Subsea fluid storage unit

Patent metadata

Field	Value
Publication number	US-11987443-B2
Application number	US-202117502858-A
Country	US
Kind code	B2
Filing date	Oct 15, 2021
Priority date	Jul 9, 2018
Publication date	May 21, 2024
Grant date	May 21, 2024

Abstract

A modular subsea fluid storage unit comprises a variable-volume inner tank having a rigid top panel and a peripheral wall that is flexible by virtue of concertina formations. The peripheral wall is extensible and retractable vertically while the horizontal width of the tank remains substantially unchanged. A side wall of a lower housing part surrounds and is spaced horizontally from the peripheral wall of the inner tank to define a floodable gap between the peripheral wall and the side wall that surrounds the tank. An upper housing part extends over and is vertically spaced from the top panel of the inner tank and overlaps the side wall to enclose the inner tank. The floodable gap and the upper housing part enhance thermal insulation and trap any fluids that may leak from the inner tank.

First claim

The invention claimed is:

1. A subsea fluid storage unit, comprising:
a variable volume inner tank having a rigid top panel and a peripheral wall that is extensible and retractable in a vertical direction to vary a height dimension of the tank while the tank remains of substantially unchanged width in a horizontal direction; and
a side wall surrounding and spaced from the peripheral wall of the inner tank in the horizontal direction to define a floodable gap that surrounds the tank between the peripheral wall and the side wall and that has a closed top, wherein the side wall is contiguous with a base to define a floodable enclosure extending beneath the inner tank, and the rigid top panel of the inner tank is supported by the side wall, wherein the side wall is surmounted by a support flange, wherein the support flange of the side wall supports a hanging flange of the rigid top panel that projects beyond the peripheral wall in the horizontal direction and wherein the hanging flange of the rigid top panel is fixed to the support flange of the side wall with ROV-accessible clamps or locking pins;
wherein the inner tank closes an open top of the enclosure and is closed by a bottom plate that extends in the horizontal direction along a bottom edge of the peripheral wall, wherein the bottom plate projects beyond the peripheral wall in the horizontal direction such that a clearance between the bottom plate and the side wall is narrower horizontally than the floodable gap.

2. The unit of claim 1 , wherein the clearance between the bottom plate and the side wall is a sliding clearance.

3. The unit of claim 1 , wherein the upper housing part overlaps the inner tank in the horizontal direction.

4. The unit of claim 1 , wherein the bottom plate supports a heating system for heating fluid contents of the tank in use.

5. The unit of claim 1 , wherein the side wall is thermally insulated.

6. The unit of claim 1 , wherein the side wall has lower thermal transmittance than the peripheral wall of the inner tank.

7. The unit of claim 1 , wherein the peripheral wall is flexible.

8. The unit of claim 7 , wherein the peripheral wall has greater stiffness in the horizontal direction than in the vertical direction.

9. The unit of claim 7 , wherein the peripheral wall comprises folded or hinged formations that are expandable in the manner of a concertina.

10. The unit of claim 1 , wherein the side wall is contiguous with a base to define a floodable enclosure extending beneath the inner tank.

11. The unit of claim 10 , wherein the floodable enclosure communicates with the floodable gap.

12. The unit of claim 10 , wherein the base is thermally insulated.

13. The unit of claim 10 , further comprising a seawater inlet/outlet communicating with the enclosure.

14. The unit of claim 10 , wherein the inner tank closes an open top of the enclosure.

15. The unit of claim 1 , further comprising a leakage sensor arranged to sense fluid in the floodable gap leaked from the inner tank and a drainage line that communicates with the floodable gap to drain the leaked fluid.

16. The unit of claim 1 , wherein the rigid top panel of the inner tank rises inwardly from the side wall to an elevated gas trap chamber for trapping gas rising from a fluid in the inner tank.

17. The unit of claim 1 , comprising subsea releasable fastenings acting in tension between the inner tank and the side wall.

18. The unit of claim 1 , wherein the side wall has at least a portion that is substantially flat.

19. A group of units of claim 1 , coupled together for fluid communication between the inner tanks of the group.

20. The group of claim 19 , wherein the units are arranged in an elongate towable array.

Assignees

• Subsea 7 Norway As

Inventors

• Saeterdal Morten
• Daasvatn Sigbjorn

Classifications

• B65D88/78 Primary

  for use in or under water · CPC title

• B63B25/16

  heat-insulated (insulating panelling B63B3/68; heating or cooling B63J) · CPC title

• B63G8/42

  Towed underwater vessels · CPC title

• B65D88/005

  of variable capacity, e.g. with movable or adjustable walls or wall parts, modular · CPC title

• B65D88/18

  bellows-shaped (B65D88/22 takes precedence) · CPC title