Variable spring rate compression element and riser tensioner system using the same

• US 5,641,248 A
• Filed: 04/04/1995
• Issued: 06/24/1997
• Est. Priority Date: 04/15/1993
• Status: Expired due to Term

• Current Assignee: Oil States Industries Incorporated (Oil States International Incorporated)
• Original Assignee: Continental Emsco Co. (LTV Corp.)
• Inventors: Arlt, Edward J. III
• Primary Examiner(s): Taylor, Dennis L.
• Application Number:
  US08/416,292
• Time in Patent Office: 812 Days
• Field of Search: 405/195.1, 405/224, 405/212, 405/213, 405/214, 405/215, 405/203, 405/204, 405/205, 166/350, 166/359, 166/367, 267/140.13, 267/140.2, 267/241.4, 267/140.4, 267/141.3, 267/141.6
• US Class Current: 405/195.1
• CPC Class Codes: E21B 19/006 including heave compensators
• CPC Class Codes: F16F 1/371 characterised by inserts or auxiliary extension or exterior elements, e.g. for rigidification F16F1/387 takes precedence; non-embedded reinforcing elements for flexibly-walled air springs F16F9/0436
• CPC Class Codes: F16F 1/3807 characterised by adaptations for particular modes of stressing
• CPC Class Codes: F16F 1/3935 Conical sleeves
• CPC Class Codes: F16F 1/40 consisting of a stack of similar elements separated by non-elastic intermediate layers F16F9/306 takes precedence; laminated constructions to protect buildings against abnormal external influences, e.g. earthquakes, E04H9/022
• CPC Class Codes: F16F 1/41 the spring consisting of generally conically arranged elements if sleeve-like, i.e. a surface of revolution F16F1/3935
• CPC Class Codes: F16F 13/26 characterised by adjusting or regulating devices responsive to exterior conditions F16F13/101 takes precedence
• CPC Class Codes: F16F 3/0873 of the same material or the material not being specified

Abstract

A compression element having a deflectable elastomeric member is disclosed. The compression element exhibits a decreasing axial spring rate in response to axial movement and compression of the deflectable member. The compression element may be used alone or in combination with other compression elements in riser tensioner systems to maintain a substantially constant upward tensioning force on a riser as it moves axially relative to a floating platform.

Claims

1. A compression element being deflectable along a longitudinal axis, said compression element comprising:

an inner flange having a curved outer coupling portion;

an outer flange having a curved inner coupling portion;

a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and

at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least one curved reinforcement share a pair of common focal points substantially displaced diametrically from said longitudinal axis in a central longitudinal cross-section and wherein relative axial movement of said inner flange toward said outer flange compresses said deflectable member and decreases said axial spring rate of said deflectable member.

2. The compression element, as set forth in claim 1, wherein said deflectable member is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being coupled to said outer coupling portion of said inner flange and said base end being coupled to said inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said deflectable member.

3. The compression element, as set forth in claim 2, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub.

4. A riser tensioner system for applying a tensioning force to a riser and allowing a floating platform to move within a given range along a longitudinal axis of said riser, said system comprising:

a compression element being deflectable along said longitudinal axis, said compression element having;

an inner flange having a curved outer coupling portion;

an outer flange having a curved inner coupling portion;

a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and

at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least one curved reinforcement share a pair of common focal points substantially displaced diametrically from said longitudinal axis in a central longitudinal cross-section;

said inner flange being coupled to said riser and said outer flange being coupled to said platform, wherein relative axial movement of said inner flange toward said outer flange compresses said deflectable member and decreases said axial spring rate of said deflectable member such that said tensioning force on said riser remains substantially constant throughout said range.

5. The system, as set forth in claim 4, wherein said deflectable member is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being coupled to said outer coupling portion of said inner flange and said base end being coupled to said inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said deflectable member.

6. The system, as set forth in claim 5, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub.

7. A riser tensioner system for applying a tensioning force to a riser and allowing a floating platform to move within a given range along a longitudinal axis of said riser, said system comprising:

a columnar stack of compression elements having a top compression element and a bottom compression element, said stack of compression elements being deflectable in response to certain relative movement between said riser and said platform along said longitudinal axis, each of said compression elements having;

an inner flange having a curved outer coupling portion;

an outer flange having a curved inner coupling portion;

a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and

at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least one curved reinforcement share a pair of common focal points substantially displaced diametrically from said longitudinal axis in a central longitudinal cross-section;

said top compression element being coupled to said riser and said bottom compression element being coupled to said platform, wherein relative axial movement of said inner flanges of said compression elements in said stack toward said respective outer flanges of said compression elements in said stack compresses said deflectable members of said compression elements in said stack and decreases said axial spring rate of each of said deflectable members such that said tensioning force on said riser remains substantially constant throughout said range.

8. The system, as set forth in claim 7, wherein at least one of said deflectable members is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being curved and complementarily coupled to said curved outer portion of said inner flange and said base end being curved and complementarily coupled to said curved inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said at least one deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said at least one deflectable member.

9. The system, as set forth in claim 8, wherein said cone of said deflectable member has a plurality of slots that extend radially outwardly from a central hub.

10. The system, as set forth in claim 7, further comprising:

a preload device coupled to said columnar stack of compression elements for compressing said columnar stack of compression elements and placing said columnar stack of compression elements within a selected deflection range.

11. The system, as set forth in claim 7, wherein said columnar stack of compression elements defines an internal space and further comprises an inlet for introducing compressible gas into said internal space, said compressible gas altering said spring rate of said columnar stack of compression elements.

12. A riser tensioner system for applying a tensioning force to a riser and allowing a floating platform to move within a given range along a longitudinal axis of said riser, said system comprising:

a support member being coupled to said riser and having a portion extending radially outwardly from said riser; and

a plurality of columns of compression elements, each column having an upper end portion being coupled to said radially extending portion of said support member and having a lower end portion being coupled to said platform, each column being deflectable in response to certain relative movement between said riser and said platform along said longitudinal axis, each column comprising compression elements having;

an inner flange having a curved outer coupling portion;

an outer flange having a curved inner coupling portion;

a deflectable member having an axial spring rate that varies within a given range, said deflectable member coupling said inner flange to said outer flange in an axially spaced apart relationship, said deflectable member having a first curved end coupled to said outer coupling portion of said inner flange and having a second curved end coupled to said inner coupling portion of said outer flange; and

at least one curved reinforcement disposed in said deflectable member, wherein said curved outer coupling portion, said curved inner coupling portion, and said at least one curved reinforcement share a pair of common focal points substantially displaced diametrically from said longitudinal axis in a central longitudinal cross-section;

wherein relative movement of said platform toward said support member along said longitudinal axis of said riser produces relative axial movement of each of said inner flanges toward each of said outer flanges in each of said compression elements in each of said columns which compresses each of said deflectable members and decreases said axial spring rate of each of said deflectable members such that said tensioning force on said riser remains substantially constant throughout said range.

13. The system, as set forth in claim 12, wherein at least one of said deflectable members is shaped like a hollow, truncated cone having a given conical angle, a truncated end, and a base end, said truncated end being curved and complementarily coupled to said curved outer portion of said inner flange and said base end being curved and complementarily coupled to said curved inner coupling portion of said outer flange, wherein relative axial movement of said inner flange toward said outer flange compresses said at least one deflectable member and increases said conical angle, thus decreasing said given axial spring rate of said at least one deflectable member.

14. The system, as set forth in claim 13, wherein said cone of said at least one deflectable member has a plurality of slots that extend radially outwardly from a central hub.

15. The system, as set forth in claim 12, further comprising:

a preload device coupled to said support member for compressing said columns of compression elements and placing said columns of compression elements within a selected deflection range.

16. The system, as set forth in claim 12, wherein each of said plurality of columns of compression elements defines an internal space and further comprises an inlet for introducing compressible gas into said internal space, said compressible gas altering said spring rate of said respective column of compression elements.