Tubular connection

Abstract

A pipe joint includes pin and box members having interengaged threads characterized as producing hoop tension in the pin member and hoop compression in the box members.

I claim: 
     
       1. In a pipe joint including pin and box members, the joint having an axis, a. a pair of interengaged threads on said members for producing hoop tension in the pin member and hoop compression in the box member in response to forcible make-up of said members,   b. the threads on said members having dove-tail interfit,   c. said thread on each member having progressively changing axial width along substantially the entire helical length thereof and at selected radical distance from said axis, whereby upon complete make-up of the joint the interengaged thread flanks produce forces tending to urge the members radially together.   
     
     
       2. The joint of claim 1 wherein each thread has greater pitch width at the thread tip than at the thread root. 
     
     
       3. The joint of claim 2 wherein each thread has opposite flanks one of which in axial radial planes extends radially. 
     
     
       4. The joint of claim 3 wherein the other flank flares toward the thread outer extent relative to said one flank in axial radial planes. 
     
     
       5. The joint of claim 2 wherein each thread has opposite flanks both of which flare toward the outer extent of the thread in axial radial planes. 
     
     
       6. The joint of claim 2 wherein said threads have opposed tips and root walls with clearances formed therebetween, thread flanks forming angles with said thread tips and root walls in axial radial planes, said angles being less than about 85°. 
     
     
       7. The joint of claim 2 wherein the threads on said members in fully made up condition have mutually wedging interfit to limit said make-up. 
     
     
       8. The joint of claim 2 including annular shoulders on said members having sealing interfit in response to said make-up. 
     
     
       9. The joint of claim 8 wherein both of said shoulders are metallic. 
     
     
       10. The joint of claim 8 wherein at least one of said shoulders is non-metallic. 
     
     
       11. The joint of claim 1 including a second pair of interengaged threads like said first pair, said two pairs defining a multiple-step thread. 
     
     
       12. The joint of claim 1 wherein said threads are axially tapered. 
     
     
       13. The joint of claim 11 including annular shoulders on said members having sealing interfit between two of the thread steps. 
     
     
       14. The joint of claim 13 wherein said sealing interfit shoulders taper axially, the interengaged threads at said two steps locking the pin and box members together against relative radial separation at opposite ends of said sealing interfit shoulders. 
     
     
       15. In a pipe joint including pin and box members, the joint having an axis, a. annular shoulders on the members having sealing interfit, and   b. first and second interengaged threads on the respective members, the threads having dovetail interfit and locking the members together against relative separation proximate one axial side of said annular shoulders, each thread having progressively changing axial width along substantially the entire helical length thereof at selected radial distance from said axis, whereby upon complete make-up of the joint the interengaged thread flanks produce forces tending to urge the members radially together.   
     
     
       16. The pipe joint of claim 15 including third and fourth interengaged threads on the respective members, the third and fourth threads having dovetail interfit and locking the members together against relative separation proximate the other axial side of said annular shoulders, each of the third and fourth threads having progressively changing axial width along substantially the entire helical length thereof at selected radial distance from said axis. 
     
     
       17. In a joint including pin and box members, the joint having an axis, a. a pair of interengaged threads on said members for producing circumferential tension in the pin member and circumferential compression in the box member in response to forcible make-up of said members,   b. the threads on said members having dove-tail interfit,   c. said thread on each member having progressively changing axial width along substantially the entire helical length thereof and at selected radial distance from said axis, whereby upon complete make-up of the joint the interengaged thread flanks produce forces tending to urge the members radially together.   
     
     
       18. The joint of claim 17 wherein each thread has greater pitch width at the thread tip than at the thread root. 
     
     
       19. The joint of claim 18 wherein each thread has opposite flanks, one of which in axial radial planes extends radially. 
     
     
       20. The joint of claim 19 wherein the other flank flares toward the thread outer extent relative to said one flank in axial radial planes. 
     
     
       21. The joint of claim 18 wherein each thread has opposite flanks both of which flare toward the outer extent of the thread in axial radial planes. 
     
     
       22. The joint of claim 18 wherein said threads have opposed tips and root walls with clearances formed therebetween, thread flanks forming angles with said thread tips and root walls in axial radial planes, said angles, being less than about 85°. 
     
     
       23. The joint of claim 18 wherein said threads on said members in fully made up condition have mutually wedging interfit to limit said make-up. 
     
     
       24. The joint of claim 18 including annular shoulders on said members having sealing interfit in response to said make-up. 
     
     
       25. The joint of claim 24 wherein both of said shoulders are metallic. 
     
     
       26. The joint of claim 24 wherein at least one of said shoulders is non-metallic. 
     
     
       27. The joint of claim 17 including a second pair of interengaged threads like said first pair, said two pairs defining a multiple-step thread. 
     
     
       28. The joint of claim 17 wherein said threads are axially tapered. 
     
     
       29. The joint of claim 24 wherein said sealing interfit shoulders taper axially, the interengaged threads locking the pin and box members together against relative radial separation at opposite ends of said sealing interfit shoulders. .Iadd. 30. A thread structure for a pin member adapted for use in a pipe joint, said pin member having an axis and adapted to be made-up with a mating box member having a complementary thread structure, said thread structure for said pin member comprising: a helical pin thread structure having at least one dove-tail flank adapted for interfitting with a complementary helical thread flank on a mating box member for producing hoop tension in said pin member and hoop compression in such box member in response to forcible make-up of said pin member with such box member to form a joint;   said helical pin thread structure having progressively changing axial width along substantially the entire helical length thereof and at selected radial distance from the axis, whereby upon complete make-up of the joint the interengaged thread flanks produce forces tending to urge said pin member radially toward such box member;   said pin member including a second pin thread like said first pin thread, said two threads defining a multiple step thread; and   said pin member, including an annular seal shoulder on said pin member between said thread steps adapted for sealing interfit with such box member. .Iaddend. .Iadd. 31. The pin member of claim 30, wherein said annular seal shoulder tapers axially, the pin threads at said two steps adapted for locking the pin and box members together against relative radial separation at opposite ends of said seal shoulder. .Iaddend. .Iadd. 32. A thread and seal structure for a pin member adapted for use in a pipe joint, said pin member having an axis and adapted to be made-up with a mating box member having a complementary thread structure to form the joint, said thread and seal structure for said pin member comprising:   an annular seal shoulder formed on said pin member adapted for sealing interfit with such box member upon make-up of the joint;   a first helical pin thread structure on said pin member adapted for interengagement with a complementary helical thread structure on such box member upon make-up of the joint;   said first pin thread structure having a flank adapted to have a dove-tail interfit with such thread flank on such box member for locking the pin member and box member together against relative separation proximate one axial side of said annular seal shoulder upon make-up of the joint; and   said first pin thread structure having progressively changing axial width along substantially the entire helical length thereof at selected radial distance from the axis wherein upon complete make-up of the joint the interengaged thread flanks produce forces tending to urge said pin member and such box member radially together. .Iaddend. .Iadd. 33. A thread structure for a pin member adapted for use in a joint, said pin member having an axis and adapted to form a joint upon make-up with a mating box member having a complementary thread structure, said thread structure for said pin member comprising:   a helical pin thread structure on said pin member adapted for producing circumferential tension in said pin member and circumferential compression in such box member in response to forcible make-up with such box member to form the joint;   said helical pin thread structure having a dove-tail flank; and   said helical pin thread structure on said pin member having progressively changing axial width along substantially the entire helical length of said pin thread structure and at a selected radial distance from said axis, whereby upon complete make-up of the joint the thread flanks produce forces tending to urge said pin member radially together with such box member. .Iaddend. .Iadd. 34. The pin member of claim 33, wherein said pin thread structure has greater pitch width at the thread tip than at the thread root. .Iaddend..Iadd. 35. The pin member of claim 34, wherein said pin thread structure has opposite flanks, one of which in axial radial planes extends radially. .Iaddend..Iadd. 36. The pin member of claim 35, wherein the other flank flares toward the thread outer extent relative to said one flank in axial radial planes. .Iaddend..Iadd. 37. The pin member of claim 34, wherein said pin thread structure has opposite flanks both of which flare toward the outer extent of the thread in axial radial planes. .Iaddend..Iadd. 38. The pin member of claim 34, wherein said pin thread flank forms an angle with said thread tips and root walls in axial cylindrical planes, said angle being less than about 85°. .Iaddend..Iadd. 39. The pin member of claim 34, wherein the thread structure on said pin member is adapted in fully made-up condition to have mutually wedging interfit with such box member having complementary thread structure to limit said make-up. .Iaddend. .Iadd. 40. The pin member of claim 34, including an annular shoulder on said member adapted for sealing interfit with a complementary shoulder on such box member in response to said make-up. .Iaddend..Iadd. 41. The pin member of claim 40, wherein said pin member annular shoulder is metallic. .Iaddend..Iadd. 42. The pin member of claim 40, wherein said pin member annular shoulder is non-metallic. .Iaddend..Iadd. 43. The pin member of claim 33, including a second thread structure like said first thread structure, said pair defining a multiple-step thread structure. .Iaddend..Iadd. 44. The pin member of claim 33, wherein said thread structure is axially tapered. .Iaddend..Iadd. 45. The pin member of claim 40, wherein said annular shoulder tapers axially. .Iaddend. .Iadd. 46. A thread structure for a box member adapted for use in a pipe joint, said box member having a complementary thread structure, said thread structure for said box member comprising:   a helical box thread structure having at least one dove-tail flank adapted for interfitting with a complementary helical thread flank on a mating pin member for producing hoop compression in said box member and hoop tension in such pin member in response to forcible make-up of said box member with such pin member to form a joint;   said helical box thread structure having progressively changing axial width along substantially the entire helical length thereof and at selected radial distance from the axis, whereby upon complete make-up of the joint the interengaged thread flanks produce forces tending to urge said box member radially towards such pin member;   said box member including a second box thread like said first box thread, said two box threads defining a multiple step thread; and   said box member including an annular seal shoulder on said box member between said thread steps adapted for sealing interfit with such pin member. .Iaddend. .Iadd. 47. The box member of claim 46, wherein said annular seal shoulder tapers axially, the box threads at said two steps adapted for locking the pin and box members together against relative radial separation at opposite ends of said shoulder. .Iaddend. .Iadd. 48. A thread structure and seal for a box member adapted for use in a pipe joint, said box member having an axis and adapted to be made-up with a mating pin member having a complementary thread structure to form the joint, said thread structure and seal for said box member comprising:   an annular seal shoulder formed on said box member adapted for sealing interfit with such pin member upon make-up of the joint;   a first helical box thread structure on said box member adapted for interengagement with a complementary helical thread structure on such pin member upon make-up of the joint;   said first box thread structure having a flank adapted to have a dove-tail interfit with such thread flank on such pin member for locking the box member and pin member together against relative separation proximate one axial side of said annular seal shoulder upon make-up of the joint; and   said first box thread structure having progressively changing axial width along substantially the entire helical length thereof at selected radial distance from the axis wherein upon complete make-up of the joint the interengaged thread flanks produce forces tending to urge said box member and such pin member radially together. .Iaddend. .Iadd. 49. A thread structure for a box member adapted for use in a joint, said box member having an axis and adapted to be made-up with a mating pin member having a complementary thread structure, said thread structure for said box member comprising:   a helical box thread structure on said box member adapted for producing circumferential compression in said box member and circumferential tension in such pin member in response to forcible make-up with such pin member;   said helical box thread structure having a dove-tail flank; and   said helical box thread structure having progressively changing axial width along substantially the entire helical length of said box thread structure and at a selected radial distance from said axis, whereby upon complete make-up of the joint the thread flanks produce forces tending to urge said box member radially together with such pin member. .Iaddend. .Iadd. 50. The box member of claim 49, wherein said box thread structure has greater pitch width at the thread tip than at the thread root. .Iaddend..Iadd. 51. The box member of claim 50, wherein said box thread structure has opposite flanks, one of which in axial radial planes extends radially. .Iaddend..Iadd. 52. The box member of claim 51, wherein the other flank flares toward the thread outer extent relative to said one flank in axial radial planes. .Iaddend..Iadd. 53. The box member of claim 50, wherein said box thread structure has opposite flanks both of which flare toward the outer extent of the thread in axial radial planes. .Iaddend..Iadd. 54. The box member of claim 50, wherein said box thread flank forms an angle with said thread tips and root walls in axial cylindrical planes, said angle being less than about 85°. .Iaddend..Iadd. 55. The box member of claim 50, wherein the thread structure on said box member is adapted in fully made-up condition to have mutually wedging interfit with such pin member having complementary thread structure to limit said make-up. .Iaddend. .Iadd. 56. The box member of claim 50, including an annular shoulder on said member adapted for sealing interfit with a complementary annular shoulder on such pin member in response to said make-up. .Iaddend..Iadd. 57. The box member of claim 56, wherein said box member annular shoulder is metallic. .Iaddend..Iadd. 58. The box member of claim 56, wherein said box member annular shoulder is non-metallic. .Iaddend..Iadd. 59. The box member of claim 49, including a second thread structure like said first thread structure, said pair defining a multiple step thread structure. .Iaddend..Iadd. 60. The box member of claim 49, wherein said thread structure is axially tapered. .Iaddend..Iadd. 61. The box member of claim 56, wherein said annular shoulder tapers axially. .Iaddend.