Note: Descriptions are shown in the official language in which they were submitted.
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SPECIFICATION
TITLE: Method of producing steel pipe
TECHNICAL FIELD
[0001] This invention relates to a method of producing a large-diameter
and
thick-walled steel pipe used in line pipe and the like.
RELATED ART
[0002] Steel pipes manufactured by a process including U-ing, 0-ing and
Expanding (UOE), referred to as UOE steel pipes, are widely used as the large-
diameter
and thick-walled steel pipe used in the line pipe. A so-called UOE steel pipe
produced
by press bending a steel plate as a material having predetermined width,
length and
thickness into a U-shaped form, further press forming into a 0-shaped form,
welding a
seam to form a steel pipe, and thereafter performing pipe expanding for
increasing a
diameter of the steel pipe to enhance a roundness. In the production method of
the UOE
steel pipe as mentioned above, however, a significant press force is required
at steps of
press-forming the steel plate into U-shaped and 0-shaped forms, so that it is
necessary
to use a large-scale press machine.
100031 There is developed a method of producing the large-diameter and
thick-walled steel pipe by reducing the press force. For example, a method of
bending a widthwise end portion of a steel plate (edge bending) and performing
plural times of three-point bending press to shape the steel plate into
substantially a
cylindrical form, welding a seam to form a steel pipe, and then inserting a
pipe
expander into the inside of the steel pipe to perform pipe expanding is put
into
practical use. The pipe expander is provided with a plurality of expander
tools each
having a curved surface of a divided circular arc, and has an action of
arranging the
form of the steel pipe to enhance the roundness by pushing the curved surface
to the
inner face of the steel pipe to enlarge the pipe (pipe expanding).
[0004] When the steel pipe is produced by the above method, if the
number of
times of the three-point bending press is increased, the roundness of the
resulting
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steel pipe is improved, whereas a long time is required for the production of
the steel
pipe and the productivity is lowered. Inversely, if the number of times of the
three-point bending press is decreased, the productivity is improved, but the
roundness of the steel pipe is lowered. To this end, it is actual to perform
the
production by setting the number of times of the three-point bending press in
accordance with the size of the steel pipe, for example, empirically setting
to 50-60
times in case of a steel pipe having a diameter of 1200 mm.
[0005] On the other hand, there is examined a technique of decreasing
the press
number applied to the steel plate and providing a steel pipe with a good
roundness.
For example, Patent Document 1 discloses a technique wherein a steel plate is
subjected to press bending with a die 4 times and further seams thereof are
welded to
form a steel pipe and then hot roll forming is applied to the steel pipe by
heating to
arrange the form thereof.
PRIOR ART DOCUMENTS
PATENT DOCUMENT
[0006] Patent Document 1: JP-A-2005-324255
SUMMARY OF THE INVENTION
TASK TO BE SOLVED BY THE INVENTION
[0007] However, the technique of Patent Document 1 requires the heating
of the
steel pipe, so that it is necessary to use a heating apparatus, which brings
about the
increase of the production cost. Also, there is a problem that excellent
properties
such as strength, toughness, weldability and the like provided to the raw
steel plate
by taking a technique of accelerated cooling or the like are deteriorated by
heating
the steel pipe.
[0008] The present invention is made in view of the above problems inherent
to
the conventional technique and is to propose a method of producing a steel
pipe
wherein the heating of the steel pipe is not required in the production of the
large-diameter and thick-walled steel pipe by performing plural times of three-
point
bending press and a good roundness can be attained even if the number of times
of
three-point bending press is decreased.
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SOLUTION FOR TASK
[0009] In the production of the steel pipe, the number of times of three-
point
bending press or the center to center spacing of dies thereof (feed pitch of
steel plate)
is usually set so as not to generate a gap in a deformation area by bending
press in
order to enhance the roundness of the steel pipe. Therefore, if the number of
times of
three-point bending press is decreased for shortening the production time of
the steel
pipe, the center to center spacing of dies is increased, and hence the
deformation area
bent by three-point bending press is are-like, while non-deformation area is
flat, so
that the roundness of the resulting steel pipe becomes low.
[0010] The inventors have turned attention to a deformation amount applied
to
the steel pipe in the pipe expanding and made further studies on the method
for
enhancing the roundness of the steel pipe produced by performing plural times
of
three-point bending press. As a result, it has been found out that when the
steel pipe
is expanded, there is a tendency that the deformation amount (expanding
amount)
becomes large at sites of contacting plural expander tools of the pipe
expander
inserted with the inside of the steel pipe, while the deformation amount
becomes
small at sites not contacting the expansion tool therewith.
100111 From the above knowledge, it has been conceived that when the
welded
steel pipe is expanded after the three-point bending press, the non-
deformation area
retained at a flat state is shaped into an arc form by pushing the expander
tool to the
non-deformation area to perform pipe expanding and forms continuously a
circular
arc together with the deformation area previously shaped into an arc form by
three-point bending press to thereby provide a steel pipe having a good
roundness,
and as a result, the invention has been accomplished. Moreover, the steel pipe
after
the welding and before the pipe expanding is called as "non-expanded pipe''
hereinafter.
100121 That is, the present invention proposes a method of producing a
steel pipe,
comprising:
= edge bending a steel plate;
= shaping the steel plate into a cylindrical form through plural times of
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three-point bending press in widthwise direction, thereby creating deformed
areas and non-deformed areas of the three-point press;
= seam-welding two opposite lateral edges of the steel plate to form a
non-expanded pipe having the deformed areas and the non-deformed areas
between the deformed areas due to the three-point bending press;
= inserting a pipe expander provided with a plurality of expander tools
inside
the non-expanded pipe wherein said plurality of expander tools is N and said
plurality of three-point press bendings is aN - 1 wherein a is an integer
number; and
= pushing the expander tools onto all the non-deformed areas to perform the
pipe expanding.
EFFECT OF THE INVENTION
[0013] According to the present invention, when a large-diameter and
thick-walled steel pipe is produced by performing three-point bending press,
the
number of times of three-point bending press can be decreased without
requiring the
heating of the steel pipe, so that it is possible to produce a steel pipe
having an
excellent roundness in a high productivity without damaging excellent
properties
such as strength, toughness, weldability and the like provided during the
production
process of the raw steel plate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIGS. 1(a) to 1(e) illustrate schematic views illustrating
production
process of a non-expanded pipe according to the present invention.
FIGS. 2(a) and 2(b) illustrates schematic views illustrating a three-point
bending press method.
FIG. 3 illustrates a schematic view illustrating a steel pipe A (Invention
Example) formed by expanding a non-expanded pipe having 12 non-deformation
areas
shaped by 11 times of three-point bending press with 12 expander tools.
FIG. 4 illustrates a schematic view illustrating a steel pipe B (Invention
Example) formed by expanding a non-expanded pipe having 20 non-deformation
areas
shaped by 19 times of three-point bending press with 10 expander tools.
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FIG. 5 illustrates a schematic view illustrating a steel pipe D (Comparative
Example) of expanding a non-expanded pipe having 12 non-deformation areas
shaped
by 11 times of three-point bending press with 12 expander tools.
FIG. 6 illustrates a schematic view illustrating a steel pipe G (Comparative
Example) of expanding a non-expanded pipe after 11 times of three-point
bending
press with 10 expander tools.
FIG. 7 illustrates a view showing a difference m.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
[0015] The production process of the non-expanded pipe in the production
method of the steel pipe according to the present invention will be described
with
reference to FIGS. 1(a) to 1(e).
[0016] After both widthwise end portions (width L) of a steel plate 3
having a
plate width W illustrated in FIG. 1(a) are curved to form bent portions
(hereinafter
referred to as "edge bending"), one half of the plate divided by a widthwise
central
line CL illustrated in FIG. 1(b) is subjected to plural times of three-point
bending
press 4 from one widthwise end of the steel plate 3 toward widthwise center
thereof
(provided that a portion of the widthwise central line CL is left unpressed),
whereby
one half of the steel plate 3 is shaped into substantially a semicircular
form. In the
three-point bending press, the steel plate 3 is placed on two lower dies 5a,
5b
arranged at a given distance and an arc-like curved surface of an upper
forming tool
6 is pressed onto the steel plate 3 to perform bending work. Also, the
distance
between positions of pressing the upper forming tool in the three-point
bending press
4 (which may be called as "feed pitch P" hereinafter) is equal distance.
However, the
three-point bending press cannot be used in the edge bending at both widthwise
end
portions of the steel plate 3. The three-point bending press cannot be
performed
because the end portion of the sheet plate 3 does not touch one of the lower
dies. To
this end, the edge bending is usually performed by pressing with a pair of
upper and
lower dies.
[0017] As illustrated in FIG. 1(c), the remaining half of the steel
plate from the
widthwise central line CL is subjected to plural times of three-point bending
press 4
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at equal distances (provided that the portion of the widthwise central line CL
is
retained unpressed), whereby the steel plate 3 is shaped into substantially a
semicircular form. Finally, as illustrated in FIG. 1(d), both the widthwise
end
portions of the steel plate 3 are butted by performing three-point bending
press 4 at
the position of the widthwise central line CL and thereafter the seam is
welded to
form a non-expanded pipe 1 illustrated in FIG. 1(e).
[0018] In the thus obtained non-expanded pipe 1, there are arc-like
deformation
areas 8 (solid line portions) and flat non-deformation areas 9 (dotted line
portions) as
illustrated by section in FIG. 3. The deformation area 8 is a site subjected
to
deformation by a series of the above three-point bending press illustrated in
FIGS.
1(a) to 1(e) (or a site subjected to deformation by pressing the arc-like
curved
surface of the upper forming tool 6), and the non-deformation area 9 is a site
not
deformed by the three-point bending press.
[0019] Then, a pipe expander provided with a plurality of expander tools
having
curved surfaces of plural divided arcs is inserted into the inside of the non-
expanded
pipe and enlarged in radial direction to expand the non-expanded pipe to
thereby
form a steel pipe. As previously mentioned, the non-expanded pipe has the arc-
like
deformation areas and the flat non-deformation areas. Therefore, it is
necessary to
deform the flat non-deformation area into an arc form for enhancing the
roundness of
the steel pipe. However, since a gap exists between the adjoining expander
tools in
the pipe expander, the non-expanded pipe cannot be expanded in the
circumferential
direction uniformly.
[0020] In the present invention, therefore, when the pipe expanding is
performed
by inserting the pipe expander provided with the plural expander tools into
the inside
of the non-expanded pipe, the arc-like curved surfaces of the expander tools
are
pushed onto all of the non-deformation areas to expand the non-expanded pipe.
Thus, the non-deformation areas are preferentially deformed while suppressing
the
deformation of the deformation area not contacting with the expander tool,
whereby
the non-deformation areas can form a continuous arc together with the
deformation
areas previously shaped into an arc form and hence the roundness of the steel
pipe
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can be enhanced.
10021] In order to deform the non-deformation areas into an arc form in
a good
roundness as mentioned above, it is preferable that the number of the
non-deformation areas in the non-expanded pipe is the same as the number of
the
expander tools in the pipe expander inserted into the inside of the non-
expanded pipe.
That is, when the number of the expander tools is N, it is preferable to
perform the
three-point bending press so as to render the number of the non-deformation
areas in
the non-expanded pipe into N sites. In this case, one welded seam and (N-1)
deformation areas are arranged in gaps of N expander tools. Also, the number
of
times of three-point bending press may be (N-1).
[0022] For instance, FIG. 3 illustrates a case that the number of the
non-deformation areas 9 is coincident with the number of the expander tools 2,
namely, a view showing an example of expanding the non-expanded pipe 1
subjected
to three-point bending press of 11 times with twelve expander tools 2. As
illustrated in FIG. 3, the number of times of three-point bending press 4
subjected to
the raw steel plate for providing twelve non-deformation areas 9 may be 5
times of
three-point bending press 4 subjected to one half of the plate divided by
widthwise
central line CL illustrated in FIG. 1(b), 5 times of three-point bending press
4
subjected to the other half of the plate divided by widthwise central line CL
in FIG.
1(c), and 1 time of three-point bending press 4 subjected at the position of
widthwise
central line CL illustrated in FIG. 1(d) (11 times in total). This is because
the
non-deformation areas are 12 sites in total between deformation areas by three-
point
press bending (10 sites) and between edge bent portion and deformation area by
three-point bending press (2 sites). Therefore, the pipe expanding may be
performed by pushing the twelve expander tools onto all of the respective 12
non-deformation areas.
[0023] In the present invention, the number of the non-deformation areas
in the
non-expanded pipe may be an integral multiple of the number of expander tools
in
the pipe expander inserted into the inside of the non-expanded pipe such as 2
times,
3 times or the like. FIG. 4 illustrates a case that pipe expanding is
performed by
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inserting a pipe expander with ten expander tools 2 into a non-expanded pipe 1
having twenty non-deformation areas 9 formed by three-point bending press of
19
times, namely, an example that the number of the non-deformation areas 9 is 2
times
of the number of the expander tools 2. In this case, each of the expander
tools can
be pushed onto all of the non-deformation areas in such a manner that one
expander
tool is pushed onto the two adjacent non-deformation areas. As illustrated in
FIG. 4,
the number of times of three-point bending press required for forming 2N sites
of
non-deformation areas corresponding to 2 times of the number of expander tools
N
may be (2N - 1).
[0024] As mentioned above, when the number of the expander tools in the
present invention is N, the number of times of three-point bending press is
(aN - 1)
(wherein a is an arbitrary integer such as 1, 2, or the like). FIG. 3
corresponds to an
example of a = 1, and FIG. 4 corresponds to an example of a = 2. Even if a is
3 or
more, each expander tool is pushed onto a site of the non-deformation areas
and then
all of non-deformation areas can be pushed onto the expander tools.
[0025] In the present invention, the feed pitch of the steel plate in
the three-point
bending press is at equal distance, so that the width of the non-deformation
area is
same as the feed pitch in the press. The feed pitch Pp is represented by the
following equation (1) when a distance of start position of three-point
bending press
from a center of plate width is Wo and the press number is M:
Pp ----- 2W0/(M-1) .... (1)
[0026] Moreover, the Wo is (W/2 - (L + Pp/2)) when the plate width of
the raw
steel plate is Wand the width of edge bending is L. Therefore, the equation
(1) is
transformed into Pp = (W - 2L)/M. Also, when the number of the expander tools
(division number of circumference) is N, the number of the sites not
contacting with
the expander tool is N, so that the interval of the non-deformation area I'd
is
represented by the following equation (2):
Pd = W/N .... (2)
[0027] Therefore, in order to push all of the expander tools onto all of
the
non-deformation areas, it is enough to set the press number M and the width of
edge
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bending L so that the value Pp is same as Pd or a value obtained by dividing
Pd by
integral multiple. In the setting of Pp, considering the width of the non-
deformation
area during three-point bending press, the whole region of the non-deformation
areas
may be pushed by the expander tools, and then the roundness can be more
improved.
[0028] By using the production method according to the present invention as
mentioned above, when the number of expander tools is N, the number of times
of
three-point bending press required for the production of large-diameter and
thick-walled steel pipes can be reduced to (aN - 1) (wherein a is an integer
of 1, 2 or
the like), so that it is possible to largely improve the productivity of the
steel pipes.
Also, all steps from edge bending of the steel plate through three-point
bending press
to pipe expanding can be conducted as cold working, so that the steel pipes
can be
produced without damaging excellent properties inherent to the raw steel
plate.
Particularly, the effect of the present invention is remarkable in the
production of
thick-walled steel pipes having a thickness of 25.4-50.8 mm.
EXAMPLES
[0029] There are provided seven raw steel plates having a plate width W
of 3713
mm (thickness: 25.4 mm, tensile strength: 745,-757 MPa). Both widthwise end
portions of the steel plate (width L: 215 mm) are subjected to edge bent with
dies
having a radius of curvature of 380 mm so as to render a bent angle after load
removal (see FIG. 1(b)) into 16.9 . Then, the edge bent steel plate is shaped
into a
cylindrical form by subjecting to three-point bending press with an upper
forming
tool having a radius of curvature of 380 mm, and the seam is welded to form a
non-expanded pipe. Thereafter, a pipe expander provided with plural expander
tools each having a radius of curvature of 580 mm at a surface pushing onto an
inner
face of the non-expanded pipe is inserted into the inside of the non-expanded
pipe
and pipe expanding is performed at a pipe expanding ratio (= 100 x (diameter
after
pipe expanding - diameter before pipe expanding)/ (diameter before pipe
expanding)
of 1% to produce a steel pipe. Moreover, conditions of three-point bending
press
other than the above condition and conditions of pipe expanding are varied as
shown
in Tables 1 and 2.
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[0030] In a steel pipe A (Invention Example), the raw steel plate is
shaped into
substantially a cylindrical form by subjecting to three-point bending press of
5 times
with a starting point at a position of 1492 mm from a widthwise central line
toward
one side at a feed pitch Pp in a direction of widthwise central line of 298
mm, then
subjecting to three-point bending press of 5 times with a starting point at a
position
of 1492 mm from a widthwise central line toward the other side at a feed pitch
Pp in
a direction of widthwise central line of 298 mm, and finally subjecting to
three-point
bending press of 1 time at a position of widthwise central line (11 times in
total), and
thereafter widthwise ends of the steel plate are welded to each other to form
a
non-expanded pipe having 12 non-deformation areas. Moreover, a bent angle of
the
steel plate 3 after load removal in three-point bending press (see FIG. 2(b))
is 29.6 .
[0031] Thereafter, a pipe expander provided with 12 expander tools in a
circumferential direction is inserted into the inside of the non-expanded pipe
and the
expander tool is pushed onto the respective non-deformation area and the
welded
portion is disposed in the gap between the expander tools to perform pipe
expanding
as illustrated in FIGS. 1(a) to 1(e), whereby a steel pipe is produced.
Incidentally, a
face of the expander tool contacting with an inner face of the non-expanded
pipe is
an arc having a radius of curvature of 580 mm and an angle of 27.7 (the same
applies hereafter when the number of expander tools is 12).
[0032] A steel pipe B (Invention Example) is an example of producing a
steel
pipe by manufacturing a non-expanded pipe having 10 non-deformation areas
under
conditions shown in Table 1, inserting a pipe expander provided with 10
expander
tools in a circumferential direction into the inside of the non-expanded pipe,
pushing
the expander tool onto the respective non-deformation area and disposing the
welded
portion of the non-expanded pipe in the gap between the expander tools to
perform
pipe expanding as the steel pipe A. Incidentally, an opening angle (circular
arc
angle) of an arc of the expander tool contacting with the inner face of the
non-expanded pipe and having a radius of curvature of 580 mm is 33.4 (the
same
applies hereafter when the number of expander tools is 10).
[0033] A steel pipe C (Invention Example) is an example of producing a
steel
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pipe by performing three-point bending press of 19 times to manufacture a
non-expanded pipe having 20 non-deformation areas as shown in Table 1,
inserting a
pipe expander provided with 10 expander tools in a circumferential direction
into the
inside of the non-expanded pipe, and pushing one expander tool onto the two
non-deformation areas as shown in Table 2 to perform pipe expanding.
[0034] On the other hand, a steel pipe D (Comparative Example) is an
example
of producing a steel pipe by inserting a pipe expander provided with 12
expander
tools as in the steel pipe A into an inside of a non-expanded pipe produced
under the
same conditions as in the steel pipe A and having 12 non-deformation areas and
pushing each of the expander tools onto the deformation area as as to place
the
non-deformation area in the gap between the expander tools as illustrated in
FIG. 5
to perform pipe expanding.
[0035] Also, a steel pipe E (Comparative Example) is an example of
producing a
steel pipe by inserting the same pipe expander provided with 10 expander tools
as in
the steel pipe B into an inside of a non-expanded pipe produced under the same
conditions as in the steel pipe B and having 10 non-deformation areas and
pushing
each of the expander tools onto the deformation area as as to place the
non-deformation area in the gap between the expander tools as illustrated in
FIG. 5
to perform pipe expanding.
[0036] Further, a steel pipe F (Comparative Example) and a steel pipe G
(Comparative Example) are examples of producing a steel pipe by manufacturing
a
non-expanded pipe having 8 or 10 non-deformation areas under conditions shown
in
Table 1, inserting a pipe expander provided with expander tools different from
the
number of non-deformation areas into the inside of the non-expanded pipe as
shown
in Table 2 and then performing pipe expanding at a state of not contacting the
expander tool with a part of the non-deformation areas. As a reference, FIG. 6
shows a case of the steel pipe G.
[0037] With respect to the thus obtained steel pipes A¨G are measured
the
roundness and productivity of the steel pipe to obtain results also shown in
Table 2.
Moreover, the roundness is evaluated by measuring a difference m between an
outer
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surface of a steel pipe 11 and virtual true circle 10 as illustrated in FIG. 7
with a dial
gauge at a distance of 150 mm in a circumferential direction to determine a
maximum value mrna, of the difference m in each steel pipe and calculating a
ratio of
mina, of each steel pipe to mmax of the steel pipe D (hereinafter referred to
as
"difference index (ratio) "). The difference index of the steel pipe D is
1.00, and as
the difference m becomes near to zero, the steel pipe becomes near to true
circle.
That is, the smaller the difference index becomes, the better the roundness of
the
steel pipe becomes. Furthermore, the productivity is evaluated by a time
required
from a start of the first three-point bending press to the end of the last
three-point
bending press.
[0038] Table 1
Steel Conditions for three-point bending press
pipe Press number N Start position Feed pitch Pp
Bent angle ( ) Time required
times) Wo mm (mm
sec/one I i ,e)
A 11 1492 298 29.6 269
B 9 1459 365 36.1 246
C 19 1555 173 17.1 391
,
D 11 1492 298 29.6 270
E 9 1459 365 36.1 246
F 7 1407 469 46.5 245
G 11 1492 298 29.6 303
[0039] Table 2
Steel Number of Conditions for pipe expanding Difference
Remarks
pipe times of Number of Number of Contact between
index
three-point expander non-deformat expander tool
bending press tools N ion areas with
(times) non-deformation
area
A 11 12 12 present 0.65
Invention
B 9 10 10 present 0.66
Example
C 19 10 20 present 0.62
D 11 12 12 absent 1.00
Comparative
E 9 10 10 absent 1.13
Example
,
F 7 10 8 partially absent 1.14
C1 11 10 12 partially absent 0.93
[0040] As seen from Table 2, the difference index in the steel pipes A¨C of
Invention Examples is 0.62-0.66, while the difference index in the steel pipes
D¨G
of Comparative Examples is 0.93-1.14, so that the roundness is excellent in
the steel
pipes of Invention Examples as compared to the steel pipes of Comparative
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Examples.
[0041] Also, the roundness of the steel pipes A and B having the small
number
of times of three-point bending press in Invention Examples is slightly poor
as
compared with that of the steel pipe C having a large number of times of three-
point
bending press, but the pressing time is shortened by not less than 30% as
shown in
Table 1, from which it can be seen that the steel pipes having a good
roundness can
be produced in a high productivity by applying the present invention.
INDUSTRIAL APPLICABILITY
[0042] The production method of steel pipes according to the present
invention
is not limited to the production of large-diameter and thick-walled steel
pipes, and
can be applied to all of methods of producing steel pipes by performing three-
point
bending press.
DESCRIPTION OF REFERENCE SYMBOLS
100431 1: non-expanded pipe
2: expander tool
3: steel plate
4: three-point bending press
5a. 5b: lower die
6: upper forming tool
7: welded portion
8: deformation area
9: non-deformation area
10: virtual true circle
11: steel pipe
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