WO2017108678A1

WO2017108678A1 - Riser hanger assembly

Info

Publication number: WO2017108678A1
Application number: PCT/EP2016/081723
Authority: WO
Inventors: Antonie Willem VAN BEEK; Melis Jacobus VAN TWILLERT; Andreas Carolus Maria VAN DER STAP
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2015-12-21
Filing date: 2016-12-19
Publication date: 2017-06-29
Also published as: BR112018012781A2; BR112018012781B1; AU2016375434A1; AU2016375434B2

Abstract

A water intake riser (1) that can be suspended from a vessel includes a riser connected to a riser hanger. The riser hanger has a first tubular element (5), a second tubular element (6) to which the riser is connected, and a connecter joining the tubular elements. The connector (14) has a first joint (15) to provide relative rotation between the first tubular element (5) and the second tubular element (6) about a first axis of rotation (17), and a second joint (16) to provide relative rotation between the first tubular element (5) and the second tubular element (6) about a second axis of rotation (19). A vessel may be provided with a water intake riser using the above-described riser hanger. A process for liquefying natural gas may include use of such a water intake riser.

Description

RISER HANGER ASSEMBLY FIELD OF THE INVENTION

The present invention relates to a water intake riser. Such a water intake riser may provide cooling water to a heat exchanger on a vessel. In particular, such a water intake riser may be used on a vessel on which a plant for liquefying natural gas is arranged. In the specification and in the claims the word vessel refers to a ship, a barge, a floating platform and so on.

BACKGROUND

An example of such a riser is described in the article by R. Franciss, Maximum stress model test of a seawater lift casing to a Petrobras PXXV platform in Albacora field, presented at 9th International symposium on Offshore Engineering, September 1995. The paper describes a floating offshore platform provided with water intake risers that are hingeably connected to the submerged pontoons of the platform. Some improved risers provide for a flexible load transfer element (e.g., chain) coupled with a hose connecting the riser to an element connected to the vessel. However, the structural rubber hose may not handle torsion well. Also out of plane bending of the chain may be a challenge for the fatigue lifetime. The conventional designs are a complex combination of mature components, while the invention described below is a relatively straightforward combination of mature components. Construction and assembly for the conventional designs is expected to be very challenging, while for the design described herein is more straight forward as standard practices can be followed. Measuring the performance of conventional designs is not possible as of now, while there are methods to inspect the status of the design described below.

SUMMARY OF THE INVENTION

The invention is directed to a water intake riser having a simple and reliable design.

A water intake riser that can be suspended from a vessel including a riser connected to a riser hanger. The riser hanger has a first tubular element, a second tubular element to which the riser is connected, and a connecter joining the tubular elements. The connector has a first joint to provide relative rotation between the first tubular element and the second tubular element about a first axis of rotation, and a second joint to provide relative rotation between the first tubular element and the second tubular element about a second axis of rotation. Similarly, a vessel may be provided with at least one water intake riser that can be suspended from the vessel including a riser connected to the above-described riser hanger. The first tubular element may be secured to the vessel.

A process for liquefying natural gas may include use of a water intake riser that can be suspended from a vessel, which water intake riser includes a riser connected to the above- described riser hanger.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with reference to the accompanying drawings, wherein

FIG. 1 shows schematically and not to scale a partial longitudinal section of an exemplary water intake riser according to the present invention;

FIG. 2 shows schematically and not to scale a cross-section of the bottom of a vessel provided with three water intake risers according to the present invention; and

FIG. 3 shows schematically and on a larger scale detail IV of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Risers used with floating structures need to be connected to the floating structure such that the motions and/or rotations of the floating structure are decoupled from the motions of the riser as much as possible, while fluid flow through the riser and riser hanger assembly is still possible without too many obstacles inside. In one exemplary embodiment of the invention, a riser hanger assembly works on the principle of using a number of hinges at the outer sides of the riser hanger assembly to transfer axial loads and provide free rotation of the risers and riser hanger assembly in two degrees of freedom while being very stiff in torsion to prevent torsional motions of riser and riser hanger assembly. At the same time, the inside of the riser hanger assembly is free, or almost free depending on the exact design, to enable large fluid flows through the riser hanger assembly.

FIG. 1 shows schematically and not to scale one exemplary water intake riser 1 according to the present invention. The water intake riser 1 of this illustration is suspended from a hull 2 of a vessel (not shown). The water intake riser 1 includes an elongated tube 3 connected to a riser hanger 4. The riser hanger 4 has 2 tubular elements, a first tubular element 5, and a second tubular element 6. The upper end part of the first tubular element 5 of this figure has an open end provided with a suspension ridge 7. The suspension ridge 7 matches with a suitably formed opening 8 in the hull 2 so that the first tubular element 5 is supported in the opening 8, and thus secured to the vessel. Securing the first tubular element 5 to the vessel (not shown) allows suspending the water intake riser 1 from the hull 2.

The riser hanger 4 also includes a second tubular element 6. The upper end of the elongated tube 3 connects to the lower end of the second tubular element 6 by any suitable means (e.g., a flanged connection as illustrated). In FIG. 1, the diameter of the connection is larger than the diameter of the opening 8. However, in alternative embodiments, the diameter of the opening 8 may be selected such that the water intake riser can be lowered through it until the suspension ridge 7 is supported in the opening 8.

The riser hanger 4 as illustrated also includes a rigid load transfer element 9 joining the tubular elements 5 and 6. In the embodiment shown in FIG. 1, the rigid load transfer element may be a tubular element or other configuration such that water may pass therethrough.

A connector 14 including a first joint 15 and a second joint 16 may secure the tubular elements 5 and 6 to one another. The first joint 15 and the second joint 16 may be present at opposite ends of the rigid load transfer element 9, as illustrated in FIG. 1. The first joint 15 may provide relative rotation between the first tubular element 5 and the second tubular element 6 about a first axis of rotation 17 and a second axis of rotation 19. For example, the first joint 15 and the second joint 16 may each include a pair of hinged connections. As illustrated in FIG. 1, joint 15 includes two hinged connections 21 and 22. Similarly, joint 16 may have two hinged connections, even though only one 23 is visible in the illustration. The two hinged connections 21 and 22 of the first joint 15 may be aligned coaxially on the first axis of rotation 17. Similarly the two hinged connections 23 and mate (not shown) may be aligned coaxially on the second axis of rotation 19.

As illustrated, the first axis of rotation 17 and the second axis of rotation 19 are orthogonal to one another (i.e., offset by 90 degrees). However, modifications could include configurations where the offset is less than 90 degrees. For example, the first axis of rotation 17 and the second axis of rotation 19 may be offset by at least 60 degrees and multiple rigid load transfer elements 9 may be used accordingly. In any event, it is desirable that the first axis of rotation 17 and the second axis of rotation 19 are not parallel. As illustrated, the first axis of rotation 17 and the second axis of rotation 19 are both orthogonal to a longitudinal axis of the first tubular element 5 and/or the second tubular element 6. One may say that the first joint 15 and the second joint 16 cooperate to form a universal joint that provides rotation about the first axis and the second axis, but is stiff in torsion, depending on the length of the rigid load transfer element 9 and other dimensioning. In some embodiments, the rigid load transfer element 9 may have a negligible length, such that the connector 14 joining the tubular elements 5 and 6 includes only the first joint 15 and the second joint 16 in the form of a universal joint (not shown).

In the water intake riser 1 of FIG. 1, multiple seals 24, 25 may be provided to form a watertight seal between the tubular elements 5 and 6 and the rigid load transfer element 9. In some cases, the seals 24, 25 may not be structural but may instead be used primarily to prevent leakage of water from the water intake riser 1 into the surrounding environment. In such a configuration, seal 24 may be secured to end part 11 of tubular element 5 and to a first (e.g., upper) portion of the rigid load transfer element 9, while seal 25 may be secured to end part 12 of tubular element 6 and to a second (e.g., lower) lower portion of the rigid load transfer element 9. Such seals 24, 25 may be rubber or other suitable material. Additionally, the hinged connections may be present on the outer diameter of the respective tubular elements 5 and 6.

FIG. 2 shows the lower part of a vessel 26 provided with at least two water intake risers. In this particular illustration, the vessel 26 is provided with three water intake risers, wherein the first tubular element (not shown) is secured to the vessel 26 and suspended from the hull 2 as shown in more detail in FIG. 1.

In order to prevent the water intake risers 1 from colliding, there may be at least one riser- spacer 27. The dynamic response of the water intake risers 1 will determine the number and the positions of the riser-spacers 27. FIG. 2 shows only one riser-spacer 27.

The riser-spacer 27 includes interconnected guide sleeves 28, one guide sleeve 28 for each water intake riser 1. Bars 29 form the interconnection. Each guide sleeve 28 defines an aperture 30 (see FIG. 3), which aperture 30 allows the elongated tubes 3 to pass freely through it and allows limited rotation of the elongated tubes 3 about a horizontal axis. The horizontal axis is an axis that is lying in a plane of symmetry of the riser-spacer 27, which plane is perpendicular to the direction of passage through the aperture 30. The riser-spacer 27 may be suspended from the vessel 26 to a predetermined depth. In the embodiment shown in FIG. 2, the riser-spacer 27 is suspended by means of a cable 31 secured in the hull 2. In an alternative embodiment, a chain may replace the cable 31, or one of the guide sleeves 28 may be secured to a water intake riser 1.

The length of the guide sleeve 28 may be in the range of one to four times an outer diameter of the water intake riser 1. The bars 29 interconnecting the guide sleeves 28 of the riser-spacer 27 may be replaced by a frame or by a solid polygon. The thickness of the solid polygon may be between three to four times the diameter of a water intake riser 1 in order to prevent vortex shedding of the water intake riser 1.

The open upper ends of the water intake risers 1 may open into a receptacle 32 inside the vessel 26 from which the water is withdrawn (not shown) for use as cooling water.

The design described herein may provide many advantages over current designs. For example, the design may respond well to extreme axial loads and torsion. The design may provide superior fatigue performance and system reliability.

The design may also mitigate challenges involved in prior designs (e.g., those described in U.S. Patent numbers 7,318,387 and 7,451,716, such as out of plane bending of the chain and failure of structural rubber due to torsion. The improved design described above may also be structurally stronger than is possible for the conventional designs. For example, the workability of hinges such as 21, 22, 23 above may be increased due to lower expected deformations of the riser hanger 4 during extreme load cases.

The present disclosure is not limited to the embodiments described above, wherein various modifications are conceivable within the scope of the appended claims. Features of respective embodiments may for instance be combined.

Claims

1. A water intake riser that can be suspended from a vessel comprising a riser connected to a riser hanger, which riser hanger comprises:

a first tubular element;

a second tubular element to which the riser is connected; and

a connecter joining the tubular elements;

wherein the connector comprises:

a first joint to provide relative rotation between the first tubular element and the second tubular element about a first axis of rotation; and

a second joint to provide relative rotation between the first tubular element and the second tubular element about a second axis of rotation.

2. The water intake riser of claim 1, wherein the connector further comprises a rigid load transfer element and wherein the first joint and the second joint are present at opposite ends of the rigid load transfer element.

3. The water intake riser of claim 1, wherein the first joint and the second joint together form a universal joint that provides rotation about the first axis and the second axis, but is stiff in torsion.

4. The water intake riser of claim 1, wherein:

the first joint comprises a pair of hinged connections aligned coaxially on the first axis of rotation; and

the second joint comprises a pair of hinged connections aligned coaxially on the second axis of rotation.

5. The water intake riser of claim 1, wherein the first axis of rotation and the second axis of rotation are not parallel.

6. The water intake riser of claim 5, wherein the first axis of rotation and the second axis of rotation are offset by at least 60 degrees.

7. The water intake riser of claim 6, wherein the first axis of rotation and the second axis of rotation are offset by 90 degrees.

8. The water intake riser of claim 1, wherein the first axis of rotation and the second axis of rotation are orthogonal to one another.

9. The water intake riser of claim 1, wherein the first axis of rotation and the second axis of rotation are orthogonal to a longitudinal axis of the first tubular element and/or the second tubular element.

10. The water intake riser of claim 1, further comprising a seal secured to respective end parts of the first tubular element and the second tubular element.

11. The water intake riser of claim 2, further comprising:

a first seal secured to an end part of the first tubular element and a first portion of the rigid load transfer element; and

a second seal secured to an end part of the second tubular element and a second portion of the rigid load transfer element.

12. The water intake riser of claim 2, wherein the rigid load transfer element is tubular.

13. A vessel provided with at least one water intake riser that can be suspended from the vessel comprising a riser connected to a riser hanger, which riser hanger comprises: a first tubular element;

a second tubular element to which the riser is connected; and

a connecter joining the tubular elements;

wherein the connector comprises:

a second joint to provide relative rotation between the first tubular element and the second tubular element about a second axis of rotation, and

wherein the first tubular element is secured to the vessel.

14. The vessel of claim 13, on which a plant for liquefying natural gas is arranged.

15. A process for liquefying natural gas, comprising use of a water intake riser that can be suspended from a vessel, which water intake riser comprises a riser connected to a riser hanger, which riser hanger comprises a first tubular element; a second tubular element to which the riser is connected; and a connecter joining the tubular elements; wherein the connector comprises: a first joint to provide relative rotation between the first tubular element and the second tubular element about a first axis of rotation; and a second joint to provide relative rotation between the first tubular element and the second tubular element about a second axis of rotation.

16. The process according to claim 15, the connector further comprising a rigid load transfer element, wherein the first joint and the second joint are present at opposite ends of the rigid load transfer element, wherein the rigid load transfer element forms a conduit for water.

17. The process according to claim 16, wherein the rigid load transfer element transfers the self-weight and the dynamic loads of the elongated tube to the first tubular element.