Expandable coupling

1. A method of providing an expanded tubular coupling, comprising:

providing a first tubular including a male thread portion on an end thereof and a second tubular including a female thread portion on an end thereof, the thread portions having flanks;

engaging the male and female thread portions to form a tubular coupling wherein each of at least one flank of the male thread portion abuts a respective adjacent flank of the female thread portion, and remaining corresponding flanks of the thread portions define gaps therebetween that have a specifically selected spacing; and

expanding the tubular coupling, whereby relative axial movement between corresponding flanks occurs during expansion of the coupling, wherein selecting the spacing is based on an amount of the relative axial movement such that the relative axial movement is accommodated by the gaps.

2. The method of claim 1 , wherein the tubular coupling is expanded using a rotary expansion tool, said rotary expansion tool causing the male thread portion to axially extend and the female thread portion to axially contract.

3. The method of claim 1 , wherein the tubular coupling is expanded using a cone expansion tool, said cone expansion tool causing the male thread portion and the female thread portion to axially contract at different rates.

4. The method of claim 1 , wherein the tubular coupling is expanded using hydraulic pressure.

5. The method of claim 1 , wherein expanding the coupling includes securing the connection during expansion by abutting at least some of the remaining corresponding flanks.

6. The method of claim 1 , wherein expanding the tubular coupling creates the relative axial movement between corresponding flanks that at least partially closes the gaps.

7. A method of retaining integrity of a tubular coupling after expansion, comprising:

providing male and female thread portions connected together to form the tubular coupling, wherein the thread portions have flanks and define a first set of flanks with corresponding flanks of the male and female thread portions abutting one another and a second set of flanks with corresponding flanks of the male and female thread portions separated from one another prior to expansion; and

causing the male thread portion to axially extend and the female thread portion to axially contract by circumferentially expanding the tubular coupling, wherein the integrity is retained due to at least some of the second set of flanks abutting one another.

8. The method of claim 7 , wherein the tubular coupling is expanded using a rotary expansion tool.

9. A method of retaining integrity of a tubular coupling after expansion, comprising:

providing male and female thread portions connected together to form the tubular coupling, wherein the thread portions have flanks and define a first set of flanks with corresponding flanks of the male and female thread portions abutting one another and a second set of flanks with corresponding flanks of the male and female thread portions separated from one another by gaps prior to expansion; and

creating relative axial movement between corresponding flanks by circumferentially expanding the tubular coupling, wherein the relative axial movement at least partially closes the gaps and at least partial closing of the gaps occurs without substantially increasing interference forces produced between respective adjacent flanks in order to retain the integrity.

10. The method of claim 9 , wherein creating relative axial movement energizes a deformable sealing material provided in at least some of the gaps.

11. The method of claim 9 , further comprising providing a leading end portion extending from the male thread portion, wherein the leading end portion is constrained in a radial direction at the tubular coupling.

12. The method of claim 11 , further comprising providing an undercut groove in a portion of the tubular coupling having the female thread portion, wherein the undercut groove receives the leading end portion.

13. The method of claim 9 , wherein creating relative axial movement includes securing the connection during expansion by abutting at least some of the second set of flanks.

14. The method of claim 9 , wherein expanding the tubular coupling includes operating a rotary expansion tool, wherein the rotary expansion tool causes the male thread portion to axially extend and the female thread portion to axially contract during expanding.

15. The method of claim 9 , wherein expanding the tubular coupling includes operating a cone expansion tool, wherein the cone expansion tool causes the male thread portion and the female thread portion to axially contract at different rates during expanding.

16. The method of claim 9 , wherein expanding the tubular coupling is via hydraulic pressure.

17. The method of claim 9 , wherein the first set of flanks is disposed in a central region between end regions of the male and female thread portions and the second set of flanks of the thread portions is disposed in the end regions.

18. The method of claim 9 , wherein the gaps between corresponding flanks of the male and female thread portions are provided by a variable thread pitch in at least one of the male and female thread portions.

19. The method of claim 18 , wherein the variable thread pitch is provided on both thread portions.

20. The method of claim 18 , wherein the thread portions include roots and the variable thread pitch is achieved by varying the width of the roots of the respective thread along the length thereof.

21. The method of claim 18 , wherein the thread portions include crests and the variable thread pitch is achieved by varying the width of the crests of the respective thread along the length thereof.

22. The method of claim 9 , wherein the thread portions define a thread which is cut in an opposite direction to a direction of rotary expansion during expanding the tubular coupling.

23. The method of claim 9 , wherein the male and female thread portions are of a dove-tail thread profile.

24. The method of claim 9 , wherein the male and female thread portions are of a square profile.

25. The method of claim 9 , wherein the thread portions are axially parallel.