TERMINAÇÃO DE RISER PARA CONECTAR UM DUTO RISER CATENÁRIA DE AÇO A UMA INTERFACE DE CONEXÃO DE TUBO EM I OU TUBO EM J DE UMA UNIDADE FLUTUANTE E MÉTODO PARA CONECTAR UM DUTO RISER CATENÁRIA OFFSHORE DE AÇO A UMA UNIDADE FLUTUANTE FPSO

Description

1 / 19 RISER TERMINATION FOR CONNECTING A STEEL CATENARY RISER PIPE TO AN I-PIPE OR J-PIPE CONNECTION INTERFACE OF A FLOATING UNIT AND METHOD FOR CONNECTING A STEEL OFFSHORE CATENARY RISER PIPE TO AN FPSO FLOATING UNIT Description

[001] The present invention relates to a rigid steel offshore riser termination and fastening system for coupling a rigid steel riser to an I-pipe coupling interface originally provided for flexible riser fastening to a floating production, storage and offloading vessel (FPSO).

[002] More specifically, the invention relates to an improved structure for connecting the upper part of a Steel Catenary Riser (SCR) to a float, for example, a monohull floating vessel, typically an FPSO type.

[003] The SCR terminology includes all rigid metallic risers with a catenary shape, particularly single catenaries (SCR) and double catenaries (SLWR), in which the metallic wall of the riser performs structural and waterproofing functions, in contrast to multilayer composite flexible risers.

[004] In a typical configuration of offshore oil and gas production systems, a set of valves and fittings used to regulate the entry and exit of products to and from a well, called trees, are positioned on the seabed and on floating units, so-called floating production, storage and offloading (FPSO) facilities, which are positioned at sea level. The trees are fluidically connected to the floating production, storage and offloading (FPSO) facilities by means of rigid or flexible oil or gas transport pipes, called risers, which extend from the seabed to sea level.

[005] This configuration allows for greater flexibility in field configurations, such as multiple individual wells and multiple drilling centers, and reduces interference within the main field construction phases: drilling, pipe laying, and FPSO fabrication. Once the subsea exploration field is completed, the floating unit (FPSO) can approach the target location, where the floating unit is anchored by means of a mooring that is normally pre-installed on the seabed. Then, the upper ends of the risers are Petition 870260020239, dated 04 / 03 / 2026, page 44 / 68 2 / 19 moved and connected to the floating production, storage and offloading (FPSO) unit to transport the petroleum product from the wells to the FPSO unit.

[006] On the other hand, the use or incorporation of risers as so-called service lines for transporting methanol or other chemicals to ensure the flow of petroleum product (flow assurance), or for transporting injection water for injecting water into the subsea soil to increase the extraction rate of oil or gas product in the well, which serves the fluid transport that occurs from the floating unit (FPSO) down towards the wells, is becoming increasingly frequent.

[007] The configuration in which the set of valves and accessories (trees) mentioned above is arranged on the seabed (called a wet tree configuration) allows for greater freedom of movement of the floating units (FPSOs) compared to a configuration in which the set of valves and accessories is arranged on the floating unit at sea level (called a dry tree configuration). This allows the use of common floats, for example, standard vessels such as Suezmax, Panamax, which are adapted to accommodate oil plants, and which are anchored by means of a specific mooring system that, depending on the local climate and sea conditions, can be fixed (e.g., a so-called spread mooring) or rotating (e.g., a so-called tower mooring).

[008] The movements of the FPSO are linked to those of the riser, and the movements and stresses are transmitted between these two structural subsystems, differently depending on the configuration in which the risers hang from the float (so-called hang-off risers, which are relevant to the present invention) and configurations in which the risers are free from the FPSO (so-called independent risers, which are less relevant to the present invention). The movements of the FPSO induce mechanical stresses in the riser, which combine with corrosive and chemical actions on it. Specific critical regions are the upper coupling of the riser (suspended region) as well as the riser support region on the seabed (touch point).

[009] To withstand dynamic mechanical loads, internal fluid loads, and corrosive and chemical attack, risers are generally made of carefully selected materials or combinations of materials, such as, for example, metallic materials for rigid risers, multiple layers of composite materials for flexible risers, so-called umbilical duct structures with dedicated duct tubes (umbilical) inside Petition 870260020239, dated 04 / 03 / 2026, page 45 / 68 3 / 19 an external protective tube, or composite polymer material in tubes that are used in particularly challenging projects.

[0010] Among the known possible forms and boundary conditions of risers, the simple catenary form (called SCR steel catenary riser) or multiple and compound catenary forms should be listed, such as, for example, the so-called slow wave steel catenary riser (SWLR) or sleeper riser, in which the tension of the upper portion of the riser is reduced at the cost of an increased length.

[0011] The structural interface between the riser and the floating unit, which is a relevant issue for the present invention, must support and influence in a desired manner the dynamic forces and movements of the two subsystems. Furthermore, specific transfer systems and equipment are provided on the floating unit that move, hold, guide, and manipulate the upper end of the riser to facilitate rapid installation of the upper end of the riser on the floating unit without occupying valuable space for the oil and gas processing plants.

[0012] Such known suspended interfaces include, in particular, the so-called I-tube interfaces.

[0013] In the I-tube support mode (which is relevant to the present invention), the upper end of the flexible riser forms a flexible joint portion to which an additional coupling adapter is connected, while a receptacle fixed to the floating unit forms a circumferentially closed tube section having an enlarged upper edge and an enlarged lower edge (hence the name I-tube), into which the upper end of the riser is inserted from below until the coupling adapter is above the upper edge of the I-tube. Subsequently, in order to lock the adapter relative to the I-tube, a locking lever mechanism on said upper edge must be activated so that the locking levers of the locking lever mechanism move between the coupling adapter and the I-tube and prevent the locking adapter from returning downwards and thus the flexible riser from sliding downwards out of the I-tube.

[0014] The necessary traction of the upper end portion of the riser into the I-tube is achieved by means of a traction cable that is inserted through the I-tube and can be further guided and redirected by means of redirection pulleys installed on the floating unit above the I-tube. Petition 870260020239, dated 04 / 03 / 2026, page 46 / 68 4 / 19

[0015] The necessary riser transfer systems and handling equipment include, for example, traction devices such as winches, cables, chains, traction heads.

[0016] Other auxiliary installation devices integrated into the floating unit (container) include, for example: - a traction system positioned on the deck of the vessel and featuring a redirection pulley system, - a traction system positioned on a main deck of the vessel where the main deck is cantilevered, and / or - a traction system suspended from the side wall of the vessel, like a counter, featuring sleds for moving the traction system into the position for its use, - a traction system mounted on a rotating slide mounted on the deck (called a rotating turret).

[0017] A known method of attaching offshore flexible risers used for tower-moored FPSOs involves the following steps: A) A messenger cable is extended through each I-tube, with one end exiting the upper opening of the I-tube and the other end exiting the lower opening of the I-tube and extending outward from the floating production, storage and offloading (FPSO) unit. B) The first end of the messenger cable is connected to the head of a draw cable. C) A construction vessel, other than the floating production, storage and offloading (FPSO) unit, enters the field and secures the upper end of a riser to the riser mounting tower, the upper end of the riser already being fitted with a pull-out head and a tripod, D) The second end of the messenger cable is passed from the floating unit to the construction vessel. E) The head of the traction cable is moved from the platform to the construction vessel. F) The tension cable is connected to an abandonment cable and to the triplate on the riser. (G) The riser is lowered to the construction vessel's landing tower, and a load transfer is made from the abandonment cable to the traction cable. H) Using the draw cable, the riser is then raised towards the lower mouth of the tube at I, Petition 870260020239, dated 04 / 03 / 2026, page 47 / 68 5 / 19 I) The abandonment cable is removed from the riser by divers, J) Using the pull cable, the riser is raised from below inside the lower mouth of the I-tube, K) A riser bend reinforcement is connected to a lower connector and can be separated from the traction head. Divers or remotely operated vehicles (ROVs) check the distances, the condition of the guides, the insertion of the riser into the I-tube and, if necessary, release the locking lever system blocks that were kept open, for example, by inflated balloons or retaining cables, and check the correct engagement of the locking lever. L) The riser head is then raised and brought above the level of the spider deck. M) The riser head is attached to the deck by means of a fixing bar, N) The traction system is repositioned for the next riser pull.

[0018] The method described is applied analogously to both traction and fixing of flexible risers in FPSO units with spread layouts and in FPSO units with rotating turrets.

[0019] Driven by economic advantages and technological constraints, there may be a desire or a need to use rigid steel risers or steel catenary risers (SCR) instead of flexible risers.

[0020] However, known rigid steel risers are by no means adapted to be coupled to the I-pipe coupling interface described above of a floating production, storage and offloading (FPSO) vessel, due to bending moment constraints caused by the engagement of the riser termination with a bend-resistant upper suspension connection point (upper balcony or I-pipe coupling) and with a bend-resistant lower I-pipe connection point (lower balcony or I-pipe coupling), which would cause the significantly stiffer rigid riser to behave as a continuously supported beam rigidly fixed at its free end and therefore involve excessive cyclic bending stresses in both the riser and the I-pipe interface of the float.The large movement response of a monohull FPSO vessel, caused by weather and marine conditions and the limited height of the FPSO vessel—that is, the relatively short distance between the upper suspended support and the lower support of the riser termination I-tube—increases the stiffness of the connection and the resulting bending moments and lateral / shear forces.

[0021] In particular, the connection between the steel catenary riser (SCR) and the float Petition 870260020239, dated 04 / 03 / 2026, pp. 48 / 68 6 / 19 (FPSO) involves the cyclic transmission of load between these two bodies, in addition to static loads, resulting in significant transverse and bending loads in, and near, the interface region between the FPSO and the SCR. The dynamic interaction between the riser and the float is therefore generally complex, and it is desirable that the coupling between the rigid steel riser and the I-tube coupling interface of the float be able to transfer loads while avoiding excessive stress levels, stress concentrations, and subsequent fatigue damage.

[0022] An additional influencing factor is the corrosion of the riser material induced by environmental agents and hydrocarbon products, including hydrogen embrittlement phenomena, which contributes to so-called stress corrosion, i.e., the combined effect of multiple factors, including a material of low toughness and high strength, a corrosive environment, tensile stresses above a certain limit, and high temperature variations.

[0023] It is observed that the specialist, faced with excessive transverse bending and fatigue loads in a structure, due to predefined boundary conditions, i.e., the I-tube connection interface, would consider two standard ways to deal with excessive stresses: A) using a more suitable material to resist the higher stresses, for example, titanium alloy instead of structural carbon steel, or B) increasing the resistant cross-section and bending modulus, making the riser stronger along its riser termination section.

[0024] Under the present circumstances, the use of titanium alloy instead of structural carbon steel would significantly increase the costs of the risers, and a uniform increase in cross-section along the entire upper riser termination would lead to possible space violations within the I-tubes and would also increase the cost of the riser. US patents 8474539B2 and BRPI0505400A describe prior solutions for riser terminal coupling systems and draft tube coupling systems.

[0025] The objective of the present invention is, therefore, to propose a new and improved rigid steel riser termination structure and fastening system adapted for connecting steel catenary risers to existing I-tube floats and suspended systems originally designed for flexible risers, wherein the riser is pulled through a lower I-tube to an upper suspended area at deck level.

[0026] The objective of the invention is achieved by an upper termination of the riser of Petition 870260020239, dated 04 / 03 / 2026, page 49 / 68 7 / 19 steel catenary and connection system for connecting the steel catenary riser to an FPSO float featuring an I-tube connection interface with an upper suspended seat (deck level) defining an upper suspended shaft and a lower I-tube disposed at a vertical distance below the upper suspended seat and defining a lower I-tube entry shaft, wherein the riser termination and connection system have the characteristics of claim 1.

[0027] Advantageous and preferred embodiments are the subject of the dependent claims.

[0028] According to one aspect of the invention, a riser termination 7 is provided for connecting a steel catenary riser duct 2 to an I-pipe or J-pipe connection interface of a floating unit 3, said connection interface comprising: - a lower tubular coupling vessel 4 (I-tube) installed on the floating unit 3 at a lower riser coupling level 5 and adapted to receive a coupling adapter 6 from a riser termination of a riser pipeline, - a locking mechanism 18 provided in the lower coupling container 4 to lock the coupling adapter 6 against being pulled downwards from the lower coupling container 4, - an upper suspension seat 19 installed on the floating unit 3 at an upper riser coupling level 21 above the lower riser coupling level 5 and adapted to receive and lock an upper suspension portion of a riser termination, Riser termination 7 comprises: - a portion of upper suspension 22, - a bottom coupling adapter 6, - a termination conduit 28 made of structural steel having an upper conduit end 29 rigidly connected to the upper suspension portion 22 and a lower conduit end 30 rigidly connected to an adjacent conduit section 31 of the rigid steel riser duct 2, forming a lower end of the riser termination 7, said termination conduit 28 extending through said coupling adapter 6 and being axially sliding relative to the coupling adapter 6, - a support structure 32 to support the termination conduit 28 inside the Petition 870260020239, dated 04 / 03 / 2026, pp. 50 / 68 8 / 19 coupling adapter 6, said support structure 32 comprising: - a circular cylindrical bearing seat 33 formed within the coupling adapter 6 and defining a bearing seat diameter 34 and a bearing seat axis 35 (being the central axis of symmetry of the bearing seat 33), - a rounded annular bearing body 36 having a bearing body diameter 37 and projecting out of said termination conduit 28 within the bearing seat 33, - wherein the diameter of the bearing body 37 is less than the diameter of the bearing seat 34 to provide at least a one-sided gap 46 between the bearing body 36 and the bearing seat 33 and to allow relative axial sliding along the axis of the bearing seat 35 and relative rotation at least around the axis of the bearing seat 35 between the bearing body 36 and the bearing seat 33.

[0029] The termination conduit 28 comprises at least one portion of conduit of variable cross-section 38 having an outside diameter 39 and a conduit wall thickness 40, both decreasing in a direction away from the bearing body 36.

[0030] The combination of the described support structure and the described variable cross-section of the termination conduit 28 allows the riser termination 7 to bend naturally within and around the lower tubular coupling vessel 4 (I-tube), without colliding with the I-tube, and allowing the riser entry angle 2 to be compatible with the riser termination 7.

[0031] The system does not require any clearance compensation between the bearing body 36 and the bearing seat 33, on the contrary, the clearance is expressly provided for and maintained, and does not involve any requirement for a straight riser termination 7, on the contrary, the riser termination is elastically bent and designed to remain bent during use.

[0032] Lateral loads and bending stresses on riser 2 and the I-tube connection interface are kept within acceptable limits. The economic advantages of rigid steel risers can be exploited more broadly. There is also an improvement in work safety, since installation methods like 'pull into I-tube' can be used without diver intervention.

[0033] The use of structural steel conduits also increases the balance of Petition 870260020239, dated 04 / 03 / 2026, pp. 51 / 68 9 / 19 reliability / cost due to extensive knowledge and accuracy in modeling fatigue phenomena, material properties, and welding procedures of structural steel compared to other materials, such as, for example, structural steel tubes, for example, titanium alloys.

[0034] In addition, the risk of galvanic corrosion due to the use of different conductive materials is reduced.

[0035] These and other features and advantages of the present invention will be evidenced from the accompanying drawings which illustrate embodiments of the invention and, together with the general description of the invention provided above, and the detailed description of the embodiments provided below, serve to explain the principles of the present invention.

[0036] Figure 1 illustrates a spread-mounted anchored floating FPSO unit with a submerged riser counter and a series of connected riser pipelines,

[0037] Figure 2 illustrates a side wall of the floating unit with a riser traction device, an upper suspended seat, a lower I-pipe counter and a traction line (but without riser) in the riser installation phase - FPSO Connection,

[0038] Figure 3 is a side view of the upper suspended seat at the top of an upper I-tube at the I-tube connection interface,

[0039] Figure 4 is a side view of the lower counter with a lower J-tube with a downward-facing angled inlet bell mouth and with a lower I-tube, of the I-tube connection interface,

[0040] Figure 5 is a cross-sectional view of an example I-tube coupling container of the lower I-tube of the I-tube connection interface,

[0041] Figure 6 is a side view of a disassembled upper riser termination according to an embodiment of the invention,

[0042] Figure 7 is a perspective view of a lower coupling portion of the upper riser termination in Figure 6,

[0043] Figure 8 is an exploded perspective view of a bolted flange connection between the upper riser termination portions in Figure 6,

[0044] Figure 9 is a perspective view of an upper suspension portion of the upper riser termination in Figure 6,

[0045] Figure 10 is a perspective view of an upper riser termination. Petition 870260020239, dated 04 / 03 / 2026, pp. 52 / 68 10 / 19 disassembled according to one embodiment of the invention,

[0046] Figures 11 and 12 are enlarged views of details of the upper riser termination in Figure 10,

[0047] Figure 13 is a cross-sectional view of a lower coupling portion, including a partially spherical portion, of the upper riser termination, in which the lower coupling portion and a bearing structure are received within a lower I-tube coupling housing of the I-tube connection interface, according to one embodiment of the invention.

[0048] Figure 14 is a side view of a disassembled upper riser termination according to one embodiment of the invention,

[0049] Figure 15 is a perspective view of the disassembled upper riser termination shown in Figure 14.

[0050] Figures 16 and 17 are enlarged views of details of the upper riser termination in Figure 15,

[0051] Figure 18 is a side view of the upper termination of the steel catenary riser installed at the I-pipe connection interface of the FPSO vessel, according to one embodiment.

[0052] With reference to the figures, a system 1 for connecting an offshore riser pipeline 2 to an FPSO floating unit 3 comprises a lower tubular coupling vessel 4 (I-tube) installed on the floating unit 3 at a lower riser coupling level 5 and adapted to receive a coupling adapter 6 from an upper riser termination 7 of said riser pipeline 2, said coupling vessel 4 having an annular side wall 8 extending around a longitudinal axis of the vessel defining a lower riser inlet axis 9, a lower downward-facing opening 10 defined by a lower end edge 11 (preferably flared outwards) of the side wall 8, forming a so-called bell mouth, an upper upward-facing opening 12 defined by an upper end edge 12 (preferably flared outwards) of the side wall 8.

[0053] System 1 further comprises a locking mechanism 18 provided in the lower coupling container 4 for locking the coupling adapter 6 of the upper riser termination 7 against downward withdrawal from the lower coupling container 4, Petition 870260020239, dated 04 / 03 / 2026, pp. 53 / 68 11 / 19

[0054] System 1 further comprises a traction device 14 installed on the floating unit 3 at a traction device level 15 above said riser coupling level 5 and adapted to pull a traction line 16 (figure 1) extended through the lower coupling vessel 4, wherein the traction line 16 is intended to be coupled to a traction head 17 on the upper riser termination 7 of the riser pipeline 2, such that the upper riser termination 7 is pulled from bottom to top into the lower coupling vessel 4.

[0055] System 1 further comprises an upper suspended seat 19 installed on the floating unit 3 at an upper riser coupling level 21 (below the traction device level 15 and above the lower riser coupling level 5) and adapted to receive and lock an upper suspension portion 22 of the upper riser termination 7.

[0056] The upper suspension seat 19 defines an upper suspension axis 24 that determines the orientation of the locked upper suspension portion 22 of the riser termination 7.

[0057] The upper riser 7 termination comprises: - the upper suspension portion 22, - the lower coupling adapter 6, - a termination conduit 28 made of structural steel having an upper conduit end 29 rigidly connected to the upper suspension portion 22 and a lower conduit end 30 rigidly connected to an adjacent conduit section 31 of the rigid steel riser duct 2, forming a lower end of the riser termination 7, said termination conduit 28 extending through said coupling adapter 6 and being axially sliding relative to the coupling adapter 6, - a bearing structure 32 for supporting the termination conduit 28 within the coupling adapter 6, said bearing structure 32 comprising: - a circular cylindrical bearing seat 33 formed within the coupling adapter 6 and defining a bearing seat diameter 34 and a bearing seat axis 35 (being the central axis of symmetry of the bearing seat 33), - a rounded annular bearing body 36 having a bearing body diameter 37 and projecting out of said termination conduit 28 within the Petition 870260020239, dated 04 / 03 / 2026, pp. 54 / 68 12 / 19 bearing seat 33, - wherein the diameter of the bearing body 37 is smaller than the diameter of the bearing seat 34 to provide at least a one-sided gap 46 between the bearing body 36 and the bearing seat 33 and to allow relative axial sliding along the axis of the bearing seat 35 and relative rotation at least around the axis of the bearing seat 35 between the bearing body 36 and the bearing seat 33.

[0058] Termination conduit 28 comprises at least one portion of conduit of variable cross-section 38 having an outside diameter 39 and a conduit wall thickness 40, both decreasing in a direction away from the bearing body 36.

[0059] The combination of the described support structure and the described variable cross-section of the termination conduit 28 allows the riser termination 7 to bend naturally within and around the lower tubular coupling vessel 4 (I-tube), without colliding with the I-tube, and allowing the riser entry angle 2 to be compatible with the riser termination 7.

[0060] Lateral loads and bending stresses on riser 2 and the I-tube connection interface are kept within acceptable limits. The economic advantages of rigid steel risers can be extensively exploited. There is also an improvement in work safety, since pull-into-I-tube riser installation methods can be used without diver intervention.

[0061] The use of structural steel conduits also increases the reliability / cost balance due to the extensive knowledge and precision of modeling fatigue phenomena, material properties, and welding procedures of structural steel compared to other materials, such as, for example, titanium alloys.

[0062] The system does not require any clearance compensation between the bearing body 36 and the bearing seat 33; on the contrary, the clearance is expressly provided and maintained, and does not involve any requirement for a straight riser termination 7; on the contrary, the riser termination is bent and is planned to remain bent during use. Detailed description of the bearing structure 32

[0063] According to one embodiment, the bearing body 36 forms a bearing sphere 52 (in other words: an outer spherical surface being Petition 870260020239, dated 04 / 03 / 2026, pages 55 / 68 13 / 19 interrupted (only) in the penetration regions of the termination conduit 28) which can contact the cylindrical bearing seat 33 always only at one (localized) point (contact region) and provides together with the bearing seat 33 a universal joint with a predetermined clearance due to the gap 46.

[0064] The bearing ball 45 can be made of forged steel and machined directly into the termination conduit 28 or connected to the termination conduit 28 by bolts, forging, welding or heat shrinking.

[0065] The bearing seat 33 can be formed directly in the coupling adapter 6 or by a tubular bearing insert fixed inside the coupling adapter 6.

[0066] The bearing ball 52 and the bearing seat 33 can only transfer lateral loads, i.e., loads orthogonal to the axis of the bearing seat 35, thus allowing some freedom of rotation of the riser termination 7 in the tubular coupling container 4 (lower I-tube). This would tend to increase the clamping moment and bending stresses in the upper suspension portion 22, which are, however, kept within acceptable limits thanks to the described cross-sectional variations of the termination conduit 28.

[0067] The outer spherical surface of the bearing ball 52, as well as an inner surface of the bearing seat 33, can be made wear-resistant by means of surface hardening treatment and / or wear-resistant coating and / or low-friction treatment or low-friction coating. Detailed description of termination conduit 28

[0068] According to one embodiment, the termination conduit 28 comprises a first portion of conduit of variable cross-section 38' having an outside diameter 39 and a conduit wall thickness 40, both decreasing in a direction away from the bearing body 36, said first portion of conduit of variable cross-section 38' extending from the bearing body 36 towards the upper suspension portion 22, thus adapting the bending resistance of the cross-section to the bending moment function along the length of the conduit.

[0069] Advantageously, the first portion of variable cross-section conduit 38' has a continuously tapered shape along at least one first tapered length. Petition 870260020239, dated 04 / 03 / 2026, pages 56 / 68 14 / 19

[0070] Alternatively, the first portion of variable cross-section conduit 38' has a step-decreasing cross-sectional shape or a combined shape of continuously tapered and step-decreasing cross-section, thus adapting the bending strength of the cross-section to the bending moment function along the length of the conduit.

[0071] According to an advantageous embodiment, the first portion of conduit with variable cross-section 38' has a gradual and / or stepped decrease in the outer diameter of the conduit 39 and the wall thickness of the conduit 40 along a first tapered length, wherein, near the bearing body 36, the outer diameter of the conduit 39 and the wall thickness of the conduit 40 are maximum and, near the upper suspension portion 22, the outer diameter of the conduit 39 and the wall thickness of the conduit 40 are minimum.

[0072] This provides relatively low bending stiffness of the riser end termination 7 near the upper suspension portion 22, so that the clamping moment and bending stresses at the upper suspension point are kept within acceptable limits.

[0073] Alternatively or additionally, the termination conduit 28 comprises a second portion of conduit of variable cross-section 38'' having an outside diameter 39 and a conduit wall thickness 40, both decreasing in a direction away from the bearing body 36, said second portion of conduit of variable cross-section 38'' extending from the bearing body 36 towards the lower end of the conduit 30, thus adapting the bending resistance of the cross-section to the bending moment function along the length of the conduit.

[0074] Advantageously, the second portion of variable cross-section conduit 38'' has a continuously tapered shape along a second tapered length that is greater than one fifth of the distance between the bearing body 36 and the upper suspension portion 22.

[0075] Alternatively, the second portion of variable cross-section conduit 38'' has a stepped decreasing cross-section shape or a combined shape of continuously tapered and stepped decreasing cross-section, thus adapting the bending strength of the cross-section to the bending moment function along the length of the conduit (downwards). Petition 870260020239, dated 04 / 03 / 2026, pages 57 / 68 15 / 19

[0076] Advantageously, the termination conduit 28 comprises both the first portion of variable cross-section conduit 38' and the second portion of variable cross-section conduit 38'', such that the outer diameter of the conduit 39 and the wall thickness of the conduit 40 both decrease from the bearing body 36 towards the upper suspension portion 22 and from the bearing body 36 towards the lower conduit end 30.

[0077] This adapts the bending strength of the conduit cross-section to the bending moment function of riser termination 7, behaving as a continuously supported beam, thus avoiding excessive bending near the tubular coupling vessel and keeping bending stresses below critical fatigue limits.

[0078] According to another embodiment, the termination conduit 28 comprises a third portion of variable cross-section conduit 42 having an outside diameter 39 and a conduit wall thickness 40, both decreasing in a direction away from the upper suspension portion 22, said third portion of variable cross-section conduit 42 extending from the upper suspension portion 22 towards a region of locally minimum bending resistance 41 of the termination conduit 28 between the upper suspension portion 22 and the bearing body 36, thus providing increased bending resistance near the suspended region and influencing the deformation function of the riser termination 7 to better adapt to the vessel wall shape and the geometry of the I-tube connection interface.

[0079] Termination conduit 28 comprises a plurality of individual conduit modules 42 that are connected to each other by welded connections 43 or by bolted flange connections 44.

[0080] In an exemplary embodiment, termination conduit 28 is made of carbon steel with standard wall thickness, fine grain size and has a thin inner layer of corrosion-resistant alloy (CRA), for example, Inconel.

[0081] In another exemplary embodiment, termination conduit 28 may be made of heavy-walled high-grade carbon steel and a thin inner layer of corrosion-resistant alloy, for example, Inconel.

[0082] For applications where the inner wall surface is provided with a corrosion-resistant alloy (CRA) to resist chemical attack from corrosive internal fluids, Petition 870260020239, dated 04 / 03 / 2026, pages 58 / 68 16 / 19 The most recommended method for applying CRA is weld overlay deposition.

[0083] The outer surface of the termination conduit 28 may be coated with a protective coating (e.g., TSA Aluminum thermal spray, polymer coating, etc.) that provides protection against corrosion as well as protection against abrasion during installation. Detailed description of the upper suspended seat 19 and the upper suspension portion 22

[0084] The upper suspended seat 19 may be associated with an upper I-tube 20 or formed as an upper end portion of the upper I-tube 20 and configured, for example, as a conventional upper suspended seat for attaching flexible risers, for example, a flange with holes for a bolted flange connection. Similarly, the upper suspension portion 22 of the upper riser termination 7 may be shaped, for example, similarly to a conventional upper portion of a flexible riser, for example, a flange with holes for a bolted flange connection.

[0085] The upper I-tube 20 may have an annular side wall 8 extending around an upper suspension axis 24 (preferably, but not necessarily, vertical), a downward-facing lower opening 25 defined by a lower end edge 26 (preferably flared outwards) of the side wall 23, Detailed description of the lower coupling vessel 4

[0086] The lower tubular coupling vessel 4 (I-tube) may be formed by a substantially straight tubular body, in which the longitudinal axis of the vessel 9 forms an inlet axis of the lower riser 9.

[0087] Alternatively, the lower tubular coupling vessel 4 (I-tube) may be formed by a bent tubular body having a section, the so-called bell mouth, defining the inlet axis of the lower riser 9 and an upper section that has a longitudinal orientation inclined relative to the inlet axis of the riser.

[0088] The inlet shaft of the lower riser 9 of the lower coupling vessel 4 can be inclined towards the side wall of the vessel 27 or away from the side wall of the vessel 27.

[0089] Advantageously, the input shaft of the lower riser 9 is inclined relative to the suspension shaft of the upper riser 9', for example, by about 7° or about 9°. Petition 870260020239, dated 04 / 03 / 2026, pages 59 / 68 17 / 19

[0090] The side wall of vessel 27 may be a stationary wall of floating unit 3 or, alternatively, a side wall of a rotating turret (or tourret) of floating unit 3.

[0091] The lower coupling container 4 is preferably made of steel and possibly connected by welding to the floating unit 3. Detailed description of the locking mechanism 18

[0092] According to embodiments, the locking mechanism 18 comprises a lever-hook mechanism connected to the lower coupling container 4 and engaging and detachable from the coupling adapter 6 positioned inside the coupling container 4.

[0093] The locking mechanism 18 can be disposed at least partially, possibly completely, inside the coupling container 4, or fixed to an external surface of the coupling container 4 with engagement portions adapted to move from outside to inside the coupling container 4 and back to engage and disengage the coupling adapter 6 inserted inside the coupling container 4.

[0094] Preferably, the locking mechanism 18 extends in the lower two-thirds, in the lower half, or in the lower third of the longitudinal extension of the coupling receiver 4. This is conveniently close to the edge of the lower end 13 which constitutes a critical point that must not be reached by the upper riser termination 7 during its movements.

[0095] The locking mechanism 18 can be self-triggered by inserting the coupling adapter 6 into the coupling container 4 or it can be activated by remote control. Detailed description of traction device 14

[0096] The traction device 14 may comprise one or more motor-driven traction winches 25, adapted for winding and unwinding an upper portion of the traction line 16, as well as possibly one or more deflecting surfaces, for example, pulleys and locking devices 26 adapted for stopping and fixing the traction device 14 and thus the traction line 16 in a desired position.

[0097] According to embodiments, the traction device 14 or the traction winch 25 is movable, for example, sliding, to a plurality of different Petition 870260020239, dated 04 / 03 / 2026, pages 60 / 68 18 / 19 traction positions above a plurality of different said coupling containers 4. Detailed description of riser duct 2

[0098] According to one embodiment, riser duct 2 is a rigid steel riser duct with upper riser termination 7 that includes or is connectable to a pull head 17, for example, by the upper suspension portion 22.

[0099] The upper suspension portion 22 is made of forged steel with a neck and terminating in a bolt-on receiving flange, for example, a standard API flange. The neck has the function of transferring axial loads from the top of the riser to the upper suspension seat 19 of the FPSO through a split flange. The API flange is used for: - Connect the traction head 17 to allow connection of the traction line 16 for riser installation and to allow temporary connection of the coupling adapter 6, and - Connect a rigid FPSO pipe or 28-inch reel duct to the steel riser duct to allow flow of liquid contents after installation is complete. Detailed description of the method

[00100] With reference to the figures, a method for approaching and connecting an offshore riser pipeline 2 to a floating FPSO unit 3 comprises: - provide a tubular bottom coupling vessel 4 (I-tube) on the floating unit 3 at a riser coupling level 5, said coupling vessel 4 having an annular side wall 8 extending around a longitudinal axis of the vessel forming a bottom riser inlet shaft 9, - Position a traction device 14 on the floating unit 3 at a level of the traction device 15 above said riser coupling level 5 and use the traction device 14 to pull a traction line 16 extended through the coupling vessel 4 and connected to a traction head 17 on an upper riser termination 7 of the rigid steel riser duct 2, so that the upper riser termination 7 of the rigid steel riser duct 2 is pulled from bottom to top into the coupling vessel 4, - provide a locking mechanism 18 on the lower coupling container 4 and use the locking mechanism 18 to lock a coupling adapter 6 of the upper riser termination 7 against withdrawal from below the coupling container 4, Petition 870260020239, dated 04 / 03 / 2026, pages 61 / 68 19 / 19 - after locking the coupling adapter 6 into the coupling container 4, receive and lock an upper suspension portion 22 of the riser termination 7 onto an upper suspension seat 19 of the floating unit 3 at an upper riser coupling level 21 below the traction device level 15 and above the lower riser coupling level 5, - to support a termination conduit 28 of the upper riser termination 7 inside the coupling adapter 6 by means of the bearing structure 32 described above, - separate the pull line 16, for example, a steel pull cable, from the upper riser termination 7 of the rigid steel riser 2, - Connect a 28 reel pipe (or pipe connection socket) to the upper riser termination 7 of the rigid steel riser pipe 2 to make a permanent hydraulic connection between the rigid steel riser pipe 2 and an oil or gas plant on board the floating unit 3.

[00101] Although the present invention has been illustrated by the description of various embodiments and although the illustrative embodiments have been described in considerable detail, it is not intended to restrict, or in any way limit, the scope of the claims appended to such details. Additional advantages and modifications may readily arise for those skilled in the art. Petition 870260020239, dated 04 / 03 / 2026, pages 62 / 68

Claims

1 / 5 Claims 1. Riser termination (7) for connecting a steel catenary riser duct (2) to an I-pipe or J-pipe connection interface of a floating unit (3), said connection interface comprising: - a lower tubular coupling vessel (4) installed on the floating unit (3) at a lower riser coupling level (5) and adapted to receive a coupling adapter from a riser termination, - a locking mechanism (18) provided on the lower coupling vessel (4) for locking the coupling adapter against downward withdrawal from the lower coupling vessel (4), - an upper suspended seat (19) installed on the floating unit (3) at an upper riser coupling level (21) above the lower riser coupling level (5) and adapted to receive and lock an upper suspension portion of a riser termination, said riser termination (7) comprising: - an upper suspension portion (22),- a lower coupling adapter (6), - a termination conduit (28) in structural steel having an upper conduit end (29) rigidly connected to the upper suspension portion (22) and a lower conduit end (30) connected to an adjacent conduit section (31) of the steel riser duct (2) and forming a lower end of the riser termination (7), said termination conduit (28) extending through said coupling adapter (6) and being axially sliding relative to the coupling adapter (6), - a bearing structure (32) for supporting the termination conduit (28) within the coupling adapter (6), said bearing structure (32) comprising: a circular cylindrical bearing seat (33) formed within the coupling adapter (6) and defining a bearing seat diameter (34) and a bearing seat axis (35),a rounded annular bearing body (36) having a diameter of Petition 870260020239, dated 04 / 03 / 2026, page. 63 / 68 2 / 5 bearing body (37) and projecting outward from said termination conduit (28) within the bearing seat (33), characterized in that the diameter of the bearing body (37) is smaller than the diameter of the bearing seat (34) to provide at least a one-sided gap (46) between the bearing body (36) and the bearing seat (33) and to allow relative axial sliding along the axis of the bearing seat (35) and relative rotation at least around the axis of the bearing seat (35) between the bearing body (36) and the bearing seat (33), wherein the termination conduit (28) comprises at least a portion of conduit of variable cross-section (38) having an outer diameter (39) and a conduit wall thickness (40), both decreasing in a direction away from the bearing body (36).

2. Riser termination (7), according to claim 1, characterized in that the bearing body (36) forms a bearing ball (52) and provides together with the bearing seat (33) a universal joint with a predetermined clearance due to the gap (46).

3. Riser termination (7), according to any one of claims 1 or 2, characterized in that the bearing ball (45) is made of forged steel and machined directly into the termination conduit (28) or connected to the termination conduit (28) by one of bolts, forging, welding and heat shrinking.

4. Riser termination (7), according to any one of claims 1 to 3, characterized in that the bearing seat (33) is formed directly in the coupling adapter (6) or by a tubular bearing insert fixed inside the coupling adapter (6).

5. Riser termination (7), according to any one of claims 2 to 3, characterized in that at least one of an outer spherical surface of the bearing ball (52) and an inner surface of the bearing seat (33) are made wear-resistant by one of: - surface hardening treatment, - wear-resistant lining, - low-friction treatment, - low-friction coating.

6. Riser termination (7), according to any of the preceding claims Petition 870260020239, dated 04 / 03 / 2026, page 64 / 68 3 / 5, characterized in that the termination conduit (28) comprises a first portion of variable cross-section conduit (38') having an outside diameter (39) and a conduit wall thickness (40) both decreasing in a direction away from the bearing body (36), said first portion of variable cross-section conduit (38') extending from the bearing body (36) towards the upper suspension portion (22).

7. Riser termination (7), according to claim 6, characterized in that the first portion of variable cross-section conduit (38') has a continuously tapered shape along a first tapered length.

8. Riser termination (7), according to claim 6, characterized in that the first portion of variable cross-section conduit (38') has a stepped decreasing cross-sectional shape or a combined shape of continuously conical and stepped decreasing cross-section.

9. Riser termination (7), according to claim 6, characterized in that the first portion of conduit with variable cross-section (38') has a gradual decrease in the outer diameter of the conduit (39) and the wall thickness of the conduit (40) along a first conical length between the bearing body (36) and the upper suspension portion (22), wherein near the bearing body (36) the outer diameter of the conduit (39) and the wall thickness of the conduit (40) are maximum and near the upper suspension portion (22) the outer diameter of the conduit (39) and the wall thickness of the conduit (40) are minimum.

10. Riser termination (7), according to any of the preceding claims, characterized in that the termination conduit (28) comprises a second portion of conduit of variable cross-section (38'') having an outer diameter (39) and a conduit wall thickness (40), both decreasing in a direction away from the bearing body (36), said second portion of conduit of variable cross-section (38'') extending from the bearing body (36) towards the lower end of the conduit (30).

11. Riser termination (7), according to claim 10, characterized in that the second portion of variable cross-section conduit (38'') has a continuously tapered shape along a second tapered length that is greater than one fifth of the distance between the bearing body (36) and the upper suspension portion (22), or between one fifth and one third of the distance between the bearing body (36) and the upper suspension portion (22).

12. Riser termination (7) characterized by being in accordance with claims 6 and 10.

13. Riser termination (7), according to any of the preceding claims, characterized in that the termination conduit (28) comprises a third portion of variable cross-section conduit (42) having an outer diameter (39) and a conduit wall thickness (40), both decreasing in a direction away from the upper suspension portion (22), said third portion of variable cross-section conduit (42) extending from the upper suspension portion (22) towards a region of locally minimum bending resistance (41) of the termination conduit (28) between the upper suspension portion (22) and the bearing body (36).

14. Riser termination (7), according to any of the preceding claims, characterized in that the termination conduit (28) comprises a plurality of individual conduit modules (42) that are connected to each other by welded connections (43) or by bolted flange connections (44).

15. Riser termination (7), according to any of the preceding claims, characterized in that the termination conduit (28) is made of one of: - fine grain size carbon steel with standard wall thickness, - high quality carbon steel for heavy walls, and having a thin inner layer of corrosion-resistant alloy or Inconel applied by means of weld overlay deposition, and a protective outer surface coating.

16. Method for connecting a steel offshore catenary riser pipeline (2) to an FPSO floating unit (3), characterized by comprising the steps of: - providing the steel riser pipeline (2) with an upper riser termination (7), as described in any of the preceding claims, - providing a tubular lower coupling vessel (4) on the floating unit (3) at a riser coupling level (5), said coupling vessel (4) having an annular side wall (8) extending around a longitudinal axis of the receiver forming a lower riser entry axis (9), - positioning a traction device (14) on the floating unit (3) at a level of the Petition 870260020239, dated 04 / 03 / 2026,pg. 66 / 68 5 / 5 pull device (15) above said riser coupling level (5) and use the pull device (14) to pull a pull line (16) extended through the coupling container (4) and connected to a pull head (17) on the upper riser termination (7) of the steel riser duct (2), so that the upper riser termination (7) of the steel riser duct 2 is pulled from bottom to top in the coupling container (4), - provide a locking mechanism (18) in the lower coupling container (4) and use the locking mechanism (18) to lock the coupling adapter (6) of the upper riser termination (7) against pulling downwards from the coupling container (4), - after locking the coupling adapter (6) in the coupling container (4),to receive and lock the upper suspension portion (22) of the riser termination (7) in an upper suspension seat (19) of the floating unit (3) at an upper riser coupling level (21) below the level of the traction device (15) and above the lower riser coupling level (5), - to support the termination conduit (28) of the upper riser termination (7) within the coupling adapter (6) by means of the bearing structure (32) of said riser termination (7), - to separate the traction cable (16) from the upper riser termination (7), - to connect a reel duct (28) to the riser termination (7) to make a permanent hydraulic connection between the rigid steel riser duct (2) and an oil or gas plant on board the floating unit (3). Petition 870260020239, dated 04 / 03 / 2026, pp. 67 / 68,

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