[0001]The present invention relates to a high strength electric resistance welded steel
pipe used for drilling into the ground to improve the ground on an inclined surface or
ground surface in ground stabilization work (including tunneling work or ground
stabilization work), and a method for using a high strength electric resistance welded
steel pipe for ground stabilization work.
Priority is claimed on Japanese Patent Application No. 2019-029437, filed
February 21, 2019, the content of which is incorporated herein by reference.
[Related Art]
[0002]
In recent years, in tunneling work or ground stabilization work for automobile
roads, railways, and the like, construction under harsh environments, including the
need for lengthening and construction on a soft ground, is required. To achieve this, a
ground improver and a structural member having a light weight and high strength are
required, and as the structural member having a light weight and high strength, a high
strength steel pipe has attracted attention.
[0003]
As a method for manufacturing a high strength steel pipe, for example, Patent
Document 1 and Patent Document 2 disclose a technique of heating to a high
- 1 -
temperature after pipe making and then performing rapid cooling to increase the tensile
strength. Furthermore, for example, Patent Document 3 discloses a technique for
improving tensile strength and toughness without a heat treatment after pipe making by
adjusting the chemical composition, yield strength, tensile strength, and yield ratio of
an electric resistance welded steel pipe for oil well casing, tubing, and drilling, which
is a kind of steel pipe buried in the ground, to specific ranges.
[0004]
As described above, in tunnel lengthening and tunnel construction on a soft
ground, it is desirable to use a ground improver and secure heavy equipment and a
work space for injecting the ground improver. However, in recent years, there are an
increasing number of construction examples in narrow spaces where heavy equipment
is difficult to enter, such as mountainous areas, in the construction of tunnels for
highways and high-speed railways. For steel pipes for the above purposes, it is
necessary that after steel pipes with a male thread and a female thread at both pipe ends
are made in a steel pipe manufacturing factory in advance, the steel pipes are processed
by an intermediate worker or at the construction place of the work site or a connection
member having a connection function is joined to both the pipe ends or one end and
transported into the construction place, and then an excavation tool and the steel pipe
or the steel pipes are connected in the work site for use.
[0005]
However, in a case where heavy equipment cannot be used, steel pipes has to
be manually transported and connected, which results in a very heavy physical load on
the workers. Particularly in recent years, with the aging of workers, reducing the load
on workers and securing a labor force have become issues, and as a solution, a steel
pipe member having high strength and a light weight is required.
- 2 -
[0006]
As a steel pipe for this purpose in the related art, for example, there is a steel
pipe according to the standard STK400, which has a tensile strength TS of 400 to 490
N/mm2
, an outer diameter D of 114.3 mm, a thickness t of 6.0 mm, a length L of 3.0 to
3.5 m, and a weight of 48 to 56 kgf/piece. On the other hand, according to the
guidelines for measures to prevent back pain in the workplace under the Labor
Standards Act of Japan, the weight of items handled manually by adult men should be
about 40% or less of the body weight. As a standard example, when the body weight
of an adult male is 70 kgf, the weight that can be handled by one person is 28 kgf.
For this reason, the steel pipe in the related art cannot be handled by a single worker,
and a reduction in the weight of the steel pipe is required from the viewpoint of a
difficulty in securing workers and labor costs.
[0007]
In many cases, a high strength steel pipe for ground stabilization work of the
present application is manufactured at a pipe making factory into a length of about 10
m or more in terms of production efficiency and cost, is cut into the above-mentioned
predetermined length by an intermediate worker or the like, is then subjected to thread
cutting or the like, and is transported to the work site for construction. When the high
strength steel pipe for ground stabilization work driven into the ground, joining with
threads or fitting with high accuracy is used because when the high strength steel pipe
is pressed into the ground, a connection portion needs to maintain the same degree of
strength as the base material portion so that even when there is an obstacle such as full
hard and solid rocks in the ground, the high strength steel pipe does not bend at the
joint portion as the origin and burying and pressing of the high strength steel pipe are
not stopped. If this is a simple fitting by expanding the steel pipe end portion or a
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simply fixing by metal fittings such as bolts, the steel pipe cannot be pressed into the
ground due to an obstacle that causes bending and coming off during burying or due to
metal fittings got stuck, which causes a problem in ground stabilization work and is
thus not preferable. Furthermore, in a case of ground stabilization for a tunnel, the
steel pipe is pressed horizontally, slightly obliquely, or laterally, so that during joining
by welding, it is extremely difficult to perform joining by welding at the work site
while securing linearity in the above directions, and it is also difficult to prepare a
welding apparatus.
[0008]
As seen in Patent Document 3 and the like, many methods have been hitherto
reported for thinning and high-strengthening for a reduction in the weight of the steel
p1pes. In addition, since most of the steel pipes for the above purpose are not
subjected to an operation of rotating the steel pipe itself during ground stabilization
construction such as tunneling work or after construction, the circularity of the pipe
center portion is not required at the time of burying the ground. However, as
described above, since substantially the steel pipe center portion in the length direction
after pipe making (hereinafter, referred to as a steel pipe center portion, a portion
closer to a steel pipe center side than a position Le distant from a steel pipe end portion,
which will be described later, by the outer diameter of the steel pipe before cutting the
steel pipe) is cut into the above-described length L, the steel pipe end portion of a steel
pipe released from a steel pipe manufacturing factory and the steel pipe end portion
formed by cutting a steel pipe at the steel pipe center portion require threading with a
rotary cutting device for joining the steel pipes at the steel pipe end portions, and thus
the steel pipe end portions require high circularity. In addition, although there are
cases where some steel pipe end portions are fitted and connected via one or a plurality
- 4 -
of jigs after similarly cutting the steel pipes into the above-described length L, the steel
pipe end portions also require high circularity for stable joining even in the above cases.
[0009]
As described above, although the steel pipe is a high strength steel pipe for
ground stabilization work requiring high circularity, since the steel pipe is
manufactured by performing cold working on a high strength steel sheet, as the tensile
strength is increased by high-strengthening, the residual stress increases during
working. This is because when the steel pipe is cut into the above-described length L
after pipe making, the residual stress is released at the steel pipe end portion of the cut
portion, and deformation at both the steel pipe end portions increases, so that the
circularity tends to deteriorate.
[0010]
Examples in which steel pipes or high strength steel pipes having a length
close to that of the high strength steel pipe for ground stabilization work are used
include automobile applications such as torsion beams and structural members, and
scaffolding members at building sites. For joining to other members in automobile
applications, mechanical connection such as welding or bolt tightening is the
mainstream, and thread cutting, which is affected by circularity, is rarely used, so that
problems such as those in the present application do not become apparent. This also
applies to scaffolding members at building sites, assembly by tightening with metal
fittings can be achieved. As other steel pipes having similar lengths, there are steel
pipes for residential foundation piles and steel pipes for electric poles for overhead
wues. However, since these steel pipes are connected by pins or simple metal fittings,
the problems as in the present application still do not become apparent.
[0011]
- 5 -
As a case of thread cutting, for example, there is a steel pipe for oil country
tubular goods. However, this is a long material of about 10m, and steel pipes that
secure circularity in a pipe making factory are subjected to thread cutting by an
intermediate worker before or after release and are connected while having the length
during the release for use. Here, there are cases where short materials for several
meters are subjected to thread cutting by an intermediate worker to adjust the length in
the final part of excavation of an oil well that reaches several thousand meters.
However, these cases are very rare, and problems regarding shape changes during
cutting and circularity do not become apparent. The high strength steel pipes for
ground stabilization work need to be cut into short lengths for use, for example, a
length L of 3.0 to 3.5 m from the length at the time of release from the factory, and
need to be connected to one another, so that circularity is important in all the portions
of the connection portions subjected to thread cutting, and there is a possibility that a
joining problem may occur. As described above, it can be said that the deterioration
of circularity at the time of cutting and the problem of joining due to thread cutting,
fitting, and the like are peculiar to the high strength steel pipe for ground stabilization
work.
[0012]
Here, as a technique for improving the circularity of a steel pipe in the related
art, drawing after pipe making and swaging in which a pipe end is pressed into a die
and subjected to warm working are generally known. However, these may be
separate steps from the steel pipe manufacturing line, and cause an increase in the
manufacturing cost. An intermediate worker does not always have swaging facilities,
and as mentioned above, the high strength steel pipe may be cut after being transported
to the construction place. In this case, the cutting cannot be dealt with in the separate
- 6 -
steps, and in the cutting by the intermediate worker and unplanned cutting at a work
site or the like, the cut steel pipe end portion needs to secure circularity. In addition,
tunneling work and ground stabilization work are extensive and use a large amount of
steel pipe, so that the steel pipes are required to be as inexpensive as possible.
[Prior Art Document]
[Patent Document]
[0013]
[Patent Document 1] Japanese Unexamined Patent Application, First
Publication No. S54-19415
[Patent Document 2] Japanese Unexamined Patent Application, First
Publication No. H6-93339
[Patent Document 3] Japanese Patent No. 5131411
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
[0014]
Therefore, the inventors provide a high strength electric resistance welded
steel pipe which has a light weight and high strength and has high circularity at a steel
pipe end portion generated by new cutting after pipe making, and a method for using a
high strength electric resistance welded steel pipe for ground stabilization work.
[Means for Solving the Problem]
[0015]
In order to solve the above problems and achieve the above object, the present
invention has adopted the following aspects.
(1) A high strength electric resistance welded steel pipe according to an aspect
of the present invention includes, by mass% or by mass ppm: C: 0.04% to 0.30%; Si:
- 7 -
0.01% to 2.00%; Mn: 0.50% to 3.00%; P: 0.030% or less; S: 0.030% or less; Al:
0.005% to 0.700%; N: 100 ppm or less; Nb: 0% to 0.100%; V: 0% to 0.100%; Ti: 0%
to 0.200%; Ni: 0% to 1.000%; Cu: 0% to 1.000%; Cr: 0% to 1.000%; Mo: 0% to
1.000%; B: 0 to 50 ppm; Ca: 0 to 100 ppm; REM: 0 to 200 ppm; and a remainder
consisting of Fe and impurities, in which DCave is 60.3 mm to 318.5 mm,
tCave/DCave is 0.02 to 0.06, a tensile strength is 590 N/mm2 or more, and in a case
where a steel pipe center portion is cut, the following expressions are satisfied,
DC ave x (-211 00) :::; x :::; DC ave x (2/1 00) (1)
YN:Sy:SYM (2)
X + K - 3 X SD :::; y :::; X + K + 3 X SD (3)
YM =MIN[ {DEave x (21100) },{ 4 x ((tEave/3)- 0.65)}] (4)
where, in Expression (4), the smaller of {DEave x (21100)} and { 4 x
((tEave/3)- 0.65)} is defined as YM,
YN = MAX[{DEave x (-21100)},{ -4 x ((tEave/3)- 0.65)}] (5)
where, in Expression (5), the larger of [{DEave x (-21100)} and { -4 x
((tEave/3) - 0.65)} is defined as YN,
K ={a+ (~/I)+ (y x TS)} x DCave (6)
SD = (~2) x (a standard deviation of an average outer diameter DCave of the
steel pipe center portion) (7)
a standard deviation of an outer diameter of the steel pipe center portion= {p
+ (q/I) + (r x TS)} x DCave (8)
where x: a vertical ellipticity (steel pipe center portion), y: a vertical ellipticity
(steel pipe end portion), DCave: the average outer diameter (mm) of the steel pipe
center portion after pipe making and before cutting, tCave: an average thickness (mm)
of the steel pipe of the steel pipe center portion after pipe making and before cutting,
- 8 -
DEave: an average outer diameter (mm) of the steel pipe end portion after pipe making
and after cutting, tEave: an average thickness (mm) of the steel pipe end portion after
pipe making and after cutting, TS: a tensile strength (N/mm2
) of a base material
portion of the high strength electric resistance welded steel pipe, a, ~' and y are
constants,
a= -1.87 X 10-3 (9)
~ = 1.35 X 104 (10)
y = -6.65 x 10-6 (11)
I is a second moment of area (mm4
) of a cross section of the steel pipe center
portion,
I = n/64 x { (DCave )4
- (DCave - 2 x tCave )4
}
p, q, and rare constants,
p = 1.39 x 10-3 (13)
q = 4.17 X 102 (14)
r = 6.05 X 10-7 (15).
(12), and
(2) In the high strength electric resistance welded steel pipe according to (1),
the tensile strength may be 780 N/mm2 or more.
(3) In the high strength electric resistance welded steel pipe according to (1)
or (2), the following expression may further be satisfied,
YN - K + 3 x SD :::; x :::; YM - K - 3 x SD (17).
( 4) In the high strength electric resistance welded steel pipe according to (1)
or (2), the following expression may further be satisfied,
DEave x (-21100)- K + 3 x SD:::; x:::; DEave x (2/100)- K- 3 x SD (18).
(5) A method for using a high strength electric resistance welded steel pipe for
ground stabilization work according to another aspect of the present invention,
- 9 -
includes: performing thread cutting on new steel pipe end portions generated by cutting
the high strength electric resistance welded steel pipe according to (1) or (2) at a steel
pipe center portion; and connecting two or more high strength electric resistance
welded steel pipes with a screw joint to be used.
(6) A method for using a high strength electric resistance welded steel pipe for
ground stabilization work according to another aspect of the present invention,
includes: connecting two or more high strength electric resistance welded steel pipes
by fitting one or both of steel pipe end portions of the high strength electric resistance
welded steel pipe according to (1) or (2) to a new steel pipe end portion generated by
performing cutting at a steel pipe center portion, via one or a plurality of jigs to be used.
[Effects of the Invention]
[0016]
According to the present invention, it is possible to provide a high strength
electric resistance welded steel pipe which has a light weight and high strength and has
high circularity at a steel pipe end portion generated by new cutting after pipe making,
and a method for using a high strength electric resistance welded steel pipe for ground
stabilization work. This makes it possible to reduce the load of connection work
between steel pipes and improve the efficiency of construction work at low cost.
[Brief Description of the Drawings]
[0017]
FIG. 1 is a diagram for showing the basis of Le determining the range of a
steel pipe center portion, and showing the relationship between the distance from a
steel pipe end portion I the outer diameter at the position and the difference between
the vertical ellipticity of a cross section at the outer diameter measurement position and
the vertical ellipticity at a 1/2length position in a pipe making direction of a steel pipe,
- 10 -
in which the steel pipe has an outer diameter of 114.3 mm, a thickness of 3.5 mm, and
a length of 7 400 mm.
FIG. 2 is a diagram showing the relationship between the tensile strength of
the steel pipe, and the vertical ellipticity (~DE) of the steel pipe end portion - the
vertical ellipticity (~DC) of the steel pipe center portion, in which the steel pipe has an
outer diameter of 114.3 mm and a thickness of 3.2 to 8.6 mm.
FIG. 3 is a diagram showing the relationship between the tensile strength of a
steel pipe for each sheet thickness and the vertical ellipticity (~DE) of the steel pipe
end portion - the vertical ellipticity (~DC) of the steel pipe center portion, in which the
outer diameter of the steel pipe is 114.3 mm.
FIG. 4 is a graph showing the relationship between the tensile strength of the
steel pipe and the standard deviation of the average outer diameter of the steel pipe
center portion, which is a case where the steel pipe has an outer diameter of 114.3 mm
and a thickness of 3.2 to 8.6 mm.
FIG. 5 is a diagram showing the relationship between the tensile strength of
the steel pipe for each sheet thickness and the standard deviation of the average outer
diameter of the steel pipe center portion, in which the outer diameter of the steel pipe is
114.3 mm.
FIG. 6 is a diagram showing the relationship between the tensile strength of
the steel pipe and the residual stress of the steel pipe center portion, which is a case
where the steel pipe has an outer diameter of 114.3 mm and a thickness of 3.2 to 8.6
mm.
FIG. 7 is a diagram schematically showing a change in the average outer
diameter of the steel pipe end portion when the steel pipe end portion is deformed by
cutting, and the state of a threaded cross section, in which, since the diagram is
- 11 -
schematically shown, the ratio of the outer diameter to the thickness is ignored.
FIG. 8 is a diagram showing the relationship between the vertical ellipticity
~DC of the steel pipe center portion (before cutting) and the vertical ellipticity ~DE of
the steel pipe end portion (after cutting) in a case where threading is performed on the
steel pipe end portion.
FIG. 9 is a diagram showing a more preferable relationship between the
vertical ellipticity ~DC of the steel pipe center portion (before cutting) and the vertical
ellipticity ~DE of the steel pipe end portion (after cutting) in a case where threading is
performed on the steel pipe end portion, in consideration of variations in
manufacturing.
FIG. 10 is a diagram showing the relationship between the vertical ellipticity
~DC of the steel pipe center portion (before cutting) and the vertical ellipticity ~DE of
the steel pipe end portion (after cutting) in a case where threading is performed on the
steel pipe end portion and a region YY is larger than a region AA.
FIG. 11 is a diagram showing the relationship between the vertical ellipticity
~DC of the steel pipe center portion (before cutting) and the vertical ellipticity ~DE of
the steel pipe end portion (after cutting) in a case where threading is performed on the
steel pipe end portion and the region YY is larger than the region AA, in consideration
of variations in manufacturing.
FIG. 12 is a diagram showing the relationship between the vertical ellipticity
~DC of the steel pipe center portion (before cutting) and the vertical ellipticity ~DE of
the steel pipe end portion (after cutting) in a case where the steel pipe end portions are
connected by fitting, (in a case where fitting is performed with jigs).
FIG. 13 is a diagram showing a more preferable relationship between the
vertical ellipticity ~DC of the steel pipe center portion (before cutting) and the vertical
- 12 -
ellipticity ~DE of the steel pipe end portion (after cutting) in the case where the steel
pipe end portions are connected by fitting, in consideration of variations in
manufacturing, (in a case where fitting is performed with jigs).
FIG. 14 is a diagram showing an example of an outline of facilities of a pipe
making machine.
[Embodiments of the Invention]
[0018]
The present inventors measured the cross-sectional dimensions of a steel pipe
at a steel pipe center portion before and after cutting in a case where the steel pipe is
cut into a predetermined length at the steel pipe center portion after pipe making and
investigated in detail changes in the cross-sectional dimensions of the steel pipe caused
by residual stress released by the cutting of the steel pipe. As a result, considering the
dimensional changes caused by the residual stress, the present inventors succeeded in
finding the cross-sectional dimensions of the steel pipe before the cutting with which
the cross-sectional dimensions of the steel pipe after the cutting are suitable for thread
cutting or connection by jigs. The cross-sectional shape of the steel pipe before the
cutting is achieved by adjusting the roll position and the like of each roll stand in a
forming step, a welding step, and a straightening step of pipe making. As will be
described in detail below, regarding manufacturing conditions, step conditions slightly
vary depending on the specifications of pipe making facilities, for example, the number
of roll stages, rolling forces, roll profiles, and the arrangement thereof, and thus the
ranges of the conditions cannot be specified unconditionally. However, the ranges of
the conditions can be specified by finding and adjusting the conditions of each step
suitable for the pipe making facilities through measurement of dimensions and
confirmation of circularity after pipe making.
- 13 -
The steel pipe is often cut by sawing, and may also be cut by a lathe.
In the present specification, there are cases where a "high strength electric
resistance welded steel pipe" is simply referred to as a "steel pipe".
In addition, in the present specification, the numerical range represented by
using "to" means the range including the numerical values before and after "to" as the
lower limit and the upper limit.
[0019]
Next, a high strength electric resistance welded steel pipe according to an
embodiment of the present invention will be described.
The high strength electric resistance welded steel pipe according to the
present embodiment contains, by mass% or by mass ppm, C: 0.04% to 0.30%, Si:
0.01% to 2.00%, Mn: 0.50% to 3.00%, P: 0.030% or less, S: 0.030% or less, Al:
0.005% to 0.700%, N: 100 ppm or less, Nb: 0% to 0.100%, V: 0% to 0.100%, Ti: 0%
to 0.200%, Ni: 0% to 1.000%, Cu: 0% to 1.000%, Cr: 0% to 1.000%, Mo: 0% to
1.000%, B: 0 to 50 ppm, Ca: 0 to 100 ppm, REM: 0 to 200 ppm, and a remainder
consisting of iron and impurities.
The outer diameter (DC ave described later) of the steel pipe is 60.3 mm to
318.5 mm. When the outer diameter of the steel pipe is 60.3 mm or more, a strength
desired by the steel pipe of the present invention can be easily obtained. When the
outer diameter of the steel pipe is 318.5 mm or less, transportation is easy. The outer
diameter of the steel pipe is preferably 113 mm to 116 mm. The outer diameter of the
steel pipe is an average outer diameter.
The ratio ( tCave/DCave) of the thickness ( tCave described later) of the steel
pipe to the outer diameter of the steel pipe (DCave described later) is 0.02 to 0.06.
When the ratio (tCave/DCave) of the thickness of the steel pipe to the outer diameter
- 14 -
of the steel pipe is 0.02 or more, the strength desired by the steel pipe can be easily
achieved. When the ratio (tCave/DCave) of the thickness of the steel pipe to the outer
diameter of the steel pipe is 0.06 or less, the purpose of weight reduction can be easily
achieved.
The tensile strength of the steel pipe is 590 N/mm2 or more. When the
tensile strength is 590 N/mm2 or more, thinning can be achieved, and the weight that
can be transported manually can be easily achieved. The tensile strength is preferably
780 N/mm2 or more. The tensile strength is preferably 1200 N/mm2 or less, and more
preferably 1500 N/mm2 or less.
When the yield ratio of the steel pipe is 86% to 99%, the joint strength of a
thread is increased, which is preferable.
The tensile strength and yield ratio of the steel pipe are obtained by collecting
a test piece of full thickness in a pipe axis direction from the base material portion of
the steel pipe after pipe making and conducting a tensile test in the pipe axis direction.
[0020]
In the present specification and the claims, terms are defined as follows.
Regarding the outer diameter of the steel pipe center portion, a weld is placed at 12
o'clock on a clock, the position thereof is set to oo, any outer diameter in a range of
±45 o is indicated as D 1, and the diameter perpendicular to D 1 is indicated as D3. The
diameter at a position of 45° clockwise from D1 is indicated as D2, and the diameter at
a position of 45° clockwise from D3 is referred to as D4.
[0021]
The outer diameters of the steel pipe center portion at D1, D2, D3, and D4 are
indicated as DC1, DC2, DC3, and DC4, and the average thereof is indicated as DCave
as the average outer diameter of the steel pipe center portion. The inner diameters of
- 15 -
the steel pipe center portion at the positions ofDl, D2, D3, and D4 are indicated as
dCl, dC2, dC3, and dC4, the average thereof is indicated as dCave as the average inner
diameter of the steel pipe center portion, the thicknesses of the steel pipe center portion
at the positions ofDl, D2, D3, and D4 are indicated as tCl, tC2, tC3, and tC4, and the
average thereof is indicated as tCave as the average thickness of the steel pipe center
portion. The units ofDCl, DC2, DC3, DC4, dCl, dC2, dC3, dC4, tCl, tC2, tC3, tC4,
DCave, dCave, and tCave are all mm.
[0022]
Next, regarding the outer diameter of a steel pipe end portion, similarly, a
weld is placed at 12 o'clock on a clock, the position thereof is set to 0°, any outer
diameter in a range of ±45° is indicated as Dl, and the diameter perpendicular to Dl is
indicated as D3. The diameter at a position of 45 o clockwise from D 1 is indicated as
D2, and the diameter at a position of 45° clockwise from D3 is referred to as D4. The
outer diameters of the steel pipe end portion at Dl, D2, D3, and D4 are indicated as
DEl, DE2, DE3, and DE4, and the average thereof is indicated as DEave as the
average outer diameter of the steel pipe end portion. The inner diameters of the steel
pipe end portion at the positions of D 1, D2, D3, and D4 are indicated as dE 1, dE2, dE3,
and dE4, the average thereof is indicated as dEave as the average inner diameter of the
steel pipe end portion, the thicknesses of the steel pipe end portion at the positions of
Dl, D2, D3, and D4 are indicated as tEl, tE2, tE3, and tE4, and the average thereof is
indicated as tEave as the average thickness of the steel pipe end portion. The units of
DEl, DE2, DE3, DE4, dEl, dE2, dE3, dE4, tEl, tE2, tE3, tE4, DEave, dEave, and
tEave are all mm.
[0023]
In a case of cutting the steel pipe at the steel pipe center portion after pipe
- 16 -
making, a portion within a position Le (mm) distant from the steel pipe end portion
toward the center portion of the steel pipe in the longitudinal direction of the steel pipe
by the outer diameter is referred to as the steel pipe end portion, and a portion distant
from Le toward the steel pipe center side is referred to as the steel pipe center portion.
The steel pipe center portion is a range in which residual stress generated during pipe
making is released at the time of cutting the steel pipe and the cross-sectional
dimensions of the steel pipe deform, and an example thereof is shown in FIG. 1. The
horizontal axis in FIG. 1 is "the distance from the steel pipe end portion I the outer
diameter at the position". The vertical axis is "the difference between the vertical
ellipticity of the cross section at an outer diameter measurement position and the
vertical ellipticity at a length 112 position in the pipe making direction". In a case
where "the distance from the steel pipe end portion I the outer diameter at the position"
on the horizontal axis is larger than 1.0, that is, in a case where the position is larger
than the position Le distant from the cut position of the steel pipe end portion toward
the center portion in the longitudinal direction of the steel pipe by the outer diameter of
the steel pipe and is on the steel pipe center side, that is, at the steel pipe center portion
before cutting, "the difference between the vertical ellipticity of the cross section at an
outer diameter measurement position and the vertical ellipticity at a length 112 position
in the longitudinal direction of the steel pipe" is almost zero, which indicates that the
vertical ellipticity is same as that at the 112 position in the length direction of the steel
pipe and there is no deformation.
[0024]
However, in a case of 1.0 or less on the horizontal axis, that is, on the steel
pipe end portion side from the position Le distant from the cut position of the steel pipe
end portion toward the center portion in the longitudinal direction of the steel pipe by
- 17 -
the outer diameter of the steel pipe, "the difference between the vertical ellipticity of
the cross section at an outer diameter measurement position and the vertical ellipticity
at a length 1/2 position in the pipe making direction" fluctuates negatively and
fluctuates toward the negative side in a direction toward the steel pipe end portion.
This indicates that in a case where the steel pipe is cut to become the steel pipe end
portion, the residual stress is released, the deformation of the steel pipe end portion
becomes large, and the circularity deteriorates.
[0025]
Here, the vertical ellipticity (~DE) of the steel pipe end portion and the
vertical ellipticity (~DC) of the steel pipe center portion will be described. When Dl
- D3, which is the difference between Dl and D3 described above in a cross section
perpendicular to the longitudinal direction is indicated as ~D as the vertical ellipticity
at the cross section, a case where a pipe cross section is vertically long satisfies Dl >
D3, so that the vertical ellipticity> 0 is satisfied, while a case where a pipe cross
section is horizontally long satisfies Dl < D3, so that the vertical ellipticity< 0 is
satisfied. In the case of a perfect circle, D 1 = D3 is satisfied, so that the vertical
ellipticity= 0 is satisfied. Therefore, the vertical ellipticity (~DE) of the steel pipe
end portion and the vertical ellipticity (~DC) of the steel pipe center portion are
Vertical ellipticity ~DC of the steel pipe center portion = DC 1 - DC3 ( 19)
Vertical ellipticity ~DE of the steel pipe end portion =DEl - DE3 (20).
[0026]
The cut position of the steel pipe, that is, the steel pipe end portion also
includes a position cut to collect a product during pipe making, both ends of a steel
pipe product at the time of release after pipe making, and a steel pipe end portion
formed by cutting by an intermediate worker or at a construction place of a work site.
- 18 -
Samples 1 and 2 in FIG. 1 have an outer diameter of 114.3 mm, a thickness of 3.5 mm,
a TS of 1000 N/mm2
, and a length L of 2000 mm to 5000 mm when a steel pipe end
portion is newly formed by cutting.
[0027]
The inventors investigated the difference between the vertical ellipticity
(~DE) of the steel pipe end portion and the vertical ellipticity (~DC) of the steel pipe
center portion at various tensile strengths in a case of an outer diameter of 114.3 mm
and a thickness of 3.2 to 8.6 mm. As a result, as shown in FIG. 2, the relationship(=
slope) of the effect of the tensile strength from the data of thicknesses of 3.2 to 3.5 mm
is clarified, and considering that this relationship is the same for each thickness, the
relationship with the thickness is clarified. When this is arranged for each thickness,
it was found that in a case of an outer diameter of 114.3 mm, there is a relationship of
FIG. 3 and Expression (21).
~DE= ~DC+ K (21)
Here, K is a constant obtained by Expression (6).
K ={a+ (~/I)+ (y x TS)} x DCave (6)
Here, TS is the tensile strength (N/mm2
) of the base material portion of the
steel pipe, and a,~' andy are constants satisfying a= -1.87 x 10-3
, ~ = 1.35 x 104
, and
y = -6.65 x 10-6
. I is the second moment of area (mm4
) of the cross section of the
steel pipe center portion, and is derived by Expression (12) below.
I= n/64 x { (DCave)4
- (DCave- 2 x tCave)4
} (12)
FIG. 3 shows an example of the calculation result of Expression (21) for each
sheet thickness.
[0028]
The inventors investigated the standard deviation of the average outer
- 19 -
diameter of the steel pipe center portion at various tensile strengths in the case of an
outer diameter of 114.3 mm and a thickness of 3.2 to 8.6 mm, as shown in FIG. 4. As
a result, as shown in FIG. 4, the relationship ( = slope) of the effect of the tensile
strength from the data of thicknesses of 3.2 to 3.5 mm is clarified, and considering that
this relationship is the same for each thickness, the relationship with the thickness is
clarified. When this is arranged for each thickness, it was found that in a case of an
outer diameter of 114.3 mm, there is a relationship of FIG. 5 and Expression (8).
Standard deviation of the average outer diameter of the steel pipe center
portion= {p + (q/I) + (r x TS)} x DCave (8)
Here, TS is the tensile strength (N/mm2
) of the base material portion of the
steel pipe, and p, q, and rare constants satisfying p = 1.39 x 10-3
, q = 4.17 x 102
, r =
6.05 x 10-7
• I is the second moment of area (mm4
) of the cross section of the steel
pipe center portion, and is derived by Expression (12) described above. FIG. 5 shows
an example of the calculation result of Expression (8) for each sheet thickness.
[0029]
In a case where steel pipes of the corresponding application are used by
connecting a plurality of steel pipes, there are two use methods. One is a method of
using steel pipes by directly threading both pipe ends of the steel pipes to form male
threads and female threads with a rotary cutting device and connecting the steel pipes,
and the other is a method of using steel pipes by fitting and connecting steel pipe end
portions via one or a plurality of jigs between the steel pipes.
[0030]
In the method of performing threading with the rotary cutting device, in order
to secure threading accuracy during processing and a threading function of a product,
and in the method of fitting the steel pipe end portions via one or a plurality of jigs
- 20 -
between the steel pipes, in order to secure the strength at the fitting surface, it is
necessary to secure high circularity as well as the outer diameter tolerance of the steel
pipes at the pipe end. Regarding the weight reduction by high-strengthening, which
is the object of the present invention, as shown in FIG. 6 as an example in the case of
an outer diameter of 114.3 mm and thicknesses of 3.2 to 8.6 mm, the higher the
strength, the higher the residual stress of the steel pipe. Therefore, at the steel pipe
end portion in the vicinity of the cut position, the residual stress is released and the
deformation force is exerted. In a case of a thin thickness, deformation is more likely
to occur, and a change in the vertical ellipticity of the pipe end tends to increase.
Therefore, securing the vertical ellipticity is an issue. The residual stress is measured
by the Crampton method (for example, described in Nippon Steel & Sumitomo Metal
Technical Report No. 397 (2013) p. 31).
[0031]
In FIG. 7, in a case where the steel pipe end portion is directly threaded, in a
case where design values of the threading, that is, the outer diameter and the thickness
are average values, in a case where the cross section is vertically long (vertical
ellipticity> 0), a change in the cross section due to the threading is schematically
shown. In FIG. 7, in order to describe the principle, the ratio between the outer
diameter and the thickness of an actual steel pipe is ignored.
[0032]
As shown in the cross section of the threaded portion in the length direction in
FIG. 7, in both male and female threads, there is a residual thickness portion which is
not cut with respect to the average thickness. For thinning and high-strengthening, it
is necessary to make the residual thickness as small as possible while securing the
strength of the entire joint and securing the soundness of the thread shape, so that it is
- 21 -
required to cause the vertical ellipticity of the steel pipe end portion to be within a
certain range. The residual thickness portion is a portion represented by Expressions
(22) and (23 ),
Residual thickness portion of the male thread = (male thread valley diameter
min - inner diameter) I 2 (22)
where inner diameter= outer diameter-2 x thickness,
Residual thickness portion of the female thread = (outer diameter - female thread
valley diameter max) I 2 (23).
[0033]
Therefore, based on the above new findings, the inventors clarified the
relationship between the vertical ellipticities of the steel pipe center portion and the
steel pipe end portions in a case where the tensile strength and size vary, that is,
clarified the relationship of the vertical ellipticity before and after cutting the steel pipe
into a predetermined length L, and found a method of causing the steel pipe end
portion after cutting the steel pipe to have high circularity by adjusting and controlling
the vertical ellipticity of the pipe center portion in forming and shaping steps during
pipe making and causing the vertical ellipticities of the steel pipe center portion, that is,
the steel pipe center portion before the cutting and the steel pipe end portion after the
cutting to be within predetermined ranges.
[0034]
FIG. 8 describes a case where the steel pipe end portions are directly threaded
with a cutting device to form male and female threads. Regarding the relationship
between the vertical ellipticity ~DC of the steel pipe center portion and the vertical
ellipticity ~DE of the steel pipe end portion, the shape of the steel pipe end portion to
be secured to secure a necessary threading function while achieving a reduction in the
- 22 -
weight of the steel pipe by making the residual thickness as small as possible through
thread cutting, that is, the steel pipe end portion after cutting is such that ~DC and
~DE satisfy a region (hereinafter, referred to as a region XX) surrounded by a region
AA and a region YY described below.
[0035]
Here, in FIG. 8, the region AA is a region required to secure the outer
diameter tolerance, is a region surrounded by points AI, A2, A3, and A4 in FIG. 8, and
is a range in which the steel pipe center portion and the steel pipe end portion satisfy
the outer diameter tolerance (No. I tolerance)± I% specified in JIS G 3444 (20I6),
Steel tube for structural purposes. The outer diameter tolerance may be changed
according to the standard. This range is a condition necessary to secure the required
circular shape when used as a structural pipe, and in a case where this range is not
satisfied, the bending moment required for a steel tube for structural purposes cannot
be secured, and bending proof stress and buckling resistance obtained therefrom cannot
be held. This range is a range necessary for securing the function as a structural pipe.
[0036]
In FIG. 8, points AI to A4 satisfy Expressions (24) to (3I).
Point AI: x(AI) = DCave x (21100) (24)
y(AI) = DEave x (21100) (25)
Point A2: x(A2) = DC ave x (211 00) (26)
y(A2) = DEave x ( -211 00) (27)
Point A3: x(A3) = DCave x (-21100) (28)
y(A3) = DEave x (-21100)(29)
Point A4: x(A4) = DCave x (-21100) (30)
y(A4) = DEave x (21100) (3I)
- 23 -
Summarizing the above, (x,y) simultaneously satisfying Expressions (32) and
(33) is the region AA.
DCave x ( -21100):::; x:::; DCave x (2/100) (32)
DEave x (-21100):::; y:::; DEave x (21100) (33)
[0037]
Next, the region YY is a range of the shape of the pipe end that has to be
secured in order to secure the necessary threading function while achieving a reduction
in the weight of the steel pipe by making the residual thickness as small as possible in
the thread cutting. The inventors found that in order to secure the strength of a joint
as a whole pipe while threading a high strength thin material, an average residual
thickness schematically shown in FIG. 7 is as in Expression (34),
Average residual thickness 2:: tEave/3 (34).
In a case where the residual thickness is equal to or less than this, it is
considered that the joint strength required for the pipe body cannot be secured, and the
function as the original use such as fracture of the joint portion during use cannot be
secured.
[0038]
On the other hand, as shown in FIG. 7, considering a case where the actual
outer diameter of the steel pipe partially deviates from the average outer diameter, the
inventors found that the residual thickness limit from the viewpoint of preventing local
deformation of a threaded portion while threading a high strength thin material is as in
Expression (35),
Residual thickness limit 2:: 0.65 mm (35)
In a case where the residual thickness is equal to or less than this value, there
are cases where there are problems in manufacturing and use, such as an increase in
- 24 -
manufacturing cost due to the occurrence of defective products caused by deformation
of a threaded portion during processing, and unavailability caused by deformation of a
threaded portion during use of a product.
[0039]
When conditions required for the shape of the pipe end to be secured in order
to secure the necessary threading function while achieving a reduction in the weight of
the steel pipe by making the residual thickness as small as possible in the thread
cutting are obtained, in a vertically long case as shown in the example of FIG. 7, the
male thread side is as in Expression (36),
Residual thickness limit = average residual thickness - (dE 1 - dEave) I 2 2::
0.65 (36).
Since a steel strip is used as the material for an electric resistance welded steel
pipe, assuming that the thickness is constant in terms of average thickness, Expressions
(37) and (38),
dEl =DEl - 2 x tEave (37)
dEave = DEave- 2 x tEave (38).
When Expression (36) is deformed from Expressions (34), (35), (37), and (38),
Expression (39),
DEl - DEave:::; 2 x { (tEave13) - 0.65} (39).
Similarly, the female thread side is as in Expression ( 40),
Residual thickness limit= average residual thickness- (DEave- DE3) I 2 2::
0.65 (40).
When the expression is deformed from Expression (34 ), Expression ( 40)
becomes Expression ( 41 ),
DEave- DE3:::; 2 x {(tEave13)- 0.65} (41).
- 25 -
When both sides of Expressions (39) and ( 41) are added, Expression ( 42),
~DE= DEl - DE3 :::; 4 x { (tEave/3) - 0.65} ( 42).
[0040]
Next, even in a horizontally long case, that is, in a case where the length and
width are reversed in FIG. 7, the male thread side is similarly as in Expression ( 43),
DEave - DEl :::; 2 x { (tEave/3) - 0.65} ( 43).
The female thread side is as in Expression ( 44 ),
DE3 - DEave:::; 2 x { (tEave/3) - 0.65} ( 44).
When both sides of Expressions ( 43) and ( 44) are added, Expression ( 45),
DE3 -DEl :::; 4 x { (tEave/3) - 0.65} ( 45).
When Expression ( 45) is rewritten, Expression ( 46),
~DE= DEl - DE3 ~ -4 x { (tEave/3) - 0.65 }( 46).
[0041]
Hereinafter, in FIGS. 8 to 13 in which the x-axis is the vertical ellipticity ~DC
of the steel pipe center portion and the y-axis is the vertical ellipticity ~DE of the steel
pipe end portion, an x -axis component and a y-axis component of a point i in the figure
are expressed as x(i) and y(i).
In addition, in the notation of the expression described below, MAX(n,m)
indicates the larger value of nand m, and MIN(n,m) indicates the smaller value of n
and m. FIGS. 8 to 9 and FIGS. 12 to 13 are under the conditions that TS = 1000
N/mm2
, the size is 114.3 mm in terms of outer diameter, and the thickness is 3.5 mm.
FIGS. 10 and 11 are under the conditions that TS = 1000 N/mm2
, the size is 114.3 mm
in terms of outer diameter, and the thickness is 4.0 mm.
[0042]
In FIG. 8, lines YH and YL that determine the range of the above-mentioned
- 26 -
region YY line are as in Expressions ( 47) and ( 48),
Line YH: y = 4 x { (tEave/3)- 0.65} (47)
Line YL: y = -4 x { (tEave/3) - 0.65} ( 48).
The region YY is a region that simultaneously satisfies Expressions ( 47) and
( 48), and is a portion surrounded by the lines YH and YL in FIG. 8. YH and YL are
the upper and lower limits of the range of ~DE required to secure the necessary
threading function while achieving a reduction in the weight of the steel pipe by
making the residual thickness as small as possible in the thread cutting. When this is
expressed as an expression, (x,y) simultaneously satisfying Expressions ( 49) and (50)
is the region YY.
-00 :S X :S 00 ( 49)
-4 x { (tEave/3) -0.65} :::; y:::; 4 x { (tEave/3) - 0.65} (50).
[0043]
The region XX surrounded by both the regions AA and YY, that is, the region
in which the outer diameter tolerance for securing the function as a structural pipe can
be secured, and the necessary threading function can be secured while achieving a
reduction in the weight of the steel pipe by making the residual thickness as small as
possible, is represented by Expressions (51) to (58) in the region surrounded by points
XI, X2, X3, and X4.
Point XI: x(Xl) = DCave x (21100) (51)
y (XI)= YM (52)
Point X2: x(X2) = DCave x (21100) (53)
y (X2) = YN (54)
Point X3: x(X3) = DCave x (-21100) (55)
y (X3) = YN (56)
- 27 -
Point X4: x(X4) = DCave x (-21100) (57)
y (X4) = YM (58)
Here, YN and YM are not shown in FIG. 8, but are as follows. When
specifying the range of the region XX, YN is the lower limit range of the y component
and is the larger value of they component y = DEave x ( -21100) of the region AA and
they component y = -4 x (tEave/3)- 0.65 of the region YY. When specifying the
range of the region XX, YM is the upper limit range of the y component and is the
smaller value of the y component y = DEave x (211 00) of the region AA and the y
component y = 4 x (tEave/3)- 0.65 of the region YY, and Expressions (4) and (5) are
established.
YN = MAX[{DEave x (-21100)},{ -4 x ((tEave/3)- 0.65)}] (5)
YM =MIN[ {DEave x (21100) },{ 4 x ((tEave/3)- 0.65)}] (4)
Summarizing the above, (x,y) simultaneously satisfying Expressions (59) and
(60) is the region XX.
DCave x ( -21100):::; x:::; DCave x (2/100) (59)
YN:Sy:SYM (60)
[0044]
Here, the inventors clarified the relationship between the vertical ellipticities
of the steel pipe center portion and the steel pipe end portion as described above and
found a method in which by using this relationship and controlling the vertical
ellipticity of the steel pipe center portion during pipe making within a predetermined
range, the vertical ellipticity of the steel pipe end portion after cutting the steel pipe can
be secured to a low level and enables thread cutting. The method and the region of a
product obtained by the method are shown below as a region PP in FIG. 8. The
region PP is a region in which the region XX described above and a region WW
- 28 -
described later overlap.
[0045]
The region WW represents the ranges of ~DC and ~DE obtained when
manufacturing is performed using the relationship between the vertical ellipticities of
the steel pipe center portion and the steel pipe end portion described above, including
variations. The region WW in FIG. 8 will be described. The vertical ellipticities of
the steel pipe center portion and the steel pipe end portion have the relationship of
Expression (61), and are represented by a line WB in FIG. 8.
y=x+K (61)
Here, y is ~DE, xis ~DC, and Expression (21) described above is established
by the substitution thereof. K is a constant obtained by Expression (6) described
above.
[0046]
As shown in FIG. 8, from the expression, the vertical ellipticity x (=~DC) of
the steel pipe center portion that has to be aimed at the time of manufacturing in order
to achieve ~DE= 0 is as in Expression (62),
X(= ~DC)= -K (62).
In FIG. 8, when forming and shaping are performed during pipe making so as
to achieve a point AIM and satisfy Expression (61), it is possible to easily reduce the
vertical ellipticity of the pipe end.
[0047]
The ranges of ~DC and ~DE of the product manufactured using the
relationship of Expression (61) become the region WW surrounded by lines WH and
WL described below when variations are taken into consideration using the standard
deviation of the average outer diameter DCave of the steel pipe center portion obtained
- 29 -
by Expression (8) described above. Here, WH indicates the upper limit of ~DE
which is + 3cr from the average, WL indicates the lower limit of ~DE which is -3cr
from the average, and Expressions (63) and (64) are established as follows.
Line WH: y = x + K + 3 x SD ( 63)
Line WL: y = x + K - 3 x SD ( 64 ).
Here, SD is the standard deviation of the vertical ellipticity, and ~D = D 1 -
D3. Therefore, from the additivity of the standard deviation, Expression (7) can be
represented as follows,
SD = (~2) x (standard deviation of average outer diameter DCave of the steel
pipe center portion) (7).
The standard deviation of the average outer diameter DCave of the steel pipe
center portion is a number obtained by Expression (8) described above. When this is
expressed as an expression, (x,y) simultaneously satisfying Expression (3) is the region
ww.
X+ K- 3 X SD:::; y:::; X+ K + 3 X SD (3)
[0048]
In the manufacturing for securing the vertical ellipticity of the steel pipe end
portion after cutting the steel pipe to a low level using the relationship of Expression
(61), the region PP in FIG. 8 is a range of a product in which a reduction in the weight
of the steel pipe can be achieved by making the residual thickness as small as possible,
and is a portion in which the region XX and the region WW overlap. When this is
expressed as an expression, (x,y) simultaneously satisfying Expressions (59), (60), and
(3) described above is the region PP.
DCave x ( -21100):::; x:::; DCave x (2/100) (59)
YN:Sy:SYM (60)
- 30 -
X+ K- 3 X SD:::; y:::; X+ K + 3 X SD (3)
When this is shown in coordinates in FIG. 8, the region PP is a region inside
the line connecting the point XI, a point PI, a point Z3, the point X3, a point P2, a
point ZI, and the point XI. Point PI: An intersection point of a line passing through
XI and X2 and the line WL. Point P2: An intersection point of a line passing through
X4 and X3 and the line WH. Point ZI: An intersection point of a line passing
through X4 and XI and the line WH. Point Z3: An intersection point of a line
passing through X3 and X2 and the line WL.
[0049]
In a case of manufacturing similarly using the relationship of Expression (6I)
described above within the range of x of Expression (59) described above, there are
cases where the region XX cannot be satisfied due to variations in the manufacturing.
Therefore, as a more preferable region in which the region XX can be stably secured in
consideration of variations in manufacturing in the thread cutting, the range of ~DC to
be set in FIG. 9 and ~DE obtained in this case are shown as a region ZZ. When this
is expressed as an expression, (x,y) simultaneously satisfying Expression (65) and
Expression (3) described above is the region ZZ.
YN - K + 3 x SD :::; x :::; YM - K - 3 x SD ( 65)
X + K- 3 X SD :::; y:::; X + K + 3 X SD (3)
When this is shown in coordinates in FIG. 9, the region ZZ is a region that
satisfies the region XX and is surrounded by the line connecting the following four
points, the point ZI, a point Z2, the point Z3, and a point Z4.
Point ZI: An intersection point of the line passing through X4 and XI and the
line WH, which is represented by Expressions (66) and (67) below.
x(ZI) = y(XI) - K- 3 x SD = YM- K- 3 x SD (66)
- 3I -
y(Z1) = y(X1) = YM (67)
Point Z2: An intersection point of x = x(Z1) and the line WL, which is
represented by Expressions (68) and (69) below.
x(Z2) = x(Z1) = y(X1) - K- 3 x SD
= YM- K- 3 x SD (68)
y(Z2) = x(Z1) + K- 3 x SD = YM- 6 x SD (69)
Point Z3: An intersection point of the line passing through X3 and X2 and the
line WL, which is represented by Expressions (70) and (71) below.
x(Z3) = y(X3) - K + 3 x SD = YN - K + 3 x SD (70)
y(Z3) = y(X3) = YN (71)
Point Z4: An intersection point of x = x(Z3) and the line WH, which is
represented by Expressions (72) and (73) below.
x(Z4) = x(Z3) = y(X3) - K + 3 x SD
= YN- K + 3 x SD (72)
y(Z4) = x(Z3) + K + 3 x SD = YN + 6 x SD(73)
[0050]
Next, when the thickness of the steel pipe increases, there are cases where the
region YY (the region necessary for securing the necessary threading function while
achieving a reduction in the weight of the steel pipe by making the residual thickness
as small as possible in the thread cutting) becomes larger than the region AA (the
range necessary for securing the outer diameter tolerance), and the region PP in this
case is shown in FIG. 10.
[0051]
In this case, the region XX, which is the overlap of the region AA and the
region YY, is the same as the region AA. When this is expressed as an expression,
- 32 -
(x,y) simultaneously satisfying Expressions (32) and (33) described above is the region
XX, and is represented by Expressions (32) and (33).
DCave x ( -21100):::; x:::; DCave x (2/IOO) (32)
DEave x (-21100):::; y:::; DEave x (21100) (33)
When this is shown in coordinates in FIG. I 0, the region XX is a region inside
the line connecting the following four points, the point XI, the point X2, the point X3,
and the point X4, and is represented by Expressions (24) to (3I).
Point XI (=point AI): x(XI) = x(AI) = DCave x (21100) (24)
y(XI) = y(AI) = DEave x (21100) (25)
Point X2 (=point A2): x(X2) = x(A2) = DCave x (211 00) (26)
y(X2) = y(A2) = DEave x (-21100) (27)
Point X3 (=point A3): x(X3) = x(A3) = DCave x (-21100) (28)
y(X3) = y(A3) = DEave x (-21100) (29)
Point X4 (=point A4): x(X4) = x(A4) DCave x (-21100) (30)
y(X4) = y(A4) = DEave x (21100) (3I)
[0052]
In FIG. IO, the region WW representing the ranges of ~DC and ~DE obtained
when manufacturing is performed using the relationship between the vertical
ellipticities of the steel pipe center portion and the steel pipe end portion described
above, including variations, is the same as in the above description, and (x,y)
simultaneously satisfying Expression (3) described above is the region WW and is
represented by Expression (3).
X+ K- 3 X SD:::; y:::; X+ K + 3 X SD (3)
[0053]
In FIG. IO, the region PP is a portion in which the region XX and the region
- 33 -
WW overlap. When this is expressed as an expression, (x,y) simultaneously
satisfying Expressions (32), (33), and (3) is the region PP.
DCave x ( -21100):::; x:::; DCave x (2/IOO) (32)
DEave x (-21100):::; y:::; DEave x (21100) (33)
X+ K- 3 X SD:::; y:::; X+ K + 3 X SD (3)
When this is shown in coordinates in FIG. I 0, the region PP is a region inside
the line connecting the point XI, the point PI, the point Z3, the point X3, the point P2,
the point Z I, and the point X I.
Point PI: The intersection point of the line passing through XI and X2 and the
line WL.
Point P2: The intersection point of the line passing through X4 and X3 and the
line WH.
Point ZI: The intersection point of the line passing through X4 and XI and
the line WH.
Point Z3: The intersection point of a line passing through X3 and X2 and the
line WL.
[0054]
The region ZZ which is a more preferable region in which the region XX can
be stably secured in consideration of variations in manufacturing in this case is shown
in FIG. II. The idea is the same as above, but the y component of the region XX is
different as follows,
y(XI) = y(X4) = DEave x (21100) (25) and (3I)
y(X2) = y(X3) = DEave x (-21100) (27) and (29).
Therefore, when this is expressed as an expression, (x,y) simultaneously
satisfying Expressions (74) and (3) is the region ZZ.
- 34 -
DEave x (-21100)- K + 3 x SD:::; x
:::; DEave x (2/100)- K- 3 x SD (74)
X+ K- 3 X SD:::; y:::; X+ K + 3 X SD (3)
When this is shown in coordinates in FIG. 11, the region ZZ is a region that
satisfies the region XX inside the line connecting the following four points, the point
Zl, the point Z2, the point Z3, and the point Z4, and is represented by Expressions (75)
to (82).
Point Zl: The intersection point of the line passing through X4 and XI and
the line WH.
x(Zl) = y(Xl) - K- 3 x SD
= DEave x (21100)- K- 3 x SD (75)
y(Zl) = y(Xl) = DEave x (21100) (76)
Point Z2: The intersection point of x = x(Zl) and the line WL.
x(Z2) = x(Zl) = y(Xl)- K- 3 x SD = DEave x (21100)- K- 3 x SD (77)
y(Z2) = x(Zl) + K- 3 x SD = DEave x (2/100)- 6 x SD (78)
Point Z3: The intersection point of the line passing through X3 and X2 and
the line WL.
x(Z3) = y(X3)- K + 3 x SD = DEave x (-21100)- K + 3 x SD(79)
y(Z3) = y(X3) = DEave x (-21100) (80)
Point Z4: The intersection point of x = x(Z3) and the line WH.
x(Z4) = x(Z3) = y(X3)- K + 3 x SD = DEave x (-21100)- K + 3 x SD (81)
y(Z4) = x(Z3) + K + 3 x SD = DEave x (-21100) + 6 x SD (82)
[0055]
Next, a case where the steel pipe end portions are fitted and connected via one
or a plurality of jigs between the steel pipes to be used will be described. In this case,
- 35 -
the region of a product obtained by a method in which, while securing the outer
diameter tolerance for securing the function as a steel pipe, by using the relationship of
the difference between the vertical ellipticity (~DE) of the steel pipe end portion and
the vertical ellipticity (~DC) of the steel pipe center portion described above, and
controlling the vertical ellipticity of the steel pipe center portion during pipe making
within a predetermined range, the vertical ellipticity of the steel pipe end portion after
cutting the steel pipe can be secured to a low level is shown as the region PP in FIG. I2,
and a more preferable region is shown as the region ZZ in FIG. I3. In the case where
the steel pipe end portions are fitted and connected via one or a plurality of jigs
between the steel pipes to be used, there is no need to consider the region YY.
[0056]
As in the case of thread cutting, when the range of the shape of the pipe end to
be secured for fitting is referred to as the region XX, the region XX is the same as the
region AA, and when this is expressed as an expression, (x,y) simultaneously
satisfying Expressions (32) and (33) is the region XX(= the region AA).
DCave x ( -21100):::; x:::; DCave x (2/IOO) (32)
DEave x (-21100):::; y:::; DEave x (21100) (33)
When this is shown in coordinates in FIG. I2, the region XX is a region inside
the line connecting the points XI, X2, X3, and X4, and is represented by Expressions
(24) to (3I).
Point XI: x(XI) = DCave x (21100) (24)
y(XI) = DEave x (21100) (25)
Point X2: x (X2) = DCave x (211 00) (26)
y(X2) = DEave x (-21100)(27)
Point X3: x (X3) = DCave x (-21100) (28)
- 36 -
y(X3) = DEave x (-21100)(29)
Point X4: x (X4) = DCave x (-21100) (30)
y(X4) = DEave x (21100) (31)
[0057]
In the case where the steel pipe end portions are fitted and connected via one
or a plurality of jigs between the steel pipes to be used, the region WW in FIGS. 12
and 13 representing the ranges of ~DC and ~DE obtained when manufacturing is
performed using the relationship between the vertical ellipticities of the steel pipe
center portion and the steel pipe end portion described above, including variations, is
the same as in the above description, and (x,y) simultaneously satisfying Expression
(3) is the region WW.
X+ K- 3 X SD:::; y:::; X+ K + 3 X SD (3)
[0058]
In FIG. 12, the region PP which is a region of a product obtained by the
method in which by using the relationship between the vertical ellipticities of the steel
pipe center portion and the steel pipe end portion described above, and controlling the
vertical ellipticity of the steel pipe center portion during pipe making within a
predetermined range, the vertical ellipticity of the steel pipe end portion after cutting
the steel pipe can be secured to a low level is a portion in which the region XX and the
region WW overlap. When this is expressed as an expression, (x,y) simultaneously
satisfying Expressions (32), (33), and (3) is the region PP.
DCave x ( -21100):::; x:::; DCave x (2/100) (32)
DEave x (-21100):::; y:::; DEave x (21100) (33)
X+ K- 3 X SD:::; y:::; X+ K + 3 X SD (3)
When this is shown in coordinates in FIG. 12, it is a region inside the line
- 37 -
connecting the points XI, the point PI, the point Z3, the point X3, the point P2, the
point Z I, and the point X I.
Point PI: The intersection point of the line passing through XI and X2 and the
line WL.
Point P2: The intersection point of the line passing through X4 and X3 and the
line WH.
Point ZI: The intersection point of the line passing through X4 and XI and
the line WH.
Point Z3: The intersection point of the line passing through X3 and X2 and
the line WL.
[0059]
Next, in FIG. I3, the more preferable region ZZ in which the region XX can
be stably secured in consideration of variations in manufacturing in the case where the
steel pipe end portions are fitted and connected via one or a plurality of jigs between
the steel pipes to be used is shown. The idea is the same as above, but the y
component of the region XX is different as follows,
y(XI) = y(X4) = DEave x (21100) (25) and (3I)
y(X2) = y(X3) = DEave x (-21100) (27) and (29).
Therefore, when this is expressed as an expression, (x,y) simultaneously
satisfying Expressions (74) and (3) is the region ZZ.
DEave x (-21100)- K + 3 x SD:::; x:::; DEave x (2/IOO)- K- 3 x SD (74)
X+ K- 3 X SD:::; y:::; X+ K + 3 X SD (3)
When this is shown in coordinates in FIG. I3, the region ZZ is a region that
satisfies the region XX and is surrounded by the line connecting the following four
points, the point ZI, the point Z2, the point Z3, and the point Z4, and is represented by
- 38 -
Expressions (75) to (82).
Point Zl: The intersection point of the line passing through X4 and XI and
the line WH.
x(Zl) = y(Xl)- K- 3 x SD = DEave x (2/100)- K- 3 x SD (75)
y(Zl) = y(Xl) = DEave x (21100) (76)
Point Z2: The intersection point of x = x(Zl) and the line WL.
x(Z2) = x(Zl) = y(Xl)- K- 3 x SD = DEave x (21100)- K- 3 x SD (77)
y (Z2) = x (Zl) + K-3 x SD = DEave x (2/100) -6 x SD (78)
Point Z3: The intersection point of the line passing through X3 and X2 and
the line WL.
x(Z3) = y(X3)- K + 3 x SD = DEave x (-21100)- K + 3 x SD(79)
y(Z3) = y(X3) = DEave x (-21100) (80)
Point Z4: The intersection point of x = x(Z3) and the line WH.
x(Z4) = x(Z3) = y(X3)- K + 3 x SD = DEave x (-21100)- K + 3 x SD (81)
y(Z4) = x(Z3) + K + 3 x SD = DEave x (-21100) + 6 x SD (82)
[0060]
Next, a method for manufacturing the high strength electric resistance welded
steel pipe of the present embodiment will be described.
A hot-rolled steel sheet used for the high strength electric resistance welded
steel pipe is manufactured by heating a steel having the above-mentioned composition,
hot-rolling the steel, and then performing controlled cooling and coiling.
The heating temperature of the steel is preferably 1150°C or higher in order to
solid-solubilize elements forming carbides such as Nb in the steel. On the other hand,
in order to obtain a fine grain structure, the heating temperature is preferably 1 ooooc
to 1280°C. When the heating temperature is too high, austenite grains become coarse,
- 39 -
and as a result, the grain size of ferrite becomes coarse. Therefore, the heating
temperature is preferably 1280°C or lower.
The finish temperature of the hot rolling is preferably 850°C or higher so that
no ferrite is generated during rolling.
When the coiling temperature exceeds 300°C, there is concern that sufficient
strength may not be secured. Therefore, the coiling temperature is preferably 300°C
or lower. The coiling temperature is more preferably 150°C or lower.
Next, the obtained hot-rolled steel sheet is continuously formed into an open
pipe by roll forming, and then the end portions of the open pipe are butted against each
other and subjected to electric resistance welding to manufacture an electric resistance
welded steel pipe. The electric resistance welded part may be subjected to a seam
heat treatment in which heating and accelerated cooling are performed. Thereafter,
the outer diameter of the steel pipe may be reduced by 0.5% to 4.0% with a sizer.
[0061]
An example of the manufacturing process of the electric resistance welded
steel pipe is shown in FIG. 14. The electric resistance welded steel pipe is
manufactured by cold working with a plurality of roll stands, and is obtained by a
forming step of bending the steel sheet into a C-section, a welding step of performing
electric resistance welding on the pipe ends, a straightening step of slightly reducing
the diameter of the pipe to adjust the shape thereof, and a cutting step of cutting the
steel pipe into a desired length with a cutting machine. An A-A' cross section is a
stand position of the welding step, a B-B' cross section is any one stand position of one
or a plurality of straightening steps, a C-C' cross section is a cross section of any
position of the center position of the roll in the final stage of the straightening step and
a position distant from a cut position between cut steel pipe end portions by a position
- 40 -
Le or larger, and aD-D' cross section is the steel pipe end portion. The pipe width
and pipe height in each of the cross sections are indicated as Ah, Av, Bh, Bv, D1 (steel
pipe center portion), D3 (steel pipe center portion), D1 (steel pipe end portion), and D3
(steel pipe end portion) (mm). The pipe width is the pipe outer surface distance
between 90° and 270°, and the pipe height is the pipe outer surface distance between
oo and 180° in a case where the electric resistance welded part is at oo position.
[0062]
In order to make ~DC an appropriate value, the pipe width Ah and the pipe
height Av of the A-A' cross section are set to appropriate values by appropriately
adjusting the upper, lower, and width rolls of the welding stand, or the pipe width Bh
and the pipe height Bv of the B-B' cross section are set to appropriate values by
appropriately adjusting the upper, lower, and width rolls of the final stage of the
straightening stand. In a case where the cold working at the time of straightening is
minimized in consideration of the toughness and corrosion resistance of the steel pipe,
the former is preferable. In a case where the steel pipe is subjected to work hardening
for further high-strengthening, the latter is preferable. The manufacturing process of
the electric resistance welded steel pipe is not limited to the case of FIG. 14, and since
the number of rolls, the number of stages, and the shape are different, it is necessary to
search for the manufacturing conditions that satisfy the conditions of the present
invention in each facility.
[0063]
In the above description, in the method in which the steel pipe end portions
are fitted and connected via one or a plurality of jigs between the steel pipes to be used,
the fitting portion also includes a case where the steel pipe and the jig are firmly joined
to each other by welding, adhesion, or mechanical joining (for example, threading,
- 41 -
fitting using a material elastic property, or pinning). The "jig" is a coupling or a
nipple, and the coupling or the nipple is joined to the steel pipe by welding or
mechanical joining instead of directly cutting threads in the steel pipe.
[0064]
The length of the high strength electric resistance welded steel pipe according
to the present invention is preferably 2000 mm to 5000 mm as described above, but
more preferably 3000 mm to 3500 mm, which is a generally used length.
[0065]
Next, the composition of the high strength electric resistance welded steel
pipe according to the present embodiment will be described.
In the following description, the term "content" simply used for each element
means the content in the steel pipe.
[0066]
As described above, the steel pipe of the present embodiment contains, by
mass% or by mass ppm, C: 0.04% to 0.30%, Si: 0.01% to 2.00%, Mn: 0.50% to 3.00%,
P: 0.030% or less, S: 0.030% or less, Al: 0.005% to 0.700%, N: 100 ppm or less, Nb:
0% to 0.100%, V: 0% to 0.100%, Ti: 0% to 0.200%, Ni: 0% to 1.000%, Cu: 0% to
1.000%, Cr: 0% to 1.000%, Mo: 0% to 1.000%, B: 0 to 50 ppm, Ca: 0 to 100 ppm,
REM: 0 to 200 ppm, and a remainder consisting of iron and impurities.
Hereinafter, each element, the content thereof, and impurities will be
described.
[0067]

C (carbon) is an element effective for improving the strength of the steel pipe.
The C content in the steel pipe of the present invention is 0.04% or more.
- 42 -
Accordingly, the steel pipe strength of the hot-rolled steel sheet is consequently
secured.
On the other hand, when the C content of C is too high, the strength of the
steel pipe becomes too high, and the toughness deteriorates. Therefore, the upper
limit of the C content is 0.30%. The upper limit of the C content is preferably 0.25%,
and more preferably 0.20%.
[0068]

Si (silicon) is effective as a deoxidizing agent.
However, when the Si content is too high, the low temperature toughness is
impaired, and the electric resistance weldability is further impaired. Therefore, the
upper limit of the Si content is 2.00%. The Si content is preferably 1.20% or less, and
more preferably 0.60% or less.
On the other hand, the Si content is 0.01% or more from the viewpoint of
more effectively obtaining the effect as a deoxidizing agent. Furthermore, the Si
content is preferably 0.10% or more, and more preferably 0.20% or more from the
viewpoint of further increasing the strength of the steel pipe by solid solution
strengthening.
[0069]

Mn (manganese) is an element that achieves high-strengthening of steel by
increasing the hardenability of the steel.
The Mn (manganese) content in the steel pipe of the present invention is
0.50% or more from the viewpoint of securing high strength. Therefore, the Mn
content is preferably 0.80% or more.
- 43 -
However, when the Mn content is too high, the formation of martensite is
promoted and the toughness deteriorates. Therefore, the upper limit of the Mn
content is 3.00%. In order to obtain higher toughness, the upper limit thereof is
preferably 2.00%.
[0070]

P (phosphorus) is an impurity.
The upper limit of the P content is 0.030% because the toughness is improved
by reducing the P content. The P content is preferably 0.020% or less.
Since it is preferable that the P content is small, the lower limit of the P
content is not particularly limited. However, from the viewpoint of the balance
between the characteristics and the cost, the P content is usually 0.001% or more.
[0071]

S (sulfur) is an impurity.
The upper limit of the S content is 0.030% because the amount of MnS
stretched by hot rolling can be reduced by reducing the S content and thus the
toughness can be improved. The S content is preferably 0.020% or less, and more
preferably 0.010% or less.
Since it is preferable that the S content is small, the lower limit of the S
content is not particularly limited. However, from the viewpoint of the balance
between the characteristics and the cost, the S content is usually 0.001% or more.
[0072]

Al (aluminum) is an element effective as a deoxidizing agent.
- 44 -
However, when the Al content is too high, the amount of inclusions increases,
and the ductility and toughness are impaired. Therefore, the upper limit of the Al
content is 0.700%.
On the other hand, the Al content is 0.005% or more from the viewpoint of
more effectively obtaining the effect as a deoxidizing agent. In order to reduce the
amount of inclusions and obtain higher ductility and toughness, the upper limit thereof
is preferably 0.100% or less.
[0073]

N (nitrogen) is an element that is unavoidably present in steel.
However, when theN content is too high, there is concern that the amount of
inclusions such as AlN may be excessively increased, causing adverse effects such as
surface damages and deterioration of toughness. Therefore, the upper limit of theN
content is 100 ppm. TheN content is preferably 80 ppm or less, and particularly
preferably 60 ppm or less.
On the other hand, although the lower limit of theN content is not particularly
limited, the N content is preferably 10 ppm or more in consideration of the cost and
economy of denitrification.
[0074]

Nb (niobium) is an element that lowers the recrystallization temperature, and
is an element that suppresses the recrystallization of austenite and contributes to the
refinement of the structure when hot rolling is performed.
However, when the Nb content is too high, the toughness deteriorates due to
the coarse precipitates. Therefore, the upper limit of the Nb content is 0.100%. The
- 45 -
Nb content is preferably 0.06% or less, and more preferably 0.05% or less.
On the other hand, the Nb content is preferably 0.010% or more, and
particularly preferably 0.020% or more, from the viewpoint of obtaining the structure
refinement effect more reliably.
[0075]

V (vanadium) is an element that produces carbides and nitrides and improves
the strength of steel by precipitation strengthening.
However, when the V content is too high, there is concern that the carbides
and nitrides may become coarse and cause deterioration of the toughness. Therefore,
the V content is 0% to 0.100%. The V content is more preferably 0.060% or less.
On the other hand, the V content is preferably 0.010% or more from the
viewpoint of further improving the strength of the steel pipe.
[0076]

Ti (titanium) is an element that forms fine nitrides (TiN), suppresses
coarsening of austenite grains during slab heating, and contributes to the refinement of
the structure.
However, when the Ti content is too high, there is concern that the TiN may
become coarsen or precipitation hardening may occur due to TiC, resulting in
deterioration of the toughness. Therefore, the Ti content is 0% to 0.200%. The Ti
content is more preferably 0.100% or less, and particularly preferably 0.050% or less.
On the other hand, from the viewpoint of further improving the toughness by
refinement of the structure, the Ti content is preferably 0.010% or more, and more
preferably 0.015% or more.
- 46 -
[0077]

Ni (nickel) is an element that achieves high-strengthening of steel by
increasing the hardenability of the steel. Ni is also an element that contributes to the
improvement of the toughness.
However, since Ni is an expensive element, the Ni content is 0% to 1.000%
from the viewpoint of economy. The Ni content is more preferably 0.500% or less.
On the other hand, from the viewpoint of further improving the toughness, the
Ni content is preferably 0.100% or more.
[0078]

Cu (copper) is an element that achieves high-strengthening of steel by
increasing the hardenability of the steel. Cu is also an element that contributes to
solid solution strengthening.
However, when the Cu content is too high, there are cases where the surface
properties of the steel pipe may be impaired. Therefore, the Cu content is 0% to
1.000%. The Cu content is more preferably 0.500% or less.
On the other hand, the Cu content is preferably 0.100% or more.
In a case where the steel pipe contains Cu, it is preferable that Ni is
simultaneous! y contained from the viewpoint of preventing deterioration of the surface
properties.
[0079]

Cr (chromium) is an element effective in improving the strength.
However, when the Cr content is too high, the electric resistance weldability
- 47 -
may deteriorate. Therefore, the Cr content is 0 to 1.000% or less. The Cr content is
more preferably 0.500% or less.
On the other hand, the Cr content is preferably 0.100% or more from the
viewpoint of further improving the strength of the steel pipe.
[0080]

Mo (molybdenum) is an element that contributes to the high-strengthening of
steel.
However, since Moisan expensive element, the Mo content is 0% to 1.000%
from the viewpoint of economy. The Mo content is more preferably 0.500% or less,
and particularly preferably 0.300% or less.
On the other hand, the Mo content is preferably 0.050% or more.
[0081]

B (boron) is an element that significantly enhances the hardenability of steel
by being contained in a small amount and contributes to the high-strengthening of steel.
However, even if the B content exceeds 50 ppm, the hardenability is not
further improved, and there is a possibility that precipitates may be generated and the
toughness may deteriorate. Therefore, the upper limit of the B content is 50 ppm.
On the other hand, B may be incorporated from raw material impurities. However, in
order to obtain a sufficient hardenability effect, the B content is preferably 3 ppm or
more.
[0082]

Ca (calcium) is an element that controls the morphology of sulfide-based
- 48 -
inclusions, improves low temperature toughness, and further refines oxides of the
electric resistance welded part, thereby improving the toughness of the electric
resistance welded part.
However, when theCa content is too high, there is concern that oxides or
sulfides may become large, which may adversely affect the toughness. Therefore, the
Ca content is 0 to 100 ppm.
On the other hand, the Ca content is preferably 10 ppm or more.
[0083]

In the present specification, "REM" means rare earth elements, and is a
general term for 17 kinds of elements including Sc (scandium), Y (yttrium), La
(lantern), Ce (cerium), Pr (placeodim), Nd (neodymium), Pm (promethium), Sm
(samarium), Eu (yuropium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho
(holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutethium).
In addition, "REM: 0 to 200 ppm" indicates that each of the above 17 kinds of
elements or any combination thereof is contained and the total amount of these 17
kinds of elements is 200 ppm or less.
REM is an element that controls the morphology of sulfide-based inclusions,
improves low temperature toughness, and further refines oxides of the electric
resistance welded part, thereby improving the toughness of the electric resistance
welded part.
However, when the REM content is too high, there is concern that oxides or
sulfides may become large, which may adversely affect the toughness. Therefore, the
content of REM is preferably 0 to 200 ppm.
On the other hand, the REM content is preferably 10 ppm or more.
- 49 -
[0084]

In the present invention, the impurities are elements contained in raw
materials or elements incorporated in a manufacturing process and indicate elements
that are not intentionally contained in steel.
Specifically, as the impurities, there are 0 (oxygen), Sb (antimony), Sn (tin),
W (tungsten), Co (cobalt), As (arsenic), Mg (magnesium), Pb (lead), Bi (bismuth), and
H (hydrogen).
Particularly, 0 is preferably controlled so that the 0 content is 0.004% or less.
[0085]
A method for using the high strength electric resistance welded steel pipe for
ground stabilization work of the present invention will be described.
In the method for using the high strength electric resistance welded steel pipe
for ground stabilization work of the present invention, new steel pipe end portions
generated by cutting the high strength electric resistance welded steel pipe described
above at the steel pipe center portion are subjected to thread cutting, and two or more
high strength electric resistance welded steel pipes are connected by screw joints to be
used.
In addition, in the method for using the high strength electric resistance
welded steel pipe for ground stabilization work of the present invention, two or more
high strength electric resistance welded steel pipes are connected to be used by fitting
one or both of the steel pipe end portions of the high strength electric resistance welded
steel pipe described above to a new steel pipe end portion generated by performing
cutting at a steel pipe center portion, via one or a plurality of jigs to be used.
[Examples]
- 50 -
[0086]
A slab having the elements listed in the tables of examples was heated to
1 050°C or higher, subjected to rough rolling at a recrystallization temperature or
higher, subsequently subjected to finish rolling with a cumulative rolling reduction
amount of 65% or more at Ar3°C to 950°C, and cooled from a temperature of Ar3°C
or higher to obtain a steel sheet. The obtained steel sheet was formed into a hollow
state by cold forming in a pipe making facility having a forming step, a welding step,
and straightening step, and thereafter subjected to electric resistance welding to
manufacture a high strength steel pipe having a tensile strength of 590 N/mm2 or more.
New steel pipe end portions generated by performing cutting at the steel pipe center
portion after pipe making were subjected to "joining after thread cutting" or "fitting via
jigs".
For the tensile strength, a test piece of full thickness was collected from the
base material portion of the steel pipe after the heat treatment in the pipe axis direction
and was subjected to a tensile test in the pipe axis direction.
[0087]
Under each condition in the tables of the examples, conditions and results of
the examples and comparative examples are shown. In each table, "G" of each region
indicates a case where each region could be satisfied, and "NG" of each region
indicates a case where each region could not be satisfied.
- 51 -
[0088]
[Table 1]
Pipe making manufacturing conditions
Material Material
Size Strength
Composition Composition
No.
Example/
Outer Thickness/outer
Comparative Example c Si Mn p s Al N Nb v Ti Cu Ni Cr Mo B Ca REM
diameter
~hickness
diameter
TS
% % % % % % ppm % % % % % % % ppm ppm ppm mm mm N/mm2
l Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
2 Comoarative Examole 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
3 Comoarative Examole 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
4 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
5 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
6 Comoarative Examole 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
7 Comoarative Examole 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
8 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
9 Comoarative Examole 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
10 Comoarative Examole 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
11 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
12 Comoarative Examole 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
l3 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
14 Com12arative Exam12le 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
15 Comoarative Examole 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
16 Comparative Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
17 Com12arative Exam12le 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
18 Comoarative Examole 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
19 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
20 Comoarative Examole 0.27 010 100 0.010 0003 0.015 35 114.3 3.5 0.03 1000
21 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
22 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
23 Comoarative Examole 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
24 Comoarative Examole 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
25 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
26 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
27 Comoarative Examole 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
28 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
29 Com12arative Exam12le 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 0.03 1000
- 52 -
[0089]
[Table 2]
Steel pipe center
Result Steel pipe center portion
Steel pipe end
Result
Steel pipe end
Joining method Outer diameter tolerance portion portion portion
Outer diameter
X
Thickness Calculation Calculation Calculation
Outer y
Thickness Residual
Example/
component diameter component
thickness
No. Outer
Comparative Example
Threading/ diameter
limit
fitting
Range min max DCave LiDC tCave K
standard
SD DEave LiDE tEave
deviation
% mm mm mm mm mm mm mm mm mm mm mm mm
l Example Threading l.O% 113.2 115.4 114.30 2.20 3.50 -0.15 0.25 0.36 114.30 1.50 3.50 0.65
2 Com12arative Exam12le Threading l.O% 113.2 115.4 114.30 2.50 3.50 -0.15 0.25 0.36 114.30 1.50 3.50 0.65
3 ComParative ExamPle Threading l.O% 113.2 115.4 114.30 1.80 3.50 -0.15 0.25 0.36 114.30 0.30 3.50 0.65
4 Example Threading l.O% 113.2 115.4 114.30 1.80 3.50 -0.15 0.25 0.36 114.30 0.70 3.50 0.65
5 Example Threading l.O% 113.2 115.4 114.30 1.80 3.50 -0.15 0.25 0.36 114.30 1.90 3.50 0.65
6 Comparative Example Threading l.O% 113.2 115.4 114.30 1.80 3.50 -0.15 0.25 0.36 114.30 2.20 3.50 0.65
7 Com12arative Exam12le Threading l.O% 113.2 115.4 114.30 1.80 3.50 -0.15 0.25 0.36 114.30 3.00 3.50 0.65
8 Example Threading l.O% 113.2 115.4 114.30 1.00 3.50 -0.15 0.25 0.36 114.30 0.85 3.50 0.65
9 Comparative Example Threading l.O% 113.2 115.4 114.30 1.00 3.50 -0.15 0.25 0.36 114.30 -0.70 3.50 0.65
10 Com12arative Exam12le Threading l.O% 113.2 115.4 114.30 1.00 3.50 -0.15 0.25 0.36 114.30 2.15 3.50 0.65
11 Example Threading l.O% 113.2 115.4 114.30 1.30 3.50 -0.15 0.25 0.36 114.30 0.85 3.50 0.65
12 ComParative ExamPle Threading l.O% 113.2 115.4 114.30 1.30 3.50 -0.15 0.25 0.36 114.30 2.22 3.50 0.65
13 Example Fitting l.O% 113.2 115.4 114.30 1.50 3.50 -0.15 0.25 0.36 114.30 0.85 3.50 0.65
14 Comparative Example Fitting l.O% 113.2 115.4 114.30 1.50 3.50 -0.15 0.25 0.36 114.30 2.42 3.50 0.65
15 Comparative Example Fitting l.O% 113.2 115.4 114.30 1.50 3.50 -0.15 0.25 0.36 114.30 3.00 3.50 0.65
16 Com12arative Exam12le Fitting l.O% 113.2 115.4 114.30 1.50 3.50 -0.15 0.25 0.36 114.30 -0.50 3.50 0.65
17 ComParative ExamPle Fitting l.O% 113.2 115.4 114.30 2.50 3.50 -0.15 0.25 0.36 114.30 1.00 3.50 0.65
18 Comparative Example Fitting l.O% 113.2 115.4 114.30 2.50 3.50 -0.15 0.25 0.36 114.30 1.80 3.50 0.65
19 Example Fitting l.O% 113.2 115.4 114.30 1.00 3.50 -0.15 0.25 0.36 114.30 0.50 3.50 0.65
20 Comparative Example Fitting l.O% 113.2 115.4 114.30 1.00 3.50 -0.15 0.25 0.36 114.30 -0.50 3.50 0.65
21 Example Fitting l.O% 113.2 115.4 114.30 -0.80 3.50 -0.15 0.25 0.36 114.30 -1.20 3.50 0.65
22 Example Fitting l.O% 113.2 115.4 114.30 -1.30 3.50 -0.15 0.25 0.36 114.30 -1.20 3.50 0.65
23 Comparative Example Fitting l.O% 113.2 115.4 114.30 -0.80 3.50 -0.15 0.25 0.36 114.30 -2.15 3.50 0.65
24 Com12arative Exam12le Fitting l.O% 113.2 115.4 114.30 -1.30 3.50 -0.15 0.25 0.36 114.30 -2.80 3.50 0.65
25 Example Threading l.O% 113.2 115.4 114.30 -0.80 3.50 -0.15 0.25 0.36 114.30 -1.00 3.50 0.65
26 Example Threading l.O% 113.2 115.4 114.30 -1.00 3.50 -0.15 0.25 0.36 114.30 -1.00 3.50 0.65
27 Com12arative Exam12le Threading l.O% 113.2 115.4 114.30 -1.00 3.50 -0.15 0.25 0.36 114.30 -2.20 3.50 0.65
28 Example Threading l.O% 113.2 115.4 114.30 -1.50 3.50 -0.15 0.25 0.36 114.30 -1.90 3.50 0.65
29 Comparative Example Threading l.O% 113.2 115.4 114.30 -1.50 3.50 -0.15 0.25 0.36 114.30 -2.20 3.50 0.65
- 53 -
[0090]
[Table 3]
RegionAA Region YY Region XX
Line Line Line Line
LineYL LineYH X component Y component
No.
Example/ A4A3 AlA2 A3A2 A4Al
Comparative Example Actual xy Actual xy min max min max Actual xy
X X y y
evaluation
y y
evaluation (X4X3) (XlX2) (X3X2) (X4Xl) evaluation
mm mm mm mm mm mm mm mm mm mm
l Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
2 ComParative ExamPle -2.29 2.29 -2.29 2.29 NG -2.07 2.07 G -2.29 2.29 -2.07 2.07 NG
3 Comparative Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
4 Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
5 Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
6 Comparative Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 NG -2.29 2.29 -2.07 2.07 NG
7 Com12arative Exam12le -2.29 2.29 -2.29 2.29 NG -2.07 2.07 NG -2.29 2.29 -2.07 2.07 NG
8 Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
9 Comparative Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
lO Com12arative Exam12le -2.29 2.29 -2.29 2.29 G -2.07 2.07 NG -2.29 2.29 -2.07 2.07 NG
ll Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
12 Comparative Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 NG -2.29 2.29 -2.07 2.07 NG
l3 Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 -2.29 2.29 -2.29 2.29 G
14 Comparative Example -2.29 2.29 -2.29 2.29 NG -2.07 2.07 -2.29 2.29 -2.29 2.29 NG
15 Com12arative Exam12le -2.29 2.29 -2.29 2.29 NG -2.07 2.07 -2.29 2.29 -2.29 2.29 NG
16 Com12arative Exam12le -2.29 2.29 -2.29 2.29 G -2.07 2.07 -2.29 2.29 -2.29 2.29 G
17 Comparative Example -2.29 2.29 -2.29 2.29 NG -2.07 2.07 -2.29 2.29 -2.29 2.29 NG
18 Comparative Example -2.29 2.29 -2.29 2.29 NG -2.07 2.07 -2.29 2.29 -2.29 2.29 NG
19 Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 -2.29 2.29 -2.29 2.29 G
20 Comparative Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 -2.29 2.29 -2.29 2.29 G
21 Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 -2.29 2.29 -2.29 2.29 G
22 Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 -2.29 2.29 -2.29 2.29 G
23 Comparative Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 -2.29 2.29 -2.29 2.29 G
24 Com12arative Exam12le -2.29 2.29 -2.29 2.29 NG -2.07 2.07 -2.29 2.29 -2.29 2.29 NG
25 Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
26 Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
27 Comparative Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 NG -2.29 2.29 -2.07 2.07 NG
28 Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
29 Com12arative Exam12le -2.29 2.29 -2.29 2.29 G -2.07 2.07 NG -2.29 2.29 -2.07 2.07 NG
- 54 -
[0091]
[Table 4]
WW value at x = f...DC
Re ionWW Region PP Region PP RegionZZ
Threading situation Steel pipe outer diameter tolerance
Example/ WL WB WH Point Pl PointP2 X component
No. Comparative Example min max min max
(yL) y (yH) Actual xy evaluation x(Pl) y(Pl) x(P2) y(P2) Actual xy satisfaction (ZlZ2) (ZlZ2) Inside or outside region Determination Determination
mm mm mm mm mm mm mm mm mm
l Example 0.98 2.05 3.13 G 2.29 1.06 -2.29 -1.36 G -0.84 1.14 Outside region Good G Good G
2 Comparative Example 1.28 2.35 3.43 G 2.29 1.06 -2.29 -1.36 NG -0.84 1.14 Outside region Good G Poor outer diameter NG
3 Comuarative Examule 0.58 1.65 2.73 NG 2.29 1.06 -2.29 -1.36 NG -0.84 1.14 Outside region Threaded uortion deformed NG Poor outer diameter NG
4 Example 0.58 1.65 2.73 G 2.29 1.06 -2.29 -1.36 G -0.84 1.14 Outside region Good G Good G
5 Example 0.58 1.65 2.73 G 2.29 1.06 -2.29 -1.36 G -0.84 1.14 Outside region Good G Good G
6 Comparative Example 0.58 1.65 2.73 G 2.29 1.06 -2.29 -1.36 NG -0.84 1.14 Outside region Threaded portion deformed NG Good G
7 Comparative Example 0.58 1.65 2.73 NG 2.29 1.06 -2.29 -1.36 NG -0.84 1.14 Outside region Threaded portion deformed NG Poor outer diameter NG
8 Example -0.22 0.85 1.93 G 2.29 1.06 -2.29 -1.36 G -0.84 1.14 Inside region Good G Good G
9 Comparative Example -0.22 0.85 1.93 NG 2.29 1.06 -2.29 -1.36 NG -0.84 1.14 Outside region Threaded portion deformed NG Poor outer diameter NG
lO Comparative Example -0.22 0.85 1.93 NG 2.29 1.06 -2.29 -1.36 NG -0.84 1.14 Outside region Threaded portion deformed NG Poor outer diameter NG
ll Example 0.08 1.15 2.23 G 2.29 1.06 -2.29 -1.36 G -0.84 1.14 Outside region Good G Good G
12 Comparative Example 0.08 1.15 2.23 G 2.29 1.06 -2.29 -1.36 NG -0.84 1.14 Outside region Threaded portion deformed NG Good G
13 Example 0.28 1.35 2.43 G 2.29 1.06 -2.29 -1.36 G -1.06 1.36 Outside region Good G
14 Comparative Example 0.28 1.35 2.43 G 2.29 1.06 -2.29 -1.36 NG -1.06 1.36 Outside region Poor outer diameter NG
15 Comparative Example 0.28 1.35 2.43 NG 2.29 1.06 -2.29 -1.36 NG -1.06 1.36 Outside region Poor outer diameter NG
16 Comparative Example 0.28 1.35 2.43 NG 2.29 1.06 -2.29 -1.36 NG -1.06 1.36 Outside region Poor outer diameter NG
17 Comparative Example 1.28 2.35 3.43 NG 2.29 1.06 -2.29 -1.36 NG -1.06 1.36 Outside region Poor outer diameter NG
18 Comuarative Examule 1.28 2.35 3.43 G 2.29 1.06 -2.29 -1.36 NG -1.06 1.36 Outside region Poor outer diameter NG
19 Example -0.22 0.85 1.93 G 2.29 1.06 -2.29 -1.36 G -1.06 1.36 Inside region Good G
20 Comparative Example -0.22 0.85 1.93 NG 2.29 1.06 -2.29 -1.36 NG -1.06 1.36 Outside region Poor outer diameter NG
21 Example -2.02 -0.95 0.13 G 2.29 1.06 -2.29 -1.36 G -1.06 1.36 Inside region Good G
22 Example -2.52 -1.45 -0.37 G 2.29 1.06 -2.29 -1.36 G -1.06 1.36 Outside region Good G
23 Comuarative Examule -2.02 -0.95 0.13 NG 2.29 1.06 -2.29 -1.36 NG -1.06 1.36 Outside region Poor outer diameter NG
24 Comparative Example -2.52 -1.45 -0.37 NG 2.29 1.06 -2.29 -1.36 NG -1.06 1.36 Outside region Poor outer diameter NG
25 Example -2.02 -0.95 0.13 G 2.29 1.06 -2.29 -1.36 G -0.84 1.14 Inside region Good G Good G
26 Example -2.22 -1.15 -0.07 G 2.29 1.06 -2.29 -1.36 G -0.84 1.14 Outside region Good G Good G
27 Comparative Example -2.22 -1.15 -0.07 G 2.29 1.06 -2.29 -1.36 NG -0.84 1.14 Outside region Threaded portion deformed NG Good G
28 Example -2.72 -1.65 -0.57 G 2.29 1.06 -2.29 -1.36 G -0.84 1.14 Outside region Good G Good G
29 Com12arative Exam12le -2.72 -1.65 -0.57 G 2.29 1.06 -2.29 -1.36 NG -0.84 1.14 Outside region Threaded 12ortion deformed NG Good G
- 55 -
[0092]
[Table 5]
Pipe making manufacturing conditions
Material Material
Size Strength
Example/ Composition Composition
No. Comparative c Si Mn p s Al N Nb v Ti Cu Ni Cr Mo B Ca REM
Outer
Thickness
Thickness/outer
TS
Example diameter diameter
% % % % % % ppm % % % % % % % ppm ppm ppm mm mm N/mm2
30 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 O.Q3 1000
31
Com12arative
0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 O.Q3 1000
Exam_llie
32 Example 0.27 0.10 0.80 0.010 0.003 0.015 35 76.3 4.5 0.06 950
33 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 76.3 4.5 0.06 1000
34 Example 0.08 0.45 2.00 0.010 0.005 0.010 25 0.300 76.3 4.5 0.06 1000
35 Example 0.27 0.10 0.80 0.010 0.003 0.015 35 165.2 4.5 O.Q3 950
36 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 165.2 4.5 O.Q3 1000
37 Example 0.08 0.45 2.00 0.010 0.005 0.010 25 0.300 165.2 4.5 O.Q3 1000
38 Example 0.27 0.10 0.80 0.010 0.003 0.015 35 267.4 8.0 O.Q3 950
39 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 267.4 8.0 O.Q3 1000
40 Example 0.08 0.45 2.00 0.010 0.005 0.010 25 0.300 267.4 8.0 O.Q3 1000
41 Example 0.27 0.10 0.80 0.010 0.003 0.015 35 114.3 3.5 O.Q3 950
42 Example 0.27 0.10 1.00 0.010 0.003 0.015 35 114.3 3.5 O.Q3 1000
43 Example 0.08 0.45 2.00 0.010 0.005 0.010 25 0.300 114.3 3.5 O.Q3 950
44 Example 0.13 1.00 2.20 0.015 0.003 0.015 33 0.030 114.3 3.5 O.Q3 1400
45 Example 0.16 0.20 0.80 0.010 0.005 0.020 40 0.030 114.3 3.5 O.Q3 630
46 Example 0.27 0.10 0.80 0.010 0.003 0.015 35 28 114.3 3.5 O.Q3 620
47 Example 0.18 0.20 1.25 0.010 0.005 0.020 40 0.030 0.275 114.3 3.5 O.Q3 790
48 Example 0.10 0.20 1.45 0.014 0.005 0.020 40 0.037 0.015 114.3 3.5 O.Q3 800
49 Example 0.20 0.20 1.50 0.010 0.005 0.020 40 0.042 0.042 114.3 3.5 O.Q3 780
50 Example 0.09 0.20 1.15 0.012 0.006 0.013 40 0.033 25 114.3 3.5 O.Q3 790
51 Example 0.22 0.15 1.30 0.010 0.005 0.030 33 0.023 0.300 15 114.3 3.5 O.Q3 790
52 Example 0.10 0.10 0.55 0.020 0.010 0.020 35 0.020 0.200 1.000 114.3 3.5 O.Q3 620
53 Example 0.10 0.20 1.25 0.020 0.015 0.010 35 0.025 0.015 30 114.3 3.5 O.Q3 800
54 Example 0.16 0.20 1.60 0.010 0.005 0.020 40 0.043 0.043 0.300 0.300 114.3 3.5 O.Q3 800
55 Example 0.12 0.45 0.90 0.010 0.005 0.020 40 0.040 0.350 0.100 0.500 114.3 3.5 O.Q3 820
56 Example 0.18 0.20 1.55 0.020 0.005 0.025 35 0.045 0.045 0.015 0.270 114.3 3.5 O.Q3 850
57 Example 0.12 0.25 1.90 0.020 0.005 0.010 35 0.050 0.045 0.015 30 25 114.3 3.5 O.Q3 950
58 Example 0.08 0.25 1.70 0.020 0.005 0.025 35 0.030 0.015 0.050 15 30 30 114.3 3.5 O.Q3 950
- 56 -
[0093]
[Table 6]
Joining
Steel pipe center
Result Steel pipe center portion
Steel pipe end
Result
Steel pipe end
Outer diameter tolerance portion portion portion
method
X Outer y
Outer diameter Thickness Calculation Calculation Calculation Thickness Residual
Example/
component diameter component
thickness
No. Outer
Comparative Example
Threading/ diameter
limit
fitting
Range min max DCave LiDC tCave K
standard
SD DEave LiDE tEave
deviation
% mm mm mm mm mm mm mm mm mm mm mm mm
30 Example Threading l.O% 113.2 115.4 114.30 -2.20 3.50 -0.15 0.25 0.36 114.30 -1.80 3.50 0.65
31 Com12arative Exam12le Threading l.O% 113.2 115.4 114.30 -2.40 3.50 -0.15 0.25 0.36 114.30 -1.80 3.50 0.65
32 Example Threading l.O% 75.5 77.1 76.30 -1.00 4.50 0.94 0.20 0.28 76.30 -0.05 4.50 0.65
33 Example Threading l.O% 75.5 77.1 76.30 -1.00 4.50 0.92 0.20 0.28 76.30 -0.06 4.50 0.65
34 Example Threading l.O% 75.5 77.1 76.30 -1.00 4.50 0.92 0.20 0.28 76.30 -0.04 4.50 0.65
35 Example Threading l.O% 163.5 166.9 165.20 1.20 4.50 -1.05 0.33 0.47 165.20 0.10 4.50 0.65
36 Example Threading l.O% 163.5 166.9 165.20 1.20 4.50 -l.lO 0.34 0.48 165.20 0.10 4.50 0.65
37 Example Threading l.O% 163.5 166.9 165.20 1.20 4.50 -l.lO 0.34 0.48 165.20 0.12 4.50 0.65
38 Example Threading l.O% 264.7 270.1 267.40 2.00 8.00 -2.12 0.53 0.75 267.40 -0.10 8.00 0.65
39 Example Threading l.O% 264.7 270.1 267.40 2.00 8.00 -2.21 0.54 0.76 267.40 -0.20 8.00 0.65
40 Example Threading l.O% 264.7 270.1 267.40 2.00 8.00 -2.21 0.54 0.76 267.40 -0.20 8.00 0.65
41 Example Threading l.O% 113.2 115.4 114.30 0.50 3.50 -0.11 0.25 0.35 114.30 0.30 3.50 0.65
42 Example Threading l.O% 113.2 115.4 114.30 0.50 3.50 -0.15 0.25 0.36 114.30 0.30 3.50 0.65
43 Example Threading l.O% 113.2 115.4 114.30 0.40 3.50 -0.11 0.25 0.35 114.30 0.25 3.50 0.65
44 Example Threading l.O% 113.2 115.4 114.30 0.35 3.50 -0.45 0.28 0.40 114.30 0.00 3.50 0.65
45 Example Threading l.O% 113.2 115.4 114.30 0.35 3.50 0.13 0.23 0.32 114.30 0.45 3.50 0.65
46 Example Threading l.O% 113.2 115.4 114.30 0.35 3.50 0.14 0.23 0.32 114.30 0.45 3.50 0.65
47 Example Threading l.O% 113.2 115.4 114.30 0.43 3.50 0.01 0.24 0.34 114.30 0.40 3.50 0.65
48 Example Threading l.O% 113.2 115.4 114.30 0.30 3.50 0.00 0.24 0.34 114.30 0.28 3.50 0.65
49 Example Threading l.O% 113.2 115.4 114.30 0.40 3.50 0.02 0.24 0.34 114.30 0.40 3.50 0.65
50 Example Threading l.O% 113.2 115.4 114.30 0.35 3.50 0.01 0.24 0.34 114.30 0.35 3.50 0.65
51 Example Threading l.O% 113.2 115.4 114.30 0.35 3.50 0.01 0.24 0.34 114.30 0.35 3.50 0.65
52 Example Threading l.O% 113.2 115.4 114.30 0.35 3.50 0.14 0.23 0.32 114.30 0.45 3.50 0.65
53 Example Threading l.O% 113.2 115.4 114.30 0.43 3.50 0.00 0.24 0.34 114.30 0.44 3.50 0.65
54 Example Threading l.O% 113.2 115.4 114.30 0.30 3.50 0.00 0.24 0.34 114.30 0.26 3.50 0.65
55 Example Threading l.O% 113.2 115.4 114.30 0.30 3.50 -0.01 0.24 0.34 114.30 0.40 3.50 0.65
56 Example Threading l.O% 113.2 115.4 114.30 0.30 3.50 -0.03 0.24 0.34 114.30 0.25 3.50 0.65
57 Example Threading l.O% 113.2 115.4 114.30 0.30 3.50 -0.11 0.25 0.35 114.30 0.16 3.50 0.65
58 Example Threading l.O% 113.2 115.4 114.30 0.35 3.50 -0.11 0.25 0.35 114.30 0.22 3.50 0.65
- 57 -
[0094]
[Table 7]
RegionAA Region YY Region XX
Line Line Line Line
LineYL LineYH X component Y component
No.
Example/ A4A3 AlA2 A3A2 A4Al
Comparative Example Actual xy Actual xy min max min max Actual xy
X X y y
evaluation
y y
evaluation (X4X3) (XlX2) (X3X2) (X4Xl) evaluation
mm mm mm mm mm mm mm mm mm mm
30 Example -2.29 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
31 Comuarative Examule -2.29 2.29 -2.29 2.29 NG -2.07 2.07 G -2.29 2.29 -2.07 2.07 NG
32 Example -1.5 1.53 -1.53 1.53 G -3.40 3.40 G -1.53 1.53 -1.53 1.53 G
33 Example -1.5 1.53 -1.53 1.53 G -3.40 3.40 G -1.53 1.53 -1.53 1.53 G
34 Example -1.5 1.53 -1.53 1.53 G -3.40 3.40 G -1.53 1.53 -1.53 1.53 G
35 Example -3.3 3.30 -3.30 3.30 G -3.40 3.40 G -3.30 3.30 -3.30 3.30 G
36 Example -3.3 3.30 -3.30 3.30 G -3.40 3.40 G -3.30 3.30 -3.30 3.30 G
37 Example -3.3 3.30 -3.30 3.30 G -3.40 3.40 G -3.30 3.30 -3.30 3.30 G
38 Example -5.3 5.35 -5.35 5.35 G -8.07 8.07 G -5.35 5.35 -5.35 5.35 G
39 Example -5.3 5.35 -5.35 5.35 G -8.07 8.07 G -5.35 5.35 -5.35 5.35 G
40 Example -5.3 5.35 -5.35 5.35 G -8.07 8.07 G -5.35 5.35 -5.35 5.35 G
41 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
42 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
43 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
44 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
45 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
46 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
47 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
48 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
49 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
50 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
51 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
52 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
53 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
54 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
55 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
56 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
57 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
58 Example -2.3 2.29 -2.29 2.29 G -2.07 2.07 G -2.29 2.29 -2.07 2.07 G
- 58 -
[0095]
[Table 8]
WW value at x = f...DC
RegionWW Region PP Region PP RegionZZ Threading situation Steel pipe outer diameter tolerance
WL WB WH Point Pl Point P2 X component
No. Example/
Comparative Example min max min max (yL) y (yH) Actual xy evaluation x(Pl) y(Pl) x(P2) y(P2) Actual xy satisfaction (ZlZ2) (ZlZ2) Inside or outside region Determination Determination
mm mm mm mm mm mm mm mm mm
30 Example -3.42 -2.35 -1.27 G 2.29 1.06 -2.29 -1.36 G -0.84 1.14 Outside region Good G Good G
31 Comparative Example -3.62 -2.55 -1.47 G 2.29 1.06 -2.29 -1.36 NG -0.84 1.14 Outside region Good G Poor outer diameter NG
32 Example -0.90 -0.06 0.79 G 1.53 1.63 -1.53 0.26 G -1.63 -0.26 Inside region Good G Good G
33 Example -0.93 -0.08 0.77 G 1.53 1.59 -1.53 0.24 G -1.59 -0.24 Inside region Good G Good G
34 Example -0.93 -0.08 0.77 G 1.53 1.59 -1.53 0.24 G -1.59 -0.24 Inside region Good G Good G
35 Example -1.27 0.15 1.57 G 3.30 0.84 -3.30 -2.94 G -0.84 2.94 Inside region Good G Good G
36 Example -1.34 0.10 1.53 G 3.30 0.76 -3.30 -2.97 G -0.76 2.97 Inside region Good G Good G
37 Example -1.34 0.10 1.53 G 3.30 0.76 -3.30 -2.97 G -0.76 2.97 Inside region Good G Good G
38 Example -2.36 -0.12 2.11 G 5.35 0.99 -5.35 -5.23 G -0.99 5.23 Inside region Good G Good G
39 Example -2.48 -0.21 2.06 G 5.35 0.86 -5.35 -5.29 G -0.86 5.29 Inside region Good G Good G
40 Example -2.48 -0.21 2.06 G 5.35 0.86 -5.35 -5.29 G -0.86 5.29 Inside region Good G Good G
41 Example -0.67 0.39 1.45 G 2.29 l.ll -2.29 -1.34 G -0.89 1.12 Inside region Good G Good G
42 Example -0.72 0.35 1.43 G 2.29 1.06 -2.29 -1.36 G -0.84 1.14 Inside region Good G Good G
43 Example -0.77 0.29 1.35 G 2.29 l.ll -2.29 -1.34 G -0.89 1.12 Inside region Good G Good G
44 Example -1.30 -0.10 1.09 G 2.29 0.64 -2.29 -1.55 G -0.42 1.33 Inside region Good G Good G
45 Example -0.48 0.48 1.45 G 2.29 1.45 -2.29 -1.19 G -1.23 0.97 Inside region Good G Good G
46 Example -0.47 0.49 1.45 G 2.29 1.46 -2.29 -1.18 G -1.24 0.96 Inside region Good G Good G
47 Example -0.57 0.44 1.45 G 2.29 1.28 -2.29 -1.26 G -1.06 1.04 Inside region Good G Good G
48 Example -0.71 0.30 1.32 G 2.29 1.27 -2.29 -1.27 G -1.05 1.05 Inside region Good G Good G
49 Example -0.59 0.42 1.43 G 2.29 1.29 -2.29 -1.26 G -1.07 1.04 Inside region Good G Good G
50 Example -0.65 0.36 1.37 G 2.29 1.28 -2.29 -1.26 G -1.06 1.04 Inside region Good G Good G
51 Example -0.65 0.36 1.37 G 2.29 1.28 -2.29 -1.26 G -1.06 1.04 Inside region Good G Good G
52 Example -0.47 0.49 1.45 G 2.29 1.46 -2.29 -1.18 G -1.24 0.96 Inside region Good G Good G
53 Example -0.58 0.43 1.45 G 2.29 1.27 -2.29 -1.27 G -1.05 1.05 Inside region Good G Good G
54 Example -0.71 0.30 1.32 G 2.29 1.27 -2.29 -1.27 G -1.05 1.05 Inside region Good G Good G
55 Example -0.73 0.29 1.31 G 2.29 1.25 -2.29 -1.28 G -1.03 1.06 Inside region Good G Good G
56 Example -0.77 0.27 1.30 G 2.29 1.22 -2.29 -1.29 G -1.00 1.07 Inside region Good G Good G
57 Example -0.87 0.19 1.25 G 2.29 l.ll -2.29 -1.34 G -0.89 1.12 Inside region Good G Good G
58 Example -0.82 0.24 1.30 G 2.29 l.ll -2.29 -1.34 G -0.89 1.12 Inside region Good G Good G
- 59 -
[0096]
In a case where the region AA cannot be satisfied, the outer diameter
tolerance required for both the steel pipe end portion and the steel pipe center portion
cannot be secured, and this can be determined by measuring the outer diameter of the
steel pipe. In this case, the circular shape necessary for use as a structural pipe cannot
be secured, so that a necessary bending moment or bending proof stress cannot be
secured, deformation or buckling occurs during use, and a necessary function as the
structural pipe cannot be satisfied.
[0097]
In a case where the region YY cannot be satisfied, the residual thickness
necessary for threads cannot be secured, deformation may occur during threading, and
the function of threads such as poor connection cannot be secured during use. This
can be visually determined by measuring the dimensions with a screw gauge or the like.
In addition, as a pipe body, the required residual thickness cannot be secured, so that
the strength of the joint cannot be secured, deformation such as bending of a joint
portion during use, fracture, and the like may occur, and the function as the original
application cannot be secured. This can be visually determined.
[0098]
The case where the region XX cannot be satisfied is, in other words, a case
where either one or both of the regions AA and YY cannot be satisfied, and in this case,
a defect which cannot be satisfied by each thereof occurs.
[0099]
In a case where the region WW cannot be satisfied, the operation result
deviates from the relationship between the vertical ellipticities of the steel pipe center
portion and the steel pipe end portion obtained in the present invention, and correct
- 60 -
forming is not performed. This means that manufacturing is not correctively
performed due to local shape defects of the product or abnormalities in facilities, and a
certain degree of quality is not obtained in the manufacturing lot, so that this cannot be
regarded as a product. This can be determined by visual inspection of the product and
inspection of the facilities. In addition, in the case where the region WW cannot be
satisfied, correct forming is not performed, so that a steel pipe shape necessary for
threading cannot be formed. Therefore, deformation may occur during threading, the
function of the threads such as poor connection cannot be secured during use, and the
outer diameter tolerance cannot be secured as a constant value in the manufacturing lot,
so that these cannot be satisfied. Securing the region WW is a prerequisite to
threading without deformation and securing of the outer diameter tolerance.
[0100]
As the evaluation of the steel pipe in the examples of Table 1, the threading
situation and the securing of the outer diameter tolerance of the steel pipe are shown.
Securing the outer diameter tolerance of the steel pipe refers to a case where both the
steel pipe end portion and the steel pipe center portion satisfy the outer diameter
tolerance.
In the threading situation, in a case where the region WW, which is a
condition for performing correct forming and securing a certain degree of quality of a
steel pipe product, is satisfied, and the region YY, which is a condition for securing the
residual thickness necessary for threads, can be simultaneously satisfied, good
threading is possible. In securing the outer diameter tolerance of the steel pipe, in a
case where the region WW, which is a condition for performing correct forming and
securing a certain degree of quality as a steel pipe product, is satisfied, and the region
AA, which is a condition for securing the outer diameter tolerance, can be
- 61 -
simultaneous! y satisfied, it is possible to secure the outer diameter tolerance of the
steel pipe.
[0101]
The case where the region PP cannot be satisfied is, in other words, a case
where either one or both of the regions XX and WW cannot be satisfied, and in this
case, a defect which cannot be satisfied by each thereof occurs. In a case where only
the region XX is not satisfied, the residual thickness necessary for threads cannot be
secured, deformation may occur during threading, and the function of threads such as
poor connection cannot be secured during use.
In a case where only the region WW is not satisfied, correct forming is not
performed, so that a steel pipe shape necessary for threading cannot be formed.
Therefore, deformation may occur during threading, and the function of threads such
as poor connection cannot be secured during use. At the same time, the outer
diameter tolerance cannot be secured as a constant value in the manufacturing lot, so
that the outer diameter tolerance cannot be satisfied either. In a case where both the
region XX and the region WW are not satisfied, the residual thickness necessary for
threads in threading cannot be secured, and accordingly, deformation occurs during
threading. In addition, since a necessary steel pipe shape cannot be formed,
deformation may occur during threading, and for both reasons, the function of the
threads such as poor connection cannot be secured during use. At the same time, the
outer diameter tolerance cannot be secured as a constant value in the manufacturing lot,
so that the outer diameter tolerance cannot be satisfied either.
[0102]
The region ZZ is the range of a better example, and even when a range
deviates from the region ZZ, the range is also an example as long as the range is within
- 62 -
the region XX or WW.
[0103]
Comparative Examples Nos. 2 and 31 of Table 1 will be described. In these
comparative examples, the outer diameter tolerance of the steel pipe is "poor", but the
threading condition situation is "good". This is a case where the outer diameter
tolerance of the steel pipe center portion was not satisfied, but the outer diameter
tolerance of the steel pipe end portion could be satisfied. In this example, since the
region WW and the region YY are satisfied, thread cutting is possible. However,
since the outer diameter tolerance of the steel pipe center portion is not satisfied, the
outer diameter tolerance is "poor", and since the function necessary as a structural pipe
is not satisfied, this cannot be a product and is a comparative example.
[0104]
While the preferred embodiments of the present invention have been
described above in detail with reference to the accompanying drawings, the present
invention is not limited to such examples. It is obvious that a person having ordinary
knowledge in the technical field to which the present invention pertains can come up
with various changes or modifications within the scope of the technical idea described
in the claims, and it is understood that these naturally belong to the technical scope of
the present invention.
[Industrial Applicability]
[0105]
According to the present invention, it is possible to provide a high strength
electric resistance welded steel pipe which has a light weight and high strength and has
high circularity at a steel pipe end portion generated by new cutting after pipe making,
and a method for using a high strength electric resistance welded steel pipe for ground
- 63 -
stabilization work. Therefore, great industrial applicability is achieved.

WE CLAIMS

1. A high strength electric resistance welded steel pipe comprising, by
mass% or by mass ppm:
C: 0.04% to 0.30%;
Si: 0.01% to 2.00%;
Mn: 0.50% to 3.00%;
P: 0.030% or less;
S: 0.030% or less;
Al: 0.005% to 0.700%;
N: 100 ppm or less;
Nb: 0% to 0.100%;
V: 0% to 0.100%;
Ti: 0% to 0.200%;
Ni: 0% to 1.000%;
Cu: 0% to 1.000%;
Cr: 0% to 1.000%;
Mo: 0% to 1.000%;
B: 0 to 50 ppm;
Ca: 0 to 100 ppm;
REM: 0 to 200 ppm; and
a remainder consisting of Fe and impurities,
wherein DCave is 60.3 mm to 318.5 mm,
tCave/DCave is 0.02 to 0.06,
a tensile strength is 590 N/mm2 or more, and
in a case where a steel pipe center portion is cut, the following expressions are
- 65 -
satisfied,
DC ave x (-211 00) :::; x :::; DC ave x (2/1 00) (1)
YN:Sy:SYM (2)
X + K - 3 X SD :::; y :::; X + K + 3 X SD (3)
YM =MIN[ {DEave x (21100) },{ 4 x ((tEave/3)- 0.65)}] (4)
where, in Expression (4), the smaller of {DEave x (21100)} and { 4 x
((tEave/3)- 0.65)} is defined as YM,
YN = MAX[{DEave x (-21100)},{ -4 x ((tEave/3)- 0.65)}] (5)
where, in Expression (5), the larger of [{DEave x (-21100)} and { -4 x
((tEave/3) - 0.65)} is defined as YN,
K ={a+ (~/I)+ (y x TS)} x DCave (6)
SD = (~2) x (a standard deviation of an average outer diameter DCave of the
steel pipe center portion) (7)
a standard deviation of an outer diameter of the steel pipe center portion= {p
+ (q/I) + (r x TS)} x DCave (8)
where x: a vertical ellipticity (steel pipe center portion), y: a vertical ellipticity
(steel pipe end portion), DCave: the average outer diameter (mm) of the steel pipe
center portion after pipe making and before cutting, tCave: an average thickness (mm)
of the steel pipe of the steel pipe center portion after pipe making and before cutting,
DEave: an average outer diameter (mm) of the steel pipe end portion after pipe making
and after cutting, tEave: an average thickness (mm) of the steel pipe end portion after
pipe making and after cutting, TS: a tensile strength (N/mm2
) of a base material
portion of the high strength electric resistance welded steel pipe, a, ~' and y are
constants,
a= -1.87 X Io-3 (9)
- 66 -
portion,
1,
~ = 1.35 X 104 (10)
y = -6.65 x 10-6 (11)
I is a second moment of area (mm4
) of a cross section of the steel pipe center
I = n/64 x { (DCave )4
- (DCave - 2 x tCave )4
}
p, q, and rare constants,
p = 1.39 x 10-3 (13)
q = 4.17 X 102 (14)
r = 6.05 X 10-7 (15).
(12), and
2. The high strength electric resistance welded steel pipe according to claim
wherein the tensile strength is 780 N/mm2 or more.
3. The high strength electric resistance welded steel pipe according to claim
1 or 2, further satisfying the following expression,
YN - K + 3 x SD :::; x :::; YM - K - 3 x SD (17).
4. The high strength electric resistance welded steel pipe according to claim
1 or 2, further satisfying the following expression,
DEave x (-21100)- K + 3 x SD:::; x:::; DEave x (2/100)- K- 3 x SD (18).
5. A method for using a high strength electric resistance welded steel pipe
for ground stabilization work, comprising:
performing thread cutting on new steel pipe end portions generated by cutting
- 67 -
the high strength electric resistance welded steel pipe according to claim 1 or 2 at a
steel pipe center portion; and
connecting two or more high strength electric resistance welded steel pipes
with a screw joint to be used.
6. A method for using a high strength electric resistance welded steel pipe
for ground stabilization work, comprising:
connecting two or more high strength electric resistance welded steel pipes by
fitting one or both of steel pipe end portions of the high strength electric resistance
welded steel pipe according to claim 1 or 2 to a new steel pipe end portion generated
by performing cutting at a steel pipe center portion, via one or a plurality of jigs to be
used.