GB2142286A - Pressurized liquid filled tendons - Google Patents
Pressurized liquid filled tendons Download PDFInfo
- Publication number
- GB2142286A GB2142286A GB08416341A GB8416341A GB2142286A GB 2142286 A GB2142286 A GB 2142286A GB 08416341 A GB08416341 A GB 08416341A GB 8416341 A GB8416341 A GB 8416341A GB 2142286 A GB2142286 A GB 2142286A
- Authority
- GB
- United Kingdom
- Prior art keywords
- tendon
- liquid
- platform
- tension leg
- pressure
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
- B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING
- B63B21/00—Tying-up; Shifting, towing, or pushing equipment; Anchoring
- B63B21/50—Anchoring arrangements or methods for special vessels, e.g. for floating drilling platforms or dredgers
- B63B21/502—Anchoring arrangements or methods for special vessels, e.g. for floating drilling platforms or dredgers by means of tension legs
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- Ocean & Marine Engineering (AREA)
- Earth Drilling (AREA)
- Examining Or Testing Airtightness (AREA)
- Revetment (AREA)
Abstract
Pressurized liquid filled tubular tendons (6) for a tension leg offshore platform (1) provide a means for detecting leaks therein. Filling the tendon (6) with a liquid having a specific gravity less than that of sea water provides increased buoyancy and reduces the weight supported by the buoyant offshore structure (1). The use of a corrosion inhibiting liquid reduces the corrosion of the interior tendon wall. <IMAGE>
Description
SPECIFICATION
Pressurized liquid filled tendons
This invention relates to tension leg platform tendons and is concerned with pressurized liquid filled tendons for detecting leaks, providing buoyancy and resisting corrosion. A change in pressure denotes a structural deficiency. An increase in tendon buoyancy reduces the weight supported by the buoyant structure.
In deep water, the use of bottom-founded structures for oil well drilling and production operations is cost prohibitive due to the expense of fabrication and installation of such large structures.
For water depths in excess of 1,000 feet (305 metres), buoyant offshore structures moored to the sea floor can be used to perform drilling and production operations cost effectively.
As water depth excees 1 ,000 feet (305 metres), the tension leg platform (TLP) concept can be introduced to perform oil drilling and production operations. A TLP consists of a buoyant offshore structure moored to fixed sea floor anchor points with vertical tension legs; also referred to as tendons. Drilling, producing and processing equipment as well as crew's quarters are contained in or on the buoyant offshore structure.
Tendon designs include both cable and tu bular leg elements, see for example U.S.
Patent 4,285,615 which discloses a mooring apparatus for a structure floating on a body of water, comprising a corrosion resistant cable system, including a multistrand cable, having voids between adjacent strands, and U.S.
Patent 4,226 555 which discloses a mooring system for a tension leg platform, comprising a tension leg, including a plurality of tubular leg elements having threaded connections between adjacent leg elements.
The use of pre-tensioned vertical mooring elements prevents vertical motion but permits lateral motion of the floating structure during the passage of waves. Pretensioning is accomplished by deballasting the buoyant offshore structure after the tendons are connected between the buoyant structure and fixed sea floor anchor bases.
Tendon inspection is necessary as both a maintenance expenditure and safety precaution. Tendon repair and replacement are both very expensive and laborious operations.
Cracks and corrosion due to exposure to sea water decrease the failure load and working lifetime of the tendon. The desirability of minimizing tendon corrosion has been recognized in the art. The aforementioned U.S.
Patent 4,285,615 discloses an invention for providing a corrosion resistant design for a tension leg cable which isolates the steel wire cable from the sea water environment.
The present invention provides an apparatus and method for detecting structural deficiencies in a tubular tendon, increasing its buoyancy and extending its useful life.
According to one aspect of the invention, there is provided an apparatus for detecting a leak in a tension leg platform tendon, comprising:
a fluid tight tubular tendon;
means for supplying liquid to said tendon;
means for pressurizing said liquid;
means for monitoring pressure, said means monitoring variations in liquid pressure in said tendon;
means for connecting an upper end of said tendon to a buoyant offshore structure; and
means for connecting a lower end of said tendon to an anchor means connected to the sea floor.
According to another aspect of the invention, there is provided a method of detecting a leak in a tension leg offshore platform tendon, comprising the steps of:
connecting a tendon between a buoyant offshore platform and an anchor means connected to the sea floor at an offshore location, said tendon being a fluid tight tubular member;
supplying a liquid to said tendon;
pressurizing said liquid; and
monitoring liquid pressure in said tendon to detect leaks therein.
According to a further aspect of the invention, there is provided a tension leg offshore platform having anchor means connectable to the sea floor;
at least one tendon connectable between said platform and said anchor means, said tendon being a fluid tight tubular member;
means for supplying liquid to said tendon;
means for pressurizing said liquid; and
means for monitoring pressure, said means being capable of monitoring variations in liquid pressure in said tendon.
The present invention provides a method and means for detecting leaks in a tubular tendon, increasing its buoyancy and extending its useful life. A plurality of tendon segments, each consisting of a tubular element and sealable couplings, are joined to provide a single elongated tubular tendon. The tubular tendon is filled with a liquid which is preferably a corrosion inhibiting liquid, having a specific gravity less than that of sea water. A compressor is utilized to pressurize contents of the tubular tendon and pressure gauges monitor variations in pressure.
The corrosion inhibiting liquid protects the interior tendon wall from salt water corrosion.
The liquid having a specific gravity less than that of sea water increases the buoyancy of each tendon, thereby reducing the weight supported by the buoyant offshore structure.
Variations in pressure indicate cracks or punctures through the tendon or an inadequate coupling seal.
The object of the present invention is to provide a method and means for detecting leaks in a tubular tendon, increasing its buoyancy and extending its useful life. A method and means for detecting leaks indicating structural deficiencies promotes safety and reduces routine maintenance expenditures. Increasing the buoyancy of the tendon reduces the weight supported by the buoyant offshore structure; permitting a more efficient design.
Increased tendon life provides more cost effective deep water drilling by reducing maintenance, repair and replacement of the tendons.
Another object of the present invention is to provide an improved design for a tension leg platform incorporating the invention described herein.
For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made to the accompanying drawing in which:
Figure 1 is an elevation schematic view, partially in section, of a tension leg platform;
Figure 2 is an enlarged detailed view of part of a tendon of Figure 1; and
Figure 3 is a section of the tendon of Figure 2 taken along the line 3-3.
Referring now to the drawing, Figure 1 shows an elevation schematic view, partially in section, of a tension leg platforirr(TLP) 1 deployed at an offshore drilling site. A lower platform 2 is provided on which may be mounted crew's living quarters, well test equipment and processing equipment. An upper platform 3 is provided on which may be mounted a pilot house, cranes, the drilling derrick, skid base, the drill string and a helicopter landing site. Similar conveniences as are known to those skilled in the art of oil exploration and production may also be stored on the lower and upper platforms. Platforms 2 and 3 are supported by a plurality of annular support columns 4. When the TLP is in its illustrated buoyant condition, columns 4 and pontoons 5 extend beneath the surface of the water.A plurality of tendons 6 extend from each support Column 4 to anchor means consisting of a foundation template 7 secured to the sea floor 8 with friction piles 9, thereby restricting movement of the structure. A drill string 10 and risers 11 extend from platform 1 or 2 between pontoons 5 to the sea floor 8 during drilling and producing operations. Well template 12 maintains the risers in a stationary position relative to the sea floor 8.
Referring to Figure 2, an enlarged detailed view of a part of tendon 6 depicts the tendon as a tubular element. A plurality of tendon segments, each consisting of a tubular element and sealable couplings, are joined to provide a single elongated tubular tendon.
The tubular element typically has a relatively thin wall compared to its overall diameter. A tubular element has been designed utilizing inside and outside diameters of 18 inches (45.7 cm) and 20 inches (50.8 cm), respectively. Figure 3 shows a section view of the tendon of Figure 2 taken along the line 3-3.
In accordance with the present invention, a liquid, preferably corrosion inhibiting and having a specific gravity less than that of sea water, enters the tendon through a conduit located at its upper end. The liquid may be water or a hydrocarbon. The liquid may contain a corrosion inhibitor. Thus the liquid can be a mixture of fresh water and hydrazine.
Subsequent to the introduction of liquid to the tendon, compressor 1 3 supplies pressure through the conduit to the tendon's contents.
A pressure in excess of the maximum hydrostatic pressure exerted by the sea water on the tendon is recommended to avoid the instance where the pressure inside the tendon is equal to the sea water pressure at the same elevation. A positive net internal pressure is utilized to detect a leak. A valve is closed to retain the pressurized contents. Pressure gauges monitor the pressure therein. Reductions in pressure, in excess of a predetermined value, activate a signal to inform crew members of a deficient tendon.
The corrosion inhibiting liquid protects the interior walls of the tubular tendon from exposure to sea water. A liquid having a specific gravity less than that of sea water provides buoyancy and reduces the tendon weight supported by the offshore buoyant structure. Barring any pressurizing malfunctions, a change in pressure indicates a leak in the tendon attributable to a crack or puncture through the tendon or an inadequate coupling seal.
Variations in the embodiment described with reference to the drawing will be readily apparent to those skilled in the art.
Claims (20)
1. Apparatus for detecting a leak in a tension leg platform tendon, comprising:
a fluid tight tubular tendon;
means for supplying liquid to said tendon;
means for pressurizing said liquid;
means for monitoring pressure, said means monitoring variations in liquid pressure in said tendon;
means for connecting an upper end of said tendon to a buoyant offshore structure; and
means for connecting a lower end of said tendon to an anchor means connected to the sea floor.
2. Apparatus as claimed in Claim 1, wherein said liquid is water.
3. Apparatus as claimed in Claim 1, wherein said liquid is a hydrocarbon.
4. Apparatus as claimed in Claim 1, 2 or 3, wherein the liquid includes a corrosion inhibitor mixed therewith.
5. Apparatus as claimed in any preceding claim, wherein said liquid has a specific gravity less than that of sea water.
6. Apparatus as claimed in any preceding claim, wherein in use the liquid pressure in said tendon is in excess of the maximum hydrostatic pressure exerted on said tendon by the sea water in an offshore location.
7. A tension leg offshore platform having anchor means connectable to the sea floor;
at least one tendon connectable between said platform and said anchor means, said tendon being a fluid tight tubular member;
means for supplying liquid to said tendon;
means for pressurizing said liquid; and
means for monitoring pressure, said means being capable of monitoring variations in liquid pressure in said tendon.
8. A tension leg platform as claimed in
Claim 7, wherein said liquid is water.
9. A tension leg platform as claimed in
Claim 7, wherein said liquid is a hydrocarbon.
10. A tension leg platform as claimed in
Claim 7, 8 or 9, wherein said liquid includes a corrosion inhibitor mixed therewith.
11. A tension leg platform as claimed in
Claim 7, 8, 9 or 10, wherein said liquid has a specific gravity less than that of sea water.
1 2. A tension leg platform as claimed in any one of Claims 7 to 11, wherein in use the liquid pressure in said tendon is in excess of the maximum hydrostatic pressure exerted on said tendon by the sea water in an offshore location.
1 3. A method of detecting a leak in a tension leg offshore platform tendon, comprising the steps of:
connecting a tendon between a buoyant offshore platform and an anchor means connected to the sea floor at an offshore location, said tendon being a fluid tight tubular member;
supplying a liquid to said tendon;
pressurizing said liquid; and monitoring liquid pressure in said tendon to detect leaks therein.
1 4. A method according to Claim 13, wherein said liquid is water.
15. A method according to Claim 13, wherein said liquid is a hydrocarbon.
16. A method according to Claim 13, 14 or 15, whereinsaid liquid includes a corrosion inhibitor mixed therewith.
17. A method according to Claim 13, 14, 1 5 or 16, wherein said liquid has a specific gravity less than that of sea water.
1 8. A method according to any one of
Claims 1 3 to 17, wheren said liquid maintains a pressure in excess of the maximum hydrostatic pressure exerted on said tendon by the sea water at said offshore location.
19. A tension leg offshore platform substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.
20. A method of detecting a leak in a tension leg offshore platform tendon, substantially as hereinbefore desribed with reference to the accompanying drawing.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US50876483A | 1983-06-28 | 1983-06-28 |
Publications (3)
Publication Number | Publication Date |
---|---|
GB8416341D0 GB8416341D0 (en) | 1984-08-01 |
GB2142286A true GB2142286A (en) | 1985-01-16 |
GB2142286B GB2142286B (en) | 1986-05-14 |
Family
ID=24023975
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB08416341A Expired GB2142286B (en) | 1983-06-28 | 1984-06-27 | Pressurized liquid filled tendons |
Country Status (6)
Country | Link |
---|---|
CA (1) | CA1220039A (en) |
ES (1) | ES8601469A1 (en) |
FR (1) | FR2548367B1 (en) |
GB (1) | GB2142286B (en) |
NO (1) | NO842599L (en) |
YU (1) | YU46143B (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4626136A (en) * | 1985-09-13 | 1986-12-02 | Exxon Production Research Co. | Pressure balanced buoyant tether for subsea use |
US4630970A (en) * | 1985-09-13 | 1986-12-23 | Exxon Production Research Co. | Buoyancy system for submerged structural member |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN107235121B (en) * | 2017-04-29 | 2019-04-05 | 大连理工大学 | A kind of monitoring device and installation method based on sound transmission tension leg VIV |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB888247A (en) * | 1960-11-11 | 1962-01-31 | Conch Int Methane Ltd | Device for the storage of liquids at very low temperatures |
GB905990A (en) * | 1959-04-17 | 1962-09-19 | Shell Int Research | Improvements in or relating to the transport of liquefied gas |
GB2109325A (en) * | 1978-12-08 | 1983-06-02 | Conoco Inc | Mooring system for tension leg platform |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3517517A (en) * | 1968-09-19 | 1970-06-30 | Pan American Petroleum Corp | Encapsulated cable for marine use |
US4116044A (en) * | 1977-04-28 | 1978-09-26 | Fmc Corporation | Packoff leak detector |
GB1599491A (en) * | 1978-01-07 | 1981-10-07 | Fmc Corp | Pipe swivel joints |
US4285615A (en) * | 1978-12-13 | 1981-08-25 | Conoco, Inc. | Corrosion resistant tension leg cables |
-
1984
- 1984-06-20 FR FR848409692A patent/FR2548367B1/en not_active Expired
- 1984-06-27 GB GB08416341A patent/GB2142286B/en not_active Expired
- 1984-06-27 NO NO842599A patent/NO842599L/en unknown
- 1984-06-27 CA CA000457508A patent/CA1220039A/en not_active Expired
- 1984-06-28 YU YU112684A patent/YU46143B/en unknown
- 1984-06-28 ES ES533817A patent/ES8601469A1/en not_active Expired
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB905990A (en) * | 1959-04-17 | 1962-09-19 | Shell Int Research | Improvements in or relating to the transport of liquefied gas |
GB888247A (en) * | 1960-11-11 | 1962-01-31 | Conch Int Methane Ltd | Device for the storage of liquids at very low temperatures |
GB2109325A (en) * | 1978-12-08 | 1983-06-02 | Conoco Inc | Mooring system for tension leg platform |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4626136A (en) * | 1985-09-13 | 1986-12-02 | Exxon Production Research Co. | Pressure balanced buoyant tether for subsea use |
US4630970A (en) * | 1985-09-13 | 1986-12-23 | Exxon Production Research Co. | Buoyancy system for submerged structural member |
Also Published As
Publication number | Publication date |
---|---|
CA1220039A (en) | 1987-04-07 |
NO842599L (en) | 1985-01-02 |
GB8416341D0 (en) | 1984-08-01 |
FR2548367A1 (en) | 1985-01-04 |
GB2142286B (en) | 1986-05-14 |
ES533817A0 (en) | 1985-10-16 |
ES8601469A1 (en) | 1985-10-16 |
FR2548367B1 (en) | 1989-04-21 |
YU112684A (en) | 1987-04-30 |
YU46143B (en) | 1993-05-28 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19940627 |