GB2156933A - Pipe connector - Google Patents

Abstract

A pin and box connector for high combined bending and tensile loads comprises pin member 10 and box member 20 each having complementary tapered threaded portions angled with respect to the longitudinal axis of the coupling. The inboard end of the box member includes a shoulder 28 which is tapered at an angle A and adjacent the shoulder there is provided a seal ring groove 34. The pin member includes a tapered nose portion 52 for engagement with shoulder 28 and a cylindrical extension 50 which overlies seal ring groove 34 in the coupled condition. The pin and the box have frustoconical threads 12 and 22 in which the load bearing faces (36, Fig. 4 and 54, Fig. 8) are also angled with respect to the longitudinal axis of the coupling in order to maintain loading if the coupling is subjected to bending forces. <IMAGE>

Description

SPECIFICATION Pipe connector Background of the invention The invention relates to large diameter tubular connectors, and in particular, to a connector subject to a combination of high internal pressure with tension and/or bending.

Large diameter pipe (16 inch od and greater) is used, in threaded joints about 50 feet long, for casing and risers in offshore oil production operations. Such pipe is subject to high internal pressure as well as high bending and/ortensile loads. Easily made up, strong, leak tight connectors are desirable for such use.

High tensile loads (orthetension side in bending) tend to cause separation of the threads, particularly toward the ends of the threaded connector. In compression, the nose of the shoulderto connector can tend to buckle inwardly. Interference type connectors create hoop stress which in some cases can be additive to the pressure stress. Strain of the connector can cause seals to leak.

Summary of the invention The connector of the invention is resistant to separation, buckling, and maintiansthe seal during straining of the connector.

Brief description of the drawings, Figure 1 is a sectional elevation of a weld-on pin and box connector; Figure 2 is a sectional elevation through one edge of the box; Figure 3 is a sectional elevation through one side of the pin; Figure.4 is a section showing the detail where the nose of the pin seats against the shoulder of the box; Figure 5 is a fragmentary sectional view of the end of the box; Figure 6 is a detail of the pin thread form; Figure 7 is a detail of the box thread form; Figure 8 illustrates a threaded and coupled connector for thin wall pipe.

Figure 9 is an enlarged fragmentary view in use; and Figure 10 shows a threaded and coupled connectorforthin wall pipe.

Referring to Figure 1, weld-on pin member 10 has an external frustoconical thread 12, and has a weld preparation 14 fo r weldi ng to pipe 16.

Box member 20 has an internal frustoconical thread 22, which is complementary to thread 12 of the pin. The box includes a weld prep 24 for welding to a pipe 26. The inboard end of the box includes a shoulder 28.

Referring to box 20 in Figures 2, 3, 4, and 5, the frustoconical thread 22 is on a first taper, at an angle P of about 21/2 with respect to the longitudinal axis.

The box includes the frustoconical internal shoulder 28 with a second taper A, of about 240 from the horizontal or 660 from the longitudinal axis. An annular runout groove 30 may be provided outboard of the threaded portion of the box with an annular surface 32 outboard thereof. the seal ring groove 34 for containing a resilient O-ring seal 38 is located adjacent to the shoulder 28.

Threads 22 include a face 36, facing toward said shoulder, the face of the thread forming an angle B of about 30 with respect to the horizontal. This angle is greater than the first taper angle of 2 1/2 .

The outboard end of the box may include an annular groove 44 with a cylindrical extension 46 immediately adjacent the outboard end of the connector. This extension has an inside diameter substantially identical to the outside diameter of the pin 10.

The pin 10 shown in Figures 6, 7, and 8 have frustoconical threads 12 on the same first taper P with respect to the longitudinal axis of the pin. The outboard end of the pin includes a cylindrical extension 50 adapted to seal agasinst resilient 0ring 38. The pin has a nose 52 having a surface 53 also at an angle A which is 240 with respect to the horizontal. This nose is accordingly complementary with the shoulder 28 of the box.

The pin thread form has a face 54 of each thread facing away from the open end of the pin having an angle B of 30 with respect to the horizontal. Figure 9 illustrates a detail of a portion of the engaged pin and box in the seal area.

Under tensile loading, the longitudinal load is passed into the pin through the teeth 12. This load being eccentric with respect to the centerline of the material tends to cause the nose 50 of the pin to strain in a direction so that it rotates inwardly. This would cause the sealing surface 50 to move away from the seal 38. The second taper of the shoulder 28 cooperating with the nose of the pin 52 limits the amount of movement which may take place in this direction, thereby limiting the movement of the nose to a very small range which the resilient seal ring can follow. Accordingly, tensile loading does not open up a leak path.

When the connector is bending the same phenomenon occurs on the tension side of the coupling.

Under compression loading (including the compression side in bending) the loaded faces 36 and 54 tend to become unloaded. The load tends to pass through the nose 52 to shoulder 28. The pin tends to buckle inwardly. Since the threads have a reverse flank angle thereon, they re-engage as the pin starts to buckle. This restoring force is applied at the initiation of buckling, thereby requiring low force, and also maintaining the sealing surface 50 near the resilient seal 38. Increasing the reverse flank angle amplifies this effect, but tends to weaken the threads in shear.

The connector relies on the nose of the pin and the shoulder to limit rotation with the connector being torqued against the shoulder. There is accordingly no radial interference between the threads, and therefore no hoop stress created during the tightening of the connector. The very slight reverse taper on the faces of the threads does not significantly affect the hoop stress during tightening.

Pressure loading tends to force the nose of the pin outwardly thereby increasing the sealing effect. The threaded space beyond the seal does not experience high pressure so that the pin tends to expand outwardly straining until it meets the box at which time it is reinforced by the box structure. The very slight reverse taper of the faces does not cause a significant loosening of the connector during its expansion, and to the extent that it does it can be seen that the nose is still retained within the shoulder since the angle of the reverse taper of the shoulder is significantly greater than that of the face of the threads.

Figure 10 illustrates a threaded and coupled form of the invention particularly adaptable to thin wall pipe.

Coupling 60 includes the reverse tapered shoulder 62, and the tapered threads 64 in the same manner as the box previously described. Pipe 70 is swaged inwardly forming inward taper 72 with the thread form 74 being machined into the pipe thereafter.

The inward swaging of the pipe provides sufficient material to avoid an unduly thin nose, which would be very susceptible to damage during handling, and which could strain excessively during operation.

Since the eccentric loading on this type connector is even greaterthan on the weld-on pin and boxthe interaction of the various tapers to prevent relaxation of the seal is even more important.

Claims (5)

1. A pipe connector for high combined tensile and pressure loading comprising: a frustoconically threaded pin member at a first taper; a frustoconically threaded box member also at said first taper and having threads complementary to those of said pin member; a frustoconical internal shoulder on said box, a second taper of said shoulder in a direction reverse of said first taper, said second taper forming an angle with said first taper of less than 90 ; a seal ring groove internally of said box outboard of and adjacent to said shoulder; a resilient seal ring in said seal ring groove; a face of said box thread facing said shoulder having a surface tapered with respect to the axis of said box in a direction opposite to the taper of said shoulder; said pin having a nose complementary to said shoulder; ; the face of said pin thread facing away from the open end of said pin having a surface complementary with that of said box; and said pin having at the outboard end an cylindrical extension for sealing with said resilient seal.

2. A pipe connector as in Claim 1 having more than two threads on each of said pin and box; said box having a cylindrical extension facing inwardly at the outboard end thereof of a diameter of substantially equal to that of the maximum dimension of the pin.

3. A pipe connector as in Claim 2 having three threads.

4. A pipe connector as in Claim 1 wherein said pin comprises the end of a pipe section which is swaged inwardly.

5. A pipe connector for high combined tensile and pressure loading, substantially as hereinbefore described with reference to the accompanying drawings.