typically unbonded to one another.

Such unbonded flexible pipes have been used for deep water (less than 3300 feet (1005.84 metres)) and ultra-deep water (greater than 3300 feet (1005.84 metres)) developments. Of course, flexible pipe may also be used for shallow water applications (for example, less than around 500 metres depth) or even for onshore (overland) applications.

Conventionally an inner bore of a flexible pipe is defined by a polymer fluid retaining layer referred to as a pressure sheath. This pressure sheath can be supported internally by a layer formed of interlocked windings. Such a layer is often referred to as a carcass layer.

As a result an internal bore, along which production fluids are transported in the flexible pipe, has an internal corrugated profile.

In the last decade it has been reported that some flexible pipes, and in particular, but not exclusively, some flexible risers which include carcass layers, have experienced high levels of piping noise and vibration. The problem has been attributed to flow induced pressure pulsations generated in the flexible pipes.

It is understood that pressure pulsations are generated due to vortex shedding and shear layer instabilities at the corrugations along the length of the flexible pipe. As vortex shedding from the internal corrugated carcass of a flexible pipe "locks on" to discreet acoustic resonances of the production fluid and pipe network severe noise and/or pipework vibration can occur at a connected pipework system. Such systems are conventionally provided by top side gas export systems to which an upper end of a riser is connected.

It is noted that the problem is particularly acute when a production fluid being transported in a flexible pipe is a dry gas. As the dry gas passes through a flexible riser an unstable shear layer is generated off each of the internal corrugations which make up the internal carcass.

Following established vortex shedding theory the perturbations have a characteristic frequency. "Lock-on" can occur when the shedding frequency is close to an acoustic natural frequency of the gas system. The most common acoustic resonators producing "lock-on" have been found to be axial modes in a riser but also dead leg" branches off a main pipework at a top or bottom region of a flexible rise.

Due to the large number of corrugations along the length of a typical flexible pipe, the perturbations generated by subsequent corrugations can interact and build up to generate significant pressure pulsation levels at a characteristic frequency. Under appropriate acoustic conditions this results in a resonant condition whereby the pressure pulsations generated along a riser "lock-on" to a single forcing frequency and that this in turn leads to a further increase in dynamic pressure pulsations. This feedback mechanism can generate significant levels of measured pressure pulsation and it is understood that an excitation of an acoustic resonance can lead to very high localised pressure pulsation amplitudes.

It is an aim of the present invention to at least partially mitigate the above-mentioned problem.

It is an aim of certain embodiments of the present invention to provide an enclosure which can be selectively secured in-line with a flexible pipe and which includes a region that can be used to attenuate an amplitude of undesired pressure waves in the enclosure.

It is an aim of certain embodiments of the present invention to maintain a reflection coefficient associated with a pressure distribution of fluid flow in a through bore below a predetermined threshold.

It is an aim of certain embodiments of the present invention to help attenuate pressure pulsation associated with flow induced pulsation (FLIP) caused by flexible pipes.

It is an aim of certain embodiments of the present invention to provide a "silencer" or "muffler" or other such attenuator which can be retrofitted to a flexible pipe at sites where large pressure fluctuations generated within a riser, and heard clearly as acoustic tones or "singing", are experienced.

According to a first aspect of the present invention there is provided apparatus for attenuating pressure pulsation in a fluid flow associated with a flow of production fluid flowing through a flexible pipe, comprising: a rigid enclosure securable in an in-line configuration, via at least one enclosure connector, to an end fitting of a flexible pipe to align a through bore that extends through the housing with a primary bore of the flexible pipe; wherein a cylindrical wall that defines at least a portion of the through bore comprises a plurality of openings and an attenuator region in the enclosure is in fluid communication with at least one of said openings to attenuate an amplitude of pressure waves in said portion of the through bore.

Aptly the cylindrical wall comprises a foraminous cylindrical inner wall of an insert that further comprises an outer wall coaxial with the inner wall and that is aligned in the housing coaxially with the through bore.

Aptly the insert further comprises a plurality of spacer members that locate the inner wall and outer wall in a substantially parallel spaced apart relationship.

Aptly the rigid enclosure comprises: a first and further enclosure connector at opposed ends of the enclosure, each connector comprising a connecting flange that is connectable to a flange of an end fitting of a respective flexible pipe, an enclosure end plate and a neck portion extending between a respective connecting flange and end plate; and a rigid cylindrical jacket connectable between an inner peripheral edge region of opposed end plates of the enclosure.

Aptly pressure distribution of fluid flow in the through bore is p=Piemt] + Premt< where Ri and Pr are incident and reflected wave amplitudes respectively and a reflection coefficient (R) is given by Rr \ P: / and R is about around 0.85 or less.

Aptly R is about around 0.75 or less.

Aptly the attenuator region provides a labyrinthine fluid communication pathway for fluid entering the attenuator region from one or more of the openings.

Aptly the attenuator region comprises an absorptive muffler.

Aptly the attenuator region comprises an annulus region of acoustic absorber material between the cylindrical wall and an outer wall of the enclosure.

Aptly the attenuator region comprises a substantially frusto conical region.

Aptly the attenuator region comprises a region containing rock wool.

Aptly the cylindrical wall comprises an inner cylindrical surface of an annular insert integrally formed from a material comprising a matrix body interspersed with a plurality of interconnected fluid communication passageways.

Aptly the attenuator region comprises a reactive muffler.

Aptly the rigid enclosure is securable in an in-line configuration between end fittings of two flexible pipes.

Aptly the enclosure is securable at a mid-line connection point between two flexible pipes disposed in an in-line configuration.

Aptly the rigid enclosure is securable in an in-line configuration between an end fitting of a flexible pipe and a connector of a structure proximate to said an end filling.

Aptly the enclosure can be retrofitted to an existing pipe system.

Aptly the enclosure is securable in an in-line configuration to either one of both a topside end or a subsea end of the flexible pipe.

According to a second aspect of the present invention there is provided a method of attenuating pressure pulsation in a fluid flow associated with a flow of production fluid flowing through a flexible pipe, comprising the steps of: via a rigid housing secured in an in-line configuration to an end fitting of a flexible pipe, providing an attenuator region in fluid communication with at least one opening in a cylindrical wall that defines at least a portion of a through bore that extends through the housing and is aligned with a primary bore of the flexible pipe; and attenuating an amplitude of pressure waves in said portion of the through bore as fluid flows along the through bore from the primary bore.

Aptly the method further comprises attenuating an amplitude of the pressure waves by is absorbing at least a portion of the pressure waves in the attenuator region.

Aptly the method as further comprises attenuating an amplitude of the pressure waves by providing at least partially out of phase pressure waves at an outlet opening proximate to said at least one opening.

Aptly the method further comprises retro fitting the rigid enclosure to an end of a flexible pipe prior to flowing production fluid along the flexible pipe.

According to a third aspect of the present invention there is provided apparatus constructed and arranged substantially as herein before described with reference to the accompanying drawings.

According to a fourth aspect of the present invention there is provided a method substantially as herein before described with reference to the accompanying drawings.

Certain embodiments of the present invention provide a method and apparatus for attenuating pressure pulsation in a fluid flow flowing from a flexible pipe into an enclosure secured in an in-line configuration with the flexible pipe. An amplitude of pressure waves is attenuated by virtue of at least one region in the enclosure.

Certain embodiments of the present invention utilise an absorptive or reactive attenuator within a rigid enclosure or housing that is securable in-line with one or more flexible pipes.

The enclosure can be retrofitted to an already in situ flexible pipe system or may be designed to be included in a pipe line with a new flexible pipe when the new flexible pipe itself is designed.

Certain embodiments of the present invention will now be described hereinafter, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates flexible pipe body; Figure 2 illustrates use of a flexible pipe; Figure 3 illustrates a rigid enclosure secured in an in-line configuration; Figure 4 illustrates an enclosure connector; Figure 5 illustrates an outer enclosure jacket; Figure 6 illustrates an annular insert providing an attenuator region; Figure 7 illustrates a frusto conical insert providing an attenuator region; Figure 8 illustrates a reactive type attenuator insert; and Figure 9 illustrates pressure wave cancelling.

In the drawings like reference numerals refer to like parts.

Throughout this description, reference will be made to a flexible pipe. It will be understood that a flexible pipe is an assembly of a portion of pipe body and one or more end fittings in each of which a respective end of the pipe body is terminated. Figure 1 illustrates how a portion of pipe body 100 (referred to as a segment) is formed from a combination of layered materials that form a pressure-containing conduit. Although a number of particular layers are illustrated in Figure 1, it is to be understood that the present invention is broadly applicable to coaxial pipe body structures including one or more layers manufactured from a variety of possible materials. For example, the pipe body may be formed from metallic layers, composite layers, or a combination of different materials. It is to be further noted that the layer thicknesses are shown for illustrative purposes only.

As illustrated in Figure 1, pipe body includes an innermost carcass layer 101. The carcass provides an interlocked construction that can be used as the innermost layer to prevent, totally or partially, collapse of an internal pressure sheath 102 due to pipe decompression, external pressure, and/or tensile armour pressure and mechanical crushing loads. The carcass layer may be a metallic layer, formed from carbon steel or the like, for example. The carcass layer may also be formed from composite, polymer, or other material, or a combination of materials. The inner surface of the carcass layer provides a corrugated or undulating surface.

The internal pressure sheath 102 acts as a fluid retaining layer and comprises a polymer layer that ensures internal fluid integrity. It is to be understood that this layer may itself comprise a number of sub-layers. It will be appreciated that the internal pressure sheath may be referred to by those skilled in the art as a barrier layer.

The pressure armour layer 103 is a structural layer with elements having a lay angle close to 90° that increases the resistance of the flexible pipe to internal and external pressure and mechanical crushing loads. The layer also structurally supports the internal pressure sheath, and is an interlocked construction of wires wound with a lay angle close to 90°.

The flexible pipe body also includes an optional first tensile armour layer 105 and optional second tensile armour layer 106. Each tensile armour layer is used to sustain tensile loads and internal pressure. The tensile armour layer may be formed from a plurality of metallic wires (to impart strength to the layer) that are located over an inner layer and are helically wound along the length of the pipe at a lay angle typically between about 10° to 55°. The tensile armour layers may be counter-wound in pairs. The tensile armour layers may be metallic layers, formed from carbon steel, for example. The tensile armour layers may also be formed from composite, polymer, or other material, or a combination of materials.

The flexible pipe body shown also includes optional layers 104 of tape which each help contain underlying layers and may act as a sacrificial wear layer to help prevent abrasion between adjacent layers.

The flexible pipe body also includes optional layers of insulation 107 and an outer sheath 108, which comprises a polymer layer used to help protect the pipe against penetration of seawater and other external environments, corrosion, abrasion and mechanical damage.

Each flexible pipe thus comprises at least one segment of pipe body 100 together with an end fitting located at at least one end of the flexible pipe. An end fitting provides a mechanical device which forms the transition between the flexible pipe body and a connector. The different pipe layers as shown, for example, in Figure 1, are terminated in the end fitting in such a way as to transfer the load between the flexible pipe and the connector.

Figure 2 illustrates a riser assembly 200 suitable for transporting production fluids such as oil and/or gas and/or water from a subsea location 201 to a floating facility 202. For example, in Figure 2 the subsea location 201 includes an end of a subsea flow line. The flexible flow line 205 comprises a flexible pipe, wholly or in part, resting on the sea floor 204 or buried below the sea floor and used in a static application. The floating facility may be provided by a platform and/or buoy or, as illustrated in Figure 2, a ship. The riser assembly 200 is provided as a flexible riser, that is to say a flexible pipe 203 connecting the ship to the sea floor installation. The flexible pipeline may be formed from a single segment or multiple segments of flexible pipe body with end fillings connected end-to-end.

It will be appreciated that there are different types of riser, as is well-known by those skilled in the art. Certain embodiments of the present invention may be used with any type of riser, such as a freely suspended riser (free, catenary riser), a riser restrained to some extent (buoys, chains) or totally restrained riser. Certain other embodiments of the present invention can be used as flowlines or jumpers or the like.

Figure 3 illustrates a rigid enclosure 300 which is securable in an in-line configuration to a flexible pipe or, as shown in Figure 3, between two flexible pipes arranged in a back-to-back arrangement. As illustrated in Figure 3 an end 305 of an end fitting of a first flexible pipe 310 faces an opposite end 315 of an end fitting of a further flexible pipe 320. Each end 305, 315 of a respective flexible pipe end fitting is terminated with a respective end filling flange 325, 330. A first enclosure connector 335 of the enclosure is shown on the right hand side of Figure 3 and this includes a connecting flange which is securable to an opposed mating flange 325 of the first flexible pipe. A further enclosure connector 340 likewise includes a connecting flange which is securable to the flange 330 of the further flexible pipe 320. The rigid enclosure 300 includes a rigid enclosure jacket 350 which extends between the two enclosure connectors to provide a sealed rigid housing. It will be appreciated that the jacket and an enclosure connector could be integrally formed or that part of the jacket could be provided as an extension of each enclosure connector.

As illustrated in Figure 3 a substantially cylindrical annual shaped insert 360 is locatable in the rigid enclosure 300 and is arranged in a substantially coaxial relationship with the outer jacket 350 and indeed an inner bore region 370 which extends around a central longitudinal axis 375. The central axis 375 of the rigid enclosure 300 is aligned with a corresponding central axis extending along the bore of the flexible pipes to either side of the rigid enclosure.

It will be appreciated that whilst the rigid enclosure 300 has been described as being connected between two adjacent back-to-back flexible pipes the enclosure housing could instead be secured to just one end of one flexible pipe with a remaining end of the enclosure being secured to a rigid structure to which the end of the flexible pipe would otherwise be secured.

Figure 4 helps illustrate the enclosure connector 340 shown on the left hand side of Figure 3 in more detail. The enclosure connector 340 includes a connecting flange 400 which is substantially circular in cross section (an end view of the connecting flange 400 is shown more clearly in Figure 4b). The connecting flange 400 has a thickness B and a diameter D1.

A rigid neck 410 extends between the connecting flange and an end plate 420 of the enclosure connector. The neck illustrated in Figure 4a has a length A which is selectable according to use. Aptly the length is 10cm. Aptly the length is about around Scm to 80cm.

Alternatively no neck may be provided. The end plate 420 has a diameter D2 which corresponds to an outer diameter of the rigid enclosure 300. It will be appreciated that the diameters and indeed shapes of the connecting flanges and necks and end plates and indeed outer jacket of the enclosure are selectable and may be equal or different. The flanges necks and plate regions are made from a rigid material such as a metal or the like.

A circular groove 430 extends around an end surface of the connecting flange 400 to help provide a seal (via an inserted gasket seal or 0" ring or the like) to an end fitting flange when the rigid enclosure is secured to an end fitting. Likewise a circular groove 440 extends around an end surface of the end plate 420 to help provide a seal between the end plate 420 and an end edge of the rigid jacket 350 when the jacket 350 is secured to the enclosure connector 340. It will be understood that more than one circular groove may be included in the connecting flanges in order to provide a double seal arrangement. An inner bore having -10-a diameter D3 is defined by a cylindrical surface (illustrated by a dotted line in Figure 4a) 450 that extends through the connecting flange, neck region and end plate. Aptly the inner diameter D3 defined by the inner bore through the neck and connecting flange and end plate of the enclosure connector exactly or at least substantially matches an inner bore diameter of the flexible pipe to which the rigid enclosure is secured.

Figure 5 illustrates the rigid enclosure jacket 350 of the rigid enclosure 300 in more detail.

As illustrated in Figure 5 the rigid jacket is a substantially cylindrical element made of a rigid material such as steel or carbon alloy or the like. The outer jacket has an outer surface 500 which is substantially cylindrical and an inner surface 510 coaxial with and spaced apart from the outer surface. The outer surface 510 is shown in Figure 5a as a dotted line. The outer jacket 350 has a length L from a first end 520 which is securable to an end plate of a first enclosure connector 335 and a further end 530 securable to an end plate 420 of the enclosure connector 340 at a remaining end of the enclosure. Circular grooves 540 extend around both ends 520. 530 of the jacket to help seal the structure. Aptly the outer diameter D4 of the rigid jacket 350 is equal to the outer diameter D2 of the end plates at the ends of the enclosure connectors. The cylindrical inner surface 510 of the rigid jacket has an inner diameter D5 between an inner bore of the enclosure and the outside of the enclosure. Aptly the inner diameter is about around 10cm to 60cm. Aptly the inner diameter is about around 44cm. Aptly the length L is about around 10cm to 100cm. Aptly the length L is about around 50cm. Aptly D4 is about around 10cm to 100cm. Aptly D4 is about around 52cm.

Figure 6 helps illustrate an insert 600 which provides an attenuator region 610 within the rigid enclosure 300. The insert 600 illustrated in Figure 6 has a substantially annular shape.

That is to say the insert has a substantially cylindrical outer surface 615 provided by a wall formed by a cylindrical sheet 620 of rigid material such as metal or plastic or the like and a coaxial cylindrical sheet 630 of rigid material such as metal or plastic or the like spaced apart from the outer sheet 620. Multiple (three shown) props 635 keep the outer and inner cylindrical walls 620, 630 in a spaced apart substantially parallel relationship and generally support the inner and outer walls. As a result a radially inner surface 640 of the inner sheet 630 of the insert 600 defines a through bore that extends throughout the enclosure where the insert is located. A radially outer surface 645 of the inner wall 630 defines a radially inner surface of an annular region within the insert. A radially inner surface 650 of the radially outer sheet 620 defines a radially inner extremity of the annular region 610. The annular region 610 illustrated in Figure 6a is filled with an absorber material. Aptly the absorber material 660 is rock wool. The absorber material provides multiple fluid -11 -communication pathways which thus provide a labyrinthine pathway for fluid flow. Aptly the absorber material is another type of fibreglass. Aptly the absorber material is a mass of steel wool. Aptly the absorber material is a honeycomb cross-section structure made from steel or ceramic material, comprising a plurality of elongate orifices. Aptly the absorber material comprises a mass of metal fibres at least partially connected (for example by sintering) to at least one of the radially inner surface 650 or radially outer surface 645. The attenuator region 610 shown in Figure 6 is thus an absorber type of attenuator. As discussed below the attenuator region is any type of region that helps wholly or partly reduce an amplitude of pressure waves of fluid in the insert and thus of fluid flowing through the enclosure. The inner wall 630 shown in Figure 6a is a foraminous cylindrical inner wall. That is to say multiple openings 670 extend through the inner wall so that fluid flowing through the inner bore 370 is in fluid communication with the attenuator region 610. For certain typos of absorber materials (for example honeycomb cross-section structures) these holes may extend beyond the inner wall and into the absorber material itself in order to better connect the inner bore to the absorber material.

Figure 7 helps illustrate an alternative rigid enclosure 700 which is securable in an in-line configuration to a flexible pipe or between two flexible pipes arranged in a back-to-back arrangement. Figure 7 helps illustrate how an end 705 of an end fitting of a first flexible pipe 710 faces the enclosure 700. A first enclosure connector 735 of the enclosure is shown on the right hand side of Figure 7 and this includes a connecting flange which is securable to an opposed mating flange 725 of the end fitting of the flexible pipe 710. It will be appreciated that a further enclosure connector 740 which optionally includes a similar connecting flange is securable to a flange of a further flexible pipe.

As illustrated in Figure 7 the rigid enclosure 700 is not substantially cylindrical in shape.

Rather the outer surface formed by an outer jacket 750 has a frusto conical shape. That is to say the enclosure has a narrow but non pointed end which flares out into a wider end. An insert 760 which provides the attenuator region 710 likewise has a frusto-conical cross section. That is to say the insert has a substantially cylindrical inner surface 765 which has multiple through holes 770 extending along all (or a part) of its length and an outer wall connected to the inner foraminous wall 765 by props 790 (two end props shown). The props keep the inner cylindrical wall 765 and outer flared wall 785 in a desired spaced apart non parallel relationship. The attenuator region 710 illustrated in Figure 7 is filled with an absorber material. Aptly the absorber material 795 is rock wool. Aptly the absorber material is another type of fibreglass. Aptly the absorber material is a mass of steel wool. Aptly the absorber material is a honeycomb cross-section structure made from steel or ceramic material, comprising a plurality of elongate orifices. Aptly the absorber material comprises a mass of metal fibres at least partially connected (for example by sintering) to at least one of the radially inner surface 650 or radially outer surface 645. The attenuator region 710 shown in Figure 7 is thus an absorber type of attenuator.

Assuming plain waves are propagating, the pressure distribution of fluid flow in the through bore is p=Pietx] + Pretx] where Ri and Pr are incident and reflected wave amplitudes respectively and a reflection coefficient (R) is given by Pt A purpose of a silencer or muffler is to help minimise this reflection coefficient R. Aptly R is about 0.5 or less. Aptly R is about 0.75 or less.

Figure 8 illustrates an alternative type of attenuator region 810 which is illustrated by way of a cylindrical insert 820 having a similar shape and configuration to that shown in Figure 6 and useable as an insert to help attenuate an amplitude of pressure pulsation in an enclosure similar to that illustrated in Figure 3, 4 and 5. It will be appreciated that this alternative attenuator is not restricted to having an annular shape. Rather than the insert 820 being an absorber type of attenuator Figure 8 helps illustrate a reactive attenuator region. The insert 800 which provides the attenuator region 810 within the rigid enclosure has a substantially annular shape. That is to say the insert has a substantially cylindrical outer surface 815 provided by a cylindrical wall 820 of rigid material such as metal or plastic or the like and a coaxial cylindrical inner wall 830 formed from a rigid material such as metal or plastic or the like spaced apart from the outer wall 820. Two holes which are spaced apart are illustrated as being provided in the inner wall 830 each hole shown may be a single hole or a row of holes or a slit or slits or other such openings. A first hole 840 is upstream.

That is to say is closest to an inlet end of the insert in a direction of fluid flow. A further hole 850 is downstream with respect to the upstream hole 840. A series of baffle plates 860 are located within the space between the outer wall 820 and inner wall 830 of the insert. The baffle plates help define a labyrinthine fluid communication pathway within the insert. Figure 9 helps illustrate fluid communication pathways through the insert whereby fluid flowing in the direction of fluid flow illustrated by arrow F through the main bore flows into the reactive type attenuator region and flows along the labyrinthine passageways until it is reflected from -13-a reflector wall formed by one or more baffle plates. The baffle plate shape and configuration is designed with respect to an expected fluid viscosity and fluid speed and with respect to the location of the holes in the through bore defining wall 830 so that fluid flowing back out from the attenuator region has a phase in terms of pulsation frequency at or about out of phase (that is to say about around 180 degrees out of phase) with the incoming fluid flow. As a result cancellation entirely or at least in part occurs of pressure pulsation as fluid flow flows through the through bore.

It will be appreciated that whilst certain embodiments of the present invention have previously been described by way of use of an insert placed within a surrounding rigid enclosure it will be appreciated that the attenuator region and access openings could alternatively be provided as a single piece with part or a whole of the enclosure. That is to say the insert would not be a separate discrete entity. Use of an insert means that the characteristics of the insert can be selected according to a pipework system where the attenuator is to be used. A common rigid enclosure can thus be used and an insert from many optional inserts selected according to use. Where circumstances are pre-known a bespoke in-line unit can be designed and manufactured without a separable insert.

Whilst certain embodiments of the present invention have been described with reference to the transportation of production fluids via a flexible pipe it will be appreciated that certain embodiments of the present invention are broadly applicable to use with any pressurised fluid flow.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to" and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so -14-disclosed, may be combined in any combination, except combinations where at least some of the features and/or steps are mutually exclusive. The invention is not restricted to any details of any foregoing embodiments. The invention extends to any novel one, or novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. -15-

Claims

CLAIMS: Apparatus for attenuating pressure pulsation in a fluid flow associated with a flow of production fluid flowing through a flexible pipe, comprising: a rigid enclosure securable in an in-line configuration, via at least one enclosure connector, to an end fitting of a flexible pipe to align a through bore that extends through the housing with a primary bore of the flexible pipe; wherein a cylindrical wall that defines at least a portion of the through bore comprises a plurality of openings and an attenuator region in the enclosure is in fluid communication with at least one of said openings to attenuate an amplitude of pressure waves in said portion of the through bore.
2. The apparatus as claimed in claim 1, further comprising; the cylindrical wall comprises a foraminous cylindrical inner wall of an insert that further comprises an outer wall coaxial with the inner wall and that is aligned in the housing coaxially with the through bore.
3. The apparatus as claimed in claim 2, further comprising: the insert further comprises a plurality of spacer members that locate the inner wall and outer wall in a substantially parallel spaced apart relationship.
4. The apparatus as claimed in any preceding claim wherein the rigid enclosure comprises: a first and further enclosure connector at opposed ends of the enclosure, each connector comprising a connecting flange that is connectable to a flange of an end fitting of a respective flexible pipe, an enclosure end plate and a neck portion extending between a respective connecting flange and end plate; and a rigid cylindrical jacket connectable between an inner peripheral edge region of opposed end plates of the enclosure.
5. The apparatus as claimed in any preceding claim wherein the pressure distribution of fluid flow in the through bore is p=Pie0uI + where Ri and Pr are incident and reflected wave amplitudes respectively and a reflection coefficient (R) is given by and R is about around 0.85 or less.
6. The apparatus as claimed in claim 5 wherein R is about around 0.75 or less.
7. The apparatus as claimed in any preceding claim, further comprising: the attenuator region provides a labyrinthine fluid communication pathway for fluid entering the attenuator region from one or more of the openings.
8. The apparatus as claimed in any preceding claim wherein the attenuator region comprises an absorptive muffler.
9. The apparatus as claimed in any preceding claim wherein the attenuator region comprises an annulus region of acoustic absorber material between the cylindrical wall and an outer wall of the enclosure.
10. The apparatus as claimed in any one of claims 1 to 8, wherein the attenuator region comprises a substantially frusto conical region.
11. The apparatus as claimed in claim 9 or claim 10 wherein the attenuator region comprises a region containing rock wool.
12. The apparatus as claimed in any one of claims 1 toE, further comprising: the cylindrical wall comprises an inner cylindrical surface of an annular insert integrally formed from a material comprising a matrix body interspersed with a plurality of interconnected fluid communication passageways.
13. The apparatus as claimed in any one of claims 1 to 7 wherein the attenuator region comprises a reactive muffler.
14. The apparatus as claimed in any preceding claim, further comprising: the rigid enclosure is securable in an in-line configuration between end fittings of two flexible pipes. -17-
15. The apparatus as claimed in claim 14, further comprising: the enclosure is securable at a mid-line connection point between two flexible pipes disposed in an in-line configuration.
16. The apparatus as claimed in any preceding claim, further comprising: the rigid enclosure is securable in an in-line configuration between an end fitting of a flexible pipe and a connector of a structure proximate to said an end fitting.
17. The apparatus as claimed in any one of claims 14 to 16, further comprising: the rigid enclosure is securable in an in-line configuration to either one of both a topside end or a subsea end of the flexible pipe.
18. The apparatus as claimed in any preceding claim wherein the enclosure can be retrofitted to an existing pipe system.
19. A method of attenuating pressure pulsation in a fluid flow associated with a flow of production fluid flowing through a flexible pipe, comprising the steps of: via a rigid housing secured in an in-line configuration to an end fitting of a flexible pipe, providing an attenuator region in fluid communication with at least one opening in a cylindrical wall that defines at least a portion of a through bore that extends through the housing and is aligned with a primary bore of the flexible pipe; and attenuating an amplitude of pressure waves in said portion of the through bore as fluid flows along the through bore from the primary bore.
20. The method as claimed in claim 19, further comprising the step of: attenuating an amplitude of the pressure waves by absorbing at least a portion of the pressure waves in the attenuator region.
21. The method as claimed in claim 19, further comprising the step of: attenuating an amplitude of the pressure waves by providing at least partially out of phase pressure waves at an outlet opening proximate to said at least one opening.
22. The method as claimed in any one of claims 19 to 21, further comprising the step of: -18-retro fitting the rigid enclosure to an end of a flexible pipe prior to flowing production fluid along the flexible pipe.
23. Apparatus constructed and arranged substantially as herein before described with reference to the accompanying drawings.
24. A method substantially as herein before described with reference to the accompanying drawings.