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EP-4337838-B1 - OFF SHORE RIGID STEEL RISER TERMINATION AND FIXATION SYSTEM TO FLOATING PRODUCTION STORAGE OFFLOADING (FPSO) VESSEL

EP4337838B1EP 4337838 B1EP4337838 B1EP 4337838B1EP-4337838-B1

Inventors

  • MARCOTULLI, AMEDEO

Dates

Publication Date
20260513
Application Date
20220407

Claims (16)

  1. A riser termination (7) for connecting a steel catenary riser duct (2) to an I - tube or J - tube connecting interface of a floating unit (3), said connecting interface comprising: - a lower tubular coupling recipient (4) installed on the floating unit (3) at a lower riser coupling level (5) and adapted to receive a coupling adapter of a riser termination, - a locking mechanism (18) provided at the lower coupling recipient (4) for locking the coupling adapter against downward withdrawal from the lower coupling recipient (4), - an upper hang off 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 hang off portion of a riser termination, said riser termination (7) comprising: - an upper hang of 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 hang off 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 slidable with respect 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 inside the coupling adapter (6) and defining a bearing seat diameter (34) and a bearing seat axis (35), - an annular rounded bearing body (36) having a bearing body diameter (37) and protruding outward from said termination conduit (28) inside the bearing seat (33), wherein the bearing body diameter (37) is smaller than the bearing seat diameter (34) to provide an at least unilateral gap (46) between the bearing body (36) and the bearing seat (33) and allow relative axial sliding along the bearing seat axis (35) and relative rotation at least about the bearing seat axis (35) between the bearing body (36) and the bearing seat (33), wherein the termination conduit (28) comprises at least one variable cross-section conduit portion (38) having an external diameter (39) and a conduit wall thickness (40) both decreasing in a direction away from the bearing body (36).
  2. The riser termination (7) according to claim 1, wherein the bearing body (36) forms a bearing ball (52) and provides together with the bearing seat (33) a universal joint with a predetermined play due to the gap (46).
  3. The riser termination (7) according to claim 1 or 2, wherein the bearing ball (45) is made of forged steel and either directly machined to the termination conduit (28) or connected to the termination conduit (28) by one of bolts, forging, welding and heat shrinking.
  4. The riser termination (7) according to any one of claims 1 to 3, wherein the bearing seat (33) is formed directly at the coupling adapter (6) or by a tubular bearing insert fixed inside the coupling adapter (6).
  5. The riser termination (7) according to any one of claims 2 to 3, wherein at least one of an external spherical surface of the bearing ball (52) and an internal surface of bearing seat (33) are made wear resistant by one of: - surface hardening treatment, - wear resistant lining, - low friction treatment, - low friction coating.
  6. The riser termination (7) according to any one of the preceding claims, wherein the termination conduit (28) comprises a first variable cross-section conduit portion (38') having an external diameter (39) and a conduit wall thickness (40) both decreasing in a direction away from the bearing body (36), said first variable cross-section conduit portion (38') extending from the bearing body (36) towards the upper hang off portion (22).
  7. The riser termination (7) according to claim 6, wherein the first variable cross-section conduit portion (38') has a continuously tapered shape over a first taper length.
  8. The riser termination (7) according to claim 6, wherein the first variable cross-section conduit portion (38') has a stepwise decreasing cross-section shape or a combined continuously tapered and stepwise decreasing cross-section - shape.
  9. The riser termination (7) according to claim 6, wherein the first variable cross-section conduit portion (38') has a gradual decrease of the conduit outer diameter (39) and the conduit wall thickness (40) over a first taper length between the bearing body (36) and the upper hang off portion (22), and in which near the bearing body (36) the conduit outer diameter (39) and the conduit wall thickness (40) are maximum and near the upper hang off portion (22) the conduit outer diameter (39) and the conduit wall thickness (40) are minimum.
  10. The riser termination (7) according to any one of the preceding claims, wherein the termination conduit (28) comprises a second variable cross-section conduit portion (38") having an external diameter (39) and a conduit wall thickness (40) both decreasing in a direction away from the bearing body (36), said second variable cross-section conduit portion (38") extending from the bearing body (36) towards the lower conduit end (30).
  11. The riser termination (7) according to claim 10, wherein the second variable cross-section conduit portion (38") has a continuously tapered shape over a second taper length that is greater than one fifths of the distance between the bearing body (36) and the upper hang off portion (22), or between one fifth and one third of the distance between the bearing body (36) and the upper hang off portion (22).
  12. The riser termination (7) according to claims 6 and 10.
  13. The riser termination (7) according to any one of the preceding claims, in which the termination conduit (28) comprises a third variable cross-section conduit portion (42) having an external diameter (39) and a conduit wall thickness (40) both decreasing in a direction away from the upper hang off portion (22), said third variable cross-section conduit portion (42) extending from the upper hang off portion (22) towards a region of locally minimum bending resistance (41) of the termination conduit (28) between the upper hang off portion (22) and the bearing body (36).
  14. The riser termination (7) according to any one of the preceding claims, in which the termination conduit (28) comprises a plurality of individual conduit modules (42) which are connected together by welded connections (43) or by bolted flange connections (44).
  15. The riser termination (7) according to any one of the preceding claims, in which the termination conduit (28) is made of one of: - standard wall thickness carbon steel fine grain size, - heavy wall high grade carbon steel, and has a thin internal layer of corrosion resistant alloy or Inconel applied by means of weld overlay deposit, and a protective external surface coating.
  16. A method for connecting an off-shore steel catenary riser duct (2) to a floating unit FPSO (3), comprising the steps of: - providing the steel riser duct (2) with an upper riser termination (7) according to any one of the preceding claims, - providing a tubular lower coupling recipient (4) on the floating unit (3) at a riser coupling level (5), said coupling recipient (4) having an annular side wall (8) extending around a recipient longitudinal axis forming a riser lower entrance axis (9), - positioning a pulling device (14) on the floating unit (3) at a pulling device level (15) above said riser coupling level (5) and using the pulling device (14) to pull a pulling line (16) extended through the coupling recipient (4) and connected to a pulling head (17) at 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 below upward into the coupling recipient (4), - providing a locking mechanism (18) at the lower coupling recipient (4) and using the locking mechanism (18) for locking the coupling adapter (6) of the upper riser termination (7) against downward withdrawal from the coupling recipient (4), - after locking the coupling adapter (6) in the coupling recipient (4), receiving and locking the upper hang off portion (22) of the riser termination (7) at an upper hang off seat (19) of the floating unit (3) at an upper riser coupling level (21) below the pulling device level (15) and above the lower riser coupling level (5), - supporting 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), - detaching the pulling line (16) from the upper riser termination (7), - connecting a spool duct (28) to the riser termination (7) for making a permanent hydraulic connection between the rigid steel riser duct (2) and an onboard oil or gas plant of the floating unit (3).

Description

The present invention relates to an off shore rigid steel riser termination and fixation system for coupling a rigid steel riser to an I - tube coupling interface originally provided for flexible riser attachment with a Floating Production Storage Offloading ("FPSO") vessel. More specifically, the invention relates to an improved structure for the connection of the upper part of a Steel Catenary Riser ("SCR") to a floater, for example a floating monohull vessel, typically an FPSO species. The terminology "SCR" includes all metallic rigid risers with a catenary shape, particularly single catenaries (SCR) and double catenaries (SLWR), in which the metal wall of the riser performs both structural and impermeability functions, in contrast to multilayer composite flexible risers. In a typical configuration of deep-sea oil and gas production systems an assembly of valves and fittings used to regulate the inflow and outflow of products from and to a well, so called trees, are positioned on the seabed and floating units, so-called Floating Production Storage Offloading ("FPSO") facilities, are positioned at sea level. The trees are fluidically connected with the Floating Production Storage Offloading ("FPSO") facilities by rigid or flexible oil or gas conveying pipes, the so-called risers, which extend from the seabed up to sea level. This configuration allows increased flexibility in field layouts, such as multiple individual wells and multiple drill centers, and reduces the interferences within the main field construction phases: drilling, pipelay and FPSO fabrication. Once the underwater exploitation field has been completed, the floating (FPSO) unit can approach its 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 moved toward and connected to the floating unit (FPSO) to transport the petroleum product from the wells to the floating unit FPSO. On the other hand, it is increasingly frequent to use or embody the risers as so-called service lines for transporting methanol or other chemical products to guarantee the flow of the petroleum product (flow assurance), or for transporting injection water for water injection in the subsea soil to increase the extraction rate of the oil or gas product in the well, that service fluid transport taking place from the floating (FPSO) unit downward towards the wells. The configuration in which the above mentioned assembly of valves and fittings ("trees") are arranged on the sea bed (so called wet trees configuration) allows a great freedom of movement of the floating (FPSO) units compared to a configuration in which the assembly of valves and fittings is arranged on the floating unit at sea level (so-called dry trees configuration). This allows to use common floaters, e.g. standard ships such as Suezmax, Panamax, which are adapted to accommodate the oil plants, and which are anchored by means of a specific mooring system which, depending on local weather and sea conditions, can be fixed (e.g. a so called spread mooring) or rotating (e.g. a so-called turret mooring). The movements of the FPSO are linked to those of the riser and movements and stresses are transmitted between these two structural sub-systems, differently between configurations in which the risers hang from the floater (so-called "hang off risers" which are relevant for the present invention) and configurations in which the risers are free from the FPSO (so-called "free standing riser" which are less relevant for the present invention). The movements of the FPSO induce mechanical stresses in the riser which combine with the corrosive and chemical actions thereon. Particular critical regions are the upper coupling of the riser (hang off region) as well as the support region of the riser on the seabed (touch down point). To withstand the dynamic mechanical loads, the internal fluid loads and the corrosive and chemical attack, the risers are usually made of carefully selected materials or material combinations, such as e.g. metallic materials for rigid risers, multiple composite material layers for flexible risers, so-called umbilical duct structures with dedicated ducting tubes (umbilical) inside an external protection tube, or composite polymeric material in pipes that are used in particularly challenging projects. Among the known possible shape and boundary conditions of the risers, there are to be listed the simple catenary shape (so-called Steel Catenary Riser "SCR") or multiple and compound catenary shapes, such as e.g. the so-called steel lazy wave catenary riser (SWLR) or the dormant riser, in which the tension of the upper portion of the riser is reduced at the expense of an increased length. The structural hang-off interface between the riser and the floating unit, which is a relevant issue for the present invention, must withstand and influence in a desired manner the dynamics, forces and movements