Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TUBULAR CONNECTION FLOATING SHOULDER RING
FIELD OF THE INVENTION
This invention relates to floating shoulder rings used between the ends,
within
the coupling, of taper threaded, shoulderless, pipe connections. Generally,
but not in a
limiting sense, the shoulder ring may be used in pipe strings installed in
wells.
BACKGROUND OF THE INVENTION
Tubulars used to drill and complete wells are typically joined by threaded
connections. The most widely used connections, in casings and tubing, have
tapered
threads without shoulders. Pipe connections depend upon sufficient torque to
seal and
secure the pipe sections in series. The couplings are of somewhat larger
diameter than
the joined pipe ends and have tapered box threads to receive the tapered,
threaded,
ends of the joined pipe sections. The threaded pipe ends are called pins.
Common surface piping connectors are usually called collars but collars in the
well drilling industry are the heavy, thick walled, pipe situated near the bit
that provides
ballast weight to load a drill bit. The term "couplings" will be used herein
to define the
short tube that joins two sections of pipe.
Well bores are seldom straight. They often jog laterally, to some degree,
quite
often. Pipe is normally straight relative to well bores and moving a straight
pipe through
less than straight well bores takes some force. Well bores are usually sized
for the pipe
to move along the well bores with manageable forces. Very often, the pipe
strings have
some cutting structure at the lower end. To negotiate a jog in the well bore
they are
often rotated to ease the downward movement, cutting some formation as
necessary.
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That rotation will often take more torque than the specification torque for
the connection
process. That excess torque may further drive the pin threads into the
couplings.
There is a need to allow the couplings to accept more torque without further
running of
the threads.
The most widely used pipe connections probably are the American Petroleum
Institute (API) standard 8-round (LTC or STC) connections and the industry
standard
coupled buttress (BTC) connections. The related couplings have threads that
advance
into the coupling from both ends and meet in the middle of the coupling with
little or no
smooth cylindrical bore remaining.
Pipe strings extending into wells that have considerable deviation from
vertical
are often rotated, with or without cutting structure on the lower end, as they
are lowered
into wells to enhance the movement into the wells.
The torque required to rotate the pipe when many sections are assembled may
exceed the acceptable torque involved in assembling the pipe string
connections. In
such cases, again, the threads may advance farther into the couplings, often
to a
destructive extent. Recently, more casing strings are fitted with cutting
structure at the
lower end to power through bridges and to deepen drilled wells.
Recently, well drilling is involving more use of the Casing Drilling System
(CDS)
in which usable rotating torque is reflected in well cost reduction. A rather
large part of
the well may be drilled with the casing string carrying a drill head, or
equivalent. The
cost reduction may diminish if shouldered pipe connections have to be used to
carry the
increased torque.
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Pipe strings are often constructed with shoulders. Such shoulders abut and
cause a sharp rise in the torque required to further advance the threads. Such
shouldered connections may take the pipe string rotating torque and avoid
damage to
the connections. Such shouldered pipe connections increase the cost of a pipe
string.
There is a need to enhance the ability of tapered shoulderless threads to
accept
increased torque without consequent damage. With an increase in the ability of
shoulderless connections to accept pipe rotating torque many more wells can be
completed with the more economical, and simpler, threaded arrangements,
without
shoulders.
It is desirable to extend the usefulness of the more economical pipe
connections
by using a shouldering ring that allows the ends of the tapered threaded pipe
sections to
engage a shoulder to prevent pipe rotating torque from overloading the threads
in both
boxes and pins.
The center of the coupling, between pipe ends, has been defined as the J-
space.
The diminishing threads in the center of the coupling can be used to confine a
floating
shoulder ring. The shoulder ring needs to remain in place during handling of
the pipe
but should be able to float when two pipe ends shorten the J-space during
thread make-
up.
A short ring having an inner diameter approximately the pipe bore and an outer
diameter approximating the radial dimension available in the coupling can
engage both
ends of pipe entering the coupling boxes and accept axial thrust that the make-
up of the
connection produces. Excess torque that would damage the threads is accepted
by the
floating ring and reduces the stress that would otherwise distort the threads
and related
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boxes and pins. The ring can provide sealing abutments, against the pipe ends,
that
can enhance the differential pressure acceptable by the connection. This
invention
addresses that objective.
A pipe section normally has one coupling, ideally bucked to specification,
before
it is introduced to the pipe string assembly area which is normally at the
rotary table. It
is also desirable to have the floating torque ring installed before it is
introduced to the
assembly area. The torque ring needs the ability to stay in place during the
pipe
handling. There is often shock to the pipe section while it is prepared for
assembly in
the pipe string. This invention addresses that objective.
The torque rings can be held in place by threads on their outer surface that
mate
with the threads in the coupling. The threads approaching the center of the
coupling,
from both ends, are of the same pitch and lay. When they meet in the middle,
however,
they are not normally in axial registry. The threads on the ring, then, need
to engage
only the threads proceeding from the coupling end receiving the ring.
The ring axial center should be quite close to the axial center of the
coupling,
considering the tolerances involved. On the eight thread standard, about seven
total
threads should be exposed between the pipe ends of the assembled connection.
Almost four threads of the ring entry end of the coupling should be exposed
beyond the
end of the pipe when assembly is complete. Two complete threads on the end of
the
ring toward the open end of the coupling could secure the ring during
handling. The
number of exposed threads may vary for different sizes of pipe involved.
When the pipe sections are delivered to the rig site, the couplings are
usually
bucked on to a pipe section to specifications. If so, the couplings would not
turn farther
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on to the mated pipe section when the final pipe section is torqued to
specification at the
rig. Unfortunately, that is not always the case. Some couplings may turn
farther onto
their mated pipe thread when the last pipe section is properly connected. Such
events
would push the installed ring axially. The ring, if it is already bound
between the pin
ends might not back away along the engaged coupling threads. The threads might
be
forced and cause damage of unpredictable consequence. There is a need for the
threads to yield axially without damage. When the second pipe section is
inserted into
the box of the coupling, the threads on the ring no longer need to function.
The threads
can be of such construction that they can hold the ring in place as required
until loaded,
then fail harmlessly. Failing harmlessly means that the connection is not
compromised
by the failure of the threads on the sleeve. This invention addresses that
problem.
If conditions change and the couplings no longer run farther onto the pipe
string
when the last pipe section is properly made up into the coupling there will be
no need
for threads on the ring that harmlessly yield axially. Normal thread forms can
be used.
That condition is anticipated by, and is within the scope of the claims.
When shoulderless pipe connections are assembled to specification the axial
space between the pipe ends has substantial variance due to allowed
tolerances. The
floating shoulder ring can be supplied in a number of different lengths such
that a
measurement of the mating parts awaiting assembly can suggest an ideal length
to
select from the varieties on hand.
The shoulder ring with shallow, well rounded, threads has been bench tested in
the worst expectable situation, after both pin ends have engaged the ring and
the
coupling runs farther onto the originally installed pipe section. The shallow,
rounded,
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threads on the ring were heard to slip a thread. After removing the last pin
installed, the
ring could be easily removed by hand, with some backward rotation of the ring.
The slip
of the ring past one, or more, thread qualified as harmless failure of the
thread on the
ring.
In some cases, depending somewhat upon the size of the pipe involved, the ring
tends to swage radially inward when sufficient axial loads are imposed by the
pin being
rotated into the coupling. In such cases, the end, or ends, of the ring can be
shaped
slightly conical and opening outward to prevent the distortion of the ring.
That is
anticipated by and is inherent in the claims.
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SUMMARY OF THE INVENTION
A floating shoulder ring is arranged to occupy the J-space between pin ends of
coupled pipe sections. The length of the ring is arranged to allow the pipe
connection to
approach the specified torque for shoulderless connections before the ring
begins to
function as an abutment between the approaching pipe ends. The torque accepted
by
the ring limits the radial force imposed by tapered threads on both pipe and
coupling.
The ring is provided with threads, or modified thread forms, on the outer
surface that
will, to some extent, engage the inner threads of the coupling, in the J-
space, to retain
the ring in the coupling during handling in preparation for assembly into a
pipe string.
Three exemplary, harmlessly yielding, thread forms are provided. They are
harmless in that their destruction, or act of yielding, will not impair the
quality of the
connection involved. The few thread forms presented are some of the possible
forms.
These and other objects, advantages, and features of this invention will be
apparent to those skilled in the art from a consideration of this
specification, including
the attached claims and appended drawings.
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BRIEF DESCRIPTION OF DRAWINGS
In the exemplary drawings, presenting a few selected options, wherein like
features have like captions,
FIG. 1 is a side view of a common pipe connection, sectioned, with the
floating
shoulder ring in place.
FIG. 2 is a portion of the connection of FIG. 1, rather enlarged.
FIG. 3 is a portion of the area shown by FIG. 2, further enlarged.
FIG. 4 is a side view, sectioned, of the floating shoulder ring.
FIG. 5 is an end view along the axis of the floating ring.
FIG. 6A and 6B are enlarged sections through the mating threads of the
floating
ring and the coupling.
FIGS. 7 and 8 show a non-destructive thread substitute on the scale and aspect
of FIG. 6A.
FIGS. 9 and 10 show an alternate thread form that is harmlessly destructive
when forced.
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DETAILED DESCRIPTION OF DRAWINGS
In the drawings, depicting some selected structure of the many variations that
may be employed by the novel features,
FIG. 1 shows a typical pipe connection with the floating shoulder ring 1 in
place,
within the coupling 4 between the ends of the joined pins 2 and 3. The
connection is
shown complete, meaning that prescribed assembly make-up torque has been
applied.
FIG. 2 shows a fragment of the assembly shown in FIG. 1, rather enlarged. The
floating shoulder ring 1 comprises metal ring 1 with modified threads 1d on
the outer
surface. It is situated in the so-called J-space. The threads 1d are of such
diameter,
contour and shape that, when axially forced, will slip axially over mating
threads in
coupling 4 causing allowable material strain but only acceptable, if any,
metal
displacement.
FIG. 3 shows a rather enlarged section cut through one side of FIG. 2 showing
metal ring 1 with the threads 1d on the outer surface.
FIG. 4 shows a side view of ring 1, in section. Generally planar surfaces 1c
are
the ends of the ring 1.
FIG. 5 shows an end view of the floating ring, viewed along the axis of the
floating ring.
FIG. 6A and 6B are taken along line 6-6, and show the axial thread slippage
allowed by the modified threads 1d. The threads are not only shallow but are
well
rounded in the area of expected surface loading when slippage occurs. The best
thread
shape can be determined by experiment and testing. A fragment of coupling 4 is
shown
associated.
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FIGS. 7 and 8 show a coil spring 5 carried in thread-like grooves 5a of the
ring,
now captioned 1 B. Sufficient axial thrust causes the spring 5 to rise from
the grooves to
be carried axially in the threads of the coupling 4. The spring will hold the
ring in place
in the coupling until displaced by axial force caused by the coupling turning
on the pipe
section onto which it was not properly bucked up.
FIGS. 9 and 10 show a weak thread form le on the ring, now captioned 1A,
which will hold enough load to retain the ring in the coupling but will be
bent by greater
axial loads. There is clearance about the base of the thread form to receive
the bent
thread.
When the couplings are properly bucked up on the attached pipe section, the
coupling will not proceed to turn farther onto the pipe string when the last
pipe stand is
assembled onto the pipe string, regular threads can be used on the floating
ring and no
axial displacement of the floating ring in the connector should occur. That is
anticipated
by, and is within the scope, of the claims.
From the foregoing, it will be seen that this invention is one well adapted to
attain
all of the ends and objects hereinabove set forth, together with other
advantages which
are obvious and which are inherent to the apparatus.
It will be understood that certain features and sub-combinations are of
utility and
may be employed without reference to other features and sub-combinations. This
is
contemplated by and is within the scope of the claims.
As many possible embodiments may be made of the assembly of this invention
without departing from the scope thereof, it is to be understood that all
matter herein set
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forth or shown in the accompanying drawings is to be interpreted as
illustrative and not
in a limiting sense.
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