CA1245689A

CA1245689A - Pipe connector

Info

Publication number: CA1245689A
Application number: CA000464027A
Authority: CA
Inventors: Mark T. Thatcher; James L. Bell, Jr.; Norman Brammer; Thomas F. Sweeney; Brian K. Phillips
Original assignee: Vetco Offshore Industries Inc
Current assignee: Vetco Inc
Priority date: 1983-10-19
Filing date: 1984-09-26
Publication date: 1988-11-29
Also published as: GB2148439A; FR2560345B1; IT8423208A0; US4601491A; GB8426094D0; AU3447384A; FR2560345A1; NO162981B; AU574728B2; IT8423208A1; NO844134L; IT1196303B; BR8405281A; GB2148439B; NO162981C

Abstract

PIPE CONNECTOR
ABSTRACT OF THE DISCLOSURE

A pipe connector with helically threaded (49, 57) frustoconical pin (10) and box (30) surfaces. The connector is axially (78) snapped together, but is rotated for disengagement. Centralizing surfaces (150, 152) on each thread form abut opposing crests (62, 54) to maintain concentrically, thereby detering disengagement under bending moments.

Description

PIPE CONNECTOR
BAC~GROU~ID OF THE INVENTTON
The invelltion relates to pipe conrlectors and in particular to releasable connectors for which rotatiorl during assembly is difficult such as piles risers and conductors used for offshore oil production.
In drivir7g of pilings for offshore platforms pipe i71 the order of 30 irlches irl diameter is used in jo1nts about 50 feet long. As the string is driven additional joirlts are added at the top. The conrlectiorl hetween JOintS should effectively transmit the pile driving forces and adequately handle the bendirlg moments and rebound forces.
Risers arld corlductors usually irl the 20 inch to 3 irlch diameter range and in jOirlts about 50 feet lorlg are sometimes pile driverl. They must reliably support tensiorl placed orl them wherl terlsiorlirlg or rurlrling the string duri~lg drilling arld producirlg operatiorls. They must also tolerate high bendlrlg forces caused for instarlce by ocean currents.
Each of the above situatiorls has irl commorl the difficulty irl makirlg up the jOirltS. Wave motiorl arld wind cr-eate COrltirluOus movemerlt especially when work is carried out from a work hoat. Equipmerlt to facilitate the operatiorl may rlot be available at this time. Welding ls time co~lsuming and presents a fire hazard. Rotated threaded connectors ar-e difficult to accurately aligrl and it is often difficult to obtain the high torque required to make up these corlrlectors~

b~l f ~

~L~ 9 With the large diameter and heavy ~joints, slight misalignment can cause cross-thr-eading or jamming of the threads.
Stab type joints with latching dogs are relatively expensive. Other snap connectors cannot be readily disassembled.
SUMMARY OF THE I~VENTION
A releasable pipe connector which is circumferentially oriented and axially snapped together. The connector may be rotated for disassembly and may be easily manufactured.
The connector comprises a cylindrical pin and box each having frustoconical surfaces which ar-e telescopically engageable. Helical thread forms on each of the pin and bo~
have crests of discreet axial length, rounded roots, and an abutting flank facing away from the open end. The pin and box each have a secondary radially extend;ng surface facing toward the open end. In a preferred embodiment this is the shoulder-of one member, and an abutting surface on the other. There are means for- circumfer-entially aligning the pin and box for dir-ect stabbing so that when the pin and box are fully engaged, both the abutting flanks of the pin and box as well as the secondary extending surfaces are in axially compressive abutment.
The lengths of crests are related to the o~erlap and the frustoconical taper, 50 that when stabhing occurs in the properly aligned position, initial contact is made between the crests. When the joint is further compressed together, the box expands and the pin compresses while the crests ride over one another, snapping into Dlace beyond the crest contact point.
A double start thread form is arranged so that the crest surfaces between the two starts are of different axial lengths, thereby providing the abllity to slide on the crest surfaces over hoth threads while engaglng only in one. A
preferred means for aligning a connector involves a slot in the box member with an alignment key secured to the pin member. This is arranged to permit relative axial motion but to prevent rotation. The key may be removed to permit disassembly of the joint.
There may be also included a centralizing surface in each thread form. This is located between crests and intermediate the radial dimension of the cr-est surface and the root. These surfaces are in contact after the joint has been snapped together and are preferably in force fit contact.
The connector may be easily manufactured since helical threads are easy to machine with precision. With proper alignment, the crest surfaces first make contact, with the box expanding and the pin contracting, as the members are forced together. The connector may be designed to operate below the elastic limit of the materials, or it may be designed to operate beyond the elastic limit where a more consistent reliable tooth engagement is achieved, at the expense of higher stabbing forces.
Where an axially preloaded joint is desired, a slight angle is included between the thread flank and the other abutting surface so that the radial movement of the connectors toward their original size operates against the flank to axially preload the connector.
The centralizing surface is provided to avoid the possibility that the teeth on one side overengage when bending is applied to the connector. Overengagement on one side tends to result in insufficient engagement on the opposite side and possible zippering action or inadvertent release of the connector.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a general arrangement of the connector showing the pin and box and the frustoconical surface;
Figure 2 is a sectional elevation of one thread form, while Figures 2a, 2b, 2c and 2d are details of the interengagirlg helical thread form during engagement and at the engaged position;

Fi~ure 3 is a stress/strain diagram which illustrates the elastic strain range;
Figures 4a & 4b illustrate measurements to be made for providing proper alignment of the pin and box;
Figures 5a 5b and 5c illustrate the gauge which may be employed for this purpose;
Figure 6 & 6a illustrate an alignmerlt key;
Figure 7 illustrates d thread form where the taper of the crests are steeper than that of the frustoconical surface;
Figure ~ illustrates a thread form having a cerltralizing surface; and Figure 9 is a netail of the thread form of Figure 8.
DESCRIPTION OF THE PREFERRED EMBnDIMENT
Referring to Figure 1 the cylindrical pin 10 has a first end 12 securable hy welding to a pipe (not shown) and an open end 14. A loading shoulder- 16 is provided to engage the pin for axially clamping. The pin includes a frustoconical outer surface 18 with a stress relief groove 20 located at one end. The pin also includes shoulder 24 in the form of radially extending surface facing toward the open end 14.
A cylindrical box 30 has a first erld 32 securable to a pipe (not shownl and a second open end 34. The box also includes a loading shoulder 36 for axially clamping the box and a frustoconlcal inner- surface 38. It includes a stress relief groove 42 and a seal ring groove 44. An O ring seal 45 is located in this groove. The box also has an end surface 46 in the for~ of a radially extending sur-face facing the open end 34. Clamps (r)ot shown) are used to supply the required axial stabbing force and then removed.
Referring now to Figure 2 the helical thread form is shown in detail. The thread is shown in its engaged position in Figu7es 2 and 2d. Pin 10 has mul~iple star~ threads which in this case are 1~0 degrees apart. A first thread with a narrow groove 50 and a sesond with a wide groove 52 result in alternate crest surfaces 54 and 5fi having different axial extents, crest 54 being wide, and crest 56 belng narrow.
Similarly, the box 30 has a dual start thread for~ 57 with narrow groove 58 and wide groove 60 producing a wide crest 62 and a narrow crest 63. Pin thread form ~9 includes flanks 64 facing away from the open end of the pin. The edges 66 of the flank and the crest should be as sharp as possible since roundirlg these edges decreases the amount of load bear;ng surface of flank 64. The grooves 50 and 52 are rounded at the root as shown at 6~ to enhance the fatigue life of the connector by reducing stress concentrations at small root radii.
Similar~y, the box 30 has f7anks 70 facing away from the open end of the box. The roots or grooves 60 and 58 also are rounded 72. The box 30 may also include a threaded opening 73 with plug 74. This permits injection of a fluid under pressure injection for the purpose of reducing the torque required to break the connector loose.
The term overlap is used to describe the dimensional difference between corresponding radii of crests such as 55 and 63 with the pin and box in the "as fabricated" condition.
This is prior to assembly with both componerlts in the unstressed condition. After assembly, the corresDonding distance 76 is the tooth engagement, representing the distance of engagement of flanks 64 and 70. This tooth en~agement will be less than the overlap when shrink fit is obtained, with strain locked in the pin and box.
If the pin and/or box exceed the elastic limit during assembly they would be permanently changed in size. The ter~
residual overlap is used to describe the dimensional difference between corresponding radii of crests such as 56 and 63 if the components were allowed to go to the unstressed condition after assembly. If the elastic limit were not exceeded during installation then the overlap and residual overlap would be identical. If, however, the elastic limit is exceededS then the residual overlap would be less than the initial overlap.

~lS6~9 The angle of the flanks 64 and 70 with respect to shoulder 24 and to box end 45 are each 12 and preferably within the range of 0 to 20~. As the pin ann box attempt to restore themselves to the unstressed condition the abutting flanks 64 and 70 cooperate along with complimentary pin and box surfaces 24 and 45 to provide an axial load on the pln and box, compressing the box end against pin shoulder 24. For pile driving, it is important: that the connector be snug and for bend;ng some preload is to be preferred. Accomplishment of preload is a function of the difference between the tooth engagement alld residual overlap, this representing the residual strain and concomitant stress existing in the box and pin. The amount of the preload is a function of the included angle.
Figure 2a illustrates the position of the pin 10 and box 30 during the stabbing opleration as initial contac~ is made. The axial distance which the pin must travel into the box after contact and before shouldering is referred to as the standoff. It is determined by the amount of overlap and the 2n taper angle. In order to avoid the possibility of a crest engaging a groove before shouldering occurs, the lead of the thread must be greater than the standoff. The crest width is then selected so that when stabbing occurs initial contact is made as illustrated between hide crest 54 and the narrow crest 63.
As stabbing continues ~n the direction shown by arrows 78, the wide crest 54 rides over narrow groove 58 so as to engage the following wide crest 62. This precludes premature engagement in the wrong thread of the thread form.
This condition is illustrated in Figure 2b.
Stabbing continues with clamping force applied on the shoulders 16, 36 approaching the maximum strain condition illustrated in Figure 2c just before the connector snaps together. Immediately after this, the connector snaps into the engaged position illustrated in Figure 2d.

Figur-e 3 illustrates a typical stress/strain curve for steel~ When operatirlg along the stress/strain curve 80 below the elastic limit 82 the material will return when unstressed to its original condition 84. The dif~erence in strain between points 82 and 84 may be considered the elastic strain range as indicated by 86.
If the elastic limit is exceeded, for instance, to point 88, the material will not return to its original condition, but will return to point 90 with a permanent residual strain in the material. The material now acts elastically throughout elastic strain range 92, representillg the difference between points 88 and 90.
If the connector in its maximum strain condition, illustrated ;n Figure 2c, has not exceeded the elastic limit 82, the residual overlap will be the same as the origirlal overlap. Tooth engagement w~ll approach this overlap as a maximum, when the residual radial strain orl the pin and box reach zero. If the elastic limit is not reached, then the tooth engagement is reduced. If orl the other hand, the maximum strain exceeds the elastic limit such as to ~oint 8~, then the full elastic range 92 will be available for contracting the connector box arld expanding the pin. The effect of dimensional tolerances on preload and tooth engagemerlt may be minimized by designing the connector so that the elastic limit i 5 exceeded even when the overlap is at t.he minimum value permitted by dimensional tolerances.
Accordingly, one may design the connector to operate in this conditiorl exceeding the elastic limit.
Since the thread forms are helical there is only one circumferential relationship where the above described characteristics will be obtained. It accordirlgly is required to locate the proper circumferential alignment for aligrling the connectors. The means for alignment may be as simple as marking on the outside of the pin and box, or may be the alignment key illustrated in Figure 6.

~ ~5i~'~3 Since the operative portions of the connector are the flanks facirlg away from the open end of each of the pln and box, as well as the pin shoulder 24 and the box face 45, the preferred method of obtaining the orientation depends on measurements of these features. A selected dimension 96 is to be used for both the pin 10 and the box 30. The location around the circumference is determined where this dimension is a preselected value 9h on pin between shoulder 24 and measuring point 98. This measuring point is selected on the flank 64 facing away from the open end of the pin. The inward dimension 100 from the surface of crest 54 is selected as one-half Df the desired tooth engagem~nt. With this point located, a similar point is located on box 30 with the dimension beins established between the pin end 45 and the corresponding engaging flank 64. The pin and box components are then either marked or machined in accordance with the measuremerlts so that the located points ar-e circumferentially aligned when the connector is to be stabbed together.
A typical gauge for this purpose is illustrated in Figure 5a, 5b and 5c.
Gauge set 101 consists of a box gauge 102 and a pin gauge 103 which are constructed from 1/8 inch thick tooling plate. The box and ~in gauges have tapered mating surfaces 104 and 105 respectively, the taper matching the frustoconical taper 18, 38 of the connector. Tooth 106 on the box gauge and tooth 107 on the pin gauge are engageable at the predetermined distance 96 from shoulder surface 108 and face surface 109 of the gauges.
The use of the gauges is shown in Figures 5b and 5c.
Referring to Figure 5b, the shoulder 108 of the gauge 102 is held against the box face 45 with the mating surface 104 against the surface of crests 62 and 63. Holding the gauge parallel to the box axis it is moved circumferentially until flank 11~ of tooth 106 contacts flank 70 of the box. The gauge location is then marked on the outside of the box.

~L~ 3~3 9 _g Similarly in Figure 5c, the face 109 of gauge 103 is held against the pirl shoulder- 24 with the mat;ng surface 105 against the surface of crests 54 and 56. It is moved circumferentially until flank 111 of tooth 107 contacts flank 64 of the pin. This location is marked on the pin.
Calibration of the gauges may be checked by resting the gauges together as shown in Figure 5a. They are correct if the gap 112 between mating surfaces 104 and 105 is equal to the desired engagement 76. This is the distance which the crest surfaces extend beyond each other when the predetermined distance 96 is held. It does not really matter what dimensio 96 is, so long dS it is the same for both gauges.
A preferred alignment means is shown in Figur-e 6 with detail of the alignment key being shown in Figure 6a. After the alignment is determined as described above, a slot 120 is machined in the box and an alignment key 122 is fastened to the pin with screws 124. This not only permits alignrnent of the pin and box for stabbing, but also operates as a guide to maintain this aligllment during the clamping operation. The alignment key 122 also serves as an anti-rotation device to preclude arly possibility of the connector rotatinq loose during operation. At the time it is desired to disassemble this joint, the alignment key is removed and the ~oint may be unscr ewed.
The maximum tooth engagement is limited by the strain range of the material. With a 100,000 psi yield strength material, and a 30 inch diameter, it can be determined hy using Young's modulus of 30 x 106 psl that the maximum elastic deflection is 0.1 inches on the diameter, which is 0.05 inches on each thread. This represents the maximum engageme1~t that can reasonably be designed for. For the connector described here, it is recommended that a radial overlap of 0.04 inches and an engagement of 0.03 ~nches per thread be the design criteria, thereby providing some preload but still maintaining substantial thread engagement.

;6~3 The corlnector, as described, can axially be stabbed together without rotation, using reasonable forces such as 30Q,000 pounds for a 30 inch outside diameter connector having a frustoconical taper of 4 degrees and the same taper on the crests. The connector may furthermore be disassembled by removing any locking key and rotating the members.
Seal ring 45 is intended as the primary seal for sealing the connector. Wherl the connector is to be disassembled, it may be found to be too tight for rotation with available equipment. Hydraulic fluid may be in~iected under pressure through hole 73 to expand the box and corltract the pin, as well as to supply lubrication. Since the pressure energization is only required to 1nitially break the connector loose, leakage is not fatal to its perFor~ance.
Should the end abutting surface of either the pin or box be damaged and require dressing, the connector need not be destroyed but can be used by again measuring the threads to find a new circumferential orientation after such dressing operations. Furthermore, the connector has the possibility of being tightened by rotation ~should the initial installatior result in a loose connector For any reason.
In the thread for~ illustrated in Figure 7, the crests 130 and 132 have a stleeper angle than that of the frustoconical surface 134. The edges 136 of the flanks 138 which are the load bearing flanks remain on the frustoconical surface. The leadillg edge 140 of each crest is, however, drawn back from the frustoconical surface to such an extent that it has a radial dimenslon substarltially equal to that of the corner 13fi of the adjoining crest. Accordingly, any crest cleared by the corner 136 will be engaged by the following crest 130, thereby, minimizing the possibility of engagirlg the flanks rather than the crests in the event of slight misaligrlment. Such a connector, however, will require more force to clamp it together, the force being approximately proportional to the tan~ent of the taper angle of the crest surfaces.

~2~5~

The co~rlectors as described in this irlverltiorl inhererltly have small tooth erlgagemerlt. It has beerl fourld that urlder high beridirlg loads the ~eeth can disen~age on the tensiorl side of the corlrlector. This appears to occur because shiftirlg of the pirl away from the tensiorl side permits diserlgagement of these teeth. As can be seen by lookirlg at the earlier described conriector wide crests such as 54 fit within wide grooves or roots 6q. Since the abutting flanks 64 are highly loaded it is required that these root surfaces be rounded and accordingly they are inhererltly deeper than the erlgagirlg crests.
Acc~rding~y an improved ~hread form is described and il?ustrated in Figures 8 and 9. This improved thread form essentially uses a portiorl of the deepened groove so that mater;al is retained in a portion thereof which abuts with the erlgaging crest. In Figure 9 the rlarrow crests 56 and the wide crest 54 carl be seen as well as the wide crests 62 and the rlarrow crests 63 orl the box. The pin 10 has withirl thread form 49 arl additiorlal axially extendirlq radially facing cerltralizirlg surface 150. Similarly the box has such an axially exterldi~lg radially facing surface 152. In each case this surface is located between a wide and narrow crest at a radial dimensiorl which is between that of the crest surface arld that of the root surface.
On final snappirlg of the conrlector irl place after stabbing initial engagirlg action occurs between the opposing flarlks 64 a~ld 70. The radial contraction occurs however orlly u~ltil centralizirlg surfaces 152 ellgage the crest 54 a~ld centralizirlg surfaces 150 erlgage crest 62. The aGtual tooth erlgagemerlt is accor-dirlgly the differerlce irl radial dime~lsio~l betweerl the outer edge of the crest immediately adjacerlt to the loaded flank arld the diameter- of the cerltralizirlg surface. These relative dimerlsiorls are easy to hold accurately. The centralizirlg surface operates to preclude the co~lnector from driftirlg off cerlter under load whereby the teeth orl the opposite side could be diserlgaged.

~L~ 9 Furthermore, it is desir-able that the cor~rlector be designed such that orl stabbing an irlterfere1lce fit is achieved between the cerltralizing surface and the crest. This minimized the teriderlcy of the box arld pin to become oval urlder bendirlg load. In the conrlector pr-eviously described, the potential tooth engagemerlt was limited to 0.05 inches. Of this, it is recommended that a shrink fit be obtairled such that 20% of this, i.e., 0.01 ir~ches, is used for- the shrirlk fit of the centralizirlg surface.
The corlnector of Figure 8 has, in additiorl to seal groove 44 arld seal ring 45, a seal groov~ 166 ar~d seal r-ing 168 in pin 10. Threaded opening 73 with plug 74 is ~ocated llear the stress relief groove 20. This avoids the possibility of the openirlg being blocked by a centralizirlg surface. Seal ring 168 improves sealing when the conrlector is pressure energized to start the r-elease of the conrlector, and also operates as a backup seal.
Aligrlmerlt of the conrlectors is based orl axial measuremerlt from the abutting shoulders to the thread form.
Therefor-e, the r-adial strain of the connector, even though it may r-esult irl a permanellt set, is rlot detrimental to the amourlt of engagemerlt obtairled. Sirlce the circumfere~tial orierltatiorl locates the thread forms at the pr-oper axial distarlce from the shoulder the radial movement of the crest surfaces as the conrlector srlaps into erlgagemerlt is what produces the irlterlded result.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A snap connector for pipes comprising:
a cylindrical pin having a frustoconical outer surface, one end thereof securable to a pipe, and the other end open;
a cylindrical box having a frustoconical inner surface, one end securable to a pipe, the other end open, and telescopi-cally engageable with said pin;
a first helical thread form on the outer surface of said pin;
a second helical thread form on the inner surface of said box;
each of said thread forms having a crest of discreet axial length, a rounded root, and an abutting flank facing away from the open end, the surface of each of said crests being said frustoconical surface of said pin and said box respectively;
each of said pin and box having a secondary radially extending surface facing toward the open end;
means for cicumferentially aligning said pin and box for correct axial stabbing, such that the distance from said sec-ondary radially extending surface of said pin to a point on an abutting flank of said pin equals the distance from said second-ary radially extending surface of said box to a point on an abut-ting flank of said box at the same axial and circumferential location, whereby when fully engaged both the abutting flanks of the pin and box and the secondary radially extending surfaces are in axially compressive abutment; and the width of said crests so related to the frustoconical taper that when stabbing in the circumferentially aligned posi-tion, initial contact is made radially between said crests of said first helical thread form and said crests of said second helical thread form, whereby the connector is forced into snap engagement without rotation.

2. A connector as in claim 1, wherein the included angle between said secondary abutting surface and said abutting flanks is not more than 12°.

3. A connector as in claim 1, wherein said alignment means comprises:
a slot in one of said pin and box; and a removable pin secured to the other of said pin and box member and arranged to slide axially into said slot.

4. A connector as in claim 1:
said heleical thread forms comprising multiple start threads;
the intermediate crests and corresponding grooves be-tween said multiple start threads being of different axial length, whereby the thread forms are engageable only in one relationship with the multiple threads.

5. A connector as in claim 1:
said helical crest surfaces having the same taper as the frustoconical surfaces.

6. A connector as in claim 1:
an axially extending centralizer surface radially lo-cated between the crest and root of at least one of each of said thread forms; and said pin and box sized and aligned such that the cen-tralizing surfaces contact the crest of the thread form of the opposing box or pin members in the overlap condition whereby said pin is precluded from drifting off center with respect to said box.

7. A connector as in claim 6:
having said axially extending centralizing surface on each of said thread forms.

8. A connector as in claim 6, wherein said centralizing surfaces contact opposing crests with a shrink fit of greater than 10% of the elastic strain range of the pin and box material.

9. A connector as in claim 1:
said pin and box aligned such that when fully engaged the surfaces are in shrink fit abutment.

10. A connector as in claim 1 said box having a radial opening therethrough, whereby fluid may be injected under pressure between the pin and box to aid in disassembly.

11. A snap connector for pipes comprising:
a cylindrical pin having a frustoconical outer surface, one end thereof securable to a pipe, and the other end open;
a cylindrical box having a frustoconical inner surface, one end securable to a pipe, the other end open, and telescopi-cally engageable with said pin;
a first substantially circumferential thread form on the outer surface of said pin;
a second substantially circumferential thread form on the inner surface of said box;
each of said thread forms having a crest of discreet axial length, a rounded root, and an abutting flank facing away from the open end;
each of said pin and box having a secondary radially extending surfacing toward the open end;
said pin and box alignable and dimensionally sized such that the distance from said secondary radially extending surface of said pin to a point on an abutting flank of said pin equals the distance from said secondary radially extending sur-face of said box to a point on an abutting flank of said box at the same axial and circumferential location, whereby, when fully engaged in the overlap condition both the abutting flanks of the pin and box and the secondary radially extending surfaces are in axially compressive abutment;
the length of said crests so related to the frustocon-ical taper that when stabbing initial contact is made between said crests;
an axially extending centralizer surface radially lo-cated between the crest and root of at least one of each of said thread forms; and said pin and box sized such that the centralizing sur-faces contact the crest of the thread form of the opposing box or pin members in the overlap condition.

12. A connector as in claim 11:
having said axially extending centralizer surface on each of said thread forms.

13. A connector as in claim 12 wherein said centralizing surfaces contact opposing crests with a shrink fit of greater than 10% of the elastic strain range of the pin and box material.

14. A snap connector for pipes comprising:
a cylindrical pin having a frustoconical outer surface, one end thereof securable to a pipe, and the other end open;
a cylindrical box having a frustoconical inner surface, one end securable to a pipe, the other end open, and telescopi-cally engageable with said pin;
a first helical thread form on the outer surface of said box;
a second helical thread form on the inner surface of said box;
each of said thread forms having a crest of discreet axial length, a rounded root, and an abutting flank facing away from the open end, the radial dimension of the edge toward the open end of each individual crest is not greater than the radial dimension of the largest radial dimension of the adjacent crest which is toward the open end, whereby any mating crest cleared by the adjacent crest during stabbing will be cleared by the edge of the corresponding individual crest;
each of said pin and box having a secondary radially extending surface facing toward the open end;
means for circumferentially aligning said pin and box for correct axial stabbing, such that the distance from said sec-ondary radially extending surface of said pin to a point on an abutting flank of said pin equals the distance from said second-ary radially extending surface of said box to a point on an abut-ting flank of said box at the same axial and circumferential location, whereby when fully engaged both the abutting flanks of the pin and box and the secondary radially extending surfaces are in axially compressive abutment; and the width of said crests so related to the frustoconi-cal taper than when stabbing in the circumferentially aligned position, initial contact is made radially between said crests of said first helical thread form and said crests of said second helical thread form, whereby the connector is forced into snap engagement without rotation.