Note: Descriptions are shown in the official language in which they were submitted.
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REPLACEABLE CORROSION SEAL F(J(~
THREADED CONNECTIONS
Cross Reference to Related Applications
This application is a continuation-in-part of U.S. Patent application Serial
No. 091679470 assigned to the Assignee of the present application.
This application claims priority from U.S. Provisional Patent Application
s Serial No. 60/262,809 filed January 20, 2001 and assigned to the Assignee of
the present application.
Field of the Invention
The present invention relates to threaded connector's used to secure the
ends of tubular bodies together. More particularly, fihe present invention
relates
t t~ to threaded connections provided with replaceable seals to prGtect the
threads
in pipe connections from exposure to corrosive fluids.
Back round of the Invention
Pipelines that extend through saltwater bodies are employed for multiple
purposes, often associated with the drilling of oil and gas wells and the
l5 production and distribution of the oil and gas produced by the wells. When
the
pipelines are not buried or otherwise solidly anchored within the saltwater
body,
they are subjected to dynamic loadings that can eventually cause the
r~ipelines
to rupture or otherwise fail. The stresses induced by dynamic loading in the
connections of the individual tubular bodies forming the pipeline are of
particular
~0 concern.
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Jointed pipelines that are secured together by the fihreaded engagement
of pin and box connectors at the ends of individual pipe sections are employed
in marine riser pipes as well as submerged pipelines and otloer bottom-to-
surface
supply lines. The marine riser pipelines are typically constructed of tubular
pipe
sections that are secured together at their ends by special connectors
designed
to withstand the destructive effects of the dynamic loading acting on the
riser.
The dynamic loading of the riser is caused by changing sea currents, changes
in surface exerted tension resulting from wind and wave action against a
surface
support of the riser, and other factors.
I0 The effects of dynamic loading on the connections used in marine
applications may be offset, in part, by the use of connectors that have the
strength required to withstand the forces imparted by the environment.
Conventional riser connections typically employ heavy tool joint type
connections
that are welded onto the end of the pipe. These connections are very resistant
t; to fatigue damage and often employ a metal-to-metal torque shoulder as an
external seal, similarto the design employed in a conventional drill pipe tool
joint.
Connections of this type have a very low stress concentration factor (SCF) and
provide an environmental seal that prevents the seawater from contacting tire
threads in the connection.
?0 The tool joint design is expensive to machine and requires the added step
and expense of welding the connector to the pipe. The welding procedure also
introduces a potential point of fatigue failure for the dynamically loaded
connector. Moreover, as compared with a conventional threarJed and coupled
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connection, the tool joint type connection is extremely heavy, requiring
additional
surface support.
Conventional threaded and coupled connections have been :~,nccessfr.rlly
employed, for short periods, as the outer riser in a marine installation. Such
s connections cost less than 1/6 the cost of tool joint type connectors. The
long-
term reliability of ti~ese conventional connections in a saltwater-
environment
under dynamic loading conditions, however, is not reasonably predictable. The
uncertainty stems from the fact that, when used as risers, the threads of
conventional threaded and coupled connectors are exposed to salt water that
can accelerate corrosion of the threaded area. The dynamic loading of the
riser
constantly flexes the connections laterally and imposes cyclical tension and
compression stresses in the connected components. Any unendaged pin
threads that have been machined into the pipe portion of the connection are
exposed to the salt water. These exposed threads concentrate the stresses
1 S exerted on the pipe. Adding the effects of corrosion to the cyclical
stress
concentration unreasonably exposes the connection to a fatigue induced failure
that will generally occur in the area of the last full thread 'formed on the
body of
the pin member of the connection.
The strength of a standard threaded and coupled connection is optimized
'_0 by forming the pin threads such that the thread roots "run out" or
continue to
decrease in depth on the external surface of the pipe until they disappear at
a
point referred to as the "last scratch." The final turns of the threads do not
make
a full depth cut into the pipe body and are not normally intended to be
engacded
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and covered by threads in the mating coupling. From the point of the last full
threaded engagement with the box threads to the last scratch of the pin
threads,
. the pin threads in a conventional threadecl and coupled connection are
exposecJ
to the surrounding environment. The corrosive effects of saltwater in this
area
s of exposure can accelerate the failure of a connector subjected to cyclical,
dynamically induced forces.
U.S. Patent Application Serial No. 9/679470, cited previously, discloses
a connector design in which the normally exposed pin runout threads on fully
engaged, threaded and coupled connections are sealed fror~n saltwater to
prevent corrosion of the threaded area that can accelerate fatigue-induced
failure in dynamically loaded pipelines. The seals may be employed with
conventional threaded and coupled connectors pemitting the fabrication of
pipelines that are inexpensive and lightweight as compared with pipelines
constructed with conventional tool joint type connectors.
t 5 The external seal portion of the invention of Application Serial No.
091679470 may be provided by metal-to-metal engagement between the pin and
box or by an elastomeric annular seal compressed between the pin and box.
The metal-to-metal external seal may be provided by engagement of the face of
the box with a shoulder formed on the pin end of a non-upset pipe. The
0 sf~oulder may also be provided by enlarging the pin outside diameter. Where
an
annular, elastomeric seal is provided, the seal may be carried on tl~e outer
surface of the pin body or may be disposed in the box of the connector.
The enlarged outside diameter of the pin portion of the parent application
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connector is formed by expanding the pipe wall radially outwardly. A
frustoconical pin seal surface is machined externally on the enlarged radial
area.
Wf~en the connector is assembled, the pii~ seal surface engryes a
frrrstoconic;al
box seal surface internally adjacent the end of the box. Engagement of the two
seal surfaces forms an external seal that prevents salt water from entering
the
threaded area of the connection. During the manufacturing process, if the pin
seal surface is not properly machined on the expanded body of the pipe, the
entire pipe section can be rendered unusable. Similarly, if a properly
machined
seal becomes defective through subsequent mishandling or usage, tile
1 t~ remaining expanded wall of the pipe may not be adequate for
reconstructing or
repairing the damaged seal, resulting in a loss of the complete pipe joint.
Summary of tire Invention
A metal-to-metal seal between the pin and box connection of a threaded
tubular is formed externally of the pin on a tubular body comprising ~ metal
seal
1 s base that is separately added to the external surface of the metal
fonrring the pin
end of the connection. An important part of the present invention is the
provision
of a third metal seal element in addition to the pin and box components that
is
separately added to the pin component to provide the desired pin seat surface.
In the event the seal formed on the seal base is damaged during
construction, handling or use, the separately added seal base may be removed
from the pin end and replaced with another seal base to provide the required
pin
seal surface. The tubular pipe body or joint on which the pin is forr~ned may
be
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reused multiple times by reconstructing or repairing the pin seal.
The outer surface of a tubular pin end connector is enlarged by welding
a metal buildup onto the surface, or by the placement of an annular metal
bocJy
about the surface, to form an external pin seal base. The pin seal base is
s machined on the welding buildup to form an annular pin sealing surface
adjacent
the pin thread pullout area of a completed threaded pin connection. Wlaerc: an
annular body is used to provide the pin seal base, the annular body rnay be
pre-
machined before being welded to the connector to provide the desired pin seal
surface adjacent the pin thread pullout area. The pin sealing surface formed
by
IO either method is adapted to engage and seal with a mating box seal surface
to
protect the engaged pin and box threads of the connector from contact with the
corrosive fluids within which the connection is deployed.
If the pin seal is improperly cut during the machining process or damaged
during the handling and use of the connector, the welding buildup or annular
1 s metal body may be removed and replaced to provide a new pin sealing
surface.
Only the seal area of the pipe joint is reworked so that the pipe joint is
conserved
during this replacement process. By contrast, repair or reconstruction of a
pin
sealing surface on a pin connector of a pipe joint formed by radially
expanding
a tubular body wall so that the radial enlargement is an integral part of the
pipe
20 joint may not be possible. Such is the case for example where the
enlargement
would not have sufficient radial extension to accommodate the required
machining to effect the repair or where~the tubular wall would be undesirably
reduced in thickness by the required machining repair.
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The enlargement of the pin end connector of the present invention may
be made by applying a weld bead to the outside diameter of the tubular body or
by welding or otloerwise securing an annular metal ring to the external
circumferential surface of the body. Once the enlargement is in place on the
tubular body, the desired pin sealing surface may be machined into the weld
bead or the angular metal ring. The metal ring may also be machined with tloe
desired sealing surface before being secured to the tubular body.
The pin sealing surface may assume the configuration of a firustroconical
surface to provide an expanded area for sealing engagement with a
correspondingly shaped box seal surface or may be formed as an annular band
with a hemispherical cross-section to provide a line contact seal with the box
seal surface.
From the foregoing it will be appreciated that a primary object of tire
present invention is to provide a tubular pipe member having an external pin
seal
t s surface that can be repaired or reconstructed if the seal is improperly
machined
or becomes damaged from handling or use.
It is also an object of the present invention to provide an improved
external seal for protecting the engaged threads in a pin and box connection
from exposure to corrosive fluids surrounding the connection.
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Brief Description of the Drawings
Figure 1 is a quarter section view, partially broken away, illustrating a
frustroconical metal-to-metal sealing surface forming an external sc;al
betwecr r
a coupling box end and a pipe pin end of the preaent invention;
Figure '1A is a detailed cross sectional illustration of the external seal of
the connector il~e present invention;
Figure 2 is a quarter sectional view of a modified coupling and pipe
connection of the present invention illustrating a line-contact, hemispherical
metal-to-metal seal forming an external seal between the pin and box
connection
of the present invention;
Figure 3 is a quarter sectional of view of a modified coupling and pipe
connection of the present invention illustrating a metal-to-metal line-contact
hemispherical seal and an elastomeric seal ring forming an external seal
between the pin and box connection of the present invention;
1, Figure 3A is a detailed cross sectional illustration of the external seal
of
the connector of Figure 3 of the present invention;
Figure 4 is an enlarged to cross sectional view illustrating details in the
formation of a weld bead forming a replaceable pin seal base on which a pin
seal
surface may be machined; and
~0 Figure 5 is an enlarged cross sectional view illustrating details in the
placement of an annular metal ring about a pin connector forming a replaceable
pin seal base on which a pin seal surface may be machined.
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Detailed Description of Preferred Embodiments
Figure 1 of the Drawings illustrates a coupling and pin connection of the
present invention indicated generally at 10. The connection 10 is formed by
llne
engagement of a coupling 15 and pipe 20. The coupling 15 is provided with
s internally threaded boxes 25 and 30 extending axially from either end of a
central
coupling area 35. Threads 40 are formed internally of the box 25 and threads
45 are formed internally of the box 30. The pipe 20 is externally threaded to
form a pin indicated generally at 50. Threads 55 formed on the external
surface
of the pin 50 are illustrated fully engaged with the box threads 40. The
coupling
15 is dimensioned axially to extend over the entire threaded area occupied by
the threads 55.
The connection 10 provides an internal seal 60 and an external seal G5
that protect the threads 40 and 55 from contact with the fluids external and
internal to the coupling and pipe. The threads 55 preferably runout to the
I ~ external surface of the pipe 20 and terminate in a "last scratch" before
reaching
the external seal 65. The internal seal 60 is provided by the metal-to-metal
engagement of the axial end area of the pin 50 with the surrounding wall of
the
coupling and an internal coupling shoulder 70.
As best illustrated in Figure 1A, the external seal 65 is provided by the
_'0 engagement of a frustroconical sealing surface 75 formed internally
adjacent the
open end of tire box 25 with a corresponding frustroconical sealing surface 80
formed externally of a replaceable annular pin seal base 85. The annular pin
seal base 85 is welded or otherwise securely connected to the external surface
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of the pipe 20.
The pin seal base 85 preferably is secured to or formed on the pipe 2~,
before the pin threads 55 are machined on the end of tlw pipe 20. ~l~lm seal
base 85 may be applied to the pipe 20 as a weld bead with a cross section as
s indicated in Figure 4 or it may be applied as a separate metal ring having a
cross
section as indicated in Figure 5. During the process of machining the threads
55 on to the pin end, the seal base is machined to produce the cross sectional
shape illustrated in Figure 1A. It will be appreciated that, in some
applications,
the seal base 85 may be preformed in the cross sectional shape illustrated in
Figure 1A and thereafter secured to the pipe 20, eliminating the need for any
further machining.
Where a line contact external seal is desired, the pin seal base: may be
machined into a hemispherical seal 90 secured to a pipe 95 as illustrated in
Figures 2, 3 and 3A. As with the frustroconical seal illustrated in Figure 1,
the
1 s seal 90 may be constructed by securing a preformecl metal ring with a
hemispherical cross-section to the pipe 95 to eliminate the recluirernent for
machining after the pin seal base is secured to the pipe. In the preferred
fond
of the Invention however, the hemispherical seal is machined with transitions
on
to the pipe body with radius fillets 96 and 97, as illustrated in I=figure 3A,
to
prevent stress risers.
When ttie material providing the pin seal base is improperly machined or
damaged during handling or use, the mafierial forming the pin seal base may be
ground off or otheryvise removed from the external surface of the pipe. The
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described process for forming a weld bead or adding an annular ring may then
be repeated to construct the desired pin seal surface.
Figures 2 and 3 illustrate a modified coupling 15a with a box 30a in which
the external metal-to-metal line contact seal is supplemented with an annular,
s elastomeric seal ring 100. The seal ring is received in an annular groove
105
formed internally of the end of the box 30a.
Figure 4 illustrates a cross section of an annular weld bead 110 provided
about the external circumference of a pipe 115. A dotted outline cross section
120 illustrates the cross sectional shape of the external pin surface
remaining
after the machining process.
Figure 5 illustrates a cross section of an annular metal ring 125 secured
circumferentially externally to a pipe 130. A dotted outline cross section 135
illustrates the cross sectional shape of the external pin surface remaining
after
the machining process. It will be appreciated that the beginning cross
sectional
t , dimensions of the weld bead or of the annular metal ring fon~ing the
external pin
seal base are selected to accommodate the desired final configuration of the
external seal.
While preferred forms of the present invention have been described in
detail herein, it will be appreciated that other forms, modifications and
variations
_'0 of the present invention may be made without departing from the spirit or
scope
of the invention, which is more fully defined within the tenors of the
following
Claims.
