Note: Descriptions are shown in the official language in which they were submitted.
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q'hi5 lr~ver~tion relates to a screw coup]ing joirl~,
more especially to a screw coupliny joint Eor rnakirlq erld-to
end connections between pipes for an oil or gas well.
Casing pipes or tubing pipes Eor oil or gas wells
which cornprise a plurality of pipe elements connec-ted -to each
other at a large depth of -the earth. For satisfactory use in
service, -the couplin~ portion is re~uired to have sufficient
strength and sealing ability. In one conventional structure
of coupling joint, the pipe is defined with a male screw on
one end thereof and with a female screw on the o-ther end,
and is provided with a step which forms a stop on an outer
circumferential surface about the -terminal part of the rnale
screw portion. The outer circumference surface on the front
end portion of the male screw and the inner circumferential
surface oE the female screw are provided with smooth tapered
faces. ~nder a condition in which the pipes of such
structure are connected at the ends, the front end portion of
the female screw contacts the step so -that a seal is forrned,
and the smooth face of -the outer circumferential surface at
the front end portion of the male screw is contacted with the
smooth face of the inner circumferential surface of the
female screw so that another seal is formed. In such a
structure having the stop at the male screw, if the female
screw contacts the stop of the male screw, the male screw
cannot be further advanced. Therefore, in order to provide
proper sealing between the smooth surface of the male screw
and the smooth surface of the female screw, the diameters of
those smooth surfaces need to be determined within severe
production tolerances.
In the case of a coupling joint using a sleeve,
generally a female screw is formed on the sleeve, and a male
:~Lq~
screw i~ formed about an end of the pipe, arld a step :i5
formed on the interior of the sleeve to serve as a stop.
Tapered smooth faces are provided on the outer circumferential
surface on the front end of the male screw and the inner
circumferential surface of the interior of the female screw.
In this structure, when the front end portion of the male
screw contacts the step, the seal is made between the smooth
surface of the male screw and the smooth surface of the
female screw. If the male screw contacts the step of the
sleeve at its end point, a further screwing cannot be effected.
Therefore severe production tolerances are required here as
mentioned above.
If the taper of the smooth surface is 1/16 and if the
diameter of the pipe changes O.lmm, the position of the end
portion of the female screw or the male screw changes as much
as 1.6mm in length of the pipe, and the production tolerance
is so severe that it is difficul-t to form a stab]e seal.
Further, the abo~e mentioned coupling joint has
difficulties as more particularly indicated hereinafter.
In the structure of the former coupling joint, a
clearance is made between the front end portion of the male
screw and the terminal portion of the female screw, as a
consequence eddy currents of fluid develop in this clearance
and corrosion occurs there. If a casing pipe were substituted
for such structure, the tubing pipe or the drill pipe to be
served within the casing pipe would be caught, due to the
clearance, at the front end portion of the male screw, and
damage would occur.
In the structure of the latter coupling joint, since
the front end portion of the male screw and the step portion
of the female screw contact each other within the coupling
joint, there OCC-lrS the disadvallt~lcJe that corroslon resi3tant
coating thereon comes o~f due to the metal-to--metal contact.
~ he present invention seeks to provide an irnprovement
in this kind of coupling joint, ancl to overcome the disadvan-
tages mentioned above.
The invention seeks to provide a coupling structure
which may form a satisfactory seal without requiring
severe production tolerances.
The invention also seeks to provide a coupling
structure which may prevent corrosion within the pipe at the
connection of the coupling joint, in which the front end
portion of the female screw contacts the step portion on the
outer circumfexential surface about the terminal part of the
male screw.
The invention furtner seeks to provide a coupling
structure which may prevent damage at the inner wall of the
coupling of the type mentioned above, when a tubing pipe or
the drill pipe is served therein.
Still further the invention seeks to provide a
coupling structure which may form the required seal between
the outer circumference of the smooth surface at the front
end portion of the male screw portion and the inner circum-
ference of the smooth surface at the inner part of the female
screw portion, even though the production tolerance is large
in a coupling joint in which the end portion of the male
screw contacts a step portion at the inner part of -the *emale
screw.
The invention also seeks to provide a coupling
structure which may avoid damage or exfoliation of ~ corrosion
resistant coating.
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In accordance with the invention there iB provid~d a
screw coupling joint for a pipe to be used in an oil or ~as
well, in which plpes are directly contacte~ end-to-end or via
a sleeve, comprising a fernale screw having a step at an inner
part thereof for contact with a front end portion of a male
screw via a packing material to provide a first and a second
seal formed between the front end portion of the male screw
and the packing material.
In particular the invention provides a screw coupling
joint for end~to-end connections between pipes for oil or gas
wells comprising a female screw means and a male screw means
adapted to engage the female screw means to form said joint,
said female screw means having a step defined in an inner
surface of an inner part, and said male screw means having a
first end, and a packing material between said front end and
said step.
In the case of a coupling joint in which the front
end portion of the female screw contacts a step defined on
the outer circumference about the terminal of the male screw,
the pac~cing material closes the clearance between the front
end portion of the male screw and the terminal part of the
female screw.
By contacting the front end portion of the male
screw to the step on the inner circumferential surface at the
inner part of the female screw, the production tolerances are
absorbed by compression of the packing material, and metal-to-
metal contact is avoided between the front end portion of the
male screw and the step at the inner part of the female screw.
The invention is illustrated in particular and
preferred embodiments by reference to the accompanyin~ drawings
in which:
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E`igure 1 :is a vertical c~oss-sectional v:iew showin~J
an embodiment of a coupling for a p:ipe in ~ccorc~ance with the
presen-t invention,
Figure 2 is a ~ertical c~ross-sectional view showing
ano-ther emhodiment of a coupling of the invention,
Figure 3 is a cross-sectional view showing one
embodiment for attachment of the packing material in accordance
with the invention, and
Figure 4 is a cross-sectional view showing another
embodiment for attachment of the packing material in accordance
with the invention.
With further reference to the drawings, Figure 1
illustrates the present invention applied to the direct con-
nection o end-to-end pipes having pipe ends la and lb. Pipe
end la is defined with a male screw 3 and pipe end lb is
defined with a female screw ~. The male screw 3 has, at its
terminal, a step 5 serving as a stop for the female screw 4. An
outer circumferential surface 6 around the step 5 is finished
smoothly. An inner circumferential surface 7 at the end
portion of the female screw ~ is also finished smoothly.
Step 5 is contacted with an end portion 8 of the female screw
4, to produce a first seal A at the contact zone and between
the outer circumferential surface 6 and the inner circumferen-
tial surface 7.
An outer circumferential surface 9 at the front end
portion of male screw 3 is defined with smooth tapered
surface. This smooth tapered surface extends lengthwise and
is convexly curved. An inner circumferential surface 10 of
the terminal part of the female screw 4 is formed smoothly
with a taper corresponding to the taper on outer circvmferen-
tial surface 9. Thus, a second seal B is provided by contact
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of the outer circumferential surface g and the inner
circumferential ~surface 10.
In such a structure, a step 11 is provided at the
inner part oE the female screw 4, [nore particularly, at the
terminal part of the smooth inner circumferential surface 10,
and this step 11 and the front end portion 13 of the male
screw 3 are contacted via a pac~ing material 12 and provide a
third seal C.
With reference to Figure 2 there is shown one
embodiment of the present invention applied to a coupling
structure using a sleeve 2. Sleeve 2 has female screws 4 and
4 formed in length at the both sides of an inner surface. A
central portion thereof is defined by a convex portion 14 both
sides of which serve as stops 11. Each of ends la and lb of
the pipes is defined with a male screw 3. The outer
circumferential surface 9 on the front end part of each male
screw 3 is finished smoothly with a taper. The smooth surface
is formed lengthwise with a convex curvature. The inner
circumferential surface 10 at the terminal part of each
female screws4 is finished smoothly with a taper correspondin~g
~o the taper of the outer circumferential surface 9. A seal
B is formed by contact between the outer circumferential
surface 9 and the inner circumferential surface 10.
Seals C are formed by contact between the respective
steps 11 and the front ends 13 of the male screws 3 via the
packing material 12.
Figures 3 and 4 each show a manner of attaching the
packing material 12. In each case, a concave groove 15 is
formed for holding the packing material 12 of R in cross-
section. The packing material 12 is fixed by means of baking,
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adhesive agent or the l.ike to the concave groove .L5 and thestep 11 at its outer circumference and outer side Eace. In
each of F'igure 3 and ~, the step 11 is formed wi~h an obli-
quity ~1 towarcl the male screw portion with respect to a
vertical line thereof, i.e. the side wall of step 11 is
disposed at an obli~ue angle with respect to the vertical, and
- the packing material 12 is also formed with an obliquity
corresponding to the obliquity l In addition to such a
structure, the packing material 12 in Figure 4 is formed on
the other side with an obliquity in correspondence to which
obliquity ~2 is provided at the end 13 of the male screw. Due
to the step 11, the side face of the packing material 12, and
the obliquity at the front end 13 of the ma:Le screw portion,
the packing material 12 is prevented from protrusion or dropping
toward the i.nterior of the pipe. It is preferable that -the
above oblique angle be not more than 20o
As the packing material, there rnay be used, for
example rubber, Teflon (trade mark), organic substances, for
example synthetic resins including fluorine synthetic resins,
20 and metals whose elastic coefficient is lower than that of
the pipe or the sleeve.
The present invention can be applied to a coupling
joint in which the outer circumferential surface of the male
: screw is straight in an axial direction.
Depending upon the coupling structure of the inven-
tion, the seals A and B are formed as shown in Figure 1 and
the seal A is formed as shown in Figure 2 by screwing the male
screw 3 into the female screw 4. Further, the seal C is
formed between the end portion 13 and the packing material 12
which is compressed by pressing the end portion 13 so that the
sealing effect is as a whole increased.
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Furthermoxe, in the structure where the stopping 5 tep
is provided at the end of the pipe 'hav.ing the rn~le screw, the
pac~ing material 12 closes the clearance between the front end
portion of t'he male screw and the term.inal portion of the
female screw, so that corrosion in this clearance is avoided.
Since the clearance is su'bstantially eliminated, and when the
coupling is used as a casing pipe, damage can be prevented
which is caused by the end portion of the female screw being
caught by the drill pipe or the tubing pipe moving within the
casing pipe.
With respect to the coupling joint having the struc-
ture provided with the step in the female screws4 as shown in
Figure 2, since the male screws 3 are screwed in the female
screws 4 while compressing the packing material 12 until the
outer circumfexential surface 9 at the front end part of each
mal.e screw 3 closely contacts the inner circumferential surface
10 of the female screw, a proper seal B may be provided even
if the sizing tolerances are large.
Thus, the present inventi.on may be applied to both
a coupling structure which directly makes an end-to-end
connection of the pipes and forms the stopping step at the
inner part of the female screw, or to the coupling structure
which uses a sleeve and forms a stopping step on the outer
circumferential surface in the vicinity of the terminal part
of the male screw, and to the other forms of the couplings.
