Note: Descriptions are shown in the official language in which they were submitted.
CA 03157822 2022-04-12
Description
Normalized UOE Welded Pipe and Manufacturing Method thereof
Technical field
The present invention relates to a steel pipe and a manufacturing method
thereof, in particular to a
welded pipe and a manufacturing method thereof.
Background
Since high-temperature steam transportation pipelines used in the petroleum
refining industry need
to be in service at high temperature for a long time, there is a high demand
for microstructure
uniformity of materials. Generally, the normalized, modulated and other heat-
treated seamless steel
pipes are adopted for their good microstructure uniformity, however, the
seamless steel pipes are
limited by diameter, and cannot meet the large capacity steam transportation
needs of some
engineering projects. As a result, it can only be achieved by increasing the
number of pipeline,
leading to increased costs.
For example: Chinese patent having publication number of CN105821335A,
published on August
3, 2016, and entitled as "Low-cost ultra-low temperature normalized steel
having excellent
weldability for pipeline and production method thereof' discloses an ultra-low
temperature
normalized steel for pipeline. In the technical solution disclosed in this
patent, a lower content of C
is employed and V is added.
For another example, Chinese patent having publication number of CN104862612A,
published on
August 26, 2015, and entitled as "4601ViPa-grade low-temperature-resistant
normalized steel, steel
pipe, and a manufacturing method for steel pipe" discloses a 460 MPa-grade low-
temperature-
resistant normalized steel. In the technical solution disclosed in this patent
document, the product
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actually produced is a seamless steel pipe rather than a welded pipe, and a
plurality of alloying
elements such as Cu, Ni, Cr, Mo, and V are added into the composition design
of the technical
solution disclosed in this patent.
For another example: Chinese patent having publication number of CN102719737A,
published on
October 10, 2012, and entitled as "High-toughness normalized steel sheet with
yield strength of 460
1ViPa and manufacturing method thereof' discloses a high-toughness normalized
steel sheet with a
yield strength of 460 MPa. In the technical solution disclosed in this patent,
the chemical
composition of which contains high content of V and N, and thus adopting a
design concept of VN
fine crystal and precipitation strengthening.
On this basis, it is expected to obtain a normalized welded pipe having low
yield ratio which can
meet the requirements of microstructure uniformity for high-temperature steam
transportation, and
has an increased diameter, thereby improving transportation efficiency,
significantly lowering the
costs in comparison to seamless steel pipes and increasing economic benefits.
Summary of the Invention
One of the aspects of the present invention is to provide a normalized UOE
welded pipe having low
yield ratio. The normalized UOE welded pipe having low yield ratio is mainly
made of C and Mn
and a small amount of Cu, Ni, Cr and Nb alloying elements, so that the
normalized UOE welded
pipe having low yield ratio would have better economic efficiency and can
provide better
weldability while satisfying the demand for strength.
In order to achieve the above aspect, the present invention provides a
normalized UOE welded pipe
having low yield ratio, and comprising the following chemical elements in
percentage by mass:
C: 0.14-0.18%, Si: 0.15-0.30%, Mn: 1.20-1.50%, Cu<0.15%, Ni<0.15%, Cr<0.15%,
Nb: 0.010-
0.030%, Ti: 0.005-0.020%, Ca: 0.001-0.005%, Al: 0.020-0.050%, B<0.0005%, the
balance being
Fe and unavoidable impurities.
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In the normalized UOE welded pipe with low yield ratio of the invention, the
design principles for
each chemical element are as follows:
C: in the normalized UOE welded pipe having low yield ratio of the invention,
C is the most basic
strengthening element. C dissolved in steel, on one hand, plays the role of
solid solution
strengthening, while on the other hand, C element is an essential element for
pearlite formation in
the normalized steel, which can increase tensile strength, and obtain a low
yield ratio. However, if
the mass percentage of C is too high, carbides with large size will be formed
during welding process,
which is not preferred. On this basis, the mass percentage of C is controlled
to 0.14-0.18% in the
normalized UOE welded pipe having low yield ratio of the present invention.
Si: in the normalized UOE welded pipe having low yield ratio of the invention,
Si is a solid solution
strengthening element, and is also a deoxidizing element in steel at the same
time, however, if the
mass percentage of Si is too high, the welding properties of the steel will be
deteriorated, and also
leads to formation of red iron claddings on the surface of the steel plate. On
this basis, the mass
percentage of Si is controlled to 0.15-0.30% in the normalized UOE welded pipe
having low yield
ratio of the invention.
Mn: in the normalized UOE welded pipe having low yield ratio of the invention,
Mn is one of the
most effective and economical solid solution strengthening elements, which can
effectively improve
the strength of normalized steel, but Mn is an element that easily segregates
which causes generation
of a hard phase structure with low toughness in the center of the steel plate,
leading to toughness
reduction. On this basis, the mass percentage of Mn is controlled to 1.20-
1.50% in the normalized
UOE welded pipe having low yield ratio of the invention.
Cu: in the normalized UOE welded pipe having low yield ratio of the invention,
Cu is a solid solution
strengthening element that helps to resist softening of welding heat affected
zones and also increases
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the corrosion resistance of steel, but Cu has a rather low melting point and
if the mass percentage
of Cu is too high, it is easy to form brittle cracks on the surface of the hot-
rolled steel plate. On this
basis, the mass percentage of Cu is controlled to Cu<0.15% in the normalized
UOE welded pipe
having low yield ratio of the invention.
Ni: in the normalized UOE welded pipe having low yield ratio of the invention,
Ni is a solid solution
strengthening element, which plays a major role in forming a particulate
composite phase with Cu
elements to avoid the occurrence of "copper cracking". However, as Ni elements
are expensive, thus,
the mass percentage of Ni is controlled to Ni<0.15% in the normalized UOE
welded pipe having
low yield ratio of the invention.
Cr: in the normalized UOE welded pipe having low yield ratio of the invention,
Cr is an important
element to improve the hardenability of the steel, and contributes to improve
the microstructure
uniformity in the thickness direction of the thick steel plate while improving
the strength, but the
mass percentage of Cr too high would cause excessive high strength and reduced
toughness. On this
basis, the mass percentage of Cr is controlled to Cr<0.15% in the normalized
UOE welded pipe
having low yield ratio of the invention.
Nb: in the normalized UOE welded pipe having low yield ratio of the invention,
Nb may act to drag
austenite grain boundaries during rough rolling, which helps to inhibit the
growth of recrystallized
austenite and refine the original austenite. In addition, strain-induced
precipitation of Nb (N, C)
particles during finish rolling has a precipitation strengthening effect, and
may also promote
polygonal ferrite nucleation, achieving the effect of grain refinement. If the
mass percentage of Nb
is too high, Nb cannot be completely dissolved during slab heating due to the
limitation of the
solubility product of C and Nb. On this basis, the mass percentage of Nb is
controlled to 0.010-
0.030% in the normalized UOE welded pipe having low yield ratio of the
invention.
Ti: in the normalized UOE welded pipe having low yield ratio of the invention,
Ti is a strong
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carbonitride forming element, which can play a role in fixing interstitial N
atoms. TiN has high
thermal stability and can prevent the growth of austenite grains during slab
heating and process of
rough rolling recrystallization. In addition, TiN can also prevent the growth
of grains in the heat
affected zones during welding, improving the welding performance of the steel.
As the effect can be
achieved with a small amount of Ti, the mass percentage of Ti is controlled to
0.005-0.020% in the
normalized UOE welded pipe having low yield ratio of the invention.
Ca: in the normalized UOE welded pipe having low yield ratio of the invention,
a small amount of
Ca is added to control the morphology of sulfides, avoiding the formation of
long-strip-shaped MnS,
but the agglomeration of CaS and CaO will also occur when the mass percentage
of Ca is too high.
On this basis, the mass percentage of Ca is controlled to 0.001-0.005% in the
normalized UOE
welded pipe having low yield ratio of the invention.
Al: in the normalized UOE welded pipe having low yield ratio of the invention,
Al is an element
added to the steel for deoxidation. The addition of an appropriate amount of
Al is beneficial to refine
the grains and improve the strength and toughness of the steel. On this basis,
the mass percentage
of Al is controlled to 0.020-0.050% in the normalized UOE welded pipe having
low yield ratio of
the invention.
B: in the normalized UOE welded pipe having low yield ratio of the invention,
B is an element with
strong hardenability, which can increase the strength but tends to precipitate
at grain boundaries,
which leads to a decrease in plasticity and toughness of the material. On this
basis, the mass
percentage of B is controlled to B<0.0005% in the normalized UOE welded pipe
having low yield
ratio of the invention.
Preferably, in the normalized UOE welded pipe of the invention, in the
unavoidable impurities: P <
0.018%, S < 0.003%, N < 0.006%, and 0 < 0.005%.
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In the above technical solution, it is considered that although a small amount
of N can form TiN
particles having high melting point with Ti to achieve an effect of inhibiting
coarsening of austenite
grains during reheating, when the mass percentage of N is too high,
interstitial N atoms will pin
dislocations, significantly increasing the yield strength and yield ratio, and
harming plasticity and
toughness. On this basis, the mass percentage of N is controlled to N <
0.0060% in the normalized
UOE welded pipe having low yield ratio of the invention.
Furthermore, given that 0 will form oxide inclusions in the steel, the mass
percentage of 0 may be
preferably controlled to be 0 < 0.0050%.
In addition, S and P are also unavoidable impurities in steel. S is prone to
forming MnS inclusions,
and has an elongated structure after rolling, while P is an element prone to
segregation, and both
elements reduce the toughness of the steel. Therefore, in the technical
solution of the present
invention, the mass percentage of S and P is controlled to S < 0.003% and P <
0.018%, respectively.
Preferably, in the normalized UOE welded pipe having low yield ratio of the
invention, the
normalized UOE welded pipe has a microstructure of polygonal ferrite +
pearlite with uniform size.
Preferably, in the normalized UOE welded pipe having low yield ratio of the
invention, phase
proportion of the ferrite is 50-90%, preferably 50-80%.
Preferably, in the normalized UOE welded pipe having low yield ratio of the
invention, the
normalized UOE welded pipe has an outer diameter of 711-1016 mm.
Preferably, the normalized UOE welded pipe having low yield ratio of the
invention has a yield
strength of 290-450 MPa, a tensile strength of 415-655 MPa, and a yield ratio
of < 0.80.
Preferably, in the normalized UOE welded pipe having low yield ratio of the
invention, pipe body,
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weld seam, and heat affected zones of the normalized UOE welded pipe with low
yield ratio have
an impact toughness that satisfies: impact energy at -10 C > 100 J.
Correspondingly, another aspect of the present invention is to provide a
manufacturing method of
the normalized UOE welded pipe having low yield ratio. According to the
manufacturing method,
low yield ratio and high toughness of the normalized UOE welded pipe having
low yield ratio can
be obtained, and the outer diameter of the normalized UOE welded pipe having
low yield ratio can
reach a large diameter of 711-1016 mm.
In order to achieve the above aspect, the present invention provides a
manufacturing method of the
normalized UOE welded pipe having low yield ratio, comprising steps of:
(1) steelmaking and continuous casting;
(2) rolling steel plate;
(3) manufacturing UOE pipe;
(4) normalizing the whole of the UOE pipe: controlling normalization
temperature to 860-920 C,
and holding time to 1.0-3.0 min/mm xwall thickness; and
(5) sizing: controlling diameter expanding-ratio to 0.6-2%.
In the technical solution of the present invention, the present inventors have
found through research
that a UOE welded pipe made of a TMCP steel plate as raw material in the prior
art will encounter
the following two difficulties: firstly, after normalizing, the strength of
the welded pipe becomes
significantly lower than that of the TMCP steel plate and the strength has to
be guaranteed by
increasing the content of C or alloy elements, but this would affect the
weldability of the steel plate;
secondly, when manufacturing welded pipes having large diameter, due to the
influence of self-
weight, the pipe shape will change during the normalizing process,
particularly increasing the
ovality, which requires subsequent sizing and this process would introduce
large cold deformation
and, as a result, demanding a lower yield ratio for the pipes.
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In contrast, the manufacturing method according to the present invention makes
it possible to
directly normalize the whole of the pipe by reasonably controlling the
alloying composition when
the steel plate is manufactured into a welded pipe, and desired normalized UOE
welded pipe having
low yield ratio will be obtained after sizing. Specifically, the normalizing
temperature is controlled
to 860-920 C in order to both guarantee sufficient austenitization and avoid
excessive grain size,
and a cross support frame can be placed at the pipe end to mitigate changes of
the pipe shape. The
holding time can be determined according to the actual wall thickness, which
is controlled to be 1.0-
3.0 min/mm xwall thickness. Given that the size of the welded pipe after the
whole pipe normalizing
will change greatly and the straightness and ovality cannot meet dimensional
accuracy requirements,
sizing is required for full-length diameter expansion. The reason for
controlling the diameter
expanding-ratio to 0.6-2% is that when the diameter expanding-ratio is less
than 0.6%, the
springback after expansion will rise and the resulting size will be difficult
to meet the requirements;
and when the diameter expanding-ratio is greater than 2%, excessive cold
deformation will lead to
an increase of the yield strength and yield ratio and a decrease of plasticity
allowance.
It should be noted that diameter expanding-ratio = (outer diameter of a welded
pipe after diameter
expansion - outer diameter of the welded pipe before diameter expansion)/outer
diameter of the
welded pipe before diameter expansion x 100%.
Preferably, in the manufacturing method according to the present invention, a
slab is obtained after
steelmaking and continuous casting in step (1), and in step (2), the slab is
rolled to a steel plate, the
rolling includes rough rolling and finish rolling and controlling a heating
temperature of slab to
1110-1180 C, a rough rolling temperature to 960-1080 C, a finish rolling
temperature to 770-850 C,
and controlling a total finish rolling reduction rate to 70-80%.
In the above solution, since heating temperature is an important factor
influencing the original
austenite grain size during the slab heating process, the heating temperature
is controlled to 1110-
1180 C in order to obtain better final properties of the normalized UOE welded
pipe having low
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yield ratio of the present invention.
In addition, given that finish rolling is performed in a non-recrystallized
zone, rolling deformation
can accumulate strain energy storage and deformation bands in austenite, which
is conducive to
phase transformation and nucleation. The lower the finish rolling temperature,
the less prone to
recovery the strain accumulation, but the finish rolling temperature should be
at Ar3 point or above.
Therefore, in the technical solution of the present invention, the finish
rolling temperature range is
770-850 C and the total finish rolling reduction rate is controlled to be >
70% so as to obtain
sufficient strain accumulation. Meanwhile, the total finish rolling reduction
rate should not be too
large and should be controlled to be in the range of 70-80% in order to give
consideration to the
rough rolling reduction rate to achieve the effect of recrystallization and
refinement of austenite
grains.
Preferably, in the manufacturing method according to the present invention, in
step (2), controlled
cooling is performed after rolling, with a cooling rate of 15-40 C/s, and the
cooling is stopped at
400-550 C.
In the above solution, the reason for controlled cooling is that: the cooling
after rolling is a phase
transformation process of deformed austenite, and an appropriate cooling rate
and the stopping
temperature for cooling are conducive to ferrite nucleation to obtain a
refined structure. Thus,
preferably, the cooling rate can be controlled to be in the range of 15-40 C/s
and the stopping
temperature for cooling can be controlled in the range of 400-550 C.
Compared with the prior art, the normalized UOE welded pipe having low yield
ratio of the present
invention has the following advantages and beneficial effects:
The normalized UOE welded pipe having low yield ratio of the present invention
is mainly made of
C and Mn, and a very small amount of Cu, Ni, Cr and Nb alloying elements
without any Mo, so that
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the normalized UOE welded pipe having low yield ratio will have better
economic benefits.
In addition, the normalized UOE welded pipe having low yield ratio of the
present invention has a
uniform structure, and has a low yield ratio while meeting the demands for
strength. In addition, the
normalized UOE welded pipe having low yield ratio of the present invention has
higher impact
toughness and is very suitable for producing a large-diameter normalized
welded pipe having a large
diameter of, e.g., an outer diameter of 711-1016 mm.
In addition to the above advantages and beneficial effects achieved, the
manufacturing method of
the invention can make the final obtained UOE welded pipe have better
properties after the whole
pipe normalizing, especially having a low yield ratio while meeting the
demands for strength, which
is very conducive to the manufacture of large-diameter welded pipes.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a typical metallographic structure of the normalized UOE welded pipe
having low yield
ratio in Embodiment 2.
DETAILED DESCRIPTION
The normalized low-yield-ratio UOE welded pipe and the manufacturing method
thereof of the
invention will be further explained and described below with reference to the
accompanying
drawings and specific embodiments. However, the explanation and description do
not constitute an
improper limitation on the technical solution of the invention.
Embodiments 1-6 and Comparative examples 1-2
Normalized UOE welded pipes in Embodiments 1-6 are manufactured by using the
following steps:
(1) steelmaking and continuous casting: wherein steelmaking may employ
converter steelmaking,
and LF+RH refining; the content of each chemical element is controlled in
accordance with the
composition design of the present invention, followed by continuous casting,
so as to satisfy slab
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thickness in continuously casting / finished product thickness > 10.
(2) rolling steel plate: controlling the heating temperature of slab to 1110-
1180 C, the rough rolling
temperature range to 960-1080 C, the finish rolling temperature range to 770-
850 C, and
controlling the total finish rolling reduction rate to be 70-80%; then,
controlled cooling is performed
after rolling with a cooling rate of 15-40 C/s, and the cooling is stopped at
400-550 C.
(3) manufacturing UOE pipe;
(4) normalizing the whole of the UOE pipe: the normalization temperature is
controlled to be 860-
920 C, and the holding time is controlled to 1.0-3.0 min/mm x wall thickness.
(5) Sizing: the diameter expanding-ratio is controlled to 0.6-2%.
In some embodiments, UOE pipe manufacturing includes the following steps:
(3a) arc guiding plate welding: welding an arc guiding plate at the four
corners of the steel plate,
which plays the role of arc guiding during welding.
(3b) Edge and bevel dimension milling: obtaining an upper bevel slope of 32-42
and a lower bevel
slope of 32-47 for a good welding morphology by a reasonable bevel dimension
design to ensure
the welding quality.
(3c) C-forming: i.e., edge pre-bending, the edges of the steel plate are bent
into a desired shape by
means of a bending device to meet the curvature requirements of subsequent 0-
forming.
(3d) U-forming: the pre-bent steel plate is pressed into a U shape based on
the diameter of the desired
welded pipe.
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(3e) 0-forming: the steel plate after U-forming is pressed into an 0 shape by
a mold having matched
diameter with the desired welded pipe. The compression ratio of the 0-forming
is controlled to 0.16-
0.22%, because if the compression ratio of the 0-forming is lower than 0.16%,
the compression
deformation of the welded pipe will be too low and causing an opening too
large due to springback
after forming, while if the compression ratio of the 0-forming is higher than
0.22%, the contact part
of the bevel at the plate edge will easily cause deformation damage, which
affects the subsequent
welding. Specifically, compression ratio of 0-forming = (Tr x (outer diameter
after pre-welding -
wall thickness) - width after edge milling) / width after edge milling x 100%.
(3f) High pressure water washing and drying: the inner and outer surface of a
slotted welded pipe
after the 0-forming is subjected to high pressure water washing to remove
contamination of iron
oxide cladding, grease, dust, etc., and then the welded pipe enters a drying
oven at a drying
temperature of 100 C-300 C.
(3g) Pre-welding: the slotted welded pipe after the 0-forming is pre-welded by
CO2 or Ar+CO2 gas
shielded welding to ensure the arc stability during subsequent inside welding
and outside welding.
(3h) Inside welding: inside welding is performed on the welded pipe by a 3-
wire or 4-wire
submerged arc welding process based on the wall thickness, wherein the first
wire adopts direct
current electrode negative, while the second, third and fourth wires adopt
alternating current and all
have a welding wire diameter of 4 mm. For the first wire, the current is 1100-
1300A and the voltage
is 30-35V; for the second wire, the current is 600-950A and the voltage is 31-
37V; for the third wire,
the current is 500-700A and the voltage is 33-39V; and for the fourth wire,
the current is 400-600A
and the voltage is 35-41V. The welding speed is 1.3-1.9 m/min. The inside
welding flux needs to be
dried in the range of 250-450 C for greater than or equal to 2h.
(3i) Outside welding: outside welding is performed on the welded pipe by a 3-
wire or 4-wire
submerged arc welding process according to the wall thickness, wherein the
first wire adopts direct
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current electrode negative, while the second, third and fourth wires adopt
alternating current and all
have a welding wire diameter of 4 mm. For the first wire, the current is 1150-
1350A and the voltage
is 31-367V; for the second wire, the current is 650-1000Aand the voltage is 33-
39V; for the third
wire, the current is 550-750A and the voltage is 35-41V; and for the fourth
wire, the current is 400-
600A and the voltage is 36-42V. The welding speed is 1.2-1.8 m/min. The
outside welding flux
needs to be dried in the range of 250-450 C for greater than or equal to 2h.
(3j) Diameter expansion: the full length of the welded pipe is subjected to
diameter expansion to
meet the size requirements of the specific welded pipe with a diameter
expanding-ratio ranging from
0.7-1.1%.
The normalized UOE welded pipes in Comparative examples 1-2 adopts the same
process as that in
Embodiments 1-6 except for chemical composition, steel plate rolling process
parameters, and the
whole pipe normalizing process, as specifically shown in Table 1 and Table 2.
Table 1 lists the mass percentage of each chemical element of the normalized
UOE welded pipe in
Embodiments 1-6 and Comparative examples 1-2. In particular, the content of
each element in
Embodiments 1-6 is within the range of the composition designed for the
present invention, while
the contents of some elements in Comparative examples 1-2 are different from
those of the invention.
Table 1 (%, the balance being Fe and other unavoidable impurities other than
P, S, 0 and N)
No. C Si Mn S P Cu Ni Cr Nb Ti Ca Al B
N 0
Embodiment 1
0.14 0.21 1.45 0.0023 0.008 0.12 0.14 0.01 0.027 0.008 0.0019 0.032 0.0003
0.003 0.003
Embodiment 2
0.15 0.26 1.39 0.0014 0.012 0.06 0.09 0.09 0.023 0.012 0.0024 0.046 0.0002
0.004 0.002
Embodiment 3
0.16 0.17 1.24 0.0017 0.009 0.01 0.01 0.14 0.022 0.013 0.0045 0.037 0.0003
0.004 0.003
Embodiment 4
0.16 0.20 1.35 0.0019 0.010 0.01 0.01 0.01 0.020 0.015 0.0013 0.033 0.0004
0.003 0.002
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Embodiment 5
0.16 0.18 1.41 0.0008 0.006 0.08 0.13 0.12 0.012 0.0160.0031 0.028
0.0003 0.004 0.004
Embodiment 6
0.17 0.28 1.38 0.001 0.0070.11 0.14 0.14 0.016 0.019 0.0034 0.022 0.0003
0.003 0.004
Comparative example 1 0.15 0.23 1.02 0.0016 0.012 0.01 0.01 0.13 0.024 0.012
0.0018 0.036 0.0003 0.003 0.004
Comparative example 2 0.10 0.21 1.14 0.0016 0.009 0.09 0.11 0.09 0.008 0.012
0.0023 0.027 0.0004 0.003 0.003
Table 2 lists the specific process parameters for the normalized UOE welded
pipe in Embodiments
1-6 and Comparative examples 1-2. In particular, the process parameters in
Embodiments 1-6 are
within the scope of the invention, while the steel plate finish rolling
temperature, the stopping
temperature for cooling, and the whole pipe normalizing process in Comparative
example 1 are
different from those in the invention and the whole pipe normalizing process
in Comparative
example 2 is different from that in the invention.
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Date Recue/Date Received 2022-04-12
o Table 2
Da
5'
x
UOE pipe Whole Sizing Specificati
o
K, Total UOE
pipe
c Rough Finish Cooling
manufacturi pipe diamete on (mm)
o Heating fmish
Coolin manufacturi Holding
0 . rolling rolling stopping
ng- normalizin r (0 outer
5' No. temperat rolling g rate ng-
time
temperatu temperatur temperatu
diameter g expandi diameter x
x ure ( C) reductio ( C/s)
compressio (min)
CD re ( C) e ( C) re ( C)
expanding- temperatur ng-ratio wall
0
CD n rate n
ratio (%)
=
ratio (%) e ( C) (%) thickness)
CD
0-
N.) Embodime
c) 1120 970-1050 780-830 73% 19 430
0.17 0.8 900 35 1.4 0914x18.4
N.)
F>) nt 1
c)
1'
r7s) Embodime
1140 975-1055 780-830 72% 23 440
0.18 0.95 910 35 1.5 0914x17.5
nt 2
Embodime
1140 970-1065 790-840 77% 26 480
0.21 1.1 870 25 1.0 0711x15.8
nt 3
P
.
Embodime
,
u,
1150 965-1060 790-840 78% 34 520 0.2
1.05 870 25 0.9 0711x14.3 ,
nt 4
2
N)
N)
.
Embodime
r.,"
1170 965-1060 790-840 77% 30 460
0.18 0.85 880 30 1.3 0813x15.8 ,
nt 5
.
,
,
N)
Embodime
01016x17.
1170 965-1060 790-840 75% 28 460 0.2
0.85 880 30 1.2
nt 6
5
Comparati
ye example 1140 990-1065 850-920 77% 26 600
0.21 1.1 940 30 1.0 0711x15.8
1
Comparati
ve example 1140 970-1065 790-840 77% 26 480
0.21 1.1 940 30 1.0 0711x15.8
2
Note: rough rolling and finish rolling include a plurality of passes with a
certain duration, so the rough rolling and finish rolling are completed by
controlling the temperature to be within the temperature range.
CA 03157822 2022-04-12
The mechanical properties of the normalized UOE welded pipe in Embodiments 1-6
and
Comparative examples 1-2 of the invention are tested, and the phase
proportions are calculated,
wherein a tensile test is performed on a Zwick Z330 tensile testing device by
using a round bar
specimen according to the ASTM A370 standard, an impact test is performed on a
Zwick PSW750
impact testing device by using a full-size Charpy impact specimen (10 x 10 x
55 mm) according to
the ASTM A370 standard, and the phase proportions are calculated according to
the ASTM E562
standard by calculating the two-phase volume fraction.
16
Date Recue/Date Received 2022-04-12
0
.)
Table 3 lists the test results of the normalized UOE welded
pipe in Embodiments 1-6 and Comparative examples 1-2.
FD.
x
CD
K-, Table 3
o
O
Pipe body impact, - Weld seam impact, -
Heat affected zone Ferrite phase
w Pipe body transverse stretching (round bar)
.6 10 C/J
10 C/J impact, -10 C/J proportion/%
x No.
0
O Tensile Yield
0 Yield strength/MPa
Elongation/% 1 2 3 Average 1 2 3 Average 1 2 3 Average
. strength/MPa ratio
0
0.
N.) Embodiment 1 342 539 0.63 34
213 209 215 212 154 147 138 146 127 166 144
146 88
0
r..)
r;) Embodiment 2 372 568 0.65 33
226 181 173 193 163 158 162 161 133 130 172
145 80
0
i' Embodiment 3 334 505 0.66 29
262 309 282 284 174 157 166 166 158 149 144
150 72
r..)
Embodiment 4 317 479 0.66 28 215 255
206 226 134 123 143 133 110 132 116 119 66
Embodiment 5 405 603 0.67 30 214 201
235 217 138 130 121 130 108 127 124 122 61
Embodiment 6 439 641 0.68 31 225 219
258 234 146 135 153 145 116 135 137 132 53
Comparative example 1 279 443 0.63 31 143 168
137 149 121 119 95 112 92 103 87 94 86 P
148
0
,
Comparative example 2 261 402 0.65 32 136 145
143 117 93 108 106 122 116 109 106 93 u,
,
0
N)
N)
N)
0
N)
N)
,
0
,
,
N)
17
CA 03157822 2022-04-12
It can be seen from Table 3 that the normalized UOE welded pipe having low
yield ratio in the
embodiments of the present invention has a yield strength of 290-450MPa, a
tensile strength of 415-
655MPa, and a yield ratio of < 0.80, and the impact toughness of the pipe
body, the weld seam, and
the heat affected zones of the normalized UOE welded pipe having low yield
ratio satisfies the
requirement that the impact energy at -10 C is > 100 J. Both strength and
toughness in the
comparative examples are lower than those in the embodiments.
Further, it can be seen from Table 2 that the normalized UOE welded pipe
having low yield ratio in
the embodiments of the present invention has larger diameter and specifically,
an outer diameter in
the range of 711-1016 mm.
Fig. 1 is a typical metallographic structure of the normalized UOE welded pipe
having low yield
ratio in Embodiment 2.
As shown in Fig. 1, the microstructure of the normalized UOE welded pipe
having low yield ratio
in Embodiment 2 is polygonal ferrite + pearlite with uniform size, and the two-
phase volume
fraction is calculated according to the ASTM E562 standard, wherein the
ferrite phase proportion is
80%.
In conclusion, it can be seen that the normalized UOE welded pipe having low
yield ratio of the
invention is mainly made of C and Mn and a very small amount of Cu, Ni, Cr and
Nb alloying
elements without any Mo so as to achieve better economic benefits for the
normalized UOE welded
pipe having low yield ratio.
In addition, the normalized UOE welded pipe having low yield ratio of the
invention has a uniform
structure, and has a low yield ratio while meeting the demands for strength.
In addition, the
normalized UOE welded pipe having low yield ratio of the present invention has
higher impact
toughness and is very suitable for producing a large-diameter normalized
welded pipe having a large
18
Date Recue/Date Received 2022-04-12
CA 03157822 2022-04-12
diameter of, e.g., an outer diameter of 711-1016 mm
In addition to the above advantages and beneficial effects achieved, the
manufacturing method of
the invention can make the final obtained UOE welded pipe have better
properties after the whole
pipe normalizing, especially having a low yield ratio while meeting the
demands for strength, which
is very conducive to the manufacture of large-diameter welded pipes.
It should be noted that the prior art portion within the protection scope of
the invention is not limited
to the embodiments given in the application, and all prior art not
inconsistent with the technical
solution of the present invention, including but not limited to prior patents,
prior publications, prior
public uses, or the like, may be included within the protection scope of the
present invention.
In addition, the combination of the technical features in the present
disclosure is not limited to the
combination described in the claims or the combination described in the
specific examples. All
technical features described herein can be freely combined in any way, unless
contradicts between
each other.
It should also be noted that the above-listed examples are only specific
examples of the present
invention. Obviously, the present invention should not be unduly limited to
such specific examples.
Changes or modifications that can be directly or easily derived from the
present disclosure by those
skilled in the art are intended to be within the protection scope of the
present invention.
19
Date Recue/Date Received 2022-04-12
