Note: Descriptions are shown in the official language in which they were submitted.
CA 02242592 1998-07-08
APPLICATION FOR PATENT
lNVENTOR: WILLIAM D. MURRAY
TITLE: MULTIPLE LEAD THREADS FOR HIGH
TORQUE TRANSFER APPLICATIONS
SPECIF~CATION
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR
DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field ofthe Invention. The present invention relates generally to threaded
connections for high torque transfer applir~*onc The present invention is particularly
rt~d for uce in drilling operationc, inclnfling but not limited to drill pipe, drill motors
10 and various other drilling appa-~lus.
2. Description of the Related Art. Many types of col~rlingc and CO~ OI ~
have been used to axially join cylinflrirql m~mbers to one another. In many ;.~ ..ces, it
is necessary to l,~rel torsional force and axial force from the one cylin~lric~l member
to the other "~ h~ n*mes, it is npcecs~ry that the coupling or conn~ctor be easily
15 connected and ~lisconnecte~l Such a re4u~eme~l e~ ;s using a welded conn~ction
to join the two m~mhers
Threaded conn~cti~mc have been used for many years to join members to one
another in torsional and axial force ~ g applic~tionc~ Th,ez~ed cc~nnpchs)nc
transfer axial COLU~)1eSSiV~ and tensile forces and also torsional forces in one direction
20 about the lc.. ,~l . .-1;. .~1 axis of the cylin~1ri~ 1 members. Generally, threaded conn~c*ons
allow easy u~....r.;t and disconnect c~pa-hili*es However, certain threaded connPctionc
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such as tapered pipe thread connections, may be more difficult to disconnect due to the
nature of the threaded engagement.
Multiple lead threads have been used in the past for purposes of rapidly threading
one member to another. Multiple lead threads include multiple start positions for the
5 beginning threading of the members together. Typically, the thread lead is greater in a
mllltiple lead thread than in a single lead thread. As a result of the increased thread lead
the travel of the one member relative to the other member is greater for each revolution
- of the threaded member than for a smaller thread lead. Thus, multiple lead threads have
been used in ;..~ cçs requiring rapid travel of one member on a long threaded member.
0 It is to be understood that the usage of mllltiple lead threads in these instances were not
for high torque transfer applictqtion~
U.S. Patent 4,564,225 to Taylor discloses multiple lead threading used for joining
sections of casing or tubing. Taylor discloses the joinder of two tubular members, each
having radially tapered exterior multiple lead threaded portions and a collar having
15 radially tapered interior multiple lead threaded portions. The threaded portions of the
collar are threaded in opposite direction~. Taylor teaches that this coupling arr~ngem~nt
decreases field make-up or knock-down time, and greatly reduces any tend~ncy to gall
and/or cross thread. In the Taylor threaded colll~c~;on assembly, the tapered threads take
the load as the connection is made up. The tapered threads have two points of contact
20 between the threads. The tapered threaded conn~ction of Taylor does not have high
torsional strength and is a connection which is not int~n~e(l to be ~lic~semhled.
In addition to having a threaded connection with high torque transferring
char~ct~rictics7 it is often required that the size and length of the threaded connection be
...~;..~ <;~fd to a ...;..;...~.. This is particularly true for many pieces of drilling eqllipm~nt
25 and downhole tools used in oil well drilling operations. One example of this limitation
is in positive ~ p~ e~ motors used to drill highly deviated wells. The positive
displ~cem~nt motor or "drill motor" rotates the drill bit and is powered by drilling mud
pl~c~... ;,~d by surface pumps lln~ to the drill motor Liou~ the drill string bore.
In this mode of flrilling the entire drill string need not be continll~lly rotated during
30 drilling. However, the plt;s~ d drilling mud acts on an int~rn~l rotating power
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tr~ncmiccion assembly in the drill motor to rotate the drill bit attached to the lower end of
the drill motor. The various components of the power tr~ncmiCcion assembly are typically
joined with threaded connections. The plurality of components forming the power
tr~ncmicsion assembly are interior of an outer housing assembly. It is important to
5 nn(3~s~nrl that the outside ~ m~t~r of the drill motor is desired to be kept at a ~
m~t~r. Furthermore, the interior components of the power tr~ncmicsion assembly are
limited by these exterior conctr~intc and the int~rn~l working operations necessary for the
- drill motor. As a result, the threaded connections m~king up and joining the various
interior components of the power tr~ncmiccion assembly have limitations as to the
10 diameter of the member and optimally the length of the mud motor is also kept to a
minimum. Typically, the threaded connections used in connecting the various
co~ ell~ of the drill motor have been a rotary shouldered connection as shown in Fig.
5. Several types of rotary shouldered connections are illustrated in Fig. 5. The rotary
shouldered co~nectinn in Fig. 5 between the outer h- ncing members, generally tlesi n~ted
15 as 6, has conical threads with outer abutting shoulders. The rotary shouldered connection
between the upper interior members, generally decigr ~t~d as 7, has straight threads with
outer abutting shoulders. The rotary shouldered cnnn~ction generally decign~ted as 8 has
straight threads with inner abutting shoulders. Typically, much of the torque capacity of
the rotary shouldered connection is attributable to the friction of the abutting shoulders
20 but a portion ofthe torque capacity is attributable to a "jackscrew" effect which is based
on the lead of the thread and tends to col-.~ress the chnlllders together.
It is desirable to have a high ~LIenglll, high torque Ll~sr~r threaded connection
between two cylin~1ric~1 members. It is desirable to have a high strength, high torque
r~l threaded connection which can be used in drilling operations, including, but not
25 limited to drill pipe, drill motors and various other drilling a~lus. It is desirable to
have a threaded connection design which o~ es the torque Ll~srel capability of the
connection given a certain thread ~ mloter.
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BRIEF SIJMMARY OF THE INVENTION
The multiple lead thread connection of the present invention provides a high
~llellg~, high torque transfer threaded co~ cl;on b~lw~e~ two cylindrical members. The
present invention can be used in drilling operations, inrlnAing but not limited to drill pipe,
5 drill motors and various other drilling ap,~ lus. The multiple lead thread connection
O~ .~s the torque ~ r~. c~r~hility of the connection given a certain thread diameter.
The multiple lead threaded coupling for tr~n~fPrring torque inchlclPs a male joint
- having a cylindrical body with a longihl(lin~l throughbore. The cylindrical body has an
PxtPm~lly threaded portion with a plurality of thread leads. The cylindrical body also has
10 a shoulder which can be a peripheral shoulder or an end of a pin. The multiple lead
threaded coupling also inchltlPs a female joint having a cylindrical body with alongit~l~lin~l throughbore. The cylindrical body has an abutment face and an intPrn~lly
threaded portion with a plurality of thread leads. The male joint is capable of threaded
çng~gPment with the female joint with the shoulder abutting the abutment face.
15 BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWINGS
In order to more fully understand the drawings refell~d to in the detailed
description of the present invention, a brief description of each drawing is presPntP~ in
which:
Fig. 1 is a partial cross-sec*on~l view of a threaded connection according to a first
20 embodiment of the mllltip1e start screw threads for high torque transfer applic~o*on~
Fig. 2 is a partial cross-sectional view of a threaded connection according to asecond embodiment of the mllltiple start screw threads for high torque transfer
applications;
Fig. 3 is a pel~e~iLiv~ view sL~wi~g the female end portion of a pipe having the25 multiple start screw threads;
Fig. 4 is an enlarged portion from Fig. l; and
Fig. 5 is a partial ~iulawa~ view of a portion of a prior art drill motor showing
several rotary shouldered threaded connPc~ion~
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DETAILED DESCRIPTION OF THE INVENTION
The present invention of mn1tirle lead threads for high torque transfer applications
will now be described in detail with reference to Figs. 1-4. Fig. 1 shows a multiple start,
tapered thread, rotary shouldered c- nnçction and Fig. 2 is a multiple start, straight thread,
s rotary shouldered connection.
~ ef~rring to Fig. 1, a pin or male threaded tubing joint 10 is threadedly connected
to the box or female tubing joint 12. The male tubing joint 10 has an e~ rn~lly threaded
- portion 14 and the box tubing joint has int~ lly threaded portion 16. Referring to Fig.
1, the threaded portions 14 and 16 are tapered to facilitate easy stab-in between the male
10 and female thread portions 14 and 16, respectively. Although not necessary in all
applications of the present invenhon, the tubing members 10 and 12 are shown having an
axial bore 18 ext~n-ling therc~.ough.
Referring to Fig. 3, an abutment face portion 28 of the female tubing joint 12 is
shown having a plurality of threads 32a-d as best shown in Fig. 1. Similarly, the male
15 tubing joint 10 includes a corresponding plurality of threads 30a-d as best shown in Fig.
1.
Referring to Fig. 4, the threads 30a-d and 32a-d have a crest 20, a root 22, andflanks 24 and 26 t~xt~nt1ing between the crest 20 and the root 22. It is to be understood
that the thread type shown in Figs. 1 and 4 is not critical to the present invention. For
20 eY~mple in Figs. 1 and 4 the threads have been tr mc~ted while in Fig. 2 the threads have
not been t~m~te-l
Referring to Fig. 3, the threads 32a-d have four leads spaced uniformly at 90~
intervals around the abutment face portion 28 of the female tubing joint 12. While not
shown in the drawings, it is to be understood that the threads 30a-d are also spaced
25 ul~ifo~ ly at 90~ intervals on the pin ~ 1ed portion 14.
It is also to be ...ul. . ~uod that the present invention is not limited to the four leads
shown in the drawings, but inclndes any mlmher of mnltirle lead threads, incllllling but
not limited to two and three leads. The leads will always be ....; rO. ~ly spaced around the
male and female tubing joints 10 and 12, lcspe~,lively. For ~Y~mrle7 three leads will be
30 spaced at 120~ intervals and two leads at 180~ intervals.
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F~f~rring to Fig. 1, the male threaded tubing joint 10 includes a shoulder 34 which
abuts the abutment face portion 28 of the female tubing joint 12 when the rotaryshouldered connection is made up. As shown in Fig. 4, there is one point of contact
between the threads. The point of contact occurring between the flanks 26.
~eferring to Fig. 2, the present invention is shown as a multiple start, straight
thread, rotary shouldered conn~ction for high torque transfer applications. Referring to
Fig. 2, a pin or male threaded tubing joint 10' is threadedly connected to the box or female
- tubing joint 12'. The male tubing joint 10' has an çxt~rn~lly threaded portion 14' and the
box tubing joint has int~rn~lly threaded portion 16'. The threaded portions 14' and 16' are
10 straight threads. Although not n~cess~ry in all applications of the present invention, the
tubing members 10' and 12' typically have an axial bore 18' çxt~n~in~ the~ ough.Referring to Fig. 2, an abutment face portion 28' of the female tubing joint 12' is
shown having a plurality of threads 32a'-d'. Similarly, the male tubing joint 10' includes
a corresponding plurality of threads 30a'-d'. As stated above, the threads 30a'-d', 32a'-d'
15 are not truncated as in Figs. 1, 3 and 4. The threads 32a'-d' have four leads spaced
, ..,; rO" "ly at 90~ inten als around the a~ul~-le.ll face portion 28' of the female tubing Joint
12'. While not shown in the drawings, it is to be understood that the threads 30a'-d' are
also spaced .~..;rollllly at 90~ intervals on the pin threaded portion 14'. As stated above,
the present invention is not limited to four leads but is intended to include generally
20 multiple leads.
Still referring to Fig. 2, the male threaded tubing joint 10' inch~(les a shoulder 34'
which abuts the abutment face portion 28' of the female tubing joint 12' when the rotary
shouldered conn~ction is made up.
The ",.~ ,lc lead, rotary shouldered conn~ction can w;ll.~ (1 a greater torque than
25 a similar single lead, rotary shouldered conn.oction. Thus, without increasing the length
of the threaded portions or the outer diameter of the threaded portions, the torsional
capacity ofthe rotary shouldered col~l.rc~;on can be increased by ~ n~ing from a single
lead thread to a multiple lead thread. A three lead thread has a greater torque capacity
than does a two lead thread.
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The increased torque capacity results from the increased lead of thread which
results from mllltirle lead threads. The lead of a thread is shown as P in Fig. 1. The lead
of a thread P is the (1ict~n~e between the threads through one revolution of 360~. It is
known in the design of threaded connec*onC that the lead of a thread P affects the
5 torsional capacity of the threaded connection. The lead of the thread P affects what is
commonly referred to as the "jackscrew" effect. The jackscrew effect is realized by the
increased angle of attack of the threads as the thread lead P increases.
- Q~ l;./ely, the jacl;scl~w contribution to the tor~ion~l capacity to yield a rotary
shouldered connection is detçrminP~ from the following equation:
YmA ~ p
Y 12 ~2~)
1 0 Where:
Ty = Turning moment or torque required to yield--ft.-lbs.
Ym = Minin~ n yield strength of the material--psi.
P = Lead of Thread - inches
A = Cross section area--sq. inches.
The above equation is taken from an industry acc~t~d equation to calculate the
torque to yield a rotary shouldered connection publiched by the ~meric~n Petroleum
Tnc*hlte (API) in API Recomm~n-led Practice 7G (1990).
Merely for eY~mrl~ry purposes, a single lead thread having a thread lead P of
0.1667" will be co~ d to a double lead thread having a thread lead P of 0.3333". If the
20 m~t~n~l yield ~1" ~Ih and area are cr~ 1 in the ~ from the above equation, the
increased thread lead P results in the mlll*rle lead, rotary chollldpred col...rcl;on having
twice the jackscrew effect of the single lead, rotary chollld~red conn~oc*on Thepercentage increase in the overall torque required to yield the particular connf~c*on
lc on other factors. However, the ~,e..;~ ge increase can easily be on the order of
25 4%fora2-1/2" ~ n~t~rrotaryshoulderedco~ ccl;on havingtwoleadswitha m~tçri~l
yield of 15Q000 pounds per square inch. The ~e.~-.l ~ increase ~roves urith a three
lead connection.
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The number of leads that can be used will in every instance will be affected by
variables such as size of the members, cost, and m~nllf~ct~lring ability. Physically, it is
anticipated that three leads can be used on threaded connections of members having a
diameter in the range of 1" to 3".
Another benefit of the multiple lead rotary shouldered connection is that highertorque load is achieved while red~cing ~e shoulder load. This further helps to ensure the
integrity of the threaded conn~ctinn As a threaded conn~ction is torqued together and the
- shoulder 34 abuts the abutment face 28, all of the torque forces are converted to axial
forces, if one ignores frictinn These axial forces load the shoulder 34 in compression and
10 load the pin threaded portion 14 in tension. The forces are ll~s~ d between the pin and
box by loading of the thread flanks 24. If the same torque is applied on two simil~rly
sized threads, one having a double lead thread and the other having a single lead thread,
and the cross-sectional areas of the two connections are the same, the reslllting shoulder
stress decreases as the lead of thread P increases. In many instances, the shoulder stress
15 is the limiting factor for a threaded cormection. With drilling equipment the goal is often
to transmit as much torque as possible. As (li~cllssed above, a multiple lead thread is able
to transmit more torque at the same reslllting stress as for a single lead thread.
Having described the invention above, various modifications of the techniques,
procedures, m~t~ri~l and e4~ ....r~.l will be a~ clll to those in the art. It is inten~e~ that
20 all such variations within the scope and spirit of the appended claims be embraced
thereby.
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