IMPROVEMENTS IN AND RELATING TO PIPE CONNECTORS

Abstract: A connector for connecting large diameter pipe sections, e.g. conductor or casing pipe sections, comprises a tubular pin member (2) and a tubular box member (1) for receiving the pin member. The box member has a generally frusto-conical internal surface portion (3) provided with a thread (4) and the pin member has a corresponding generally frustro-conical external surface portion (5) provided with a corresponding thread (6). Each thread has a leading flank surface portion (42, 62) facing the free end of the respective member and a crest surface portion (43, 63), the junctions between the leading flank surface portions and the crest surface portions being cut away to provide contact surface portions (45, 65) which are arranged to come into contact when the members are initially telescoped together with a predetermined relative angular orientation, regardless of any axial misalignment of the members. The contact surface portions are inclined to both the leading flank surface portions and the crest surface portions and intersect the crest surface portions. The cone angles of the surface portions (3, 5) and the pitch of the threads (4, 6) are selected so that the members are fully engageable with a relative rotation of less than 360 DEG .

Description: Improvements in and relating tφ pjpe onnector-*? The present invention relates to a pipe connector comprising a pin member and a box member forming part of, or to be connected to, adjacent ends of pipe sections to be connected together, and designed particularly, but not exclusively, for connecting pipe sections having large diameters, for example of the order of 20" to 30". Pipe connectors comprising a pin member and a box member, each having a frusto-conical threaded surface, are known. Such connectors have the advantage that the members can be axially telescoped together to partially introduce the pin member into the box member, before the members have to be rotated to inter-engage the threads. However they suffer the disadvantage that, if the members are not exactly axially aligned when they are telescoped together, the threads can cross and the members jam together as they are rotated. Particularly in the oil industry, for speed of make¬ up of such a connector, there is a need to reduce the amount of relative rotation required to fully engage the members together. Although this can be achieved by appropriate selection of the pitch of the thread in conjunction with the cone angle of the threaded surfaces, there are economic factors, as well as engineering factors, which have to be taken into account. According to the present invention there is provided a connector comprising a tubular pin member connected, or for connection, to one end of a pipe section, a tubular box member for receiving the tubular pin member and connected, or for connection, to one end of another pipe section, the box member comprising a generally frusto-conical internal surface portion formed with a thread and the pin member com¬ prises a generally frusto-conical external surface portion provided with a thread for engagement with the said thread on the box member, each thread having a leading flank sur¬ face portion which faces the free end of the member, a trailing flank surface portion facing in the opposite direc¬ tion and a crest surface portion, characterised in that a contact surface portion is provided between the leading flank surface portion and the crest surface portion of each thread, the contact surface portions of the threads on the two members being arranged so that they come into contact when the members are telescoped together with a predeter¬ mined angular orientation. Advantageously, the axial and radial extents of the contact surface portions are such that, with the predeter¬ mined angular orientation, contact will be maintained regardless of any axial misalignment between the pin and box members. Preferably, the cone angles of the frusto-conical surface portions and the pitch of the threads are selected so that the members are fully engageable together with a relative rotation of the members of less than 360 * The contact surface portions preferably have a convex profile so that the contact surface portions of the threads of the two members make line contact. The surfaces may be part circular in cross-section with the centres of the circles lying on a straight line which passes through the contact point between the contact surfaces when in con¬ tact with the predetermined angular orientation and axially aligned. This line may extend at about 60° to the axis of the connector. Advantageously, the leading flank surface portions are, in cross-section, generally inclined to the axis of the respective member. Preferably, the parts of the leading flank surface portion which overlap when the connector is fully made up are linear in cross-section, with the same angles of inclination to the respective axis, so that these surface portions can be in full surface contact as the members are engaged together and can be brought into full load bearing surface contact when the connector is under compression. Preferably, when the connector is fully made up, the trailing flanks of the threads are brought into abutment by abutment between annular surfaces on the pin and box members. These annular surfaces may, for example, be pro¬ vided in the region of or on the free end of the pin member and in the region of the root of the box member or may be provided in the region of the root of the pin member and in the region of or on the free end of the box member. Preferably, when the connector is fully made up, a clearance is provided between the crest surface portions of the threads on the two members and the root surface portions spacing the turns of the threads apart. A clearance may also be provided between the leading flank surface portions. To minimise this clearance, each thread may be cut away at the junction between the crest surface portion and the trailing flank surface portion. To reduce stress in the threads, each root surface portion may be formed by an intermediate frusto-conical sur¬ face portion connected to the trailing flank surface portion by a generally parabolic surface or a surface comprising a first curved portion having a relatively large radius of curvature and a second curved portion having a smaller radius of curvature. The crest surface portion of each thread preferable lies on a frusto-conical envelope, the cone angles of the envelopes of the threads on the two members being substan¬ tially the same. Alternatively, the crest surface portions may extend parallel to the axis of the respective member, the leading and trailing ends of the surface portions lying on frusto-conical envelopes, the cone angles of the envel¬ opes being substantially the same. Preferably each member is provided with a single (or single start) thread but the members may each be provided with a plurality of threads (or a multi-start thread) . Advantageously, each member is provided with gener¬ ally cylindrical surface portions at each end of the threaded surface portion. These generally cylindrical sur¬ face portions serve to guide the members as they are teles¬ coped together to correct any substantial misalignment of the members before the contact surface portions come into contact, and are dimensioned axially so that there is overlap between the corresponding guide surface portions on the members before the contact surface portions come into con¬ tact. Further features and advantages of the present invention will become apparent from the following descrip¬ tion of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an axial section through an embodiment of a box member of an embodiment of a connector according to the present invention; Figure 2 is an axial section through an embodiment of a pin member for engagement with the box member of Figure 1; Figures 3 and 4 are enlarged sections through parts of the box and pin members respectively of Figures 1 and 2; Figures 5 and 6 show the parts shown in Figures 3 and 4 during engagement and when fully engaged; Figure 7 is an elevation showing a details of the members of Figures 1 and 2 when fully engaged; and Figure 8 is a view in the direction of the arrow VIII in Figure 7. The connector shown in the drawings is intended for connecting conductor or casing pipe sections, e.g. of 20" to 30" diameter, but may also be used for connecting smaller or larger diameter pipe sections. The connector comprises a box member 1 connected, or for connection, to the end of one pipe section and a pin member 2 for engagement with the box member 1 which is connected, or for connection, to one end of another pipe section, as is conventional. The box member 1 is tubular with a generally frusto-conical internal sur¬ face portion 3 which, as shown, is provided with a single (or single start) helical thread 4. The pin member is also tubular and has a corresponding generally frusto-conical external surface portion 5 provided with a corresponding helical thread 6 for engagement with the thread 4 on the box member. In a modification, the surface portions 3, 5 are each provided with a plurality of threads (or a multi-start thread). Each thread 4, 6 has a trailing and a leading flank surface portion 41, 42, 61, 62 respectively, a crest surface portion 43, 63 respectively and a root surface portion 44, 64 respectively. The leading flank surface portion 42, 62 of each thread is that facing the free end of the respective member and the trailing flank surface portion 41, 61 is that facing the inner end of the respective member. The crest surface portions of the threads 43, 63 lie on frusto-conical envelopes having the same cone angle as the cone angle of the respective surface portion 3, 5, and the cone angles of the surface portions 3, 5 are preferably the same. The root surface portions 44, 64 are also generally frusto-conical and lie generally on envelopes having the same cone angle as the respective surface 3, 5. At each end of each of the threaded surface portions 3, 5, generally cylindrical guide surface portions 7, 8, 9 ,10 are provided, surface portions 7, 8 being provided on the box member and surface portions 9, 10 being provided on the pin member. As shown, surface portions 8 and 10 are stepped intermediate their ends and each comprises two por¬ tions 8a, 8b and 10a, 10b of different diameters. These surface portions 7, 9 and 8, 10 serve to guide the members 1, 2, to correct any axial misalignment, as the members are initially telescoped together. Although, as shown, surface portions 7, 8, 9, 10 are cylindrical they may all, or corresponding pairs of them may, be frusto-conical. Each of the members 1, 2 is also provided with an annular abutment surface 11, 12, which surfaces are brought into abutment when the connector is fully made up. As shown, the annular abutment surface 11 on the box member is provided at the inner end of the inner guide surface portion 7 and abuts annular surface portion 12 provided on the free end of the pin member. Alternatively these abutment sur¬ faces 11, 12 may be provided at or in the region of the free end of the box member and the inner end of the pin member respectively. As shown, surfaces 11, 12 extend in radial planes for full load bearing in the axial direction of the connector and are designed to withstand piling forces. Where the connector will not be subject to piling forces, these surfaces may be reduced in area. Additionally, they may be correspondingly frusto-conical. The members are intended to be initially telescoped together without relative rotation until surfaces, as will be described hereafter, of the threads come into abutment (Figure 5). One member is then rotated relative to the other to bring the abutment surfaces 11, 12 into abutment and the trailing flank surface portions 41, 61 of the threads into contact and abutment (Figure 6) and, if required, into stressed abutment to pre-stress the connector. As shown in Figure 6, when the connector is fully made up, clearances are provided between the crest surface portions 43, 63 and the root surface portions 44, 64 and between the leading flank surface portions 42, 62. As shown, the trailing flank surface portions 41, 61 extend in radial planes but they may be slightly inclined positively or negatively to the respective radial plane. The leading flank surface portions 42, 62 are generally inclined to the radial plane for example at an angle of about 25° but this angle may be reduced if, in use, the surfaces are intended to be brought into abutment when the connector is under compression. The parts of the leading flank surface portions 42, 62 which overlap when the connector is fully made up, and which are in contact as the members are rotated relatively into full engagement, are preferably linear in cross-section and have the same angles of inclination, so that during this relative rotation of the members these surfaces will be in full contact over their overlapping extents, and so that, if these surfaces are brought into contact and abutment when the connector is under compression, they will be in full load bearing surface abutment. The connector is designed to be capable of being fully made up by rotating the members through less than 360° and for this reason the threads are relatively coarse with a relatively large cone angle. This has the additional advan¬ tage that the risk of cross-threading as the members are telescoped together is significantly reduced. The relationship between the pitch (p), the cone angle (9O of the crest surfaces of the threads, the thread overlap (t) on full engagement and the minimum angle (θ) of relative rotation of the members for full engagement is: θ = t . 360° p.tanώ Thus for θ . 360° , t 1.0. p.tani For economic material requirements for this embodiment: ≤. 15° and p ^ 1.0 which means that t . 0.250". In a particular embodiment of a connector for connecting 30" diameter pipe sections, the threads have a pitch (p) of 0.625", the cone angle (o) of the frusto- conical surface portions 3 and 5 is about 9.0 and the thread overlap (t) when the connector is fully made up is 0.08". With these dimensions, if the members are approp¬ riately orientated, which orientation can be predetermined as they are telescoped together, it should be possible to achieve full engagement with a relative angular rotation of about 0.81 of a turn. To facilitate make up of the connector, each of the threads 4, 6 is cut away at the junction between the leading flank surface portion 42, 62 and the crest surface portion 43, 63 to provide a contact surface portion 45, 65, the con¬ tact surface portions being brought positively into contact when the members are initially telescoped together with an appropriate predetermined relative angular orientation. The axial and radial extents of the contact surface portions are such that, with the appropriate predetermined orientation of the members, contact will be maintained regardless of any axial misalignment between the pin and box members. As shown, the contact surface portions 45, 65 are generally curved or convex so that this initial contact is line contact between the contacting surface portions 45, 65 and to ensure that the surface portions will ride on each other in the event that there is any initial axial misalign¬ ment between the members. Advantageously the surface por¬ tions 45, 65 are circular in cross-section with the centres of the circles lying on a line which passes through the point of contact between the surface portions 45, 65 when the surfaces are in contact with the predetermined angular orientation and axial alignment of the members. The line connecting the centres of the circles may extend at an angle of about 60 to the axis of the connector. The radius of these surface portions is relatively large. In a modifica¬ tion one of the surface portions 45, 65 may be linear and inclined to the axis, the other being convex so that line contact is maintained. The contact surface portions 45, 65 do not merge with the adjacent crest surface portions 43, 63 to provide a continuous surface but instead these surface portions inter¬ sect at an obtuse angle. Similarly, as shown, surface por¬ tions 45, 65 do not merge with the adjacent flank surface portions 42, 62 but intersect these surfaces at an obtuse angle. In a modification, the junction between surface por¬ tions 45, 42 and 65, 62 may be radiused so that these sur¬ faces do merge continuously. Having brought the two members, in the predetermined orientation, into initial contact at their surface portions 45, 65 by relative axial movement, the members are then relatively rotated to progressively engage the threads and bring the annular surfaces 11, 12 into abutment. This can be achieved with a relative rotation of less than one turn (360°) and the amount of relative rotation required is reduced by the provision of the contact surface portions, which permit the members to be telescoped together to a greater extent than they would be in the absence of these surfaces. As will be appreciated from the foregoing, if, when the members are axially telescoped together, they are axially misaligned, the misalignment will be corrected as the contact surface portions 45, 65 of the members are brought into full contact. This then minimises the risks of jamming of the members as they are subsequently relatively rotated to bring them into full engagement. To reduce interference between the edges of the threads between the trailing flank surface portions 41, 61 and the crest surface portions 63, 43 as the members are telescoped together and taken apart, the edges between these surfaces are also cut away providing inclined clearance sur¬ face portions 46, 66. One or, as shown, both of these sur¬ face portions 46, 66 are convex and are preferably circular in cross-section like surface portions 45, 65 and with about the same radius of curvature. If only one of the surface portions 46, 66 is convex, the other is linear in cross- section and inclined to the axis of the respective member. As with the contact surface portions, the clearance surface portions 46, 66 do not merge with the adjacent crest surface portions 43, 63 but intersect these surface portions at an obtuse angle. The surface portions 46, 66 may merge, or intersect at an obtuse angle, with the flank surface por¬ tions 41, 61. To reduce the stresses in the threads, the junctions of the root surface portions 44, 64 with the flank surface portions are radiused. The need for stress reduction is mainly in the region of the junction with the trailing flank surface portions. Here, each of the trailing flank surface portions 41, 61 merges into a surface portion which is generally parabolic. As shown, each surface portion comp¬ rises a first radiused surface portion 47, 67 having a small radius of curvature which merges with a second radiused por¬ tion 48, 68 having a substantially larger radius of curva¬ ture which forms part of the root surface 44, 64. This particular configuration of the root and flank surface portions combined with the contact and clearance surfaces facilitates production of the threads. Normally the threaded surface of each member is first turned and then the thread is cut with a single finishing tool which cuts the crest, root and flank surface portions simultaneously and which, if it is damaged or becomes worn, has to be replaced as a whole. With the threads as described above, the crest surface portions may be formed by the initial turning of the respective surface so that only the root, flank, contact and clearance surface portions have to be cut subsequently. The provision of the contact and clearance surface portions provides the additional advantage that they can be cut without simultaneously cutting the crest surface portions because there is no risk of leaving a step in the respective crest surface portion. These surface portions may be cut by two separate finishing tools, one of which cuts the contact and leading flank surface portions and part of the root surface portion and the other of which cuts the clearance and trailing flank surface portions and the adjacent part of the root surface portion. To provide a sealed connector, an O-ring seal may be provided in one of the guide surface portions of one of the members for sealing against the corresponding guide surface portion of the other member. As shown, an O-ring seal is provided in an annular groove 14 in guide surface portion 10a of the pin member for sealing against guide surface por¬ tion 8a of the box member. Alternatively, the annular groove and seal may be provided in surface portion 7 for sealing against surface portion 9. The connector may be provided with means for preven¬ ting reverse relative rotation of the pin and box members 1, 2 when the connector has been fully made up. As shown, the free end of the box member provides an axially extending flange 15 which, when the members are fully engaged together, overlies a portion of the pin member which is pro¬ vided with at least one recess 16. In this embodiment, a plurality of recesses, e.g. six, are provided equally angu¬ larly spaced around the circumference of the pin member. When the connector has been fully made up, an axially exten¬ ding cut 17 (Figures 7 and 8) is made in flange 15 in align¬ ment with what is in effect the downstream end edge 16a of each recess in terms of the direction of rotation of the pin for making up the connector (shown by a solid arrow in Figure 7). A generally triangular flap 18 formed from the flange 15 is then bent into the recess 16 with the cut edge arranged to abut the downstream end edge 16a of the recess to prevent reverse rotation. The above described means may alternatively or additionally be used to prevent further forward relative rotation of the pin and box members in a direction to over¬ tighten the connector, e.g. on piling. For this purpose, the cut 17 is made in alignment with the upstream end edge of the or each recess (or some of the recesses) and the corresponding triangular flap bent into the recess. Both prevention means may be provided on one connector, some of the recesses 16 being used for reverse rotation prevention and some for further forward rotation prevention. For supporting the box member while a pin member is being connected to it, the box member is, as is conven¬ tional, provided with a lifting shoulder 19 in the region of the end where it is or is to be connected to a pipe section and, adjacent the shoulder, the external surface of the box member is cut away to provide a generally frusto-conical surface 20 to improve stress distribution. For supporting the pin member while a box member is being connected to it, the pin member is also similarly provided with a lifting shoulder 21. In view of the fact that, to achieve make-up of the connector with a rotation of less than 360 , the pin and box members must be assembled with a predetermined relative angular orientation, marks may be provided on the exterior surfaces of the pin and box members to show the required orientation. Additionally, to assist visual determination of full assembly of the members 1, 2, guide surface 10b may be provided with a visibly distinct finish, e.g. it may be coated with a fluorescent paint. As the members are pro¬ gressively engaged together, surface 10b is progressively covered by the free end of the box member so that the coated surface 10b will progressively disappear. The coating is arranged so that, when the members are fully engaged, it will no longer be visible. The members may, as is conventional, be made of metal for use in the oil industry.

Claims: CLAIMS : 1. A connector comprising a tubular pin member (2) connected, or for connection, to one end of a pipe section, a tubular box member (1) for receiving the tubular pin member (2) and connected, or for connection, to one end of another pipe section, the box member (1) comprising a gener¬ ally frusto-conical internal surface portion (3) formed with a thread (4) and the pin member (2) comprises a generally frusto-conical external surface portion (5) provided with a thread (6) for engagement with the said thread (4) on the box member, each thread having a leading flank surface por¬ tion (42, 62) which faces the free end of the member, a trailing flank surface portion (41, 61) facing in the opposite direction and a crest surface portion (43, 63), characterised in that a contact surface portion (45, 65) is provided between the leading flank surface portion (42, 62) and the crest surface portion (43, 63) of each thread, the contact surface portions (45, 65) of the threads on the two members being arranged so that they come into contact when the members are telescoped together with a predetermined angular orientation. 2. A connector as claimed in Claim 1, wherein the axial and radial extents of the contact surface portions are such that contact will be maintained regardless of any axial misalignment between the pin and box members. 3. A connector as claimed in either Claim 1 or Claim 2, wherein the contact surface portion (45, 65) of at least one of the said threads has a convex profile so that the contact surface portions of the said threads of the two members make line contact. 4. A connector as claimed in Claim 3, wherein the con¬ tact surface portions (45, 65) of both the said threads have convex profiles. 5. A connector as claimed in either Claim 3 or Claim 4, wherein the or each said contact surface portion (45, 65) is part circular in cross-section with the centre of the circle lying on a straight line which passes through the point of contact between the contact surface portions when the members are axially aligned and in contact with the pre¬ determined angular orientation. 6. A connector as claimed in any of the preceding claims, wherein the cone angles of the frusto-conical sur¬ face portions and the pitch of the threads are selected so that the members (1, 2) are fully engageable together with a relative rotation of the members of less than 360°' 7. A connector as claimed in any of the preceding claims, wherein the leading flank surface portions (42, 62) of the threads are, in cross-section, generally inclined to the axis of the respective member, the parts of the leading flank surface portions (42, 62) which overlap when the connector is fully made up are linear in cross-section, with the same angle of inclination to the respective axis, so that these surfaces can come in full surface contact as the members are engaged together. 8. A connector as claimed in any of the preceding claims, comprising annular surfaces (11, 12) provided on the members (1, 2) which are brought into abutment, to bring the trailing flank surface portions (41, 61) of the said threads into abutment, when the connector is fully made up. 9. A connector as claimed in Claim 8, wherein the annular surfaces (11, 12) are provided in the region of, or on the free end of, the pin member and in the region of the root of the box member. 10. A connector as claimed in Claim 8, wherein the annular surfaces (11, 12) are provided in the region of the root of the pin member and in the region of, or on the free end of, the box member. 11. A connector as claimed in any of the preceding claims, wherein each thread is cut away at the junction between the crest surface portion (43, 63) and the trailing flank surface portion (41, 61). 12. A connector as claimed in any of the preceding claims, wherein, to reduce stress in the threads, each root surface portion (44, 64) is formed by an intermediate frusto-conical surface portion connected to the trailing flank surface portion by a generally parabolic surface por¬ tion. 13. A connector as claimed in any of Claims 1 to 11, wherein, to reduce stress in the threads, each root surface portion (44, 64) is formed by an intermediate frusto-conical surface portion connected to the trailing flank surface por¬ tion by a surface comprising a first curved portion (48, 68) having a relatively large radius of curvature and a second curved portion (47, 67) having a smaller radius of curva¬ ture. 14. A connector as claimed in any of the preceding claims, wherein the crest surface portion (43, 63) of each thread lies on a frusto-conical envelope, the cone angles of the envelopes of the threads on the two members being sub¬ stantially the same. 15. A connector as claimed in any of Claims 1 to 14, wherein the crest surface portion of each thread extends parallel to the axis of the respective member, the leading and trailing ends of the surface portions lying on frusto- conical envelopes, the cone angles of the envelopes being substantially the same. 16. A connector as claimed in any of the preceding claims, wherein each member is provided with a single thread. 17. A connector as claimed in any of Claims 1 to 15, wherein each member is provided with a plurality of threads.

Inventors: LUMSDEN NORMAN, PERRIE ARCHIBALD, LUMSDEN, NORMAN, PERRIE, ARCHIBALD
Applicants: HUNTING OILFIELD EQUIPMENT HOL, HUNTING OILFIELD EQUIPMENT HOLDINGS LIMITED
Application year: 1992
Main classification: E21B17
IPC codes: E21B17, F16L15