Patent EA-003431-B1 (EA)
Title: Screw-threaded pipe joint
Inventor: HIGNETT IAN HAROLD
IPC: F16L15/06
Filed: 2001-01-12
Abstract: 1. A screw-threaded joint for pipes comprising a first pipe length (10) having a male screw threaded portion (11) at one end and a second pipe length (12) having a female portion at one end, the end having a complementary screw thread (13), the threads being adapted to inter engage along the greater part of the axial length thereof the threads (11,13) being inclined in the same direction and at an acute angle to the central longitudinal axis of the joint, the male thread (11) extending at least to a stop shoulder (31) having a head portion which is positioned adjacent a complementary stop shoulder on the female portion, characterised in that the complementary stop shoulder comprises a cone receiver having a conical cross-section and a rounded receiver apex, the cone receiver adapted to sealingly receive the head portion which has a conical cross-section and rounded apex of radius greater than the radius of the apex of the cone receiver, thereby providing a sealing surface upon application of a torque to the joint. 2. A screw-threaded joint according to claim 1, characterised in that the in-use outwardly facing cone wall (33) of the head portion subtends an angle of from 28 to 36[deg.] with respect to the longitudinal axis of the joint. 3. A screw-threaded joint according to claim 2, characterised in that the cone wall (33) subtends an angle of from 30 to 32[deg.] with respect to the longitudinal axis of the joint. 4. A screw-threaded joint according to any preceding claim, characterised in that the in-use inwardly facing cone wall (22) on the cone receiver subtends an angle of 28 to 38[deg.] with respect to the longitudinal axis of the joint. 5. A screw-threaded joint according to any preceding claim, characterised in that the angle subtended by the in-use inwardly facing cone wall (22) of the cone receiver is greater than that subtended by the in-use outwardly facing cone wall (33) of the head portion. 6. A screw-threaded joint according to any preceding claim, characterised in that the male screw-threaded portion comprises a second stress dispersing surface (37) connecting the stop shoulder (31) to the thread (36) of the pipe. 7. A screw-threaded joint according to claim 6, characterised in that in cross-section the second stress dispersing surface (37) describes a concave curve interacting longitudinally with the stop shoulder (31). 8. A screw-threaded joint according to claim 7 characterised in that the radius of curvature of the concave curve of the second stress dispersing surface (37) is from 0.075 to 0.085 cm. 9. A screw-threaded joint according to claim 8, characterised in that the radius of curvature of the concave surface of the second stress dispersing surface (37) is from 0.081 cm. 10. A screw-threaded joint according to any preceding claim, characterised in that the male screw threaded portion (10) comprises an end-shoulder (34) which subtends an angle of from 14 to 24[deg.] with respect to the plane perpendicular to the longitudinal axis of the pipe. 11. A screw-threaded joint according to claim 10, characterised in that the end-shoulder (34) subtends an angle of from 18 to 20[deg.] with respect to the plane perpendicular to the longitudinal axis of the pipe. 12. A screw-threaded joint according to any preceding claim, characterised in that the female threaded portion (12) comprises an end-shoulder (23) which subtends an angle of 12-24[deg.] with respect to the plane perpendicular to the longitudinal axis of the male threaded portion. 13. A screw-threaded joint according to claim 12, characterised in that the end-shoulder of the female threaded portion (12) subtends an angle from 14 to 18[deg.] with a plane perpendicular to the longitudinal axis of the male threaded portion. 14. A screw-threaded joint according to either of claims 12 or 13, characterised in that the angle subtended by the end-shoulder (23) of the female threaded portion is less than that subtended by the end-shoulder (34) of the male threaded portion. 15. A screw-threaded joint according to any preceding claim, characterised in that the in-use inner surface (41) of the stop shoulder (31) of the male threaded portion is concave when viewed from the inside of the pipe. 16. A screw-threaded joint according to claim 15, characterised in that the radius of the concave surface (41) is from 4.9 to 5.2 cm. 17. A screw-threaded joint according to claim 16, characterised in that the radius of the concave surface (41) is 5.1 cm.