Flexible pipe joint having an annular flexible boot thermally or chemically insulating an annular elastomeric flexible element

A flexible pipe joint has a body and an annular elastomeric flexible element flexibly coupling an extension pipe to the body for pivoting of the extension pipe with respect to the body. The flexible pipe joint also has an annular flexible boot for thermally or chemically insulating the annular elastomeric flexible element from the fluid flowing through a lumen of the flexible pipe joint. The annular flexible boot encircles the lumen, and the annular flexible boot has a first annular end attached to the extension pipe and a second annular end mounted so that pivoting of the extension pipe with respect to the body causes a flexing of the annular flexible boot, and a majority of the annular flexible boot has a shape conforming to shape of neighboring components of the flexible pipe joint.

FIELD OF THE INVENTION

The present invention relates to an annular flexible boot for insulating an annular elastomeric flexible element in a flexible pipe joint from thermal or chemical exposure to fluid flowing through the flexible pipe joint.

BACKGROUND ART

Elastomeric flexible elements are often used in the oil industry in flexible pipe joints for coupling or supporting segments of a pipeline or riser. A limitation of the elastomeric flexible elements is reduced performance when exposed to heat from fluid flowing in the pipeline or riser, and to chemicals in the fluid. A conventional way of dealing with this limitation is by using a two-stage bellows.

For example, as described in Whightsil, Sr. et al. U.S. Pat. No. 5,133,578, a flexible joint is employed to sealingly connect a pair of tubular members while still permitting limited articulated movement there between. The flexible joint includes a housing with upper and lower ring-like plates coaxially arranged about the tubular members. A pair of annular elastomeric bearings is positioned within the housing and acts against shoulders of the tubular members to flexibly retain the tubular members within the housing. A bellows sealingly couples the tubular members together while permitting movement there between. An annular chamber formed between the bellows and housing is filled with a fluid, such as silicon or oil. Means is provided for adjusting the volume of the chamber or volume of fluid in the chamber to maintain an approximately zero pressure differential across the bellows.

Additional ways of limiting exposure of the elastomeric flexible element to the heat of fluid flowing in a pipeline or riser are described in Moses et al. U.S. Pat. No. 7,341,283 issued Mar. 11, 2008. The flexible joint includes a heat shield of low heat conductivity material integrated into the inner profile of the pipe extension and interposed between the central bore of the pipe joint and the flexible element, low heat conductivity metal alloy components between the hot production fluid and the flexible element, high temperature resistant elastomer at least in the warmest inner elastomer layer of the flexible element, and a flexible element constructed to shift strain from the warmer inner elastomer layers to the colder outer elastomer layers by providing greater shear area, different layer thickness, and/or higher elastic modulus elastomer for the warmer inner elastomer layers.

SUMMARY OF THE DISCLOSURE

A two-stage bellows is the typical way of providing thermal or chemical insulation of an annular elastomeric flexible element of a flexible pipe joint from fluid flowing through the flexible pipe joint. Depending on the particular shape or configuration of the flexible pipe joint, an annular flexible boot, as further described below, will provide thermal or chemical insulation of the annular elastomeric flexible element and will provide one or more advantages in comparison to a two-sage bellows. For example, the annular flexible boot may be more economical to manufacture than a two-stage bellows, and may require a smaller space to be reliably installed or operate in a reliable manner, and may be less sensitive to buckling under certain loads, and may reduce a pressure head on the flexible joint. In many cases, the annular flexible boot can be used as an alternative to a two-stage bellows or in addition to a two-stage bellows, and by specifically adapting the shape of the boot to the type of flexible pipe joint on which it is used, the boot will improve upon the benefits of a two-stage bellows.

For example, the materials of the annular flexible boot may be selected to address specific operational requirements, and the boot may include multiple component layers that provide chemical isolation, thermal insulation, and/or pressure containment. The multiple component layers may include plastic or metal alloy foil, which may, for example, be adhered or bonded to fabric reinforced elastomer layers, in order to construct a redundant system to both isolate the annular elastomeric flexible element from the fluid flowing through the flexible pipe joint and thermally insulate the annular elastomeric flexible element from the fluid.

The annular flexible boot encircles the lumen of the flexible pipe joint, and the annular flexible boot has a first annular end attached to the extension pipe and a second annular end mounted so that pivoting of the extension pipe with respect to the body causes a flexing of the annular flexible boot, and a majority of the annular flexible boot has a shape conforming to the shape of neighboring components of the flexible pipe joint. For example, the annular ends are secured and sealed by adhesive boding agent, and a mechanical connection may also be used to add to the effectiveness of the attachment and the seal. An end portion of the annular flexible boot may be cylindrical for sealing against an inner cylindrical surface of an extension pipe, attachment member, body, or center ring of the flexible pipe joint. An end portion may be shaped in the form of an annular disk or spherical zone for sealing against an end of an extension pipe, attachment member, or centering ball.

In contrast to a bellows, a majority of the annular flexible boot is shaped to conform to neighboring members of the flexible pipe joint. This provides a more compact size for the flexible pipe joint, and a reduction in weight of the housing of the flexible pipe joint. In many cases, a majority of the annular flexible boot may be mechanically supported by contact with the neighboring members of the flexible pipe joint.

In accordance with a basic aspect, a flexible pipe joint includes a body, an attachment member mechanically coupled to the body for attaching the body to a first segment of a pipeline, and an extension pipe extending from the body for attaching the body to a second segment of the pipeline. The flexible pipe joint further includes at least one annular elastomeric flexible element flexibly coupling the extension pipe to the body to permit articulation of the flexible pipe joint by pivoting of the extension pipe with respect to the body. The attachment member and the extension pipe define a lumen through the flexible pipe joint for fluid from the pipeline to flow through the flexible pipe joint, and the at least one annular elastomeric flexible element encircles the lumen. The flexible pipe joint further includes an annular flexible boot for thermally or chemically insulating the at least one annular elastomeric flexible element from the fluid flowing through the flexible pipe joint, wherein the annular flexible boot encircles the lumen, and the annular flexible boot has a first annular end attached to the extension pipe and a second annular end mounted so that pivoting of the extension pipe with respect to the body causes a flexing of the annular flexible boot, and a majority of the annular flexible boot has a shape conforming to the shape of neighboring components of the flexible pipe joint.

In a first example, the annular flexible boot has a cylindrical shape conforming to a cylindrical central lumen of a flexible pipe joint. The cylindrical boot functions as a central sleeve for containing and sealing the fluid medium within the central lumen, and chemically and/or thermally insulating the elastomeric flexible element from the fluid medium. Each end of the cylindrical boot may be sealed against an end of a respective extension pipe or attachment member. The sealing of each end of the cylindrical boot may include use of an adhesive boding agent and use of a mechanical connection to add to the effectiveness of the seal. The cylindrical boot may also pass through a center ring of a pressure isolation unit including two diametrically disposed coaxial secondary elastomeric flexible elements coupling the centering ball to an extension pipe and an attachment member, and in this case each end of the cylindrical boot may be sealed against a respective end of the pressure isolation unit, or against an end of a respective extension pipe or attachment member.

In a second example, the annular flexible boot has a shape conforming to an outer shape of the annular elastomeric flexible element. The annular flexible boot is manufactured, for example, by forming individual sheets of elastomer layers and impervious material into the outer shape of the elastomeric flexible element, and laminating the individual sheets together. Once the annular flexible boot is installed, ends of the boot seal against respective mounting bodies of the annular elastomeric flexible element. The small volume between the annular elastomeric flexible element and the annular flexible boot may be filled with a hydraulic fluid that is compatible with the elastomeric material of the annular elastomeric flexible element, in order to provide support to the boot during operation of the annular elastomeric flexible element.

In a third example, an annular flexible boot has a body portion including an outer toroidal shaped portion and two inner portions conforming to the shape of an end of an extension pipe, attachment member, or center ring. The outer toroidal shaped portion is disposed between the two inner portions. For example, each inner portion includes a spherical portion neighboring the toroidal portion and having a shape of a spherical zone, and an end portion for sealing attachment to an inner surface of the extension pipe, attachment member, or center ring. The sealing of each end of the toroidal boot may include use of an adhesive boding agent and use of a mechanical connection to add to the effectiveness of the seal. The end portions may be cylindrical, and seal against an internal cylindrical surface of the extension pipe, attachment member, or center ring. The toroidal boot is manufactured by forming the individual sheets of impervious material and fiber reinforced elastomer layers into a toroidal shape, which is designed to fit between an end of the extension pipe and an end of an attachment member or center ball. In operation, the toroidal boot accommodates articulation of the flexible pipe joint by rolling over an inner ring of the elastomeric flexible element, on one side, and over the surface of the end of the attachment flange or center ring, on the other side. To contain the fluid medium under high pressure, the cavity behind and encircling the toroidal boot can be filled with a hydraulic fluid compatible with the elastomeric material of the elastomeric flexible element, in order to provide mechanical support to the toroidal boot. To contain the fluid medium under low to intermediate pressure, fiber reinforcement of the toroidal boot may sustain the pressure load without the support of hydraulic fluid.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown in the drawings and will be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms shown, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference toFIG. 1, there is shown an offshore drilling and production vessel generally designated10floating on a water surface11. The floating vessel in particular is a tension leg platform (TLP) secured to the seabed12by means of tendons13,14and foundation templates15,16. Although not visible inFIG. 1, there is a set of tendons depending from each of four corners of the TLP platform10to a respective one of four foundation templates15,16. In addition, each of the four lower corners of the TLP platform10is secured by a respective lateral mooring line17,18used to move the platform laterally and to resist lateral storm loadings.

For conveying drilling fluids and a drill string from the TLP to a well bore19in the seabed12, and for removing hydrocarbons from the well when drilling has been completed, a production riser generally designated20extends from the well bore19up to the TLP10. The riser20consists of a number of rigid pipe sections21joined by flexible pipe joints22.

Also shown inFIG. 1is an export riser generally designated24hanging from a leg of the TLP10in a catenary configuration and touching down on the seabed12. The export riser24, for example, is a pipeline from the TLP10to an on-shore facility (not shown), or to a buoy system for loading floating production storage and offloading vessels (FPSO's). The export riser24is similar to the production riser20in that it is comprised of a number of rigid pipe sections25joined by elastomeric flexible pipe joints26. A flexible pipe joint27at the top of the riser24is mounted in a side entry slotted receptacle34attached to a leg of the TLP10.

FIG. 2shows the side entry slotted receptacle34. The receptacle34is a weldment consisting of a forged, machined load ring41and a number of plates42,43. The plates42,43, performing as webs and flanges, serve to stabilize the load ring41as well as bridge loads between the TLP leg and the export riser.

During installation, the rear portion of the receptacle34is welded or otherwise secured to the leg of the TLP, and the upper flexible pipe joint of the export riser is inserted into the load ring41. The receptacle includes a front slot generally designated44for ease of side entry of the export riser during installation.

Flexible joints for risers and for mounting tendons to a TLP have been manufactured and stocked in various sizes for handling various standard sizes of risers or tendons. In addition, there are various kinds of flexible pipe joints especially adapted for different ranges of articulation, axial force (compression or tension), pressure, and temperature. Therefore, the flexible pipe joint22in the production riser20may be a first kind of flexible pipe joint especially adapted for axial compression and tension when conveying high temperature production fluid, the flexible pipe joint26in the export riser24may be a second kind of flexible pipe joint especially adapted for axial compression and tension when conveying low temperature production fluid, and the flexible pipe joint27at the top of the export riser may be a third kind of flexible pipe joint especially adapted for axial tension and not compression.

Each of the first, second, and third kinds of flexible pipe joint may use an annular elastomeric flexible element for permitting the flexible pipe joint to articulate under axial tension. The annular elastomeric flexible element encircles a central longitudinal lumen of the flexible pipe joint, and the production fluid flows through this lumen. The annular elastomeric flexible element functions as an elastomeric bearing having various advantages over a sliding contact mechanical bearing such as a ball-and-socket joint. For example, the annular elastomeric flexible element has no wear or static friction due to any sliding mechanical contact, and the elastomeric bearing provides a restoring force tending to minimize articulation of the flexible pipe joint, and provides some dampening of the flexing of the flexible pipe joint. The annular elastomeric flexible element may also contain pressure of the production fluid. However, the production fluid may heat the annular elastomeric flexible element, and in some cases chemicals from the production fluid may come into contact with the annular elastomeric flexible element. The heat or chemicals from the production fluid may degrade the elastomer in the annular elastomeric flexible element, and reduce the useful lifetime of the annular elastomeric flexible element.

A two-stage bellows is the typical way of providing thermal and chemical insulation of an elastomeric flexible element of a flexible pipe joint from fluid flowing through the flexible pipe joint. Depending on the particular shape or configuration of the flexible pipe joint, an annular flexible boot, as further described below, will provide thermal or chemical insulation of the annular elastomeric flexible element and will provide one or more advantages in comparison to a two-sage bellows. For example, the annular flexible boot may be more economical to manufacture than a two-stage bellows, and may require a smaller space to be reliably installed or operate in a reliable manner, and may be less sensitive to buckling under certain loads, and may reduce a pressure head on the flexible joint. In many cases, the annular flexible boot can be used as an alternative to a two-stage bellows or in addition to a two-stage bellows, and by specifically adapting the shape of the boot to the type of flexible pipe joint on which it is used, the boot will improve upon the benefits of a two-stage bellows.

FIG. 3shows an example of the first kind of flexible pipe joint22. The flexible pipe joint22includes a cylindrical body50, an attachment member51, and an extension pipe53extending from the body50. An upper attachment flange54is disposed on an outer end of the extension pipe53for attaching an upper segment of a pipeline to the flexible pipe joint22, and a lower attachment flange55is disposed on an outer end of the attachment member51for attaching a lower segment of a pipeline to the flexible pipe joint22. The body50is split into an upper half52and a lower half49, and the lower half49is integral with the attachment member51. A circular debris shield56is mounted on top of the body50to cover a circular array of threaded studs60attaching the upper half of the body50to the lower half of the body49. For example, these components are made of a corrosion resistant steel alloy. The lower half49of the body50has an array of cooling ports57,58,59spaced about its circumference to permit circulation of seawater for removal of heat from the flexible pipe joint22when high temperature fluid is conveyed though the flexible pipe joint.

FIG. 4shows a lateral cross-section of the flexible pipe joint22. In general, the components of the flexible pipe joint22are radially symmetric about a central longitudinal axis61. The attachment member51and the extension pipe53define a lumen63through the flexible pipe joint22for fluid from the pipeline to flow through the flexible pipe joint. A primary annular elastomeric flexible element62mounts the extension pipe53to the body50for pivoting about a center point48with respect to the body51. The annular elastomeric flexible element62is referred to as a “primary” annular elastomeric flexible element because it may support tensile load upon the flexible pipe joint, and historically support of tensile load has been the primary function of an annular elastomeric flexible element in a flexible tendon or pipe joint.

Pivoting of the extension pipe53with respect to the body50results in articulation of the flexible pipe joint22. In general, the pivoting of the extension pipe53about the center point48with respect to the body50may occur in any radial direction from the central longitudinal axis61, up to a certain maximum pivot angle. For example, the pivoting may occur in a forward or backward direction, or a left or right direction, or in a combination of these directions.FIG. 5shows a pivoting of the extension pipe of about five degrees to the right.

The primary annular elastomeric flexible element62encircles the central lumen63extending from the upper attachment flange54to the lower attachment flange55. In this example, the primary annular elastomeric flexible element62also encircles the extension pipe53. The primary annular elastomeric flexible element62is mounted between a hemispherical flange64disposed on a lower end of the extension pipe53, and a load ring65seated against the upper part52of the body50, which functions as a retainer flange retaining the annular elastomeric flexible element62within the body50.

For example, during a process of molding the primary annular elastomeric flexible element62, elastomer of the primary annular elastomeric flexible element is bonded to the hemispherical flange64, and elastomer of the primary annular elastomeric flexible element is bonded to the load ring65. For example, the annular elastomeric element64includes metal reinforcing rings66sandwiched between layers of the elastomer. Each metal reinforcement ring66has the shape of spherical zone centered on the center point48. For example, the metal reinforcements66have a thickness in the range of 0.15 to 0.20 inches (3.8 to 5 mm), and the elastomer layers have a thickness in the range of 0.07 to 0.20 inches (1.8 to 5 mm). After the molding of the assembly of the primary elastomeric flexible element66and the hemispherical flange64and the load ring65, the upper attachment flange54is welded to the hemispherical flange64to produce the extension pipe53.

The flexible pipe joint22further includes a pressure isolation unit70. The pressure isolation unit70is described in Danton Gutierrez-Lemini et al. U.S. Pat. No. 8,038,177 issued Oct. 18, 2011 and U.S. Pat. No. 8,985,636 issued Mar. 24, 2015. The pressure isolation unit70includes a first liner71, a center ring72, a second liner73, a first secondary annular elastomeric flexible element74disposed between the first liner71and the center ring72, and a second secondary annular elastomeric flexible element75disposed between the center ring72and the second liner73. The annular elastomeric flexible elements74,75are called “secondary” annular elastomeric flexible elements because they do not have a primary function of carrying an axial tensile load upon the flexible pipe joint22, and instead their primary function is to carry a compressive axial load upon the flexible pipe joint33, or carry a pressure load from pressure of fluid within the central lumen63. The secondary annular elastomeric flexible elements74,75, the liners71,72, and the center ring72all encircle the central lumen63.

For example, the pressure isolation unit70is molded as an integral unit, so that elastomer of the first secondary annular elastomeric flexible element74is bonded to the first liner71and bonded to the center ring70, and elastomer of the second secondary annular elastomeric flexible element75is bonded to the center ring70and bonded to the second liner73. The two secondary elastomeric flexible elements74,75may include metal reinforcements, each having the shape of a spherical zone centered on the center point48. The center ring70is spherical and centered on the center point48, and the two secondary annular elastomeric flexible elements74,75have the shape of spherical zones centered on the center point48. The two secondary annular elastomeric flexible elements74,75are coaxial with the central axis61, and the center point48resides between the two secondary annular elastomeric flexible elements.

The first inner liner71is disposed in the extension pipe53, and the second inner liner73is disposed in a pipe section of the attachment member51, so that the central lumen63passes through the pressure isolation unit70. The secondary annular elastomeric flexible elements74,75can be made of softer elastomer capable of withstanding higher strain that the primary elastomeric flexible element62, so that the secondary annular elastomeric flexible elements74,75may be thinner than the primary elastomeric flexible elements even though the secondary annular elastomeric flexible elements are closer to the center point48than the primary annular elastomeric flexible element62.

In order to insulate the annular elastomeric flexible elements62,74, and75from heat and chemicals from fluid flowing through the central lumen63, a flexible annular boot76in the form of a cylindrical tube provides a segment of the wall of the central lumen63. To insulate the two secondary annular elastomeric flexible elements74,75, the boot76is elongated so that the boot is encircled by each of the two annular elastomeric flexible elements74,75. To further insulate the primary annular elastomeric flexible element62, the boot76is further elongated so that the boot is also encircled by the primary annular elastomeric flexible element62. In this example, the central lumen63has a constant internal diameter along its length, so that the boot76does not obstruct or disrupt the flow of fluid through the lumen63, or the passage of objects through the lumen63, such as drill bits, down-hole tools, or pigs.

To assist the boot76in maintaining its dimensional integrity under heat and pressure, a majority of the boot has a shape conforming to the shape of neighboring components of the elastomeric flexible pipe joint22, so that the boot may contact and be supported by these neighboring components. For example, the upper end of the boot76is snugly received in a cylindrical recessed internal wall77of the extension pipe53. For chemical insulation and pressure containment, a layer of adhesive bonds the upper end of the boot76to the cylindrical recessed internal wall of the extension pipe. The lower end of the boot76is snugly received in a cylindrical recessed internal wall78of a pipe segment of the attachment member51. For chemical insulation and pressure containment, a layer of adhesive bonds the upper end of the boot76to the cylindrical recessed internal wall77of the extension pipe.

The boot76has a clearance fit with cylindrical internal walls of the first liner71, the centering ring70, and the second liner73. The clearance fit facilitates assembly of neighboring components71,72,73around the boot76and also enables axial strain upon the boot during pivoting of the extension to be distributed uniformly along the length of the boot in order to minimize build-up of axial strain at any particular location along the length of the boot. Yet the clearance fit permits the boot76to be mechanically supported to maintain its cylindrical shape by contact with the neighboring components71,72,73during flexing of the boot caused by articulation of the flexible pipe joint22.

For example, the flexible pipe joint22is assembled by coating the recessed internal wall78of the attachment member51and the lower end of the boot76with adhesive bonding agent, and inserting the lower end of the boot76into the recess of the internal wall78. Then the pressure isolation unit is slipped onto and lowered down over the boot76and seated into the attachment member51. Then the recessed internal wall77of the extension pipe53and the upper end of the boot76are coated with adhesive bonding agent. Then the assembly of the extension pipe53, load ring65, and primary annular elastomeric flexible element66is seated upon the first inner liner71of the pressure isolation unit, and pushed down so that the upper end of the boot76becomes inserted into the recess of the internal wall77of the extension pipe53, and the load ring65is received in the lower half49of the body50. Then the threaded studs60are screwed into the lower half49of the body50. Then the retainer flange52is assembled onto the studs60, and lowered down onto the load ring65. Then nuts79are threaded onto the studs60to seat and secure the retainer flange52onto the lower half49of the body50. Then the debris shield56, which is optional, may be assembled over the studs60. For example, the debris shield56is a split ring that is assembled around the extension pipe53, so that the debris shield56may have an internal diameter smaller than the outer diameter of the upper flange54.

FIG. 5shows flexing of the boot76caused by articulation of the flexible pipe joint22. The center ring70rotates about the center point48by half the angle of pivoting of the extension pipe53about the center point48. Deformation of the boot76from its initial cylindrical shape inFIG. 4occurs primarily at a first annular region81where the boot is near to the first secondary annular elastomeric flexible element74, and a second annular region82where the boot is near to the second annular elastomeric region.

The annular regions81,82of the boot76are not mechanically supported by contact with any of the components of the pressure isolation unit70. Instead, there are annular gap regions83,84around the annular regions81,82of the boot76. These annular gap regions83,84can be filled with an incompressible fluid to transfer a majority of the pressure from fluid inside the lumen63to the secondary annular elastomeric elements74,75. For example, the incompressible fluid is water-based hydraulic fluid compatible with the elastomer of the secondary flexible element, and the water-based hydraulic fluid consists essentially of a mixture of water and an antifreeze agent, such as ethylene glycol or propylene glycol. A suitable incompressible fluid is Compenol water-based hydraulic fluid. For example, the incompressible fluid is introduced into the gap regions83,84after the lower end of the boot76has been inserted into and bonded to the recessed internal wall78of the attachment member51, and before the extension pipe53has been assembled onto the first insert71of the pressure isolation unit70.

It is also possible to use a boot76having sufficient internal reinforcement and made with suitable materials to contain high pressure at the temperature of the fluid flowing through the central lumen63, so that there would be no need to fill the annular gap regions83,84with incompressible fluid. For example, if the temperature of the fluid flowing through the central lumen63has a temperature no greater than 150 degrees centigrade, then the boot76may have a construction similar to that of conventional high temperature high pressure flexible hydraulic tubing, provided that the fluid flowing through the central lumen does not contain chemicals incompatible with the polymer material used in such conventional hydraulic tubing. For example, conventional high temperature high pressure flexible hydraulic tubing is made of polychloroethylene thermoplastic, and has one or more layers of steel wire braid reinforcement.

For operation at high temperature, and for compatibility with chemicals in the fluid flowing through the central lumen, there are a number of commercially available polymers that could be substituted for polychloroethylene. For example, substitutes include polyether ether ketone (PEEK), and a variety of fluoropolymers, such as polyvinylidene fluoride (PVDF), Viton® fluoroelastomer, fluorinated ethylene propylene (FEP), and perfluoroalkoxy polymer (PFA). The substitutes have different advantages and disadvantages with respect to desired characteristics such as flexibility, a high maximum operating temperature at which significant creep would occur under the desired operating pressure, chemical stability of the thermoplastic over time at the desired operating temperature, compatibility with respect to chemicals in the fluid flowing through the central lumen, low permeability with respect to chemicals in the fluid flowing through the central lumen and that are incompatible with the elastomer of the secondary annular elastomeric flexible elements, low cost, ease of molding by injection or thermo-compression, and an ability to encapsulate and bond with high temperature resistant reinforcement such as steel wire, fiberglass, or polyaramid fiber (such as Nomex® or Kevlar® fiber). PEEK and PFA may permit operation at temperatures up to 250 degrees Centigrade.

Hydrogen sulfide is a chemical that is often found in hydrocarbon production fluid, and hydrogen sulfide is incompatible with elastomers commonly used in the annular elastomeric flexible elements. For example, the annular elastomer flexible elements are typically made with natural rubber or nitrile butadiene rubber (NBR). For high temperature applications, the annular elastomer flexible elements may be made with temperature resistant rubber such as peroxide cured hydrogenated nitrile butadiene rubber (HNBR). If natural rubber, NBR, or HNBR is subjected to a sufficient concentration of hydrogen sulfide, the hydrogen sulfide may diffuse into and build up in the rubber, and cause blistering of the rubber upon decompression. Hydrocarbon production fluid may contain other invasive gasses that have a similar effect upon the rubber.

In order to insulate the annular elastomer flexible elements from invasive gas, the boot76may include one or more metal layers providing a diffusion barrier to invasive gas. The metal layers should also be resistant to any chemical attack from the invasive gas. For example, hydrogen sulfide has a corrosive effect upon common ferrous steel. Stainless steels have more resistance to hydrogen sulfide, but some suffer from stress corrosion cracking when exposed to hydrogen sulfide. Stainless steels resistant to stress corrosion cracking when exposed to hydrogen sulfide include stainless steels having a high percentage of nickel, a low percentage of iron, a moderate percentage of chromium, and a moderate percentage of molybdenum, such as Alloy C276 (e.g., 59% nickel, 5.5% iron, 15% chromium, 16% molybdenum, 3.5% tungsten) or Alloy 625 (e.g., 61% nickel, 5% iron, 21% chromium, 9% molybdenum, 3.5% niobium-tantalum).

In one form of construction, the boot76has an inner metal layer providing a diffusion barrier to invasive gas, and the inner metal layer is a cylindrical tube having helical corrugations and constituting the inner wall of the boot76. For example, the metal layer is made of a stainless steel resistant to stress corrosion cracking when exposed to hydrogen sulfide. The inner metal layer is then surrounded by one or more outer reinforced polymer layers.

In another form of construction, the boot includes a plurality of thin metal layers providing a diffusion barrier to invasive gas. Strain on each metal layer due to deformation from flexing of the boot is reduced by reducing the thickness of each metal layer. Plural metal layers provide redundancy in the event of cracking a single layer. By disposing polymer between the metal layers, the polymer provides resistance to the diffusion of invasive gas even if all the metal layers become cracked, and this resistance is much greater than the diffusion resistance if the metal layers were absent because of misalignment of the cracks in one layer with the cracks in a neighboring layer.

FIG. 6shows the boot76constructed with a reinforced inner layer91, a middle region92, and a reinforced outer layer93. For example, the inner layer91is temperature resistant polymer reinforced with a single braid95of hydrogen sulfide resistant stainless steel wire. The outer layer93is temperature resistant polymer reinforced with two braids96,97of hydrogen sulfide resistant stainless steel wire. The inner layer91protects the middle region92from abrasion and de-lamination. The outer layer93provides pressure containment and ensures dimensional stability of the boot76rigidity despite a tendency of the polymer to creep when subjected to heat and pressure. The middle region92includes metal layers97,98presenting a diffusion barrier to invasive gas.

In a convenient form of construction, the multiple metal layers in the middle region92are made by winding at least one metal foil strip or metalized polymer strip. For example, the metalized polymer is made by deposition of metal onto a polymer sheet. For example, the metal is deposited by vacuum deposition of sputtered metal, or the metal is deposited from a liquid solution by an electroless plating process. For example, the sputtered metal is a hydrogen sulfide resistant stainless steel, or the metal deposited by electroless plating is nickel. It is also possible to electroplate nickel, chromium, or nickel-chromium alloy upon a sputtered metal film or an electroless plated metal film.

In order to reduce strain due to flexing of the boot76upon the metal layers97,98in the middle region92, each of the metal layers has helical corrugations. For example, a sheet of metal foil, or a sheet of metalized polymer, is corrugated by feeding the sheet through a pair of intermeshing rollers. Helical corrugations in the metal layers97,98are obtained by cutting a corrugated sheet into strips so that each strip has diagonal corrugations, and then winding the strips.FIG. 7shows one such strip101. A number of corrugated strips could be stacked upon each other before winding them to form the middle layer92.

In a convenient form of construction, the boot76is manufactured by injection molding or thermo-compression molding. Polymer and metal strips are wound upon, and wire braid is slipped over, a cylindrical mandrel defining the inner diameter of the boot76. Then the assembly of the cylindrical mandrel and the wire braid is placed in a mold defining the outer diameter of the boot76. For example, the mold has two identical pieces that are clamped around the assembly. In a thermo-compression process, the clamping of the mold may provide compression for fusing the polymer layers together.

A thermo-compression process may have a tendency to flatten the corrugations in the metal layers in the middle region92. This tendency could be reduced by filling the corrugations of the strips with reinforcements such as stainless steel wire, fiberglass, or polymer fiber. For example,FIG. 8shows reinforcements102inlaid in the corrugations of the strip101.

For high temperature operation, a mechanical connection may maintain the integrity of the attachment and the seal between the upper end of the boot76and the extension pipe53, and the integrity of the attachment and the seal between the lower end of the boot and the attachment member51. For example,FIG. 9shows an alternative construction in which an expandable metal ring110provides a mechanical connection between the lower end of the cylindrical tubular boot111and the attachment member112of a flexible pipe joint. An internal annular grove113is machined into the attachment member112. The lower end of the boot111is received in an annular recess114in the upper portion of the expandable metal ring110. The expandable metal ring110also has a lower rim115conforming to internal annular recess in the body112.

FIG. 10shows a tool116inserted into the body112. The tool has a cylindrical portion118and a lever117. The lever is operated to expand the expandable ring110by expanding the lower rim115into the internal annular groove113. A similar tool could be used to expand the upper portion of the expandable ring110to secure the lower end of the boot111in the annular recess114.

FIG. 11shows a lateral cross-section of the second kind of flexible pipe joint26. The flexible pipe joint26has radial symmetry around a central axis120. The flexible pipe joint has an annular body121, an extension pipe122extending from the body, and an attachment member124bolted to the body121. These components of the flexible pipe joint are made of corrosion resistant steel.

The flexible pipe joint26has an annular elastomeric flexible element123flexibly mounting the extension pipe122to the body121. The annular elastomeric flexible element123encircles the extension pipe122. Elastomer of the annular elastomeric flexible element123is bonded to a hemispherical flange125on the upper end of the extension pipe122, and bonded to an internal seating area of the body121. The annular elastomeric flexible element123has a plurality of metal reinforcements126, which are constructed and separated by elastomer layers, in a fashion described above with respect to the primary annular elastomeric flexible element62inFIG. 4.

The attachment member124has an upper attachment flange127and a lower flange128spaced by a very small gap from the hemispherical flange125. Opposing surfaces of the lower flange128and the hemispherical flange125have the shape of a spherical zone centered on a center point129. The close proximity and contoured surfaces of flange128and flange125are designed so that upon accidental (or managed) load reversal on extension122, flange125comes into early contact with flange128, limiting the amount of axial stretching of the flexible element, and thus preventing the development of damaging tri-axial tension stresses in the elastomeric pads of flexible element123. The flexible pipe joint26has a central lumen130extending from the upper attachment flange127and down through the extension pipe122. Fluid flowing through the central lumen130seeps through the gap between the hemispherical flanges125,128and fills an annular cavity131surrounding the lower flange128and surrounding a portion of the annular elastomeric flexible element123. This annular cavity131is sealed at the top by a ring seal132(such as an O-ring, or a metal gasket) clamped between the cover124and the body121. At the bottom, the cavity131is sealed by the annular elastomeric flexible element123.

In order to insulate the annular elastomeric flexible element123from heat and chemicals in the fluid that has seeped from the central lumen130into the annular cavity131, an annular flexible boot133is disposed in the cavity131. As shown inFIGS. 11, 12, 13, 14, and 15, the annular flexible boot133is folded to fit between and conform to the shape of an outer wall of elastomer of the annular elastomeric flexible element123and a cylindrical inner wall of the body121. The shape of the flexible boot133changes by a rolling action to continue to conform to the shape of the outer wall of the annular elastomeric flexible element123and the cylindrical inner wall of the body121as the extension pipe122pivots about the center point129. The rolling action is seen by a comparison ofFIG. 13toFIG. 12, in which a fold at the bottom of the boot133has a height that changes with the angle of inclination of the extension pipe122.

The flexible boot133could be directly bonded with adhesive to the inner wall of the body121and the top of the hemispherical flange125. As shown inFIG. 11, however, the flexible boot133is directly bonded with adhesive to an inner ring134and an outer ring135. The inner ring134has the shape of a washer in order to be seated on top of the hemispherical flange125, where it is bonded with adhesive to the top of the hemispherical flange125. The outer ring135has the shape of a short tubular cylinder in order to fit snugly in the body121against the inner wall of the body, where it is bonded with adhesive to the inner wall of the body. The inner ring134and the outer ring135facilitate installation of the flexible boot133by maintaining the desired shape of the flexible boot133during installation.

As shown inFIG. 14, an annular region136between the flexible boot133and the elastomer wall of the annular elastomeric flexible element123is filled with incompressible fluid so that the incompressible fluid transfers a majority of the pressure from fluid inside the central lumen130to the annular elastomeric element123. For example, the incompressible fluid is water-based hydraulic fluid compatible with the elastomeric material of the annular elastomeric flexible element123. The water-based hydraulic fluid consists essentially of a mixture of water and an antifreeze agent, such as ethylene glycol or propylene glycol. A suitable incompressible fluid is Compenol water-based hydraulic fluid. For example, a measured amount of the incompressible fluid is introduced just before installation of the flexible boot133, and the flexible boot is pressed down during installation to remove any air that would otherwise be trapped under the flexible boot.

FIG. 16shows an alternative construction for mechanical connections of an annular flexible boot141similar to the flexible boot133. As shown inFIG. 16, an inner portion of the flexible boot141is bonded to a first inner ring142similar to the inner ring134, and a second inner ring143is assembled over the first inner ring142and secured by fasteners144(such as bolts or machine screws) to clamp the inner end of the flexible boot141between the second inner ring143and the first inner ring142. The fasteners144, for example, fasten the assembly of the first inner ring142and the second inner ring143to the top of a hemispherical flange of an extension pipe.

An outer portion of the flexible boot141is received in an annular groove in a lower end of an outer ring145. The outer ring145has an outer diameter sized to fit snugly with the inner wall of a flexible pipe joint body, and sufficient radial thickness for securely fastening the flexible boot to the outer ring by action of a crimping tool that reduces the radial gap width of the annular groove146.

The flexible boots133and141can be made from cylindrical tubular layers of elastomer, reinforcement, and metalized polymer film. The cylindrical tubular layers are laminated, deformed, and then bonded in a molded process. The cylindrical tubular layers should have elastic properties or corrugations for expansion and contraction in a circumferential direction, and some resiliency against deformation in the longitudinal direction.

For example,FIG. 17shows a cylindrical tubular layer151of resilient metal reinforcements152,153,154and metalized polymer film155. For example, the resilient metal reinforcements are stainless steel wires or narrow strips extending in a longitudinal direction.

FIG. 18shows a cylindrical tubular layer156of woven fiber reinforcements157,158. For example, each fiber reinforcement is a thread of polyaramid fiber, such as Nomex® fiber or Kevlar® fiber. The fiber reinforcements157,158are woven as a braid, or as cloth that is cut into a strip that is rolled to form the layer156.

FIG. 19shows a top cross-section view of an assembly161of the cylindrical tubular layer151of resilient metal reinforcements and metalized polymer film as shown inFIG. 17sandwiched between two cylindrical tubular layers162,163of woven fiber reinforcements. Each of the layers162,163of woven fiber reinforcements is similar to the layer156shown inFIG. 18. The assembly161is formed, for example, when the layers151,162,163are laid up over an inner tube171of a two-piece mold170as shown inFIG. 20. An outer tube172of the mold170is slipped onto the assembly in order to form the flexible boot133by injection molding or thermo-compression molding. After the flexible boot133is removed from the mold170, the lower half of the boot is rolled-up upon itself to produce the shape show inFIGS. 11 to 14.

FIG. 21shows a lateral cross-section of the third kind of flexible pipe joint27. The flexible pipe joint27has radial symmetry around a central axis180. The flexible pipe joint27has an annular body181, an extension pipe182extending from the body, and an attachment member184bolted to the body. These components of the flexible pipe joint are made of corrosion resistant steel.

The flexible pipe joint27has an annular elastomeric flexible element183mounting the extension pipe182to the body181. The annular elastomeric flexible element183encircles the extension pipe182. Elastomer of the annular elastomeric flexible element183is bonded to a hemispherical flange185on the upper end of the extension pipe182, and bonded to an internal seating area of the body181. The annular elastomeric flexible element183has a plurality of metal reinforcements186, which are constructed and separated by elastomer layers, in a fashion described above with respect to the primary annular elastomeric flexible element62inFIG. 4.

The attachment member184has an upper attachment flange187and a lower flange188spaced by a gap from the hemispherical flange185. Opposing surfaces of the lower flange188and the hemispherical flange185have the shape of a spherical zone centered on a center point189. The flexible pipe joint27has a central lumen190extending from the upper attachment flange187and down through the extension pipe182. The annular elastomeric flexible element183encircles the extension pipe182and thus encircles the central lumen190. Fluid flowing through pressure relief passages194,195from the central lumen190fills an annular cavity191surrounding the lower flange188and surrounding a portion of the annular elastomeric flexible element183. This annular cavity191is sealed at the top by a metal gasket or an elastomeric ring seal192clamped between the attachment member184and the body181. At the bottom, the cavity191is sealed by the annular elastomeric flexible element183.

In order to insulate the annular elastomeric flexible element183from heat and chemicals from fluid flowing through the central lumen190, an annular flexible boot193in the shape of half of a toroid extends into the gap between the lower flange188and the hemispherical flange185on the upper end of the extension pipe182. As shown inFIGS. 21, 22, 23, 24, and 25, the toroidal flexible boot193is folded to fit between and conform to the shape of the opposing surfaces of the lower flange188and the hemispherical flange185. The flexible boot193also has end portions196,197that conform to the shape of the central lumen190. The upper end portion197conforms to a conical shape of the central lumen190on an inner wall of the lower flange188. The lower end portion197conforms to a cylindrical shape of the central lumen190on an inner wall of the extension pipe182.

When the extension pipe182pivots about the center point189, the shape of the flexible boot193changes by a rolling action to conform to the shape of the opposing surfaces of the lower flange188and the hemispherical flange185. The rolling action is seen by a comparison ofFIG. 21toFIG. 22, in which a fold at the outer circumference of the boot193has a height and radius from the central axis180that changes with the angle of inclination of the extension pipe182.

FIG. 23shows that the upper end197of the flexible boot193is directly bonded with adhesive198to the inner wall of the lower flange188, and the lower end196of the flexible boot193is directly bonded with adhesive199to the inner wall of the extension pipe182.

FIG. 24shows an alternative construction similar to the construction shown inFIG. 23. In this example, a toroidal flexible boot201(which is identical to the toroidal flexible boot193) is mechanically secured to a lower flange202and to an extension pipe203. An upper metal ring205has an annular groove to receive an upper end of the toroidal flexible boot201. The upper metal ring205is radially expanded into an internal annular groove207in the lower flange202. A lower metal ring208has an annular groove209to receive a lower end of the flexible boot201. The lower metal ring208is radially expanded into an internal annular groove210in the extension pipe203.

The toroidal flexible boot193can be made from layers of elastomer, reinforcement, and metalized polymer film in a way similar to the way described above with reference toFIGS. 17 to 20for manufacturing the flexible boot133. The flexible boot193, however, has a more convoluted shape than the flexible boot133, and therefore a more complicated mold is used for molding the flexible boot193.

FIG. 26shows a mold210for molding the flexible boot193. The mold includes an annular bottom piece211, an annular internal piece212, and an annular top piece213. The component layers of the flexible boot193are laid up upon the internal annular piece, and then the mold is closed by engaging the lower piece211with the internal piece212, and engaging the top piece213with the lower piece and the internal piece. The component layers are fused together by injection of molten polymer or by thermo-compression. After the flexible boot193has been molded, the top piece213and the bottom piece211are removed, and then the flexible boot193is removed from the internal piece.

If the flexible boot is so heavily reinforced that it would be damaged by forcible removal from the internal piece212, then the internal piece could be made of sacrificial material. In this case the internal piece212would be destroyed in order to liberate the flexible boot193from the internal piece at the end of the molding process. For example, the internal piece212could be machined from aluminum or zinc alloy that would be readily soluble in acid or alkali, or the internal piece could be molded from cement made acid soluble or crushable by the addition of calcium carbonate.

In the examples above, the annular flexible boots have been described as having at least one metal layer impervious to invasive gas. If deleterious invasive gas is absent from the fluid, then the metal layers could be omitted from the flexible boot, and the flexible boot could still provide thermal insulation and/or pressure isolation of the annular elastomeric flexible element.

In the examples above, a different kind of annular flexible boot for thermal or chemical insulation has been used in each of three different kinds of flexible pipe joint having an annular elastomeric flexible element flexibly mounting an extension pipe to a body of the flexible pipe joint. It is also possible to use the different kinds of annular flexible boot in the same flexible pipe joint. This would provide more than one layer of thermal or chemical insulation of the annular elastomeric flexible element. For example, the flexible boot76inFIG. 4could be added to the flexible pipe joint26inFIG. 11, or added to the flexible pipe joint27inFIG. 21. The flexible boot133inFIG. 11could be added to the flexible pipe joint22inFIG. 4, or added to the flexible pipe joint27inFIG. 21. Alternatively, for example, the flexible boot76inFIG. 4and the flexible boot193inFIG. 21could be added to the flexible pipe joint26inFIG. 11, to form a triply-redundant isolation boot system. If high temperature fluid were flowing through the flexible pipe joint, then more than one layer of thermal insulation would result in the annular elastomeric flexible element operating at a lower temperature to extend the lifetime of the annular elastomeric flexible element. In addition, by using more than one flexible boot for thermal insulation, protection from invasive gas could be achieved by including a metal layer in only one of the flexible boots, and the metal layer could be put in the colder one of the flexible boots, so that stress corrosion cracking of this metal layer would be reduced by the lower temperature due to the thermal insulation of the warmer one of the flexible boots.

In the examples above, each flexible pipe joint has an attachment member for attaching the flexible pipe joint to a first segment of a pipeline, and an extension pipe for attaching the flexible pipe joint to a second segment of the pipeline, in order to permit fluid from the pipeline to flow through the flexible pipe joint. The attachment member and the extension pipe may be attached to the pipeline segments in various ways, such as by welding as well as bolting or clamping flanges together. Moreover, the attachment member may have various forms, such as a second extension pipe flexibly mounted to the body by an additional annular elastomeric flexible element, and in this case, the flexible pipe joint may have a second primary flexible boot for thermally or chemically insulating the second primary annular elastomeric flexible element. If the attachment member were a second extension pipe flexibly mounted to the body by a second primary annular elastomeric flexible element and the flexible pipe joint uses a flexible boot in the form of a cylindrical tube having one end attached to an end of the first extension pipe, then the second end of the cylindrical tube could be attached to an internal end of the second extension pipe.

The flexible thermal or chemical insulating boots described above could be used in flexible pipe joints that have additional means for thermal or chemical insulation of a secondary flexible element. The additional means for thermal or chemical insulation may include, for example, a two-stage bellows, a heat shield of low heat conductivity material integrated into the inner profile of the pipe extension and interposed between the central bore of the pipe joint and the annular elastomeric flexible element, and low heat conductivity metal alloy components between the hot production fluid and the flexible element, for example as described in Moses et al. U.S. Pat. No. 7,341,283 issued Mar. 11, 2008.