Specification
THREADED CONNECTION FOR STEEL PIPE
[Teclmical Field of the Invention]
[0001]
The present invention relates to a threaded connection for a steel pipe.
Priority is claimed on Japanese Patent Application No. 2013-184717, filed on
September 6, 2013, the content of which is incorporated herein by reference.
[Related Art]
[0002]
In an oil well or a natural gas well (hereinafter, collectively referred to as an
"oil well"), as oil-well pipes such as a casing or tubing, steel pipes which are
sequentially connected by threaded connections are used. In general, in this kind of
threaded connection, a connection having only a tapered tlu·ead defined by the American
Petroleum Institute standard is applied. The threaded connection is configured of a
first pipe having a tapered male thread portion and a second pipe having a tapered
female thread portion. The male thread pmtion of the first pipe is screwed into the
female thread portion of the second pipe, and thus, the first pipe and the second pipe are
connected to each other.
[0003]
Threaded connections for a steel pipe are roughly classified into two types: a
coupling type and an integral type. In a case of the coupling type, the first pipe is a
steel pipe and the second pipe is a coupling (shmt pipe). In this case, male tlu·ead
pmtions are formed on both end portions of the steel pipe, and female tlu·ead pmtions
are formed on both end portions of the coupling. That is, in the coupling type, steel
pipes adjacent to each other are connected to each other via the coupling.
[0004]
Meanwhile, in a case of the integral type, both the first pipe and the second
pipe are steel pipes, and the coupling is not used. In this case, the male thread portion
is formed on one end portion of the steel pipe, and the female thread pmtion is formed
on the other end portion. That is, in the integral type, the steel pipes adjacent to each
other are directly connected to each other without using the coupling.
[0005]
In general, the connection portion of the first pipe on which the male tln·ead
pmtion is formed includes an element inserted into the female thread portion, and thus,
is referred to as a pin. Meanwhile, the connection portion of the second pipe on which
the female tlu·ead pmtion is formed includes an element receiving the male thread
2
portion, and thus, is referred to as a box. Hereinafter, the connection portion including
the male thread portion is also referred to as the pin, and the connection portion
including the female tlnead portions is also referred to as the box.
[0006]
In the threaded connection for a steel pipe, the male tlu·ead portion of the pin is
screwed into the female tlu·ead pmiion of the box, and the male thread portion and the
female tlu·ead pmiion are fitted in close contact with each other. In this way, in the
tlu·eaded connection of the API standard which does not have a sealing surface
(threadless surface), the male thread portion and the female tlu·ead portion are fitted in
contact with each other, and thus, the sealing performance and pressure resistance of the
tlu·eaded connection are secured.
[0007]
In recent years, according to an increase in depth and severity of circumstances
of oil wells in which the tlu·eaded connection is used, particularly, in a tlu·eaded
connection of a steel pipe having a large diameter used in a casing, a more improved
sealing performance and pressure resistance are required. Accordingly, the threadless
surface (sealing surface) is provided on an outer surface of the pin and an inner surface
of the corresponding box, and a metal touch seal which fits the sealing surfaces is
widely used as a sealing mechanism.
[0008]
In the metal touch seal, an outer diameter of the pin is set to be slightly larger
than an inner diameter ofthe box (this diameter difference is referred to as a "seal
interference amount"). In the metal touch seal, the pin and the box are fitted and
interfere with each other in a radial direction, and an elastic recovery force to return to
the original diameter is generated between the box in which the diameter is increased
and the pin in which the diameter is decreased. The elastic recovery force causes the
sealing surface to tightly come into close contact with sealing surfaces.
[0009]
In order to improve the sealing performance and the pressure resistance,
threaded cmmections disclosed in Patent Documents I to 3 are suggested.
[0010]
For example, in a tlu·eaded connection for a pipe disclosed in Patent Document
I, a seal portion is provided at a position away from a nose tip, a nose portion extends
from the seal portion to a shoulder portion (abutment surface), and thus, the sealing
performance and the pressure resistance are improved.
[0011]
3
In tlu·eaded cmmections for a steel pipe disclosed in Patent Documents 2 and 3,
a first pipe (pin) and a second pipe (box) include tapered threads (male thread portion
and female thread pmiion) which are fitted in close contact with each other, and a
sealing surface and an abutment surface. Accordingly, in the threaded cmmections for
a steel pipe disclosed in Patent Documents 2 and 3, the sealing surfaces of the pin and
the box tightly come into contact with each other according to screwing of the pin, and a
seal (metal touch seal) by a metal contact is formed. In addition, the abutment surfaces
of the pin and the box abut into contact with each other according to the screwing of the
pin, and the abutment surfaces take a role of a stopper which limits the screwing of the
pin, and a role of applying a load in a direction opposite to a screwing direction, that is,
a so-called make-up axial force of a tlu·ead to the male thread portion.
[Citation List]
[Patent Document]
[0012]
[Patent Document 1] Japanese Unexamined Patent Application, First
Publication No. 2012-149760
[Patent Document 2] PCT International Publication No. WO 2011/060894
·[Patent Document 3] Japanese Unexamined Patent Application, First
Publication No. 2012-506000
[Summary of the Invention]
[Problems to be Solved by the Invention]
[0013]
At a site of an oil well, when two pipes are connected to each other, a pin is
screwed into a box using a make-up device referred to as a power tongue. At this time,
since a make-up torque and a screwing state (an increase in the number of make-up
turns) are in a relationship shown in FIG. 8, the screwing state of the pin to the box (a
state of the make-up between the pin and the box) is understood by observing
(measuring) the make-up torque required for the screwing.
[0014]
When the screwing of the pin to the box is normally performed, as shown in
FIG. 8, the make-up torque is smoothly and monotonously increased according to the
screwing state (the increase in the number of make-up turns). Moreover, the abutment
surfaces abut into contact with each other immediately before the screwing is completed,
and thus, the make-up torque is abruptly increased (this is referred to as shouldering).
[0015]
Meanwhile, when abnormality such as galling occurs in a process of the
4
screwing, the make-up torque is excessively increased before the shouldering is
occurred.
[00 16]
In the threaded cmmection for a pipe disclosed in Patent Document 1, the seal
surfaces of the pin and the box slide while coming into contact with each other at a
narrow contact width and a high average contact pressure in a process in which the
threaded connection is screwed and made-up, and thus, occurrence of galling is not
easily prevented. In addition, in the threaded connections for a steel pipe disclosed in
Patent Documents 2 and 3, even when the screwing of the pin to the box is normally
performed, the make-up torque is excessively increased or irregularly changed
(so-called humping ofthe make-up torque occurs) in the process of the screwing.
[0017]
FIG. 10 shows a schematic view showing a relationship between the number of
make-up turns and the make-up torque when the humping of the make-up torque is
occurred. As shown in FIG. 10, if the humping of the make-up torque is occurred in
the process of screwing the pin, it is difficult to correctly understand the screwing state
of the pin. Accordingly, it may be determined that the screwing is completed at the
time of occurrence of the humping. If the completion of the screwing is erroneously
determined, the screwing is not sufficient, and there is a concern that the connection
between the first pipe and the second pipe may be incomplete.
[0018]
Accordingly, the present invention has been made in consideration of the
above-described circumstances, and an object thereof is to provide a threaded
cmmection for a steel pipe capable of preventing humping of a make-up torque which is
occurred when a pin and a box are made-up.
[Means for Solving the Problem]
[0019]
In order to solve the above-described problems, the present invention adopts
the following.
( 1) According to a first aspect of the present invention, there is provided a
threaded cmmection for a steel pipe, which cmmects a first pipe and a second pipe, the
threaded connection including: a box which is an opening end of the second pipe; and a
truncated cone shaped pin which is an end of the first pipe and is inserted into the box,
wherein the pin includes a male thread portion which is a tapered thread, and a seal
portion which includes a tapered surface, and the box includes a female t!u·ead portion
which is a tapered t!n·ead, and a seal portion which includes a tapered surface, and
5
wherein when the male thread portion and the female thread portion are made-up by
screwing, a root of the male thread portion and a crest of the female tlu·ead portion come
into contact with each other after the seal portion of the pin and the seal portion of the
box come into contact with each other, in a process of the make-up, and in a state before
the make-up, a minimum diameter of the tapered surface of the pin is smaller than a
maximum diameter of the tapered surface of the box.
(2) In the aspect according to the above (1), the seal portion of the pin may be
provided on each of a tip side of the pin fi·om the male thread portion and a base side of
the pin fi·om the male thread portion.
(3) In the aspect according to the above (I) or (2), the pin may further include
an R portion which is provided on a tip side of the pin from the seal portion of the pin,
and the box may further include an R pm1ion which is provided on a tip side of the box
from the seal portion of the box.
(4) In the aspect according to any one of the above (1) to (3), the male thread
portion may be divided into a plurality of male thread portions along a pipe axis
direction of the first pipe, and the seal portion of the pin may be further provided
between the male thread pm1ions adjacent to each other in the pipe axis direction.
(5) In th(fa~pect according to any one of the above (I) to (4), the pin may
fmiher include an abutment surface which is provided on a tip or a base of the pin.
(6) In the aspect according to any one of the above (1) to (5), each of the first
pipe and the second pipe may be a steel pipe.
(7) In the aspect according to the above (6), an outer diameter of a body of
the first pipe may be 190 mm or more, an outer diameter of a body of the second pipe
may be 190 nun or more, and in the state before the make-up, an outer diameter of the
box may be more than 100% of the outer diameter of the body of the first pipe, and be
less than 104% of the outer diameter of the body of the first pipe.
(8) In the aspect according to the above (7), in the state before the make-up, a
difference between· the minimum diameter of the tapered surface of the pin and the
maximum diameter of the tapered surface of the box may be more than 0% of the outer
diameter of the body of the first pipe, and be 0.3% or less of the outer diameter of the
body of the first pipe.
(9) In the aspect according to any one of the above (1) to (5), the first pipe
may be a steel pipe and the second pipe may be a coupling.
(10) In the aspect according to the above (9), an outer diameter of a body of
the first pipe may be 190 mm or more.
(11) In the aspect according to the above (I 0), in the state before the make-up,
6
a difference between the minimum diameter of the tapered surface of the pin and the
maximum diameter of the tapered surface of the box may be more than 0% of the outer
diameter of the body of the first pipe, and be 0.3% or less of the outer diameter of the
body of the first pipe.
[Effects of the Invention]
[0020]
According to each of the aspects, it is possible to prevent humping of a
make-up torque which is occurred when a pin and a box are made-up.
[Brief Description of the Drawings]
[0021]
FIG. 1A is a longitudinal sectional view which shows a main portion of a
threaded connection for a steel pipe according to a first embodiment of the present
invention and shows a state before a pin and a box are made-up.
FIG. 1 B is a view showing a begitming of the make-up between the pin and the
box in the tlu·eaded connection for a steel pipe shown in FIG. 1A.
FIG. 1 C is a view showing a state when the make-up between the pin and the
box is completed in the threaded connection for a steel pipe shown in FIG. lA.
FIG. 2Ais an enlarged view of FIG. lB which shows a tip side of the pin.
FIG. 2B is an enlarged view of FIG. 1B which shows a base side of the pin.
FIG. 3A is an enlarged view which shows a portion indicated by X in FIG. 1B
and shows a male tlu·ead portion and a female thread pmtion.
FIG. 3B is an enlarged view which shows a portion indicated by Yin FIG. 1 C
and shows the male thread portion and the female thread portion.
FIG. 4A is a view which shows a state during the make-up between the pin and
the box in the threaded connection for a steel pipe shown in FIG. lA and shows the tip
side of the pin.
FIG. 4B is an enlarged view of FIG. 1 C, and shows the tip side of the pin.
FIG. 5Ais a view which shows the state during the make-up between the pin
and the box in the tlu·eaded connection for a steel pipe shown in FIG. lA and shows the
base side of the pin.
FIG. 5B is an enlarged view of FIG. JC, and shows the base side of the pin.
FIG. 6 is a longitudinal sectional view showing a modified example of the
threaded connection for a steel pipe according to the first embodiment of the present
invention.
FIG. 7 is a longitudinal sectional view showing a tlu·eaded connection for a
steel pipe according to a second embodiment of the present invention.
7
FIG. 8 is a schematic view showing a relationship between the number of
make-up turns and a make-up torque in the threaded connection for a steel pipe
according to the first embodiment of the present invention.
FIG. 9A is an enlarged view which shows the tlu·eaded COimection for a steel
pipe at which humping of the make-up torque is occurred and shows the tip side of the
pm.
FIG. 9B is an enlarged view which shows the threaded connection for a steel
pipe in which the humping of the make-up torque is occurred and shows the base side of
the pin.
FIG. I 0 is a schematic view showing the relationship between the number of
make-up turns and the make-up torque in the threaded connection for a steel pipe in
which the humping of the make-up torque is occurred.
[Embodiments of the Invention]
[0022]
Hereinafter, each embodiment of the present invention will be described in
detail with reference to the drawings. Moreover, in the present specification and the
drawings, the same numeral references are assigned to the same components having
substantially the same function and configuration, and overlapped descriptions thereof
are omitted.
[0023]
(First Embodiment)
[Configuration Example of Threaded Connection for Steel Pipe]
First, a threaded connection I for a steel pipe (hereinafter, also simply referred
to as a "threaded connection") according to a first embodiment of the present invention
will be described. FIGS. lA to lC are longitudinal sectional views showing the
tlu·eaded connection 1 for a steel pipe according to the first embodiment. Moreover,
FIG. lA is a view showing a state before the pin 20 is screwed into the box 30 (a state
before a pin 20 and a box 30 are made-up), FIG. lB is a view showing a state before the
screwing of the pin 20 (a state before the make-up between the pin 20 and the box 30),
and FIG. 1 Cis a view showing a state when the screwing of the pin 20 is completed (a
state when the make-up between the pin 20 and the box 30 is completed). The
make-up between the pin 20 and the box 30 will be described below.
[0024]
As shown in FIGS. lA to lC, the tlll"eaded connection 1 for a steel pipe
according to the first embodiment is used to connect Goin) an upper pipe 2 (a first pipe)
and a lower pipe 3 (a second pipe) in series along a direction of a pipe axis CL
8
(longitudinal direction of a pipe, a connection direction, or a vetiical direction: refer to
FIG. lA). The threaded connection I for a steel pipe includes a truncated cone shaped
pin 20 which is provided on one end (lower end) of the upper pipe 2, and a box 30
which is provided on an opening end (upper end) of the lower pipe 3. In addition, the
threaded connection I for a steel pipe is an integral type threaded connection in which
both the upper pipe 2 and the lower pipe 3 are steel pipes. In addition, hereinafter, the
direction of the pipe axis CL is referred to as a "pipe axis direction".
[0025]
As shown in FIG. I A, in the truncated cone shaped pin 20 provided on the
lower end (one end) of the upper pipe 2, a tip surface 25, a first R portion26 (a first
curved portion), a first seal portion 22, a male thread pmiion 21, a second R portion 27
(a second curved portion), a second seal pmiion 23, and an abutment surface 24 are
provided in this order from a tip side of the pin 20. Moreover, in FIG. lA, the first R
portion 26 and the second R pmiion 27 are not shown. The male thread portion 21 is a
tapered thread and is spirally formed on an outer circumferential surface of the pin 20.
The abutment surface 24 is an annular surface along a radial direction (a direction
perpendicular to the pipe axis direction) and is slightly inclined in the radial direction.
For example, preferably, an inclination angle of the abutment surface 24 is less than or
equal to 20°, and more preferably, is 15°. Here, the tapered thread means a thread
which is provided on an outer surface or an inner surface of a truncated cone.
In addition, in FIG. lA, the lower side is the tip side (front end side) in the pin
20, and the upper side is the tip side (front end side) in the box 30. Moreover, sides
opposite to the tip sides of the pin 20 and the box 30 are referred to as base sides (rear
end sides). Hereinafter, these are similarly applied to all the drawings in the present
specification.
[0026]
Moreover, as shown in FIG. lA, in the box 30 provided on the opening end
(upper end) of the lower pipe 3, a base surface 35, a third seal portion 32, a third R
portion 36 (a third curved pmiion), a female thread portion 31, a fourth seal portion 33,
a fomih R portion 3 7 (a fourth curved portion), and an abutment surface 34 are provided
in this order from a base side of the box 30. Moreover, in FIG. lA, the third R portion
36 and the fourth R portion 37 are not shown. Similar to the male thread portion21,
the female thread portion 31 is a tapered thread and is spirally formed on an itmer
circumferential surface of the box 30.
[0027]
The third seal portion 32, the female thread pmiion 31, the fourth seal pmiion
9
33, and the abutment surface 34 of the box 30 are provided to correspond to the first
seal pmiion 22, the male thread portion 21, the second seal pmiion 23, and the abutment
surface 24 of the pin 20, respectively. Moreover, although it will be described below,
thread teeth of the male thread portion 21 of the pin 20 and thread teeth of the female
thread portion 31 of the box 30 have an invmied trapezoid shape (hereinafter, referred to
·as a dovetail shape) when viewed from a cross section parallel to the pipe axis direction,
and mesh with each other.
[0028]
FIG. 2A is an enlarged view of FIG. 1B, and shows the tip side of the pin 20
(the base side of the box 30). As shown in FIG. 2A, the first seal potiion 22 includes a
first tapered surface 22a (a first seal tapered surface) and a first curvature surface 22b
which are formed on the outer circumferential surface of the pin 20.
[0029]
When the pin 20 is viewed from the cross section parallel to the pipe axis
direction, the first tapered surface 22a is inclined at a predetermined angle (taper angle).
That is, the first tapered surface 22a forms a tmncated cone surface in which the
diameter is gradually decreased from the base side of the pin 20 toward the tip side on
the outer circumferential surface of the pin 20. For example, preferably, the taper
angle of the tapered surface 22a is 2° to 21 o, more preferably, is 2° to 15°, and most
preferably, is 2° tor.
[0030]
When the pin 20 is viewed from the cross section parallel to the pipe axis
direction, the first curvature surface 22b is formed in a curve which is drawn at a
predetermined curvature such as an arc, and smoothly connects the first seal pmiion 22
(first tapered surface 22a) and the male tlu·ead portion21. In this way, the first
curvature surface 22b is provided, the first seal portion 22 (first tapered surface 22a) and
the male thread portion21 are smoothly connected to each other, and thus, it is possible
to prevent galling at the time of the make-up. In addition, the first curvature surface
22b may include an arc and may include a curve other than an arc.
[0031]
The first R portion 26 (a front R portion of the pin 20) of the pin 20 has a slight
and small round shape (refer to an oblique line portion of FIG. 2A), and smoothly
cmmects the first seal portion 22 and the tip surface 25. That is, the first R portion 26
(first curved pmiion) includes a surface (curvature surface orR surface) corresponding
to a circumferential surface of a rotating body which is obtained by rotating a curve
drawn at a predetermined curvature such as an arc around the pipe axis CL. In this
10
way, the first R portion 26 is provided and smoothly connects the first seal portion 22
and the tip surface 25, and thus, it is possible to prevent galling at the time of the
make-up. Moreover, the first R pmtion 26 may include an arc and may include a curve
other than an arc.
[0032]
In addition, as shown in FIG. 2A, the third seal pmtion 32 of the box 30
includes a third tapered surface 32a (a third seal tapered surface). When the box 30 is
viewed from the cross section parallel to the pipe axis direction, the third tapered
surface 32a is inclined at a predetermined angle (taper angle). That is, the third
tapered surface 32a forms a truncated cone surface in which the diameter is gradually
increased from the base side of the box 30 toward the tip side on the inner
circumferential surface of the box 30. For example, preferably, the taper angle of the
third tapered surface 32a is 2° to 21 o, more preferably, is 2° to 15°, and most preferably,
is 2° to 7°.
[0033]
The third R portion 36 (a rear R pmtion of the box 30) of the box 30 has a
slight and large round shape (refer to an oblique line pmtion of FIG. 2A), and smoothly
connects the third seal portion 32 and a rear end 31 e of the female thread portion 31 (not
shown in FIG. 2A). That is, the third R portion 36 (third curved portion) includes a
surface (curvature surface or R surface) corresponding to a circumferential surface of a
rotating body which is obtained by rotating a curve drawn at a predetermined curvature
such as an arc around the pipe axis CL. In this way, the third R portion 36 is provided
and smoothly connects the third seal portion 32 and the rear end 31 e of the female
t1n·ead portion 31, and thus, it is possible to prevent galling at the time of the make-up.
Moreover, the third R portion 36 may include an arc and may include a curve other than
an arc.
[0034]
The taper angle of the first tapered surface 22a of the pin 20, and the taper
angle of the third tapered surface 32a of the box 30 are constant. In addition, the taper
angle of the first tapered surface 22a is substantially the same as the taper angle of the
third tapered surface 32a. Here, the taper angles being substantially the same as each
other means that a difference of ±0.75° is allowed.
[0035)
Moreover, the third tapered surface 32a is longer than the first tapered surface
22a. That is, a distance between a front end 32b and a rear end 32c in the third tapered
surface 32a is longer than a distance between a front end 22c and a rear end 22d in the
first tapered surface 22a.
[0036]
11
In addition, as shown in FIG. 2A, the first seal portion 22, the third seal portion
32, the first R portion 26, and the third R portion 36 are threadless pmiions.
[0037]
Moreover, preferably, the third seal portion 32 is configured of only the third
tapered surface 32a. In this case, since the tapered surfaces come into contact with
each other with a wider surface area, an average contact pressure can be suppressed.
As a result, galling resistance performance can be improved.
[0038]
FIG. 2B is an enlarged view of FIG. lB, and shows the base side of the pin 20
(the tip side of the box 30). As shown in FIG. 2B, the second seal pmiion 23 of the pin
20 includes a second tapered surface 23a (a second seal tapered surface) formed on the
outer circumferential surface of the pin 20.
[0039]
When the pin 20 is viewed fi·om the cross section parallel to the pipe axis
direction, the second tapered surface 23a is inclined at a predetermined angle (taper
angle). That is. the se'1?1\4.1apered surface 23a forms a truncated cone surface in
which the diameter is gradually decreased from the base side of the pin 20 toward the
tip side on the outer circumferential surface of the pin 20. For example, preferably, the
taper angle of the second tapered surface 23a is 2° to 21°, more preferably, is 2° to 15°,
and most preferably, is 2° tor.
[0040]
The second R pmiion 27 (a rear R portion of the pin 20) of the pin 20 has a
slight and large round shape (refer to an oblique line pmiion of FIG. 2B), and smoothly
connects the second seal pmiion 23 and the rear end 2le of the male thread portion 21
(not shown in FIG. 2B). That is, the second R pmiion 27 (second curved portion)
includes a surface (curvature surface or R surface) corresponding to a circumferential
surface of a rotating body which is obtained by rotating a curve drawn at a
predetermined curvature such as an arc around the pipe axis. In this way, the second R
portion 27 is provided and smoothly connects the second seal portion 23 and the rear
end 21 e of the male thread portion 21, and thus, it is possible to prevent galling at the
time of the make-up. Moreove1~ the second R portion 27 may include an arc and may
include a curve other than an arc.
[0041]
The fourth seal portion33 of the box 30 includes a fourth tapered surface 33a
12
(fourth seal tapered surface) and a second curvature surface 33b which are formed on
the inner circumferential surface of the box 30.
[0042]
When the box 30 is viewed from the cross section parallel to the pipe axis
direction, the foutih tapered surface 33a is inclined at a predetermined angle (taper
angle). That is, the fomih tapered surface 33a forms a truncated cone surface in which
the diameter is gradually increased from the base side of the box 30 toward the tip side
on the inner circumferential surface of the box 30. For example, preferably, the taper
angle ofthe fourth tapered surface 33a is 2° to 21°, more preferably, is 2° to 15°, and
most preferably, is 2° tor.
[0043]
When the box 30 is viewed from the cross section parallel to the pipe axis
direction, the second curvature surface 33b forms a curve which is drawn at a
predetermined curvature such as an arc and smoothly connects the fourth seal portion 33
(foutih tapered surface 33a) and the female thread pmiion 31 (not shown in FIG. 2B).
In tltis way, the second curvature surface 33b is provided and smoothly connects the
fomih seal portion 33 (fourth tapered surface 33a) and the female thread portion 31, and
thus, it is possible to prevent galling at the time of the make-up. Moreover, the second
curvature 33b may include an arc and may include a curve other than an arc.
[0044]
The fourth R pmiion 37 of the box 30 (front R portion of the box 30) has a
slight and small round shape (refer to an oblique line potiion of FIG. 2B), and smoothly
connects the fomih seal pmiion 33 and the abutment surface 34 of the box 30. That is,
the fourth R pmiion 37 (fomih curved portion) includes a surface (curvature surface or
R surface) corresponding to a circumferential surface of a rotating body which is
obtained by rotating a curve drawn at a predetermined cmvature such as an arc around
the pipe axis CL. In this way, the fourth R portion 37 is provided, and the fourth seal
pmiion 33 and the abutment surface 34 of the box 30 are smoothly connected to each
other, and thus, it is possible to prevent galling at the time of the make-up. Moreover,
the fomih R portion 37 may include an arc and may include a curve other than an arc.
[0045]
The taper angle of the second tapered surface 23a of the pin 20, and the taper
angle of the fourth tapered surface 33a of the box 30 are constant. In addition, the
taper angle of the second tapered surface 23a is substantially the same as the taper angle
of the fourth tapered surface 33a. Here, the taper angles being substantially the same
as each other means that a difference of ±0.75° is allowed.
13
[0046]
Moreover, the second tapered surface 23a is longer than the fomih tapered
surface 33a. That is, a distance between a front end 33c and a rear end 33d in the
fourth tapered surface 33a is shorter than a distance between a front end 23b and a rear
end 23c in the second tapered surface 23a.
[0047]
In addition, as shown in FIG. 2B, the second seal portion 23, the fourth seal
portion 33, the second R portion 27, and the fomih R portion 37 are tlu·eadless portions.
[0048]
Moreover, preferably, the second seal portion 23 of the pin 20 is configured of
only the second tapered surface 23a. In this case, since the tapered surfaces come into
contact with each other with a wider surface area, an average contact pressure can be
suppressed. As a result, galling resistance performance can be improved.
[0049]
FIG. 3A is an enlarged view which shows a pmiion indicated by X in FIG. IB,
and shows the male thread pmiion 21 and the female thread portion 31. As shown in
FIG. 3A, the male tlu·ead portion 21 includes a crest 2lc, a root 2ld, a stabbing flank
smface 21 a, and a load flank surface 21 b. Since the pin 20 has a tapered shape,
diameters of the crest 21 c and the root 21 d are changed along the pipe axis direction.
The crest 21 c and the root 21 d are parallel to the pipe axis direction. A connection
curved portion is provided in each of the crest 21 c and the root 21 d.
[0050]
In addition, the male tlu·ead portion 21 has a dovetail shape in which a width (a
length of the crest 21 c in the pipe axis direction) of the crest 21 c is wider than a width
of a base portion (a root portion of a tlu·ead tooth).
[0051]
In addition, as shown in FIG. 3A, the female thread portion 31 includes a crest
31c, a root 31d, a stabbing flank smface 31b, and a load flank surface 31a. Since the
box 30 has a tapered shape, diameters of the crest 31c and the root 31d are changed
along the pipe axis direction. The crest 31 c and the root 31 d are parallel to the pipe
axis direction. A cmmection curved pmiion is provided in each of the crest 31c and
the root 31 d.
[0052]
In addition, similar to the male thread portion 21, the female tlu·ead potiion 31
also has a dovetail shape (inverted trapezoid shape).
[0053]
14
The crests 21c and 31c, and the roots 21d and 3ld have widths which arc
changed along the pipe axis direction. For example, a width L of the crest 21c is
represented as follows.
L = Lo +Ax ... (Equation 1)
Here, Lo and A are constants, x is a position along the pipe axis direction, and
the width Lis measured to be parallel to the pipe axis direction.
[0054]
In the threaded connection 1 for a steel pipe, the width of the crest 21 c of the
male thread portion 21 is decreased along the pipe axis direction (that is, the width of
the crest is decreased from the base side of the pin 20 toward the tip side), and the width
of the root 21 d of the male thread p01iion 21 is increased along the pipe axis direction
(that is, the width of the root is increased from the base side of the pin 20 toward the tip
side). Moreover, the width of the crest 31c of the female thread p01iion 31 is increased
along the pipe axis direction (that is, the width of the crest is increased from the tip side
of the box 30 toward the base side), and the width of the root 31 d of the female thread
p01iion 31 is decreased along the pipe axis direction (that is, the width of the root is
decreased from the tip side of the box 30 toward the base side).
[0055]
Next, a process of screwing the pin 20 into the box 30 (a process of a make-up
between the pin 20 and the box 30) will be described.
[0056]
When the upper pipe 2 and the lower pipe 3 are connected to each other (when
the pin 20 and the box 30 are made-up), first, as shown in FIG. lA, the pin 20 is inserted
into the box 30 along the pipe axis direction. Next, the pin 20 is relatively rotated with
respect to the box 30 around the pipe axis CL. In this way, the pin 20 is screwed into
the box 30 along the pipe axis direction, and the screwing of the pin 20 (the make-up
between the pin 20 and the box 30) progresses. That is, the screwing of the pin 20 to
the box 30 progresses from the base side of the pin 20 toward the tip side (a progression
direction of the screwing).
[0057]
As shown in FIG. 3A, in a state when the make-up between the pin 20 and the
box 30 begins, the stabbing flank surface 21a of the male thread portion 21 comes into
contact with the stabbing flank surface 31 b of the female thread portion 31 by the entire
weight of the upper pipe 2. In other words, in the state when the make-up begins,
except for the stabbing flank surfaces 21 a and 31 b, the male tln·ead portion 21 and the
female thread portion 31 do not come into contact with each other.
15
[0058)
If the pin 20 is further screwed into the box 30 along the pipe axis direction
from the state when the make-up begins, which is shown in FIGS. 1 B and 3A, the first
seal portion 22 and the second seal pm1ion 23 of the pin 20 come into close contact with
the third seal portion 32 and the fomih seal pm1ion 33 of the box 30, respectively. If
the pin 20 is further screwed into the box 30 from this state, the root 2ld of the male
thread portion 21 and the crest 31 c of the female thread portion 31 come into contact
with each other.
[0059]
Moreover, if the pin 20 is further screwed into the box 30, as shown in FIG. lC,
the abutment surface 24 of the pin 20 and the abutment surface 34 of the box 30 abut
into contact with each othet~ the abutment surface 24 of the pin 20 is pressed to the
abutment surface 34 of the box 30, and the screwing of the pin 20 (the make-up between
the pin 20 and the box 30) is completed. In this way, the abutment surfaces 24 and 34
abut into contact with each other, the screwing of the pin 20 is limited, and a load in a
direction opposite to the progression direction of the screwing, that is, a make-up axial
force of a thread is applied to the male tlu·ead pm1ion 21 of the pin 20.
[0060]
In addition, as shown in FIG. 1 C, since the first seal pm1ion 22 and the third
seal portion 32 interfere with each other in the radial direction while coming into
contact with each other, a structure (metal touch seal) in which at least a part of the first
seal portion 22 comes into close contact with at least a part of the third seal pmtion 32
over the entire circumference is obtained. The sealing by the first seal pm1ion 22 and
the third seal portion 32 takes a role of mainly sealing an inner pressure Pin of the upper
pipe 2 and the lower pipe 3.
[0061]
Similarly, since the second seal portion 23 and the fourth seal portion 33
interfere with each other in the radial direction while coming into contact with each
other, a stmcture (metal touch seal) in which at least a part of the second seal portion 23
comes into close contact with at least a part of the fourth seal pm1ion 33 over the entire
circumference is obtained. The sealing by the second seal pm1ion 23 and the fourth
seal portion 33 takes a role of mainly sealing an outer pressure Pout of the upper pipe 2
and the lower pipe 3.
[0062]
FIG. 3B is an enlarged view which shows a pm1ion indicated by Yin FIG. 1 C,
and shows the male thread portion and the female tlu·ead pm1ion in a state when the
16
make-up is completed. As shown in FIG. 3B, in the state when the make-up is
completed, the load flank surface 21b of the male t!U"ead pmtion 21 and the load flank
surface 31 a of the female tln·ead pmtion 31 opposing the load flank surface 21 b come
into close contact with each other, and thus, the root 2ld of the male thread portion 21
and the crest 31c of the female tln·ead pmtion 31 come into close contact with each other.
Moreover, as shown in FIG. 3B, in the state when the make-up is completed, there is a
gap between the stabbing flank surface 21a of the pin 20 and the stabbing flank surface
31 b of the box 30 in the pipe axis direction, and there is a gap between the crest 21c of
the pin 20 and the i·oot 31 d of the box 30 in the radial direction.
[0063]
As described above, the pin 20 is screwed into the box 30, the make-up
between the pin 20 and the box 30 is completed, and thus, the upper pipe 2 and the
lower pipe 3 are connected to each other.
[0064]
[Cause of Humping]
Next, a cause in which the humping of the make-up torque occurs will be
described. FIGS. 9A and 9B are enlarged views showing a tln·eaded connection 50 for
a steel pipe in which the humping occurs. In addition, FIG. 9A shows the tip side of
the pin 20 and FIG. 9B shows the base side of the pin 20.
[0065]
As described above, in the state when the make-up between the pin 20 and the
box 30 begins, the stabbing flank surface 21 a of the male thread portion 21 and the
stabbing flank surface 31 b of the female thread portion 31 come into contact with each
other. However, except for the stabbing flank surfaces, the male tln·ead portion 21 and
the female thread portion 31 do not come into contact with each other (refer to FIG. 3A).
That is, in the state when the make-up begins, a gap exists between the root 21 d of the
male thread portion 21 and the crest 31 c of the female thread pmtion 31. In addition,
gaps also exist between the crest 21c of the male thread pmtion 21 and the root 31d of
the female tln·ead portion 31, and between the load flank surface 21 b of the male thread
portion 21 and the load flank surface 31a of the female t!U"ead portion 31.
[0066]
That is, in the state when the make-up between the pin 20 and the 30 begins,
since the male thread portion 21 of the pin 20 and the female thread portion 31 of the
box 30 slightly mesh with each other, there is feasibility in the engagement of the
t!U"eads. Accordingly, in the process in which the screwing progresses, the pipe axis
(center) of the upper pipe 2 and the pipe axis (center) of the lower pipe 3 may be
mis-aligned each other.
[0067]
17
Under these circumstances, in a state before the pin 20 and the box 30 are
made-up, when the pin 20 and the box 30 are in the following (i) and (ii), it is
determined that humping occurs although abnormality such as galling does not occur.
(i) A diameter D 1 of the front end 22c in the first tapered surface 22a of the pin
20 is larger than a diameter D3 of the front end 32b in the third tapered surface 32a of
the box 30 (refer to FIG. 9A). That is, the minimum diameter Dl of the first tapered
surface 22a is larger than the maximum diameter D3 of the third tapered surface 32a.
(ii) A diameter D2 of the front end 23b in the second tapered surface 23a ofthe
pin 20 is larger than a diameter D4 of the front end 33c in the fomth tapered surface 33a
of the box 30 (refer to FIG. 9B). That is, the minimum diameter D2 of the second
tapered surface 23a is larger than the maximum diameter D4 of the fourth tapered
surface 33a of the box 30.
[0068]
Here, the diameter of the tapered surface is a diameter when the truncated cone
shaped seal p01tion configured of the tapered surface is viewed from the cross section
perpendicular to til~; pipe axis direction.
[0069]
In the cases of(i) and (ii), if the make-up between the pin 20 and the box 30
progresses, the humping of the make-up torque occurs due to the following
phenomenon.
[0070]
If the pin 20 is screwed into the box 30 fi·01n the state shown in FIG. 9A, the
first R portion 26 of the pin 20 comes into contact with the third R portion 36 of the box
30 before the f11·st seal p01tion 22 of the pin 20 comes into contact with the third seal
p01tion 32 of the box 30. When the first R portion 26 and the third R portion 36 come
into contact with each other, the first seal p01tion 22 is not smoothly inserted into the
third seal p01tion 32 by the shapes and the dimensions of the curvature surfaces (R
surfaces), and thus, the pipe axis ofthe upper pipe 2 and the pipe axis of the lower pipe
3 are easily mis-aligned each other.
[0071]
Similarly, as shown in FIG. 9B, the second R portion 27 of the pin 20 comes
into contact with the fourth R portion 37 of the box 30 before the second seal p01tion 23
of the pin 20 comes into contact with the fourth seal portion 33 of the box 30. In this
way, when the second R portion 27 and the fomth R portion 37 come into contact with
18
each other, the second seal portion 23 is not smoothly inserted into the fourth seal
pmtion33 by the shapes and the dimensions of the curvature surfaces (R surfaces), and
thus, the pipe axis of the upper pipe 2 and the pipe axis of the lower pipe 3 are easily
mis-aligned each other.
[0072]
As described above, in the state where the first R portion 26 of the pin20
comes into contact with the third R pmtion 36 of the box 30, the pin 20 is screwed into
the box 30 while the first R portion 26 of the pin 20 unstably comes into contact with
the third R portion 36 ofthe box 30. Similarly, in the state where the second R portion
27 of the pin 20 comes into contact with the fomth R portion37 of the box 30, the pin
20 is screwed into the box 30 while the second R pmtion 27 of the pin 20 unstably
comes into contact with the fourth R portion37 of the box 30. As described above,
since there is feasibility in the engagement of the tlu·eads, which is between the male
thread portion 21 of the pin20 and the female thread portion 31 of the box 30, the
unstable screwing generates a temporary increase and irregular variation of the make-up
torque. In this way, the humping of the make-up torque occurs even when the galling
does not occur.
[0073]
In order to prevent the above-described humping, in the tlu·eaded connection 1
for a steel pipe according to the first embodiment, as shown in FIG. 2A, in the state
before the pin 20 and the box 30 are made-up, the diameter D 1 of the front end 22c in
the first tapered surface 22a is smaller than the diameter D3 ofthe front end 32b in the
third tapered surface 32a.
[0074]
Similarly, in the tlu·eaded connection 1 for a steel pipe according to the first
embodiment, as shown in FIG. 28, in the state before the pin 20 and the box 30 are
made-up, the diameter D2 of the front end 23b in the second tapered surface 23a is
smaller than the diameter D4 of the fi·ont end 33c in the fourth tapered surface 33a.
[0075]
That is, in the threaded com1ection 1 for a steel pipe according to the first
embodiment, in the state before the pin 20 and the box 30 are made-up, a first condition
(Dl < D3) in which the minimum diameter D1 of the first tapered surface 22a is smaller
than the maximum diameter D3 of the third tapered surface 32a, and a second condition
(D2 < D4) in which the minimum diameter D2 of the second tapered surface 23a is
smaller than the maximum diameter D4 of the fourth tapered surface 33a of the box 30
are satisfied.
19
[0076]
FIG. 4A is an enlarged view which shows the state in the process of the
make-up between the pin 20 and the box 30, and shows the tip side of the pin 20.
Moreover, the state in the process of the make-up means that the state where the pin 20
is further screwed into the box 30 from the state when the make-up begins, which is
shown in FIG. 2A. In the threaded connection 1 for a steel pipe, as described above, in
the state before the pin 20 and the box 30 are made-up, the pin 20 and the box 30 satisfy
the relationship of the first condition (D I < D3). Accordingly, as shown in FIG. 4A,
the first R portion 26 of the pin 20 does not come into contact with the third R pmtion
36 of the box 30, and the first tapered surface 22a and the third tapered surface 32a
smoothly come into contact with each other.
[0077]
FIG. 4B is an enlarged view which shows the state when the make-up between
the pin 20 and the box 30 is completed, and shows the tip side of the pin 20. As
described below, in the threaded connection I for a steel pipe, the abutment surface 24
of the pin 20 and the abutment surface 34 of the box 30 abut into contact with each
other, and thus, the make-up between the pin 20 and the box 30 is completed (refer to
FIG. SB). As shown in FIG. 4B, in the state when the make-up between the pin 20 and
the box 30 is completed, a part or whole of the first seal pottion 22 comes into close
contact with the third tapered surface 32a over the entire circumference. At this time,
there is a gap between the tip surface 2S of the pin 20 and the base surface 3S of the box
30.
[0078]
Moreover, in the state when the make-up is completed, since the first seal
pmtion 22 and the third seal portion 32 interfere with each other in the radial direction,
the diameters D I and D3 in the state before the make-up do not necessarily coincide
with diameters D I' and D3' in the state when the make-up is completed.
[0079]
Moreover, in FIG. 4B, the first tapered surface 22a and the third tapered surface
32a come into contact with each other. However, at least one of the first curvature
surface 22b and the first tapered surface 22a may come into contact with the third
tapered surface 32a.
[0080]
FIG. SA is an enlarged view which shows the state in the process of the
make-up between the pin 20 and the box 30, and shows the base side of the pin 20.
Moreover, FIG. SA corresponds to FIG. 4A. As described above, in the state before the
20
pin 20 and the box 30 are made-up, the pin 20 and the box 30 satisfy the relationship of
the second condition (D2 < D4). Accordingly, as shown in FIG. SA, the second R
portion27 of the pin20 does not come into contact with the fourth R portion37 of the
box 30, and the second tapered surface 23a and the fourth tapered surface 33a smoothly
come into contact with each other.
[0081]
FIG. SB is an enlarged view which shows the state when the make-up between
the pin 20 and the box 30 is completed, and shows the base side of the pin 20.
Moreover, FIG. SB is a view corresponding to FIG. 4B. As shown in FIG. SB, in the
state when the make-up is completed, a pa1t or whole of the fourth seal pmtion33
comes into close contact with the second tapered surface 23a over the entire
circumference. Moreover, in the threaded connection 1 for a steel pipe, the abutment
surface 24 of the pin20 and the abutment surface 34 of the box 30 abut into contact
with each other, and thus, the make-up between the pin20 and the box 30 is completed.
[0082]
In addition, in the state when the make-up is completed, since the second seal
portion 23 and the fourth seal portion33 interfere with each other in the radial direction,
the diameters D2 and D4 in the state before the make-up do not necessarily coincide
with diameters D2' and D4' in the state when the make-up is completed.
[0083)
Moreover, in FIG. 5B, the second tapered surface 23a and the fomth tapered
surface 33a come into contact with each other. However, at least one of the fourth
tapered surface 33a and the second curvature surface 33b may come into contact with
the second tapered surface 23a.
[0084]
In addition, as described above, when the pin20 and the box 30 are made-up, it
is possible to use a make-up device referred to as a power tong.
[0085]
As described above, in the threaded cmmection I for a steel pipe 1 according to
the first embodiment, the R portions 26 and 27 of the pin 20 do not come into contact
with the R portions 36 and 37 of the box 30, respectively. As a result, in the process in
which the pin 20 is screwed into the box 30, the pipe axis (center) of the pin 20 and the
' pipe axis (center) of the box 30 align with each other, and thus, the screwing is
smoothly performed. Accordingly, it is possible to prevent the humping of the
make-up torque.
[0086)
21
Moreover, when the R portions 26 and 27 of the pin 20 come into contact with
the R portions 36 and 37 of the box 30, since the curvature surfaces come into contact
with each other, the contact area is decreased. In this case, a high contact pressure is
generated in the regions in which the R pot1ions 26 and 27 of the pin20 and the R
portions 36 and 37 of the box 30 come into contact with each other, and thus, galling
easily occurs. However, in the threaded cmmection 1, the contacts between the R
pmtions 26 and 27 of the pin 20 and the R pmtions 36 and 37 of the box 30 can be
avoided, and as a result, it is possible to prevent the galling. Accordingly, in the
tlu·eaded cmmection 1, there is an advantage that the galling does not easily occur.
[0087]
Any of an integral type or a coupling type can be applied to the tlu·eaded
connection 1 according to the first embodiment. In the case of the integral type, both
the upper pipe 2 and the lower pipe 3 are steel pipes. In the case of the coupling type,
the upper pipe 2 is a steel pipe, and the lower pipe 3 is a coupling (short pipe).
[0088]
Moreover, since the humping of the make-up torque easily occurs when steel
pipes having large diameters are connected to each othet~ preferably, the tlu·eaded
connection 1 according to the first embodiment is used to connect steel pipes having
large diameters. For example, in the case of the integral type, preferably, the outer
diameters of the main bodies (portions except for the pin and the box) of the upper pipe
2 (steel pipe) and the lower pipe 3 (steel pipe) are equal to or more than 190 mm, more
preferably, equal to or more than 240 mm, and most preferably, equal to or more than
290mrn.
Moreover, the humping of the make-up torque easily occurs as the thickness of
the box 30 is decreased. For example, in the state before the make-up begins, when
the outer diameter of the box 30 of the lower pipe 3 is more than 100% and less than
104% with respect to the outer diameter of the body (the portion except for the pin 20 in
the upper pipe 2) of the upper pipe 2, the humping of the make-up torque easily occurs.
Accordingly, when the outer diameter of the box 30 of the lower pipe 3 is more than
100% and less than 104% with respect to the outer diameter of the body of the upper
pipe 2, suppression effects with respect to the humping are increased by the threaded
connection 1.
[0089]
The upper limit of the outer diameter of each of the main bodies (the portion
except for the pin 20 in the upper pipe 2 and the portion except for the box 30 in the
lower pipe 3) of the upper pipe 2 and the lower pipe 3 is not particularly limited.
22
However, in a case when used in oil-well pipes, a metal seal is not nearly used in a
tln·eaded connection for an oil-well pipe having a super large diameter (more than 600
mm) such as a conductor which is buried by a shallow depth. In consideration of this,
the threaded connection I can be properly used in a steel pipe in which the outer
diameter of the body is less than or equal to 600 mm.
[0090]
Also in the coupling type, similarly, preferably, the outer diameter of the body·
of the upper pipe 2 (steel pipe) is equal to or more than 190 mm, more preferably, equal
to or more than 240 mm, and most preferably, equal to or more than 290 mm.
[0091]
Here, in general, dimension accuracy of the steel pipe may be decreased as the
size (diameter, length, and the like) of the steel pipe is increased. In the case of steel
pipes having large diameters, in the state before the pin 20 and the box 30 are made-up,
the decrease in the dimension accuracy influences roundness in the seal portions
(tapered surface) of the pin 20 and the box 30. Accordingly, when the threaded
cOimection I according to the first embodiment is used to connect steel pipes having
large diameters, in consideration of the roundness of each seal portion (each tapered
surface), preferab.ly, the diameters Dl and D2 of the pin 20 and the diameters D3 and
D4 of the box 30 in the state before the pin 20 and the box 30 are made-up are properly
designed.
[0092]
Specifically, when differences between the diameters D I and D2 of the pin 20
in the state before the make-up and the diameters D3 and D4 of the box 30 in the state
before the make-up are small, effects of preventing the humping cam10t be sufficiently
obtained when the roundness is greatly decreased. Moreover, when surface treatment
such as chemical conversion treatment or plating is performed on the pin 20 or the box
30, the effect of preventing the humping cannot be sufficiently obtained if the difference
between the dianieter D I and the diameter D3 and the difference between the diameter
D2 and the diameter D4 are not provided to be equal to or more than the thickness of
the surface treatment. In addition, when the contact between the tapered surfaces starts,
since there are many gaps between the male tln·ead potiion 21 and the female tln·ead
portion 31, it is possible to increase the effect of preventing the humping if a margin in
the diameter difference is provided.
Meanwhile, if the differences between the diameters D I and D2 of the pin 20
in the state before the make-up and the diameters D3 and D4 of the box 30 in the state
before the make-up are set more than required, it is necessary to lengthen the tapered
23
surface of the seal portion, and thus, the manufacturing cost is increased due to a
wastefi.ll design.
[0093]
According to the above, preferably, the difference between the diameter D 1 and
the diameter D3, and the difference between the diameter D2 and the diameter D4 are
more than 0% and less than or equal to 0.3% of the outer diameter of the body of the
steel pipe (upper pipe 2), and more preferably, more than 0.05% and less than or equal
to 0.2%.
[0094]
The first embodiment shows the case where the seal pmiions (first seal portion
22 and second seal portion 23) are provided on the tip side and the base side of the pin
20 and the seal portions (third seal portions 32 and fourth seal portion 33)
corresponding thereto are provided on the box 30. However, according to the sealing
performance and the pressure resistance required in the threaded connection 1 for a steel
pipe, the seal portion may be provided on either the front side (tip side) or the rear side
(base side) of the region in which the tapered thread (male thread potiion 21 or the
female thread portion 31) is formed. That is, only any one of the first seal portion 22
and the second seal poriion 23 may be provided, and according to this, the third seal
portion 32 or the foUtih seal portion 33 may be provided on the box 30.
[0095]
In addition, the first embodiment shows the case where the abutment surface 24
of the pin 20 is provided on the base (the rear end of the pin 20) of the pin 20, and
according to this, the abutment surface 34 of the box 30 is provided on the tip (the front
end of the box 30) of the box 30. However, in consideration of the sealing
performance and the pressure resistance required in the tlueaded connection I for a steel
pipe, as shown in FIG. 6, the abutment surface 25a may be provided on the tip surface
25 of the pin 20, and according to this, the abutment surface 35a may be provided on the
base surface of the box 30.
[0096]
(Second Embodiment)
Next, a threaded connection I 00 for a steel pipe according to a second
embodiment of the present invention will be described. Moreover, the same reference
numerals are assigned to the same components as the above-described components, and
the descriptions thereof are omitted below.
[0097]
FIG. 7 is a longitudinal sectional view showing the threaded connection I 00 for
a steel pipe according to the second embodiment. In the first embodiment, only one
region of the tapered thread is formed. Howevet~ in the second embodiment, as shown
in FIG. 7, the male thread portion 21 of the pin 20 is divided into two along the pipe axis
direction, and an upper male thread portion 128 and a lower male thread portion 129 are
formed. Similarly, the female thread portion 31 of the box 30 is divided into two along
the pipe axis direction, and an upper female tlu·ead potiion 138 and a lower female
thread portion 139 are formed. A fifth seal portion 121 is provided on a potiiou (on an
intermediate portion) between the upper male thread portion 128 and the lower male
tln·ead portion 129, and a sixth seal portion 131 is provided on a potiion between the
upper female tluead potiion 138 and the lower female tluead pmiion 139. Moreover,
the fifth seal potiion 121 and the sixth seal portion 131 are configured from a fifth
tapered surface 121 a and a sixth tapered surface 131 a, respectively.
[0098]
Compared to the first embodiment, in the tln·eaded connection 1 00 for a steel
pipe according to the second embodiment, since the fifth seal portion 121 and the sixth
seal portion 131 serve as backup seals even when leak occurs in any one of the first seal
portion 22, the second seal potiion 23, the third seal portion 32, and the fourth seal
pmiion 33, it is possible to fmiher improve the sealing performance and the pressure
resistance.
[0099]
In addition, in the threaded connection 100 according to the second
embodiment, the male threaded connection 21 of the pin 20 may be divided into tln·ee or
more, and the female tln·eaded portion 31 of the box 30 may be divided into tlu·ee or
more. In this case, a seal portion may be provided between the divided male tluead
portions 21, and according to this, a seal portion may be provided between the divided
female thread portions 3 I.
[0100]
In the above, embodiments of the present invention are described. However,
the embodiments are presented as examples, and the scope of the present invention is
not limited to the embodiments. In the embodiments, various aspects can be
performed, and various omissions, replacements, and modification examples can be
performed within a scope which does not depart from the gist of the invention. If the
embodiments or the modification examples are included in claims or the gist of the
invention, the embodiments or the modification examples are included in the scope
equivalent to the inventions described in claims.
[0101]
25
For example, a threaded connection in which the upper pipe 2 (first pipe)
includes the box 30 and the lower pipe 3 (second pipe) includes the pin 20 may be
adopted.
[Example]
[01 02]
In order to confirm effects of the present invention, a steel pipe in which
integral type threaded connections shown in Table I and Table 2 were configured was
manufactured, and a test with respect to make-up between a pin and a box was
performed using a make-up device. Characteristics with respect to a material and
dimensions of the steel pipe are shown in Table 1.
[0103]
[Table 1]
Outer Diameter in
Body of Steel Pipe (mm)
Thickness in
Body of Steel Pipe (mm)
Grade of Steel Pipe
Thread Shape
Thread Pitch
Height of Load Flank Surface
(Load Surface) of Male Thread Portion
Target of Contact Amount
(mm)
(Interference Amount) between Root of
Male Thread Portion and
Crest of Female Thread Portion (mm)
Taper Angle of Seal Portion (degree)
Curvature Radius of First R Portion
(Front R Portion of Pin) (mm)
Curvature Radius of Second R Portion
(Rear R Portion of Pin) (mm)
Curvature Radius of Third R Portion
(Rear R Portion of Box) (mm)
Curvature Radius of Fourth R Portion
(Front R Portion of Box) (mm)
[0104]
406.4
16.66
P110 Steel of API Standard
(0_ 2% Proof Stress 758MPa)
Tapered Thread
having Dovetail Shape
Double-Start Thread having
1. 5 Thread Teeth Per Inch
1.3
0.1
5.7
0.6
8
8
0.6
A dimension relationship between the diameter Dl of the front end in the first
tapered surface of the pin and the diameter 03 of the fi·ont end in the third tapered
surface of the box, and a dimension relationship between the diameter 02 of the front
26
end in the second tapered surface of the pin and the diameter D4 of the front end in the
fourth tapered surface of the box are shown in Table 2.
[0105]
[Table 2]
D1 D3 (mm) D2 D4 (mm)
Example -0. 15 -0.45
Comparative Example 1.2 0. 5
[0106]
In Example, in both the first seal portion and the second seal portion of the pin,
since the diameters D I and D2 ofthe front ends in the tapered surfaces of the pin were
smaller than the diameters D3 and D4 of the front ends in the tapered surfaces of the
box, respectively, as shown in FIG. 8, the humping of the make-up torque did not occur.
In Comparative Example, in both the first seal portion and the second seal portion of the
pin, since the diameters D I and D2 of the front ends in the tapered surfaces of the pin
were larger than the diameters D3 and D4 of the front ends in the tapered surfaces of the
box, respectively, as shown in FIG. 10, the humping of the make-up torque occurred.
[Industrial Applicability]
[01 07]
According to the present invention, it is possible to provide a threaded
com1ection for a steel pipe capable of preventing humping of a make-up torque which is
occurred when a pin and a box are made-up.
[Brief Description of the Reference Symbols]
[0108]
I: threaded coilllection for steel pipe (first embodiment)
2: upper pipe (first pipe)
3: lower pipe (second pipe)
20: pin
21: male thread portion
22: first seal portion (seal portion of pin)
22a: first tapered surface (tapered surface of first seal portion)
22b: first curvature surface (curvature surface of first seal portion)
22c: front end of first tapered surface
22d: rear end of first tapered smface
23: second seal portion (seal p01tion of pin)
23a: second tapered surface (tapered surface of second seal portion)
27
23b: front end of second tapered surface
23c: rear end of second tapered surface
24: abutment surface of pin (base surface of pin)
25: tip surface of pin
26: first R potiion (front R p01iion of pin)
27: second R p01iion (rear R portion of pin)
30:box
31: female thread portion
32: third seal portion (seal portion of box)
32a: third tapered surface (tapered surface of third seal portion)
32b: fi·ont end of third tapered surface
32c: rear end of third tapered surface
33: fourth seal p011ion (seal p01iion of box)
33a: fourth tapered surface (tapered surface of fomih seal potiion)
33b: second curvature surface (curvature surface offomih seal portion)
33c: fi·ont end of fourth tapered surface
33d: rear end of fourth tapered surface
34: abutment surface of box (tip surface of box)
35: base surface of box
36: third R portion (rear R portion of box)
37: fourth R portion (fi·ont R p01iion of box)
100: threaded connection for steel pipe (second embodiment)
121: fifth seal portion (seal portion of pin)
12la: fifth tapered surface (tapered surface of fifth seal p011ion)
128: upper male thread portion
129: lower male thread portion
131: sixth seal portion (seal portion of box)
13la: sixth tapered surface (tapered surface of sixth seal p01iion)
138: upper female thread portion
139: lower female thread portion
D 1: diameter of front end of first tapered surface (minimum diameter of first
tapered surface)
D2: diameter of front end of second tapered surface (minimum diameter of
second tapered surface)
D3: diameter of front end of third tapered surface (maximum diameter of third
tapered surface)
28
04: diameter of front end of fourth tapered surface (maximum diameter of
fomth tapered surface)
CL: pipe axis
Pin: inner pressure
Pout: outer pressure

CLAIMS
I. A threaded cmmection for a steel pipe, which connects a first pipe and a second pipe,
the tln·eaded connection comprising:
a box which is an opening end of the second pipe; and
a truncated cone shaped pin which is an end of the first pipe and is inserted into
the box, wherein
the pin includes a male thread portion which is a tapered thread, and a seal
portion which includes a tapered surface, and
the box includes a female tlu·ead pmtion which is a tapered thread, and a seal
portion which includes a tapered surface, and wherein
when the male thread portion and the female tlu·ead portion are made-up by
screwing, a root of the male thread portion and a crest of the female tlu·ead pmtion come
into contact with each other after the seal portion of the pin and the seal portion of the
box come into contact with each other, in a process of the make-up, and
in a state before the make-up, a minimum diameter ofthe tapered surface of the
pin is smaller than a maximum diameter of the tapered surface of the box.
2. The threaded ~:;onnection for a steel pipe according to Claim 1,
wherein the seal portion of the pin is provided on each of a tip side of the pin
fi·om the male tln·ead portion and a base side of the pin from the male thread pmtion.
3. The tln·eaded connection for a steel pipe according to Claim 1 or 2,
wherein the pin fmiher includes an R portion which is provided on a tip side of
the pin from the seal portion of the pin, and
the box further includes an R portion which is provided on a tip side of the box
fi·om the seal pmiion of the box.
4. The tlu·eaded connection for a steel pipe according to any one of Claims 1 to 3,
wherein the male tln·ead portion is divided into a plurality of male thread
portions along a pipe axis direction of the first pipe, and
the seal portion of the pin is futther provided between the male thread portions
adjacent to each other in the pipe axis direction.
5. The threaded connection for a steel pipe according to any one of Claims 1 to 4,
wherein the pin further includes an abutment surface which is provided on a tip
or a base of the pin.
I
30
. 6. The tiu·eaded cmmection for a steel pipe according to any one of Claims I to 5,
wherein each of the first pipe and the second pipe is a steel pipe.
7. The threaded cmmection for a steel pipe according to Claim 6,
wherein an outer diameter of a body .of the first pipe is 190 mm or more,
an outer diameter of a body of the second pipe is 190 nm1 or more, and
in the state before the make-up, an outer diameter of the box is more than
100% of the outer diameter ofthe body of the first pipe, and is less than 104% of the
outer diameter of the body of the first pipe.
8. The tlu-eaded coru1ection for a steel pipe according to Claim 7,
wherein in the state before the make-up, a difference between the minimum
diameter of the tapered surface of the pin and the maximum diameter of the tapered
surface of the box is more than 0% of the outer diameter of the body of the first pipe,
and is 0.3% or less of the outer diameter of the body of the first pipe.
9. The threaded connection for a steel pipe according to any one of Claims I to 5,
wherein the first pipe is a steel pipe, and
the second pipe is a coupling.
10. The tlu·eaded cotmection for a steel pipe according to Claim 9,
wherein an outer diameter of a body of the first pipe is 190 mm or more.
11. The threaded com1ection for a steel pipe according to Claim 10,
wherein in the state before the make-up, a difference bet\veen the minimum
diameter of the tapered surface of the pin and the ma_ximum diameter of the tapered
surface of the box is more than 0% of the outer diameter of the body of the first pipe,
and is 0.3% or less of the outer diameter of the body of the first pipe.