Note: Descriptions are shown in the official language in which they were submitted.
B-2~102
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ALL METAL SEAL FOR PRESSURE SEALING
TECHNICAL FIELD
This invention relates to sealing connections,
and in particular to a self-sealing threaded
connection for use in high pressure environments such
as found in the petroleum industry.
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BACKGROUND OF THE INVENTION
The threaded connection of pipe to form a pipe
string or line is common. Often, some type of
sealing will be required in the connection to prevent
high pressure material within the pipe from entering
the thread area or passing to the exterior of the
pipe. In other applications, the exterior of the
pipe may have the high pressure environment from
which the threads and interior of the pipe must be
protected. One common use of such threaded
connections is in the petroleum industry where long
strings of pipe extend down hole into high pressure,
hot and often corrosive environments.
Many prior seals have been formed in threaded
connections with the use of a sealing element, such
as an O-ring or compression seal. While these can be
effective in certain circumstances, they have several
disadvantages. Initially, it is difficult to assure
that the operator places the seal element in the
proper position as each threaded connection is made
up. This is particularly so in the petroleum
industry. The sealing elements may also be damaged
while the connection is being made up and their
service life is often quite short, particularly in
hostile environments, requiring frequent replacement.
As noted, O-rings have previously been used to
form the seal element. In a typical application, a
first pipe section will have an end known as a pin or
stinger which has a male thread. This end will be
made up with an end of a second pipe which has a box
with female threads for receiving the male threads of
the first pipe. One or more O-rings will be
positioned in annular grooves on either the pin or
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box to seal between the two pipe members. However,
in higher pressure environments, these O-rings tend
to extrude out from the grooves along the annular
space between the two pipe elements, destroying the
integrity of the seal.
In an effort to overcome the disadvantages of a
separate seal element, attempts have been made to
design a self-sealing threaded connection. One
example is disclosed in U.S. Patent No. 3,489,437,
issued January 13, 1970 to Duret. Other examples are
disclosed in U.S. Patent No. 2,258,066 to Oyen; U.S.
Patent No. 2,793,059 to Woodling; U.S. Patent No~
3,856,337 to Ehm; U.S. Patent No. 4,398,756 to Duret
et al.; and U.S. Paten$ No. 4,489,963 to Raulins.
However, none of these prior sealing designs has
proven totally satisfactory. Therefore, a need
exists for a self-sealing threaded connection which
will work reliably within the desired applications.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present
invention, a sealing connection is provided-for
connecting a first member to a second member- with the
passages through each of the members being
connected. Each of the members has an elongate
central axis. The first member has a male end. ~he
male end tor snout) has an annular outer frusto-
conical sealing surface facing radially outward from
the central axis of the first member. The male end
further has an annular inner frusto-conical surface
facing radially inward toward the central axis of the
first member. The minimum diameter of the outer
sealing surface and the maximum diameter of the inner
surface generally coincide. The intersection of the
cone which contains the outer sealing surface and the
cone which contains the inner surface defines a
hypothetical male sealing circle of predetermined
radius about the central axis of the first member
The second pipe has a female sealing pocket. The
female sealing pocket has an annular outer frusto-
conical sealing surface facing radially inward toward
the central axis of the second member. The sealing
pocket also includes an annular inner frusto-conical
~5 surEace facing radially outward from the elongate
axis of the second member. The minimum diameter of
the ouker sealing surface of the sealing pocket and
the maximum diameter of the inner surface of the
sealing pocket generally coincide. The intersection
of the cone which contains the inner surface and the
cone which contains the outer sealing surface defines
a hypothetical female sealing circle of second
predetermined radius about the central axis of the
second member.
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The h~pothetical male sealing circle on the
undeformed male end has a larger radius than the
hypothetical female sealing circle. Structure is
provided to urge the male outer frusto-conical
sealing surface into contact with the female outer
frusto-conical sealing surface, deflecting the male
end radially inward and forming a seal therebetween.
In accordance with another aspect of the present
invention, the outer frusto-conical sealing surface
of the second member extends at an angle relative to
the central axis of the second member be~ween about
10 and 45. The outer frusto-conical sealing
surface on the male end extends at an angle from the
center axis of the first member less than the angle
of the frusto-conical sealing surface of the second
member to ensure contact between the sealing
surfaces. The inner frusto-conical surface of the
first member extends at a lesser angle relative to
its central axis than the inner frusto-conical
surface of the second member to prevent contact
between the inner surfaces prior to a seal being
formed between the outer sealing surfaces.
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BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present
invention, reference is now made to the following
detailed description, taken in conjunction with the
accompanying drawings, in which:
FIGURE 1 is a vertical cross-sectional view of a
threaded connection between a first and second pipe;
FIGURES 2a and 2b illustrate a portion of the
threaded connection illustrating how the male end of
the pin contacts the female sealing pocket, with the
male end being deflected radially inward against the
sealing pocket to form a seal;
FIGURE 3 is a partial cross-sectional view of
the end of the pin illustrating the configuration of
the frusto-conical surfaces at the end;
FIGURE 4 is a partial cross-sectional view of
the box i~lustrating the sealing pocket and the
frusto-conical surfaces thereon;
FIGURE 5 is a partial cross-sectional view of
the male threads;
FIGURE 6 is a partial cross-sectional view of
the female threads; and
FIGURES 7a-7c illustrate the sealing action of
the sealing elements.
DETAILED DESCRIPTION
Referring now to the drawings, wherein like
reference characters designate like or corresponding
parts through several views, FIGURE 1 illustrates a
sealing connection 10 forming a first embodiment of
the present invention. The sealing connection 10 is
made between a first pipe 12 and second pipe 14.
Both pipes 12 and 14 have a uniform thickness 16
along subst~n~ially their entire length and each has
a central axis 13 or 15. The pipes define passages
18 and 20 therethrough which form a continuous
passage for the flow of fluids and the like when the
sealing connection 10 is made.
At the end of the pipe 12 illustrated, a male
member or pin 22 is formed. Similarly, the
illustrated end of the second pipe 14 defines a
female member or box 24. In the usual case, pipe 12
will have a female member at its opposite end, and
pipe 14 a male member at its opposite end for
constructing a pipe string.
Preferably, but not necessarily, the pin 22 has
a tapered male thread 26 which extends along most of
the pin 22, except for an unthreaded male end or
snout 28. As can be seen, the tapered threads taper
radially inwardly toward the snout 28.
The box 24 has mating tapered female threads 30
formed on its inner surface which taper radially
inwardly and terminate at a sealing pocket 32 formed
in the box 24. It will be understood that, while the
embodiment of the invention disclosed herein has
tapered male and female threads 26 and 30, other
mating thread configurations, as well as other
structure for making up the seal, such as clamps,
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bolts etc. can be used while employing the advantages
of the present invention.
With reference now to FIGURES 3 and 7a-c, the
male end 28 of pin 22 can be seen to define an
exterior cylindrical surface 34 which extends
substantially parallel to the center axis 13 of the
first pipe 12. The cylindrical surface 34 can be
seen to merge into the male tapered threads 26 at one
end thereof. However, the opposite end joins with an
outer annular frusto-conical primary sealing surface
36. An inner annular frusto-conical secondary
sealing surface 38 is also provided.
The secondary sealing surface 38 lies radially
within the primary sealing surface 36. As can be
seen, the minimum diameter of the primary sealing
surface 36 is merged into the maximum diameter of the
secondary sealing surface 38. Ideally, it would be
preferred to have surfaces 36 and 38 intersect at a
fixed angle. However, due to limitations in
materials and cutting tools, there will always be a
transition zone 37 between the surEaces 36 and 38, as
best seen in FIGURES 7a-7c. Transition zone 37
preferably has a constant radius of curvature Rs.
If it were possible to form the surfaces 36 and
38 to intersect at a fixed angle, as illustrated by
lines 100 and 102 in FIGURES 7a-7c, the circle
defined by the intersection between the surfaces 36
and 38 would define a hypothetical male sealing
circle 40 at a radius R1 from the center axis 13.
Hypothetical male sealing circle 40 corresponds to
the circle of intersection between the cones on which
surfaces 36 and 38 lie. The male sealing circle 40
would define the furthest extent of the pin 22 into
the box 24 if it were possible to reduce Rs to zero.
With reference now to FIGURES 4 and 7a-c, the
structure of the sealing pocket 32 of box 24 will be
described in greater detail. The sealing pocket 32
defines an interior cylindrical surface 42 which
extends generally along the center axis 15 of the
second pipe 14. The edge of the cylindrical surface
4~ adjacent the end of the box 24 merges into the
female tapered threads 30~ The opposite end of the
cylindrical surface 42 transitions into an outer
annular frusto~conical primary sealing surface 44
which generally faces radially inward. An inner
annular frusto-conical secondary sealing surface 46
extends from the radially innermost portion of the
primary sealing surface ~4 toward the center axis
13. Again, if it were possible, the surfaces 44 and
~6 would intersect at a fixed angle. However, a
transition zone 45 is necessary which preferably has
a constant radius of curvature Rp If it were
possible to form surfaces 44 and 46 to intersect at a
fixed angle, as illustrated by lines 104 and 106 in
P'IGURES 7a~7c, the circle of intersection between
surfaces 44 and 46 would define a hypothetical female
sealing circle 48 have a radius from center axis 15
of R2. ~ypothetical female sealing circle 48
corresponds to the circle of intersection between the
cones on which surfaces 44 and 46 lie. Preferably,
Rs is longer than Rp so sealing contact between the
pin 22 and pocket 32 is avoided within the transition
zone 45. In one connection formed of 4130 steel, a
radius Rs of 0.041" and a Rp of 0.031" proved
satisfactory. A difference in radius of at least
0.010" is recommended as the tolerance in each of the
cutting tools forming zones 37 and 45 is about
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0.005". For other types of materials or cutting
techniques, the difference between Rs and Rp Should
be sufficient to prevent bottoming out in spite of
unavoidable variations in dimensional tolerances.
In the preferred embodiment, the diameter of the
male sealing circle 40 when the male end is
undeformed is larger than the diameter of the
hypothetical female sealing circle 48 by the value
~R. The value of ~R will depend on the materials and
dimensions of the pipes, and the function of the
threaded connection. For a reusable threaded
connection/ the value ~R is chosen so that neither
the snout nor the sealing pocket will be plastically
de~ormed as the seal is made between sealing surfaces
36 and 44. For example, a diameter difference ~R of
O . nos inches for pipe made of 4130 steel with a four
inch O.D. has proven satisfactory. With reference to
FIGURES 2a and 2b, it can be seen that this assures
that the primary sealing surface 36 on the pin 22
will contact the primary sealing surface 44 in the
box 24 as the threads are made up. Further rotation
of the first pipe into the second pipe will then
cause the end 28 of pin 22 to deflect radially inward
toward the now coincident center axes 13 and 15,
while the box 24 will expand radially outward to a
lesser degree at surface 44 due to the greater wall
thickness relative to end 28, with a tight, virtually
line contact metal-to-metal seal being formed between
the primary sealing surfaces 36 and 44. If it were
possible to form the materials of the connection with
Rs and Rp approaching zero, the line of sealing
contact would be between male sealing circlP 40 and a
portion of surface 44. As actually constructed, the
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seal contact will be virtually a line contact between
portions of surfaces 36 and 44.
The outer annular frusto-conical prima-ry sealing
surface 44 preferably lies at an angle to the center
axis 15 of ~etween about 10 and 45, with the
embodiment illustrated having an angle of about
30. To use an angle less than 10 would increase
the risk of plastic deformation of the materials. To
use an angle of more than 45 would increase the
force necessary to make up the seal to an undesirable
level. The outer annular frusto-conical primary
sealin~ surface 36 also preferably lies at an angle
to the center axis 13 in the same range as surface
44, but at an acute angle less than the angle of
1S surface 44. With the radius R1 of the undeformed
hypothetical male sealing circle 40 greater than the
radius R2 of the hypothetical female sealing circle
48, and taking into account average production
tolerances and pin angular deflection upon sealing,
the angle of surface 36 is preferably about 21~o less
than the angle of surface 44. This angle dif~erence
should be sufficient to consistently assure that line
contact sealing will occur (as shown in Figs. 7b
~nd/or 7c) between the pin and the box even
accounting for manufacturing tolerances and pin
deflection. In the embodiment illustrated (see Fig.
3), the surface 36 lies at an angle of 271/2 to axis
13.
~he angles of intersection of surfaces 38 and 46
with axis 13 and 15 are selected so that surface 38
will not contact surface 46 as the primary seal is
made between surfaces 36 and 44. Pre~erably the
angle of intersection of surface 38 with its axis is
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smaller than the angle of intersection of surface 46
with its axis to avoid such contact. In the-
embodiment illustrated, the angles of surface 38 and
surface 46 with their respective axes are 69D and
70, respectively, (or 21 and 20, respectively,
relative to planes perpendicular to their axes as
shown in FIGURES 3 and 4).
As the first pipe is threaded ever tighter into
the second pipe, the radially inward deflection of
the end 28 of the pin 22 simply increases the
effectiveness of the seal between the primary sealing
surface 36 and primary sealing surface 44. As torque
is applied, the radius difference ~R will decrease as
the end 28 and sealing poc3cet 32 deflect, as best
seen in FIGURE 7b. While there will normally be a
small gap between the secondary sealing surfaces 38
and 45, as seen in FIGURE 2b, due to their geometry,
if sufEicient torque is applied, the end 28 and
sealing pocket 32 can be so deformed as to create a
Second seal between the secondary sealing surfaces 38
and 46 as best seen in FIGURE 7c. Preferably, the
pipes 12 and 14 will be formed of materials, and the
dimensions o~ the male end 28 and sealing pocket 32
will be such that the end 28 and sealing poclcet 32
are only elastically deformed when the joint is made
up, permitting multiple use of the connection.
However, limited plastic deformation can be designed
into the connection.
The primary seal between surfaces 36 and 44 is
primarily for resisting bursting pressures from
inside the pipes. Use of the secondary seal between
surfaces 38 and 46 will provide added resistance to
collapse pressures from without.
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As best seen in FIGURES 5 and 6, the tapered
male and female threads 26 and 30 are pre~erably
buttress threads. The engagement faces 50 a~d 52 of
the threads which are in contact as the threaded
connection is made up are preferably tilted at an
angle of 3 from a plane perpendicular to the
respective center axes 13 and 15 of the pipes and
tilted in the direction of motion of the pin 22 as it
is threaded into the box 24. The trailing faces 54
and 56 are preferably formed at an angle of about 10
relative to a plane perpendicular to the center axes
13 and 15 in the direction of movement of the pin 22
as it is unthreaded from the box 24. The height 58
of each tooth 60 on the male thread 26 is preferably
less than the length of the tooth along the center
axis 13. Similarly, the depth 62 of the helical
groove 64 in the female threads 30 is also less than
the length of the groove 64 along the center axis
15.
As can be seen, connection 10 is disclosed which
is capable of multiple reuses while providing an
effective metal-to-metal seal between the pin ~2 and
box 24, without the need of any additional sealing
members. While an effective seal is formed by the
threaded connection 10, it can clearly be
supplemented with other sealing techniques such as O-
rings or compression seals. In addition, the make up
force to form the sealed connection need not be
supplied by a threaded engagement, but can be
supplied by any suitable technique, such as clamps,
bolts, etc.
Although a single embodiment of the invention
has been illustrated in the accompanying drawings and
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described in the foregoing detailed description, it
will be understood the invention is not limited to
the embodiment disclosed, but is capable of ~umerous
rearrangements, modifications and substitutiDns of
parts and elements without departing from the spirit
of the invention.
