U.S. patent number [Application Number ] was granted by the patent office on 1981-06-16 for united states patent: re30647 ( 1.
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United States Patent |
RE30,647 |
|
Issue Date: |
June 16,
1981 |
Current U.S.
Class: |
285/332.2;
285/334; 403/343 |
Current CPC
Class: |
E21B
17/0423 (20130101); F16L 15/002 (20130101); E21B
17/0426 (20130101); F16L 15/007 (20130101); Y10T
403/68 (20150115) |
Current International
Class: |
E21B
17/042 (20060101); E21B 17/02 (20060101); F16L
15/06 (20060101); F16L 15/00 (20060101); F16L
015/00 () |
Field of
Search: |
;285/334,333,355,390,332.2,332.3 ;403/343,118 ;85/46 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
568114 |
|
Jan 1933 |
|
DE2 |
|
137777 |
|
Jan 1920 |
|
GB |
|
528932 |
|
Nov 1940 |
|
GB |
|
Primary Examiner: Callaghan; Thomas F.
Attorney, Agent or Firm: Pravel, Gambrell, Hewitt, Kirk,
Kimball & Dodge
Claims
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.degree..
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.degree..
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.degree..
.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.degree.. .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.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to thread connected joints as
usable in oil well tubing, casing, line pipe and drill pipe (all of
which will be referred to as pipe, for convenience). More
particularly, it concerns a means for connecting joint pin and box
members in a manner to provide minimal hoop, radial or axial
stresses induced by assembly or applied torque.
With increased concern for protection of our environment, it is
becoming more important that tubular joint connections used in oil
industry be capable of performing with maximum security under all
conditions characteristic of the operating tasks they are relied
upon to fulfill. Basic fundamental technology required to meet
these performances must be satisfied through all operating stress
or strain levels. Today there are no tubular connections produced
anywhere in the world which will meet these requirements through
all operating stress or strain conditions characteristic of
services to which they may be exposed. In most cases, margins of
safety are inherently smaller as severity of performance increases.
There is a need for a connection that will have mechanical
integrity which will not be weakened by load stresses or strains
induced by tension, compression, internal pressure, external
pressure, torsion, bending, thermal variances, or any combination
of these until the material itself has failed by limitations of
metallurgical properties in rupture or fracture.
SUMMARY OF THE INVENTION
It is a major object of the invention to provide a pipe joint
meeting the above need. Basically, the joint comprises interengaged
thread means on pin and box members for producing hoop tension in
the pin member and hoop compression in the box member in response
to forcible make-up of the members, the thread means having a
dove-tail interfit. As will appear, the thread means includes
helical threading on each of the pin and box members, with greater
pitch distance at the thread tip than at the thread root. Also, the
threading typically has progressively reducing axial width along
its helical length, so that the conditions of hoop tension and
compression as described will be created upon final make-up, at
which time the interengaged threads preferably having wedging flank
interfit to limit such make-up.
As will appear, the dove-tail (semi or full) thread flanks will
interlock the elements of the connection. When torque is applied to
assemble the connection, rotational movement between elements will
stop when the wedges (threads) are made up on the flanks of the
groove between the threads. Since the threads are wedge type and
interlocked by a negative face angle on the back flank and the
crests and roots are parallel, the strain reactions to applied
torque are primarily axial in direction. Torque is resisted by the
axial "squeezing" of the threads. Since back flank is intended to
always be negative (back flank to the root plane will be less than
90.degree.), thread strain reactions against this surface will
cause the box member to be pulled radially inward and the pin
member to be pulled radially outward. Therefore, the box member
attains a condition of hoop compression while the pin will be in
hoop tension. Excessive torque will only result in high axial
squeezing forces on the threads and have very little effect in
inducing other extraneous stresses other than some minor degree of
bending of end threads.
Further, the threads are so designed that possible clearances
between mating crests and roots will be minimal while flanks will
be in wedging interference. In this manner the threads will be
functionally leak resistant. The primary resistance to leakage
through this connection will typically be accomplished by a
separately functional metal to metal seal. One or more such seals
may be incorporated for this requirement. In any case, the seals
will be located adjacent to or within the thread areas so that they
can receive the benefits of the interlocking threads. When properly
located and suitable interference (radial) established, the leak
resistance of the connection will not be affected by torque,
tension, internal or external pressures, bending axial compression,
or radical thermal changes in response to internal or externally
applied termperature differences.
It is another object of the invention to provide a pin and box
connection employing thread means as described which will interlock
in such manner as to prevent opening up of a seal between the
members in response to fluid pressure (internal or external)
application to the seal zone; further, it is an object to provide
the interlock at axially opposite sides of the seal zone so that
the pin and box members are clamped against relative radial
separation at opposite ends of the seal zone, preventing opening up
of the latter in response to fluid pressure application.
Accordingly important objects and benefits to be obtained from a
tubular connection constructed as described are:
1. To offer torsional strength equivalent to that of the full pipe
body, without the use of either an internal or an external
shoulder.
2. To obtain a joint strength in either tension or compression
equivalent to the strength of the full pipe body.
3. To resist radial strain differentials caused by the application
of either external or internal pressures which normally reduce the
effective interferences between sealing elements.
4. To mechanically interlock the two joint elements so that high
bending stresses will be ineffective to the leak resistant
integrity of the connection.
5. To produce a connection or non-upset pipe that will have full
performance properties comparable to those of integral upset
products.
6. To make it possible to recover used or damaged upset pipe by
cutting off the upset ends and apply the new connection as threaded
and coupled, with performance capabilities comparable to new
integral upset end connections.
7. To make a connection for line pipe that will be virtually
self-locking with high resistance to unscrewing.
These and other objects and advantages of the invention, as well as
the details of illustrative embodiments, will be more fully
understood from the following description and drawings, in
which:
DRAWING DESCRIPTION
FIG. 1 is a section in an axial radial plane through a pipe joint
embodying the invention;
FIG. 2 is an enlarged view of made-up threading (full dove-tail) in
the FIG. 1 joint;
FIG. 3 is an enlarged view of pin or box member threading as seen
in FIG. 2;
FIG. 4 is a perspective showing of a projected thread as seen in
FIG. 3;
FIG. 5 is a view like FIG. 2, but showing the threading prior to
completion to make-up;
FIG. 6 is a section in an axial radial plane through a two-step
pipe joint embodying the invention;
FIG. 6a is a view like FIG. 6 showing a variation; FIG. 7 is an
enlarged view of made-up threading (semi-dove-tail) in the FIG. 6
joint;
FIG. 8 is an enlarged view of pin or box member threading as seen
in FIG. 7; and
FIG. 9 is a view like FIG. 2 but showing axially tapering
threading.
DETAILED DESCRIPTION
Referring first to FIGS. 1-5, a pipe joint 10 includes pin and box
members 11 and 12, the joint defining an axis 13. Interengaged
thread means on the members include helical threading or threads 14
and 15 characterized as producing hoop tension in the pin member,
and hoop compression in the box member in response to forcible
make-up of the members. As such time, the threads 14 and 15 have
dove-tail interfit as at flank 16 on thread 14 engaged with flank
17 on thread 15, and opposite flank 18 on thread 14 engaged with
flank 19 on thread 15. In other words, the angles .alpha. and
.beta. as shown are acute, angle .alpha. formed between flank 18
and root wall 20 of thread 14 (or between flank 19 and root wall 21
of thread 15); and the angle .beta. formed between flank 16 and
root wall 20 (or between flank 17 and root wall 21). Walls 20 and
21 are cylindrical, and parallel to axis 13. Note the clearances at
22 and 23 between those root walls and the cylindrical tips 24 and
25 of the threads 14 and 15, respectively. Further, flanks 16 and
18 on thread 14 flare toward the thread lips 24, and flanks 17 and
19 flare toward thread tip 25. Thus threads 14 and 15 define full
dove-tail.
It will be noted the helical thread 14 has greater pitch distance
(i.e. in an axial direction) between flanks 16 and 18 at the thread
tip than at the thread root; likewise, helical thread 15 has
greater axial pitch distance between flanks 17 and 19 at the thread
tip than at the thread root. Further, each thread 14 and 15 has
progressively reducing width, or pitch distance, along the helical
length thereof. This is clear from FIG. 1 by comparison of the
widths of the thread 15 at locations 15a . . . 15f, and of the
widths of the thread 14 at axially spaced locations 14a . . . 14c.
The linear projection of thread 14 in FIG. 4 clearly shows
progressive width decrease along the thread length. At the same
time, the pitch distance between corresponding points on successive
thread turns, in axial radial planes, is the same as is clear from
comparison of FIGS. 2 and 5.
It is a further clear from FIGS. 1 and 2 that the threads 14 and 15
have vertically wedging interfit to limit make-up. Prior to
completion of such make-up, i.e. in partialy made-up condition,
there are gaps between the threads 14 and 15, as is clear from FIG.
5. The latter may, for exmaple, illustrate the position of thread
section 15a, as it is rotated past section 14b, such section also
being indentified in FIG. 1. Note gaps 30 and 31 in FIG. 5.
The angles .alpha. and .beta. should be less than about 85.degree.
to enable the interengaged flanks to resist unscrewing or
disassembly of the joint. When the connection is assembled power
tight, the sealing surfaces will be locked together because of the
thread from which secures the two joint elements in intimate
contact through any degree of, or direction of, radial strain.
Maximum load stresses can be transmitted through the connection in
any direction (radial or axial) without disengagement of the two
mating elements. Multi-directional stresses may be applied without
decreasing performance capabilities of the connection. The wedging
action of the front and back flanks of made up threads not only
offers a positive stop for make-up without the use of an auxiliary
shoulder but offers maximum attainable resistance to torque,
tension, compression, or any other induced load condition without
resulting in detrimental strain reaction to the sealing qualities
of the joint. This flank wedging action also prevents the normal
tendency of threads to bend or deflect under high axial load
conditions which normally lead to possible "pullout" or joint
separation followed by leakage, or telescoping from compressive
loads. The connection is securely interlocked in a manner which
resists strain differentials between the two joint elements when
subjected to load stresses in any direction or from any operational
cause.
FIG. 1 also shows the provision of annular beveled shoulders 33 and
34 on the respective members 11 and 12, and having metal-to-metal
sealing interfit in response to joint make-up. In addition, the
interengaged flanks 16 and 17, and 18 and 19, provide
metal-to-metal seals along the thread length.
FIGS. 6-8 illustrate another form of the invention, wherein semi
dove-tail threads 40 and 41 are formed on pin and box members 42
and 43 forming joint 44. The latter is shown in the form of a two
step thread, with a second pair of threads 40' and 41'
(corresponding to threads 40 and 41) at a greater radius from the
center line or axis 45 than threads 40 and 41. Note metal-to-metal
annular seals which are established at locations 46 and 47 upon
full make-up of the joint.
In FIG. 7, the angularity .gamma. of interengaged flanks 48 and 49
(of respective threads 40 and 41) from the direction of the axis 45
should be less than about 85.degree., but greater than zero, in a
manner similar to angles .alpha. and .beta. in FIG. 2; on the other
hand, interengaged flanks 51 and 52 on threads 40 and 41 extend
radially, in axial radial planes.
Referring back to FIG. 6, a tapered metal-to-metal annular seal is
formed at 55 between the pin and box members; also, the nose 56 the
pin 42 annularly engages a non-metallic (as for example molded
tetrafluoroethylene) seal ring 57 received in an annular recess 58
in the box member 43 to block leakage of corrosive well fluid to
the interengaged threads.
FIG. 9 illustrates an application of the invention to a joint 60
wherein threads 61 and 62 on pin and box members 63 and 64 taper,
axially. Note the fully dove-tailed threading of the type seen in
FIG. 2; however the tips 65 and 66 of the threads progress toward
axis 67 along the thread lengths.
FIG. 6a is like FIG. 6, but varies in that annular shoulders are
provided on the members at 89 and 90, these being axially tapered
as shown. Such shoulders come into pressural interengagement upon
make-up of the members, and have sealing interfit in a zone between
axial cylinders indicated at 91 and 92. Cylinder 91 is defined by
the crests of threads 140 (corresponding to threads 40 in FIG. 6)
which mesh with threads 141 (corresponding to threads 41 in FIG.
6), and cylinder 92 is defined by the crests of threads 141'
(corresponding to threads 41' in FIG. 6) meshing with threads 140'
(corresponding to threads 40' in FIG. 6). The interengaged threads
at the two steps serve to positively lock or clamp the pin and box
members 142 and 143 together against relative radial separation, at
or proximate opposite ends of the sealing interfit shoulders 89 and
90, whereby the latter cannot open up to leak fluid pressure
therebetween. All of this may be provided in a non-upset joint, or
in an upset joint, as desired. Fracture of the joint cannot occur
at the seal zone because strain is minimized or non-existent in the
members defining the seal zone, due to the positive interlock
provided by the interlocked threads.
Finally, the thread elements of the connection may be either single
or multiple pitch. The variance in pitch between joints will be
related to product requirements of performance rather than size or
other physical dimensions.
* * * * *