Note: Descriptions are shown in the official language in which they were submitted.
12~0~8
This invention relates generally to oil and gas
well tubing and more particularly has to do with the con-
stru~tion of high pressure tubular joints operable when
made-up and run into a well to withstand extreme fluid
5 pres3ures, both internal and external, that seek escape
throlgh the tubular assembly at the joints.
The search for oil and gas reserves has brought
abou~ the exploration of ever deeper formations. These
deep~r formations require longer strings of production pipe,
10 casing, liners and drill pipe used in the exploration and
production of oil and gas at extremely high pressures.
This increased length of tubular strings imposes the upper
portion of the string to very high tensile loads and in
addition, the tubular strings are exposed to extremes of
15 pressure both from within the tubing and also from the
exterior of the tubing.
Prior art metal-to-metal sealing mechanisms have
provided seals that resist mainly internal pressure or
mainly external pressure, as long as the surrounding tubu-
20 lar ~eometry remains in the elastic range. The prior artsealing mechanisms have not solved the sealing problem of
withstanding extremes of internal pressure, or external
pressure, either pressure acting during circumstances of
high tension, torque or compression forces acting on the
25 tubing.
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U.S. Patent No. 2,992,019 to M.D. MacArthur shows
a casing joint having metal-to-metal sealing means responsive
primarily to extremes of inside fluid pressure. The dis-
closed interior sealing for the pin and box provides a
5 fourteen degree (14) interior seal that is spaced a
distance from the threaded inner connection to enable the
deformation or strain on the pin, in response to the in-
side fluid pressure, to flex the pin interior sealing sur~
face against the box interior sealing surface and obtain
10 a greater sealing force. In addition, during such strain,
the sealing contact area decreases which increases the
sealing force over the reduced area. In particular, the
distance between the pin and the seal surface remains the
same while the center of the sealing area moves slightly
15 toward the thread during such sealing flexing.
U.S. Patent No. 4,009.893 issued to Schatton, et
al. discloses a tubing or casing joint with box and pin
members having two axially spaced thread sections separated
by a radial step zone which includes for the pin member, an
20 annulus having an axial undercut. The endface of the an-
nulus bears against a complementary face in the step zone
of the box member and serves to act as a complementary
thread stopface, in addition to a stopface at the end of
the pin member and in the box member.
There has been a long-felt need for metal-to-
metal sealing mechanisms for use in tubular joints which
are able to hold mating members together for complete leak
resistance against both internal and external pressures,
regardless of the forces of tension, compression, inter- .
3~ nal pressure, external pressure, torque or any combina-
tion thereof that are applied to the joint.
It is therefore a primary object of this inven-
tion to provide a trapping mechanism in a joint to hold
the mating members together for complete leak resistance in
35 the face of multiple forces acting on the joint.
Not only must the joint be sealed, it must be
capable of being made up and disassembled numerous times
_3~ 38
without galling and without the danger of stripping
threads or cross-threading. It is of course, desirable
and therefore an advantage of the joint according to the
invention disclosed herein in that it may be "stabbed" and
that thereafter it can be made up with a relatively small
number of turns.
It is common to use an integra~~ or upset joint
wherein the threaded portion of the pipe is thickened by a .'
forging technique so as to provide more metal in the area ~?
where threads are cut. The invention disclosed below may
advantageously be used with an integral or upset type of
joint, and it may also be used with a threaded and coupled
joint wherein both ends of the tubular elements are pro-
vided with male joining elements and a coupling member is
provided with female joint elements.
The Dresent invention therefore provides a joint
- for tubular elements comprising, an internally threaded
female member and an externally threaded male member
adapted to be threadably connected, the threads of the
female and male members having negative angle load flanks
and at least two radial steps axially separated from one
another by a reverse angle torque shoulder having at least
one adjacent conical sealing surface where the taper angle
of the conical sealing surface of the member having the
thinner wall thickness at the seal surface is inclined at
a smaller angle with respect to the axis of the threaded
connection than the complementary conical seal surface
of the mating member, whereby, said shoulder serves as a
positive assembly stop and produces radial Dositional inter-
ference of the conical sealing surfaces when the male andfemale members are fully assembled, and the negative load
flank angle of the threads and the reverse torque shoulder
angle are selected to interlock the male and female members
and to prevent differential radial separation of the conical
sealing surfaces when the joint is exposed to internal
pressure, external pressure or both.
Further features and advantages of the invention
will be better understood from the following description
of preferred embodiments of the invention taken in con-
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~ection with the accompanying drawings in which:
. Figure 1 illustrates a longitudinal cross-sec-
tional section through a joint according to the invention
showing in detail in Figures lA and lB, the negative flank
5 angle and the reverse torque shoulder features of the in-
vention;
Figure 2 illustrates an alternative embodiment of ~-
the invention with a longitudinal cross-section showing
threads cut on a taper angle with respect to the axis of
10 the male and female members of the joint;
Figure 3 and Figure 3A shows an embodiment of the
invention where the conical sealing surfaces of the male and
female ~embers are machined at slightly different angles;
and
Figures 4A and 4B illustrate alternative embodi-
ments O.c the invention where Figure 4A shows conical seal-
ing sur~aces on both sides of the reverse angle torque
shoulder and Figure 4B illustrates the use of a reverse
angle torque shoulder between two or more stepped threads.
Figure 1 illustrates, according to the invention,
a joint shown generally at 10 comprising female or box mem-
ber 20 in threaded connection with pin or male member 30 and
having ~wo step threads shown generally at 70 and 80 inter-
connect~d by a conical sealing surface 40. The joint is
25 characterized, according to the invention, by providing a
negative angle load flank 44 on the threads shown general-
ly in more detail in Figure lA and a reverse angle torque
shoulder 43 shown in more detail in Figure lB.
Figure lA illustrates that the load flank 44 on
30 the thr~ads is at an angle ~ which is measured counter- ~-
clockwi;e from the vertical to the longitudinal plane of i!
the thr-ads.
Figure lB illustrates that the sealing surfaces
41 and ~2 of the ~in and box members terminate in the tor-
35 que shoulder 43 which is at a reverse angle ~ measured
038
--5--
clockwise from the ~erpendicular to the longitudinal
axis of the joint.
The initial sealing surface contact of surfaces
41 and 42 is established at assembly by metal-to-metal
interference. The seal pressure retention characteristic p
of the threaded connection is related to the ability of
the sealing surfaces 41 and 42 to remain in contact
with one another as radial deflection of the joint
occurs from either internal pressure or external pres-
sure. The unique seal retention according to the inven-
tion results from the trapping effect of the negative
load flank threads of both the large step threads 70
and the small step threads 80 in co~ination with the -
reverse angle shoulder 43 in the intermediate region
between the steps thereby preventing loss of surface
contact between surfaces 41 and 42. The trapping effect
causes the two surfaces 41 and 42 to deflect as one.
The seal is establishea regardless of differences
in the annular section areas of each member 41 and 42
thus providing a pressure containment wherein forces
act from either side of the seal. In addition, the
ap~lication of an axial tensile load will cause the
seal surface to remain in contact. Similarly, torque
forces on the ioint do not ad~ersely affect the seal of
the joint. Advantageously, the only way that the seal-
ing surfaces can separate is for extreme forces acting
on the joint to cause the threads to ,~
, .._ ,_
038
-- 6
shear, the shoulder to shear, or both.
Although Figure 1 shows the threads 70 and 80 to be
cut parallel to the axis of box member 20 and pin member 30,
an alternative embodiment is shown in Figure 2 where threads
5 70 and 80 are cut on a taper angle shown generally as ~ . ~
Although Figure 2 illustrates the sealing surfaces 41 and -
42 to be cut at the same taper angle ~ as are the threads 70
and 80, they may advantageously be provided at a taper an-
gle different from the thread taper.
Figure 3 shows another alternative embodiment of
the invention whereby the conical sealing surfaces 41 and 42
of the top step are machined to slightly different angles
with respect to the axis of the joint. According to a fur- `
ther preferred aspect of the invention, the conical seal
15 surface of the member having the thinner wall thickness at
the seal surface may be machined to a smaller angle with
respect to the axis of the threaded connection than the com-
plementary conical seal surface of the mating member. In-
dividual sealing shoulder members are shown in more detail
20 in Figure 3A. Because the conical seal at the upper step
illustrated in Figure 3A occurs at a region where the female
member 20 wall thickness is less than the wall thickness of
the male member, the sealing surface 42 of the female member
is machined to an angle of incline which is slightly less
25 than the angle of incline of sealing surface 41. Figure 3A
indicates the angle difference to be ~ . The mismatch of
the angles of inclines of conical sealing surfaces 42 and
41 is selected for any particular seal geometry such that
at final make-up, the bearing load has a relatively even
30 distribution across the entire sealing surface in contact,
thus broadly distributing make-up stresses and minimizing
their negative effects.
Referring to Figure 3A where for the upper step
having the female conical sealing surface 42 machined at an
35 angle slightly less than that of male surface 41, when the
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pin member 30 initially mates with box member 20, the bear-
ing load is substantially on the leadi~g edge of the box
sealing surface 42 with the trailing edge of the pin seal-
ing surface 41. After the sealing surfaces are fully made-
5 up, the stress as a function of axial width becomes moreuniform than for the case where the taper angles of the
sealing surfaces are the same or where the taper angle of
the box sealing surface is greater than the taper angle of
the pin sealing surface.
Metal-to-metal seal taper angles commonly are
provided in a range of from two degrees (2) to fourteen
degrees (14). The exact angular taper mismatch of the
sealing angles of surfaces 41 and 42 varies depending on the
seal angle of the more rigid member, the width of the seal-
15 ing surface, the thickness of the thinner member, desired
tolerances and other factors. It can be shown that seal
mismatch for very low angle seals of approximately one-half
(1~2") inch in axial width can be as low as one-quarter
degree (1/4~. High angle seals of equal axial width may
20 require a mismatch of one degree tl) or more for complete
balancing of bearing loads upon full make-up. Finite ele-
ment analysis may be used as a tool to verify the optimum - ~
seal angle mismatch on any given seal and connection geometry.
Figure 3 also shows that threads 70 and 80 may be
25 interference fitting threads.
Figures 4A and 4B illustrate alternati~e embodi-
ments of the invention. Figure 4A illustrates the reverse
angle torque shoulder 43 between the two step thread.s and
having not only conical sealing surface 40 (as illustrated
30 in Figure 1) on the large step, but also conical sealing
surface 45 on the small step. Alternatively a conical seal-
ing surface 45 could be provided solely on the small step
with no sealing surface being provided on the large step.
Thus, one conical sealing surface provided on either step
35 adjacent the reverse angle torque shoulder, or two seal-
- 8 _ ~2A~038
ing surfaces, one provided on each of the steps, serve in
~onjunction with the reverse angle torque shoulder and the
negative angle load flank threads to create the uni~ue
trapping effect of the invention.
Where as illustrated in Figure 4A, a conical seal-
ing surface is provided as at 45 on the small step and the
female member 20 wall thickness is greater than the thick- e
ness of the male member, the sealing surface of the female ~
member is machined to an angle of incline which is slightly
10 greater than the angle of incline of the sealing surface of
the male member.
Figure 4B illustrates that the combination of
negative load flank threads and reverse angle torque
shoulder between stepped threads may be used for tubular
15 connections or joints having two or more stepped threads.
For example, triple radial step threads 170, 190, and 180
may advantageously be used for thick walled tubulars. Ac-
cording to the invention, reverse angle torque shoulders
43' and 43" are provided between thread steps 170 and 190
20 and between thread oteps 190 and 180. Providing one conical
sealing surface such as 40' or 40" on each axial side of
shoulder 431 and one conical sealing surface such as 41'
or 42' or both 41' and 42' on each axial side of shoulder
43" serves to achieve the trapping effect discussed above
25 when used in combination with negative load flank threads.
More stepped threads with intermediate reverse angle torque
shoulders and associated conical sealing surfaces could ad-
vantageously find applications for tubulars having extreme-
ly thick walls.
In all the embodiments of this invention the mag-
nitude of the negative thread flank angle or the angle of
the reverse angle shoulder should not exceed thirty degrees
(30). In addition, it has been found that the magnitude
of the angle of the conical sealing surfaces relative to
35 the joint axis should not be greater than fifteen degrees
(15). Finally, for that embodiment of the invention il-
lustrated in Figure 3, the dissimilarity of the angles of
~241038
incline of the sealing surfaces of the male and female
members should be less than one degree where the angle of
incline of the member having the greater wall thickness
should be greater than that of the member having the les-
5 ser wall thickness.
From the foregoing, it is apparent that there has
been provided a sealing surface for use in joints, and in- j
terconnecting tubular members especially useful in oil and r
gas wells. Various modifications and alterations in the
10 described structures will be apparent to those skilled in
the art from the foregoing description which do not depart
from the scope of the invention.
