U.S. patent application number 16/032727 was filed with the patent office on 2018-11-08 for balanced thread form, tubulars employing the same, and methods relating thereto.
This patent application is currently assigned to National Oilwell Varco, L.P.. The applicant listed for this patent is National Oilwell Varco, L.P.. Invention is credited to Michael Joseph Jellison, Andrei Muradov.
Application Number | 20180320456 16/032727 |
Document ID | / |
Family ID | 55272638 |
Filed Date | 2018-11-08 |
United States Patent
Application |
20180320456 |
Kind Code |
A1 |
Muradov; Andrei ; et
al. |
November 8, 2018 |
Balanced Thread Form, Tubulars Employing the Same, and Methods
Relating Thereto
Abstract
A threaded pin connector disposable at one end of a tubular
member and having a longitudinal axis is disclosed. The threaded
pin connector includes a pin external shoulder and a pin internal
shoulder axially spaced from the external shoulder. In addition,
the threaded pin connector includes a plurality of threads in a
region between the external shoulder and the internal shoulder that
taper relative to the longitudinal axis at 1.0 to 1.5 inches per
foot. The plurality of the threads have a bearing strength and a
shear strength. The plurality of the threads are configured such
that the bearing strength is within +/-5% of the shear
strength.
Inventors: |
Muradov; Andrei; (Houston,
TX) ; Jellison; Michael Joseph; (Houston,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
National Oilwell Varco, L.P. |
Houston |
TX |
US |
|
|
Assignee: |
National Oilwell Varco,
L.P.
Houston
TX
|
Family ID: |
55272638 |
Appl. No.: |
16/032727 |
Filed: |
July 11, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14602947 |
Jan 22, 2015 |
10041307 |
|
|
16032727 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 17/042 20130101;
F16L 15/001 20130101 |
International
Class: |
E21B 17/042 20060101
E21B017/042; F16L 15/00 20060101 F16L015/00 |
Claims
1. A threaded pin connector disposable at one end of a tubular
member and having a longitudinal axis, wherein the threaded
connector includes: a pin external shoulder configured to engage a
box external shoulder on a mating threaded box connector when the
pin connector is threadably engaged with the box connector; a pin
internal shoulder axially spaced from the pin external shoulder,
wherein the pin internal shoulder is configured to engage with a
box internal shoulder on the box connector when the pin connector
is threadably engaged with the box connector; and a plurality of
threads in a region between the pin external shoulder and the pin
internal shoulder that taper relative to the longitudinal axis at
1.0 to 1.5 inches per foot, wherein each of the plurality of the
threads includes: a crest; a root disposed radially inward from the
crest; a stab flank extending between the crest and the root; and a
load flank extending between the crest and the root, wherein the
stab flank is more proximate the pin internal shoulder than the
load flank; wherein the plurality of the threads has a bearing
strength that represents a measure of the force required to
plastically deform the load flank; and wherein the plurality of the
threads has a shear strength that represents a measure of the axial
force required to shear the thread between the load flank and the
stab flank; and wherein the plurality of the threads is configured
such that the bearing strength is within +/-5% of the shear
strength.
2. The threaded pin connector of claim 1, wherein each of the
plurality of the threads further includes: a first radius extending
between the crest and the stab flank and having a first radius of
curvature; and a second radius extending between the crest and the
load flank and having a second radius of curvature; wherein the
first radius of curvature is larger than the second radius of
curvature.
3. The threaded pin connector of claim 2, wherein the first radius
of curvature is at least four times larger than the second radius
of curvature.
4. The threaded pin connector claim 3, wherein the first radius of
curvature is 0.065 in, and wherein the second radius of curvature
is 0.015 in.
5. The threaded pin connector of claim 1, wherein the stab flank on
each of the plurality of the threads is oriented at a first angle
.alpha. relative to a radius of the longitudinal axis, and wherein
the load flank on each of the plurality of threads is oriented at a
second angle .beta. relative to the radius, wherein .alpha. is
equal to .beta..
6. The threaded pin connector claim 1, wherein the stab flank on
each of the plurality of the threads is oriented at a first angle
.alpha. relative to a radius of the longitudinal axis, and wherein
the load flank on each of the plurality of threads is oriented at a
second angle .beta. relative to the radius, wherein .alpha. is
larger than .beta..
7. The threaded pin connector of claim 6, wherein .alpha. is equal
to 45.degree. and .beta. is equal to 30.degree..
8. The threaded pin connector of claim 7, wherein the roots of each
of the subset of threads have an elliptical curvature when viewed
in cross-section along the longitudinal axis.
9. The threaded pin connector of claim 1, wherein the plurality of
threads taper relative to the longitudinal axis at 1.25 inches per
foot.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 14/602,947 filed Jan. 22, 2015, and entitled "Balanced Thread
Form, Tubulars Employing the Same, and Methods Relating Thereto,"
which is hereby incorporated herein by reference in its entirety
for all purposes.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
BACKGROUND
[0003] This disclosure relates generally to threaded connections.
More particularly, this disclosure relates to threaded connections
for downhole tubulars (e.g., drill pipe).
[0004] Threaded tubulars are common in many industrial
applications, such as, for example, oil and gas drilling,
production, transportation, refining, etc. In oil and gas drilling
operations, a drill bit is threadably attached at one end of a
threaded tubular and the tubular is rotated (e.g., from the
surface, downhole by a mud motor, etc.) in order to form a
borehole. As the bit advances within the formation, additional
tubulars are threadably attached at the surface, thereby forming a
drill string. During these operations, it is desirable that the
threaded connections between each adjacent tubular along the drill
string have sufficient strength to withstand all expected service
loads (e.g., torsion, tension, compression, etc.), such that the
integrity of the drill string is ensured.
BRIEF SUMMARY OF THE DISCLOSURE
[0005] Some embodiments of this disclosure are directed to a
threaded pin connector disposable at one end of a tubular member
and having a longitudinal axis. In an embodiment, the threaded pin
connector includes a pin external shoulder configured to engage a
box external shoulder on a mating threaded box connector when the
pin connector is threadably engaged with the box connector, and a
pin internal shoulder axially spaced from the pin external
shoulder, wherein the pin internal shoulder is configured to engage
with a box internal shoulder on the box connector when the pin
connector is threadably engaged with the box connector. In
addition, the pin connector includes a plurality of threads in a
region between the pin external shoulder and the pin internal
shoulder that taper relative to the longitudinal axis at 1.0 to 1.5
inches per foot. Each of the plurality of the threads includes a
crest, a root disposed radially inward from the crest, a stab flank
extending between the crest and the root, and a load flank
extending between the crest and the root, wherein the stab flank is
more proximate the pin internal shoulder than the load flank. The
plurality of the threads has a bearing strength that represents a
measure of the force required to plastically deform the load flank.
The plurality of the threads has a shear strength that represents a
measure of the axial force required to shear the thread between the
load flank and the stab flank. The plurality of the threads is
configured such that the bearing strength is within +/-5% of the
shear strength.
[0006] Other embodiments are directed to a method for manufacturing
a tubular member including a longitudinal axis, a first end, and a
second end opposite the first end. In an embodiment, the method
includes (a) forming a threaded pin connector on the first end of
the tubular member, wherein the threaded pin connector includes a
pin external shoulder and a pin internal shoulder axially spaced
from the pin external shoulder. In addition, the method includes
(b) forming a threaded box connector on the second end of the
tubular member, wherein the threaded box connector includes a box
external shoulder and a box internal shoulder axially spaced from
the box external shoulder. Further, the method includes (c) forming
a plurality of pin threads along the pin member in a region between
the pin external shoulder and the pin internal shoulder and a
plurality of box threads along the box member in a region between
the box external shoulder and the box internal shoulder. The pin
threads and the box threads each taper relative to the longitudinal
axis at 1.0 to 1.5 inches per foot, and the plurality of the pin
threads and the plurality of box threads have an axial density
measured in a number of threads per inch (TPI). Each of the
plurality of pin threads and each of the plurality of box threads
includes a crest, a root, a stab flank extending between the crest
and the root, and a load flank extending between the crest and the
root. The stab flank on each pin thread is more proximate the pin
internal shoulder than the load flank on the pin thread. The stab
flank on each box thread is more proximate the box external
shoulder than load flank on the box thread. When the pin member is
threadably engaged with a box member on another tubular member,
each of the plurality of pin threads contacts a corresponding box
thread along a projected radial distance H.sub.C along the load
flank. When the box member is threadably engaged with a pin member
on a another tubular member, each of the plurality of box threads
contacts a corresponding pin thread along the projected radial
distance H.sub.C along the load flank. The plurality of pin threads
and box threads are configured such that the product of 2( {square
root over (3)})(H.sub.C)(TPI) for the pin threads and the box
threads is greater than or equal to 0.95 and less than or equal to
1.05.
[0007] Still other embodiments are directed to a tubular member
having a longitudinal axis, a first end, a second end opposite the
first end. In an embodiment, the tubular member includes a first
threaded box connector disposed at the first end and a first
threaded pin connector disposed at the second end. The first pin
connector includes a pin external shoulder configured to engage a
box external shoulder on a second threaded box connector of another
tubular member when the pin connector is threadably engaged with
the second box connector and a pin internal shoulder axially spaced
from the pin external shoulder, wherein the pin internal shoulder
is configured to engage with a box internal shoulder on the second
box connector when the pin connector is threadably engaged with the
second box connector. In addition, the first pin connector includes
a plurality of threads in a region between the pin external
shoulder and the pin internal shoulder that taper relative to the
longitudinal axis at 1.0 to 1.5 inches per foot. Each of the
plurality of threads includes a crest, a root disposed radially
inward from the crest, a stab flank extending between the crest and
the root, and a load flank extending between the crest and the
root. The stab flank is more proximate the pin internal shoulder
than the load flank. The plurality of threads has an axial density
measured in a number of threads per inch (TPI). When the pin
connector is threadably engaged with the second box connector, each
of the plurality threads on the threaded pin connector contacts a
corresponding box thread on the second box connector along a
projected radial distance H.sub.C along the load flank. The
plurality of threads are configured such that the product of 2(
{square root over (3)})(H.sub.C)(TPI) is greater than or equal to
0.95 and less than or equal to 1.05.
[0008] Embodiments described herein comprise a combination of
features and advantages intended to address various shortcomings
associated with certain prior devices, systems, and methods. The
foregoing has outlined rather broadly the features and certain
technical advantages of the disclosed exemplary embodiments in
order that the detailed description that follows may be better
understood. The various characteristics described above, as well as
other features, will be readily apparent to those skilled in the
art upon reading the following detailed description, and by
referring to the accompanying drawings. It should be appreciated by
those skilled in the art that the conception and the specific
exemplary embodiments disclosed may be readily utilized as a basis
for modifying or designing other structures for carrying out the
same purposes of the embodiments described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] For a detailed description of the disclosed exemplary
embodiments, reference will now be made to the accompanying
drawings in which:
[0010] FIG. 1 is a schematic side view of an embodiment of a
drilling system for drilling a borehole into a subterranean
formation in accordance with the principles disclosed herein;
[0011] FIG. 2 is a perspective cross-sectional view of one of the
drill pipes for use within the drilling system of FIG. 1;
[0012] FIG. 3 is a side cross-sectional view of one of the drill
pipes for use within the drilling system of FIG. 1;
[0013] FIG. 4 is an enlarged cross-sectional view of a portion of
the pin threaded connector of the drill pipe of FIGS. 2 and 3;
[0014] FIG. 5 is an enlarged cross-sectional view of a portion of
the box threaded connector of the drill pipe of FIGS. 2 and 3;
[0015] FIG. 6 is an enlarged cross-sectional view of the fully
formed threads disposed on the pin threaded connector of FIG.
4;
[0016] FIG. 7 is an enlarged cross-sectional view of an alternative
embodiment of the fully formed threads disposed on the pin threaded
connector of FIG. 4;
[0017] FIG. 8 is an enlarged cross-section view of a threaded
connection formed by the threaded pin connector of FIG. 4 and the
box threaded connector of another tubular member;
[0018] FIG. 9 is an enlarged cross-sectional view of engaged
threads within the connection of FIG. 8; and
[0019] FIG. 10 is a block diagram of a method for manufacturing a
tubular member in accordance with the principles disclosed
herein.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0020] The following discussion is directed to various exemplary
embodiments. However, one skilled in the art will understand that
the examples disclosed herein have broad application, and that the
discussion of any embodiment is meant only to be exemplary of that
embodiment, and not intended to suggest that the scope of the
disclosure, including the claims, is limited to that
embodiment.
[0021] The drawing figures are not necessarily to scale. Certain
features and components herein may be shown exaggerated in scale or
in somewhat schematic form and some details of conventional
elements may not be shown in interest of clarity and
conciseness.
[0022] In the following discussion and in the claims, the terms
"including" and "comprising" are used in an open-ended fashion, and
thus should be interpreted to mean "including, but not limited to .
. . ." Also, the term "couple" or "couples" is intended to mean
either an indirect or direct connection. Thus, if a first device
couples to a second device, that connection may be through a direct
connection, or through an indirect connection via other devices,
components, and connections. In addition, as used herein, the terms
"axial" and "axially" generally mean along or parallel to a central
axis (e.g., central axis of a body or a port), while the terms
"radial" and "radially" generally mean perpendicular to the central
axis. For instance, an axial distance refers to a distance measured
along or parallel to the central axis, and a radial distance means
a distance measured perpendicular to the central axis. Any
reference to up or down in the description and the claims is made
for purposes of clarity, with "up", "upper", "upwardly", "uphole",
or "upstream" meaning toward the surface of the borehole and with
"down", "lower", "downwardly", "downhole", or "downstream" meaning
toward the terminal end of the borehole, regardless of the borehole
orientation. As used herein, the words "approximately and
"substantially" mean plus or minus 10%.
[0023] As previously described, during oil and gas drilling
operations, it is desirable that the threaded connections between
adjacent tubulars forming the drill string have sufficient strength
to withstand all expected service loads (e.g., torsion, tension,
compression, etc.). Particularly, it is desirable that the threaded
connections between adjacent tubular members making up the drill
string have a sufficient torsional strength, which is a measure of
the amount of torque applied about the centerline of the tubular
connection required to cause failure. In order to optimize the
resulting torsional strength of the threaded connections making up
the drill string, the threads must be designed to have a sufficient
bearing and shear strength to avoid the common failures resulting
from elevated torsion. Bearing strength is a measure of the amount
of force required to cause deformation (e.g., plastic deformation)
of engaged surfaces (e.g., thread flanks) of the threaded
connection, and the shear strength is a measure of the amount of
force required to shear the threads between the thread flanks along
a plane which is substantially parallel to the connection
centerline.
[0024] If a threaded connection is over designed in terms of
bearing strength, the threads may have an excessive radial height
(i.e., the threads may be too "tall"), which thereby results in a
reduction in the critical cross-sectional area (since the threads
are cut radially deeper into the pin and box members) of the
threaded connection, which contribute to an overall reduction in
the torsional strength of the resulting connection. Alternatively,
if a threaded connection is over designed in terms of shear
strength, the threads may be excessively long along the connection
centerline (e.g., axial length), which thereby reduces the
available contact area at the internal shoulder, which also
contribute to an overall reduction in the torsional strength of the
resulting connection. Thus, this disclosure presents threaded
connections (which in some embodiments may be double shouldered
connections) for downhole tubulars (e.g., drill pipe, heavy weight
drill pipe (HWDP), drill collars, and other drill stem components)
that are designed to balance bearing strength and shear strength in
an effort to optimize the overall torsional strength of the
resulting connection.
[0025] Referring now to FIG. 1, an embodiment of a drilling system
10 is schematically shown. In this embodiment, drilling system 10
includes a drilling rig 20 positioned over a borehole 11
penetrating a subsurface formation 12, a casing 14 extending from
the surface 17 into the upper portion of borehole 11 along a
central or longitudinal axis 15, and a drillstring 30 suspended in
borehole 11 from a derrick 21 of rig 20. Drill string 30 has a
central or longitudinal axis 31 that, in this embodiment, is
aligned with axis 15 of casing 14 (note: such alignment is not
required), a first or uphole end 30a coupled to derrick 21, and a
second or downhole end 30b opposite end 30a. In addition,
drillstring 30 includes a drill bit 40 at downhole end 30b, and a
plurality of drill pipe joints 50 (or more simply drill pipes 50)
extending from bit 40 to uphole end 30a. Drill pipes 50 are
connected end-to-end, and bit 40 is connected to a lower end of the
lowermost pipe 50. A bottomhole assembly (BHA) (not shown) can be
disposed in drill string 30 proximal the bit 40 (e.g., axially
between bit 40 and the lowermost pipe 50).
[0026] In this embodiment, drill bit 40 is rotated by rotation of
drill string 30 from the surface. In particular, drill string 30 is
rotated by a rotary table 22 that engages a kelly 23 coupled to
uphole end 30a of drillstring 30. Kelly 23, and hence drill string
30, is suspended from a hook 24 attached to a traveling block (not
shown) with a rotary swivel 25 which permits rotation of drill
string 30 relative to derrick 21. Although drill bit 40 is rotated
from the surface with drill string 30 in this embodiment, in
general, the drill bit (e.g., drill bit 40) can be rotated with a
rotary table or a top drive, rotated by a downhole mud motor
disposed in the BHA, or combinations thereof (e.g., rotated by both
rotary table via the drillstring and the mud motor, rotated by a
top drive and the mud motor, etc.). For example, rotation via a
downhole motor may be employed to supplement the rotational power
of a rotary table 22, if required, and/or to effect changes in the
drilling process. Thus, it should be appreciated that the various
aspects disclosed herein are adapted for employment in each of
these drilling configurations.
[0027] During drilling operations, a mud pump 26 at the surface 17
pumps drilling fluid or mud down the interior of drill string 30
via a port in swivel 25. The drilling fluid exits drill string 30
through ports or nozzles in the face of drill bit 40, and then
circulates back to the surface 17 through the annulus 13 between
drill string 30 and the sidewall of borehole 11. The drilling fluid
functions to lubricate and cool drill bit 40, carry formation
cuttings to the surface, and maintain the pressure necessary to
prevent blowouts.
[0028] Referring now to FIGS. 2 and 3, each drill pipe 50 making up
drill string 30 is an elongate tubular member that is configured to
be threadably connected to each adjacent drill pipe 50 or other
component (e.g., drill bit 40, BHA, etc.). Each pipe 50 includes a
central or longitudinal axis 55 that is aligned with axis 31 of
drill string 30 during operations, a first or upper end 50a, a
second or lower end 50b opposite upper end 50a, a radially outer
surface 50c extending axially between ends 50a, 50b, and a radially
inner surface 50d defining a throughbore 52 that also extends
axially between ends 50a, 50b.
[0029] A threaded connector is disposed at each end 50a, 50b to
facilitate the threaded connection of joint 50 within drillstring
30 as previously described. In particular, a female or box threaded
connector 80 (or more simply "box 80") is disposed at upper end 50a
and a male or pin threaded connector 60 (or more simply "pin 60")
disposed at lower end 50b. As will be described in more detail
below, box 80 includes a plurality of internal threads that are
configured to threadably mate and connect with the threads of a pin
connector (e.g., pin 60) of an axially adjacent drill pipe 50
(e.g., with respect to axis 31) and pin 60 includes a plurality of
external threads that are configured to threadably mate and connect
with the threads of a box threaded connector (e.g., box 80) of an
axially adjacent drill pipe 50 (e.g., with respect to axis 31).
Further details of box 80 and pin 60 will be described in more
detail below.
[0030] Referring still to FIGS. 2 and 3, drill pipe 50 also
includes a pair of upsets each extending axially from one of the
threaded connectors 60, 80 to a central tubular region 58. As used
herein, the term "upset" generally refers to an increase in the
cross-sectional area of joint 50 relative to the cross-section area
within central tubular region 58. In particular, in this
embodiment, joint 50 includes a first or upper upset 54 extending
axially between box 80 and central tubular region 58 and a second
or lower upset 56 extending axially between pin 60 and central
tubular region 58. Each upset 54, 56 includes an expanded
cross-sectional area such that radially outer surface 50c is
expanded radially outward from axis 55 at upsets 54, 56 relative to
region 58 and radially inner surface 50d is expanded radially
inward toward axis 55 at upsets 54, 56 relative to region 58.
However, it should be appreciated that in other embodiments, upsets
54, 56 include a radial expansion along only one of the surfaces
50c, 50d, and in still other embodiments, no upsets 54, 56 are
included on joint 50 while still complying with the principles
disclosed herein.
[0031] As shown in FIGS. 2 and 3, drill pipe 50 is assembled by
forming upsets 54, 56 at the axial ends of region 58. Thereafter,
threaded connectors 60, 80 are secured to upsets 56, 54,
respectively, by any suitable method (e.g., welding, integral
formation, etc.). In addition, upsets 54, 56 may be formed on
tubular region 58 by any suitable method while still complying with
the principles disclosed herein. For example, in some embodiments,
upsets 54, 56 are formed by heating the axial ends of tubular
region 58, and impacting each heated end along axis 55, thereby
forcing surface 50c, 50d to radially expand in the manner described
above (and shown).
[0032] Referring now to FIG. 4, pin threaded connector 60 includes
a first or external annular shoulder 62 that extends radially
inward from radially outer surface 50c and a second or internal
annular shoulder 64 that extends radially outward from radially
inner surface 50d at lower end 50b. Thus, shoulders 62, 64 are
axially spaced from one another along axis 55. It should be
appreciated that in some embodiments, external shoulder 62 may also
be referred to herein as a "pin base" 62 and internal shoulder 64
may be referred to herein as a "pin nose" 64. As will be described
in more detail below, shoulders 62, 64 are configured to engage
with corresponding shoulders in a box threaded connector (e.g.,
shoulders 82, 84, respectively on box 80) on a mating drill pipe
50.
[0033] A plurality of external threads 66 are formed along pin 60
in a region extending axially between shoulders 62, 64. External
threads 66 on pin 60 are formed along a line of taper 65 that is
angled relative to axis 55 at an angle .theta.. In this embodiment,
external threads 66 preferably taper from approximately 1.0 to 1.5
inches of diameter per foot of axial length ("inches per foot" or
"in/ft") (i.e., the angle .theta. ranges from approximately
2.39.degree. to 3.58.degree.), more preferably from approximately
1.2 to 1.3 in/ft (i.e., the angle .theta. more preferably ranges
from approximately 2.86.degree. to 3.10.degree.), and still more
preferably at 1.25 in/ft (i.e., the angle .theta. still more
preferably approximately equals 2.98.degree.). However, it should
be appreciated that other values are possible for the taper and the
angle .theta. while still complying with the principles disclosed
herein. In addition, in this embodiment, threads 66 include a
plurality of run-out threads 67 and a plurality of fully formed
threads 68. As used herein, the term "run-out threads" refers to a
set of one or more threads that are not fully formed along pin 60.
Specifically, run-out threads 67 represent a region where the
cutting tool (e.g., a profile) used to form (i.e., cut) the threads
into pin 60 is gradually disengaged with or radially moved away
from the outer surface of pin 60 such that threads 67 are gradually
cut at an decreasing depth as the cutting tool is moved axially
along axis 55 away from end 50b after cutting fully formed threads
68.
[0034] Referring now to FIG. 5, box threaded connector 80 includes
a first or external annular shoulder 82 that extends radially
inward from radially outer surface 50c at upper end 50a and a
second or internal shoulder 84 that extends radially outward from
radially inward from radially inner surface 50d. Thus, shoulders
82, 84 are axially spaced from one another along axis 55. It should
be appreciated that in some embodiments, external shoulder 82 may
also be referred to herein as a "box nose" 82 and internal shoulder
84 may also be referred to herein as a "box base" 84. As will be
described in more detail below, shoulders 82, 84 are configured to
engage with corresponding shoulder in a pin threaded connector
(e.g., shoulders 62, 64, respectively on pin 60) on a mating drill
pipe 50.
[0035] A plurality of internal threads 86 are formed along box 80
in a region extending axially between shoulders 82, 84. Internal
threads 86 on box 80 are formed along a line of taper 85 that is
angled relative to axis 55 at the angle .theta., which is
substantially the same as previously described for line 65 of
internal threads 66 of pin 60, previously described. Thus, threads
86 on box 80 taper relative to axis 55 from approximately 1.0 to
1.5 in/ft (i.e., the angle .theta. ranges from approximately
2.39.degree. to 3.58.degree.), more preferably from approximately
1.2 to 1.3 in/ft (i.e., the angle .theta. more preferably ranges
from approximately 2.86.degree. to 3.10.degree.), and still more
preferably at 1.25 in/ft (i.e., the angle .theta. still more
preferably approximately equals 2.98.degree.). Like threads 66 on
pin 60, internal threads 86 includes a plurality of run-out threads
87 and a plurality of fully formed threads 88, where the term
"run-out" is utilized in the same manner as described above for
threads 66.
[0036] Referring now to FIG. 6, fully formed threads 68 on pin 60
are shown. It should be appreciated that fully formed threads 88 on
box 80 are formed substantially the same as threads 68, except that
threads 88 are flipped both horizontally and vertically relative to
threads 68. As result, the description below of threads 68 fully
describes threads 88 and a separate detailed description of threads
88 is omitted in the interest of brevity.
[0037] Each thread 68, includes a crest 92, a root 94 radially
spaced from crest 92, a leading or stab flank 96 extending between
crest 92 and root 94, and a following or load flank 98 extending
between crest 92 and root 94 of the immediately axially adjacent
thread 68 along axis 55. Thus, as one of ordinary skill would
appreciate, the stab flank 96 of each thread 68 is more proximate
the pin internal shoulder 64 than the pin load flank 98 on that
same thread 68. Similarly, while not specifically shown, one of
ordinary skill will also appreciate that the stab flank 96 on each
thread 88 is more proximate the box external shoulder 82 than the
load flank 98 of that same thread 88. In this embodiment, since
threads 68 are external threads disposed on pin 60, crest 92 of
each thread 68 is radially spaced outward from each root 94;
however, for each internal thread 88 on box 80, crest 92 is
radially spaced inward of each corresponding root 94. Each stab
flank 96 is angled relative to a radial line 95 extending from axis
55 at an angle .alpha., each load flank 98 is angled relative to
radial line 95 at an angle .beta., and each corresponding pair of
flanks 96, 98 on each threads 68 are angled relative to one another
at an angle .phi., which is the sum of the angles .alpha. and
.beta. (i.e., .phi.=.beta.+.alpha.). In this embodiment, the angles
.alpha. and .beta. are equal to one another, and each is equal to
30.degree.. As a result, in this embodiment, the angle .phi. is
approximately equal to 60.degree.. However, it should be
appreciated that other angles are possible, and thus, in other
embodiments the values of the angles .alpha., .beta., and .phi. may
range greatly while still complying with the principles disclosed
herein.
[0038] In addition, the transitions between each of the crests 92,
roots 94, and flanks 96, 98 are curved or radiused. In particular,
in this embodiment, the transition between the load flank 98 and
crest 92 of each thread 68 is a first radius R.sub.98-92, the
transition between the crest 92 and stab flank 96 is a second
radius R.sub.96-92, and each root 94 includes a radius R.sub.94.
For each thread 68, the radius R.sub.98-92 has a radius of
curvature that is smaller than that radius of curvature of the
radius R.sub.96-92. More particularly, in this embodiment, the
radius of curvature of radius R.sub.96-92 is more than four (4)
times larger than the radius of curvature of radius R.sub.98-92.
Still more particularly, in this embodiment, the radius of
curvature of radius R.sub.96-92 is equal to 0.065 in, and the
radius of curvature of radius R.sub.98-92 is equal to 0.015 in;
however, it should be appreciated that the values of radii
R.sub.96-92, R.sub.98-92 may range greatly in other embodiments
while still complying with the principles disclosed herein. In
addition, in this embodiment, the radius R.sub.94 of each root is a
substantially circular radius having a radius of curvature equal to
0.05 in; however, like the radii R.sub.96-92, R.sub.98-92, the
specific value of radius R.sub.94 may range greatly in other
embodiments.
[0039] Further, threads 66 along pin 60 have an axial thread
density that is typically measured in the number of threads per
some unit of axial length with respect to axis 55 (i.e., threads
per inch or "TPI"). In particular, in this embodiment, threads 66
on pin (and thus threads 86 on box 80) have a thread density
ranging between 2 and 4 TPI, and preferably have a thread density
of 3 threads per inch. It should be appreciated that other
embodiments may preferably have a thread density of 3.5 TPI, and
that still other embodiments may have higher or lower threads
densities while still complying with the principle disclosed
herein.
[0040] Referring now to FIG. 7, an alternative embodiment of fully
formed threads (designated as threads 68') on pin 60 is shown.
Threads 68' are substantially similar to threads 68 previously
described, and thus, like numerals are used to designate like
components and the discussion below will concentrate on the
difference between threads 68', 68. In particular, each stab flank
96 is oriented at the angle .alpha.' relative to radial line 95
rather than the angle .alpha. and the flanks 96, 98 of each thread
68' are angled relative to one another at the angle .phi.' rather
than the angle .phi.. In at least some embodiments, the angle
.alpha.' is larger than the angle .beta.. In particular, in this
embodiment, the angle .alpha.' is equal to 45.degree. while the
angle .beta. remains at 30.degree. such that the angle .phi.' is
equal to 75.degree. (i.e., .phi.'=a'+13). However, it should be
appreciated that the specific values for the angles .alpha.',
.beta., and .phi.' may range greatly in other embodiments while
still complying with the principles disclosed herein.
[0041] In addition, threads 68' include a root 94' in place of the
circular profiled root 94 on threads 68. As is shown in FIG. 7,
root 94' includes an elliptical profile when viewed radially in
cross-section (i.e., the view shown in FIG. 7). In particular, root
94' is cut or otherwise formed to conform to a portion of the outer
surface of an imaginary ellipse 97 that is shown in FIG. 9 for
clarity. Ellipse 97 includes a length L.sub.97 oriented along the
major axis and a height H.sub.97 oriented along the minor axis of
the ellipse 97. In this embodiment, the length L.sub.97 is
approximately equal to 0.080 in and the height H.sub.97 is
approximately equal to 0.040 in, and thus, in at least some
embodiments, the length L.sub.97 is approximately twice the height
H.sub.97. Although, it should be appreciated that other values and
relationships for both length L.sub.97 and H.sub.97 are possible
while still complying with the principles disclosed herein. Also,
as is also shown in FIG. 7, ellipse 97 defining root 94' is canted
or rotated relative to the centerline (e.g., axis 55) at an angle
.omega. that in some embodiments ranges from 0.degree. to
10.degree., and is preferably equal to 5.degree..
[0042] Further, it should be appreciated that when threads 68' are
utilized on pin 60 in place of threads 68, threads 88 on box are
similarly formed to match threads 68' (and would in this case be
designated as threads 88') except that threads 88' would be flipped
both horizontally and vertically relative to threads 68'. As
result, the description above of threads 68' fully describes
threads 88' and a separate detailed description of threads 88' is
omitted in the interest of brevity.
[0043] Referring now to FIGS. 8 and 9, regardless of the particular
thread form used (e.g., threads 68, 88 or 68', 88') during
connection operations pin 60 is threadably engaged with a box 80 on
another drill pipe 50 to form a threaded connection 100. In
particular, pin 60 and box 80 are threadably engaged with one
another by aligning the axes 55 of each pipe 50 and rotating one
pipe 50 (e.g., the pipe 50 carrying pin 60) about the aligned axes
55 relative to the other pipe 50 (e.g., the pipe 50 carrying box
80). When pin 60 is threadably engaged with box 80 in the manner
described, external shoulder 62 on pin 60 engages with external
shoulder 82 on box 80 and internal shoulder 64 on pin 60 engages
with internal shoulder 84 on box 80. Thus, connection 100 may be
referred to here in a dual or double shouldered threaded
connection.
[0044] In addition, as is best shown in FIG. 9, when pin 60 is
threadably engaged with box connector 80, the stab flanks 96 of the
corresponding threads 68, 88 engage with one another, the load
flanks 98 of corresponding threads 68, 88 engage with one another,
and crest 92 on each of the threads 68, 88 is proximate a root 94
on a corresponding thread 88, 68, respectively (or root 94' when
threads 68', 88' are employed). Further, when pin 60 and box 80 of
two tubular joints 50 are threadably mated as described above, a
contact height H.sub.C is formed which represents the projected
radial distance (e.g., along radius 95 from axis 55) along which
each corresponding mating pairs of threads 68, 88 engage one
another along mating load flanks 98. It should be appreciated that
while FIG. 9 shows only the engagement of threads 68, 88, the same
or similar engagement shown is achieved when threads 68', 88' are
instead employed on pin 60 and box 80.
[0045] Referring now to FIGS. 4-8, threads 66, 86 (e.g.,
particularly threads 68, 88 or alternatively threads 68', 88') on
pin 60 and box 80, respectively are formed, sized, and arranged
such that the resulting bearing strength and shear strength of
connection 100 are substantially balanced. As previously described,
such a balance is advantageous as it avoids an overall reduction in
the resulting torsional strength of the connection 100 caused by
over designing connection 100 for either bearing or shear strength
(e.g., which may cause the resulting threads to be either too tall
or too long, respectively).
[0046] In particular, without being limited to this or any other
theory, the bearing strength S.sub.B of connection 100 may be
calculated by the following equation:
S.sub.B=2.pi.Y.sub.sR.sub.tL.sub.t(TPI)H.sub.C;
[0047] where: [0048] Y.sub.s is the yield strength of the material
making up the connection 100; [0049] L.sub.t is the axial length of
the threaded region of the pin 60 (which may be measured from a
defined gauge point along pin 60 less the pin nose length); [0050]
R.sub.t is the mean thread radius; and [0051] TPI is thread density
per unit length along the central axis (e.g., axis 55) and is
typically represented in the number of threads per inch of axial
distance.
[0052] In addition, without being limited to this or any other
theory, the shear strength S.sub.SH of threaded connection 100 may
be calculated by the following equation:
S SH = .pi. 3 Y s R t L t . ##EQU00001##
[0053] When these equations for bearing strength S.sub.B and shear
strength S.sub.SH are equated, the following relationship is
produced:
2 .pi. Y s R t L t ( TPI ) H C = .pi. 3 Y s R t L t ;
##EQU00002##
[0054] which reduces to:
2 ( TPI ) H C = 1 3 . ##EQU00003##
[0055] When this expression is further reduced it results in the
following relationship:
2 {square root over (3)}(TPI)H.sub.C=1.
[0056] Thus, according to the principles disclosed herein, pin 60
and box 80 are configured such that the relationship 2 {square root
over (3)}(TPI)H.sub.C for the resulting connection 100 is
approximately equal to 1 or is substantially close to 1. In other
words, in at least some embodiments, the resulting connection 100
is sized and arranged such that 2 {square root over
(3)}(TPI)H.sub.C is greater than or equal to 0.95 and less than or
equal to 1.05 (i.e., 0.95.ltoreq.2 {square root over
(3)}(TPI)H.sub.C.ltoreq.1.05). As a result, in at least some
embodiments, the resulting connection 100 may exhibit a shear
strength that is within +/-5% of the bearing strength. In one
specific example, the threads on pin 60 and box 80 are configured
and arranged such that they have a TPI of 3.0 and a resulting
H.sub.C of 0.0967 in (thereby causing the relationship 2 {square
root over (3)}(TPI)H.sub.C to equal 1.00). In still another
specific example, the threads on pin 60 and box 80 are configured
and arranged such that they have a TPI of 3.5 and a resulting
H.sub.C of 0.0830 in (thereby causing the relationship 2 {square
root over (3)}(TPI)H.sub.C to equal 1.01).
[0057] Referring now to FIG. 10, a method 200 for manufacturing a
tubular member (e.g., tubular joints 50) is shown. Initially the
method 200 includes forming a pin connector (e.g., pin 60) on a
first end (e.g., lower end 50b) of a tubular member (e.g., joint
50) and forming a box connector (e.g., box 80) on a second end
(e.g., upper end 50a) of the tubular member in blocks 205 and 210,
respectively. Next, method 200 includes forming a plurality of
external pin threads (e.g., threads 66) on the pin connector and a
plurality of internal box threads (e.g., threads 86) on the box
connector in block 215. Finally, in block 220 method 200 includes
forming the pin threads and box threads such that when they are
engage with threads on box and pin connectors, respectively, on
other adjacent tubular members, the engaged threads satisfy the
relationship 0.95.ltoreq.2 {square root over
(3)}(TPI)H.sub.C.ltoreq.1.05, where H.sub.C and (TPI) are the same
as previously described above.
[0058] In the manner described, a threaded connection in accordance
with the principles disclosed herein (e.g., connection 100) is
formed that includes threads (e.g., threads 68, 88, 68', 88')
having substantially balanced shear and bearing strengths.
Therefore, through use of a threaded connection in accordance with
the principle disclosed herein (e.g., connection 100) the torsional
strength of the connection is optimized.
[0059] While preferred embodiments have been shown and described,
modifications thereof can be made by one skilled in the art without
departing from the scope or teachings herein. The embodiments
described herein are exemplary only and are not limiting. Many
variations and modifications of the systems, apparatus, and
processes described herein are possible and are within the scope of
this disclosure. Accordingly, the scope of protection is not
limited to the embodiments described herein, but is only limited by
the claims that follow, the scope of which shall include all
equivalents of the subject matter of the claims. Unless expressly
stated otherwise, the steps in a method claim may be performed in
any order. The recitation of identifiers such as (a), (b), (c) or
(1), (2), (3) before steps in a method claim are not intended to
and do not specify a particular order to the steps, but rather are
used to simplify subsequent reference to such steps.
* * * * *