JP2004298961A - Method for manufacturing electric resistance welded steel tube excellent in quality of weld zone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an electric resistance welded steel tube which can stably and securely decrease defective welding caused by the production of oxides on a weld zone without deteriorating productivity so that the manufactured electric resistance welded steel tube is excellent in the characteristics of the weld zone such as low temperature toughness, corrosion resistance and cold workability. <P>SOLUTION: In the method for manufacturing the electric resistance welded steel tube, a steel plate is formed into a tubular shape and the end faces to be butted are subjected to electric resistance welding. At the time of the electric resistance welding, high-temperature reducing combustion flame or high-temperature non-oxidizing plasma is blown against the end faces to be butted throughout an area at least from the point of welding to a position 1/5 of the power supplying distance off toward the upstream of welding. The blow velocity is 200 m/s or higher for the high-temperature reducing combustion flame or 30-230 m/s for the high-temperature non-oxidizing plasma. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention mainly relates to a method for producing an electric resistance welded steel pipe used for oil or natural gas line pipe, oil well pipe, nuclear power, geothermal, chemical plant, mechanical structure, general piping, etc. The present invention relates to a method for manufacturing an electric resistance welded steel pipe for reducing the occurrence of welding defects when forming a tubular shape and performing an electric resistance welding of the butt portion.

  Generally, in ERW steel pipes, after a strip-shaped coil is continuously formed into a tube with a number of rolls, induction heating with a work coil or direct energization heating with a contact tip is performed to heat and melt the steel sheet end to a predetermined temperature. It is manufactured by welding while pressing with a squeeze roll.

  Conventionally, an electric resistance welded steel pipe is formed by performing electric resistance welding on a steel sheet (chromium steel, chromium molybdenum steel, stainless steel, DP steel, TRIP steel, etc.) containing a large amount of components particularly easily generating oxides such as Cr, Ti, and Si. In the case of producing steel, a welding defect caused by an oxide called a penetrator is apt to occur in a welded portion thereof, which causes deterioration in low-temperature toughness, corrosion resistance and cold workability.

  As a countermeasure, various inert gas shields such as argon and helium are used to reduce the oxygen in the atmosphere of the ERW weld, suppress the surface oxidation of the joint end face, and reduce welding defects caused by oxides in the weld. Has been proposed. However, it is difficult to reduce the oxygen concentration stably due to entrainment of air in the atmosphere of the electric resistance welded portion, and it was not possible to sufficiently reduce welding defects caused by oxides (for example, Patent Document 1 and 2).

  Further, a method has been proposed in which an inert gas or a nitrogen gas containing 1 to 20% by volume of hydrogen is used as a shield gas for a welded portion to activate the effect of suppressing and reducing the surface oxidation of the joint end face (for example, see, for example). And Patent Document 3).

Further, the oxygen concentration in the non-oxidizing shielding gas atmosphere of the welded portion was 0.1% or less, the dew point of 10 ° C. or less, the ratio of H ₂ partial pressure / H ₂ O partial pressure 3 below and the hydrogen concentration of 4% A method has been proposed in which the following control is performed to suppress steam oxidation below the explosive limit concentration of H ₂ and reduce welding defects (for example, see Patent Document 4).

  However, in the methods proposed in Patent Documents 3 and 4, in order to enhance the shielding properties of the welded portion and control the welding atmosphere to a low oxygen concentration and a low dew point, the entire welded portion is surrounded and its high airtightness is maintained. A large-scale shield device is required. Therefore, when manufacturing steel pipes having different outer diameter sizes, it is necessary to prepare a shield device for each size in advance, which greatly reduces the productivity of the steel pipes.

JP-A-53-53562 JP-B-59-33071 JP-A-53-53561 JP-A-5-228551

  The present invention has been made in view of the above-described conventional technology, and has been proposed to stably and reliably reduce welding defects caused by generation of oxides in a welded portion without lowering productivity, and to reduce low-temperature toughness, corrosion resistance, and cold workability. It is an object of the present invention to provide a method for producing an electric resistance welded steel pipe having excellent weld characteristics such as the above.

  The present inventors have intensively studied to reduce welding defects caused by the formation of oxides in a weld. As a result, at the time of ERW, the oxide can be reduced by blowing a reducing high-temperature combustion flame of 1400 ° C. or more or a non-oxidizing high-temperature plasma on the butt end face at a predetermined flow rate, and the oxide can be further discharged. To complete the present invention.

  The gist of the present invention is as follows.

  (1) In a method for manufacturing an ERW steel pipe, when a steel sheet is formed into a tubular shape and its butted end faces are subjected to ERW welding, at least a position at least 1/5 of a power supply distance from a welding point to a welding upstream side is provided. An electrode having excellent welding quality, characterized in that a reducing high-temperature combustion flame having a temperature of 1400 ° C. or more is blown onto a butt end face in the entire range at a flow rate of 200 m / s or more. Manufacturing method of sewn steel pipe.

  (2) In the method of manufacturing an electric resistance welded steel pipe, when a steel sheet is formed into a tubular shape and the butt end faces thereof are subjected to electric resistance welding, at least a position at least 1/5 of a power supply distance from a welding point to a welding upstream side. Excellent weld quality characterized by spraying a non-oxidizing high-temperature plasma having a temperature of 1400 ° C. or more at a flow rate of 30 to 230 m / s in a non-oxidizing atmosphere over the butt end face in the entire range. Manufacturing method of ERW steel pipe.

(3) The reducing high-temperature combustion flame contains one or two of CO: 1 to 5% by volume and H: 1 to 10% by volume, and is generated by a combustion reaction according to the following formula (1). (1) The method for producing an electric resistance welded steel pipe having excellent weld quality according to the above (1).
_{C x H y M + (1/2} ) zO 2 → xCO 2 + (1/2) yH 2 O + M + ηCO + ξH
・ ・ ・ (1) where M: other components other than C and H in the fuel,
z <4x + y, x> 0, y> 0, z> 0, η> 0, ξ> 0

(4) The non-oxidizing high-temperature plasma is a single gas of Ar or a mixed gas of Ar and at least one of N ₂ , H _2, and He. Of ERW steel pipe with excellent weld quality.

  Advantageous Effects of Invention According to the present invention, welding defects caused by the formation of oxides in a welded portion are stably and surely reduced without lowering productivity, and low-temperature toughness, corrosion resistance, and cold workability are improved in weldability. An excellent electric resistance welded steel pipe can be produced, and the industrial contribution in producing the electric resistance welded steel pipe according to the present invention is great.

  Hereinafter, the details of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram for explaining an electric resistance welding method according to the present invention.

  In a normal ERW pipe manufacturing process, the steel sheet 1 is formed into a tubular shape by a large number of rolls (not shown) while being continuously conveyed (in the conveying direction 10), and the butted end surface 4 is induction-heated by the high-frequency coil 2. Then, an upset is added from the squeeze roll 3 to form a weld seam 5 on the butt end face 4 to obtain an electric resistance welded steel pipe. In addition, here, the electric resistance welding is performed by induction heating using the high-frequency coil 2, but it is also possible to perform direct electric heating using a contact tip.

  In the electric resistance welding in the process of manufacturing the electric resistance welded steel pipe, the butt end face 4 is exposed to the air, and an oxide is generated on the surface of the butt end face 4 and remains without being squeezed out. An object-induced welding defect may occur.

  In the present invention, as means for suppressing the occurrence of the welding defect, a butt joint over the entire range from at least the welding point to a position separated by 1/5 of the power supply distance from the welding point to the upstream side in the welding direction during the electric resistance welding. First, a reducing high-temperature combustion flame having a temperature of 1400 ° C. or more is sprayed on the end face 4 at a flow rate of 200 m / s, and secondly, a non-oxidizing atmosphere. And a non-oxidizing high-temperature combustion flame having a temperature of 1400 ° C. or more is blown at a flow rate of 30 to 230 m / s.

  By blowing the reducing high-temperature combustion flame or the non-oxidizing high-temperature plasma 9, the butt end face 4 at the time of the electric resistance welding is set in a non-oxidizing atmosphere and at a temperature of 1400 ° C. (melting point of steel) or more. By suppressing the oxidation reaction in the above, the oxide is reduced and the oxide is promoted to be discharged from the butt end face at a high temperature.

  In FIG. 1, the entire range 6 from the welding point 7 to a position separated by 給 電 of the power supply distance upstream in the welding direction from the welding point 7 has a heating temperature of the butt end face of 800 ° C. or higher during the electric resistance welding, and the surface is oxidized. The inventors have confirmed through experiments and the like that the occurrence of welding defects is significant. Here, the upstream side of the welding direction is the direction of the transport direction 10 of the welded steel sheet 1 shown in FIG. 1 and means a direction opposite to the welding direction.

  Therefore, in the present invention, in order to obtain the effect of suppressing welding defects by the above action, in a reducing atmosphere, in a reducing high-temperature combustion flame 9 having a temperature of 1400 ° C. or more, or in a non-oxidizing atmosphere, and at a temperature of 1400 ° C. or more. The range in which the non-oxidizing high-temperature plasma 9 having a temperature is blown is defined in the butt end face 4 in the entire range 14 (see FIG. 2) at least from the welding point to the position upstream of the welding by a distance of 1/5 of the power supply distance. I do.

  In the present invention, the temperature of the reducing high-temperature combustion flame 9 or the non-oxidizing high-temperature plasma 9 suppresses an oxidation reaction on the surface of the butt end face 4 and discharges already generated oxide from the butt end face in a high temperature state. In order to promote the action and sufficiently suppress welding defects caused by oxides, the temperature must be 1400 ° C. or higher. The upper limit of the temperature does not need to be particularly limited. The higher the temperature, the more the action of discharging the already generated oxide from the butt end face in a high temperature state is promoted. Therefore, it is preferable to reduce welding defects. In the case of a high-temperature combustion flame, the upper limit temperature is about 3000 ° C. in theory of gas combustion, and in the case of non-oxidizing high-temperature plasma, the upper limit temperature is about 10,000 ° C. in theory.

  In the present invention, the high-temperature atmosphere formed when each of the reducing high-temperature combustion flame 9 and the non-oxidizing high-temperature plasma 9 is blown at a predetermined flow rate has a sufficient non-oxidizing property to suppress an oxidation reaction on the surface of the butt end face 4. In order to stably obtain this function and effect, it is desirable to define the gas composition of the reducing high-temperature combustion flame or the non-oxidizing high-temperature plasma as follows.

The reducing high temperature combustion flame, liquid fuel (kerosene) or gaseous fuel (acetylene, propane, _{etc.) (C x H y M,} M: a third component: C and H) and oxygen (O _2: oxygen gas or air (Oxygen in) is formed by a combustion reaction represented by the following formula (1).
_{C x H y M + (1/2} ) zO 2 → xCO 2 + (1/2) yH 2 O + M + ηCO + ξH
・ ・ ・ (1)
However, M: other components other than C and H in the fuel,
z <4x + y, x> 0, y> 0, z> 0, η> 0, ξ> 0

In the above equation (1), when z = 4x + y is satisfied, a complete combustion reaction represented by the following equation (2) occurs, and the combustion flame becomes neutral without containing CO or H. Under these conditions, when the reducing high-temperature combustion flame is blown to the butt end face, the influence of air entrapment is large, which is not preferable because the high-temperature atmosphere at the butt end face is stably maintained to be non-oxidizing.
_{C x H y M + (1/2} ) zO 2 → xCO 2 + (1/2) yH 2 O + M
・ ・ ・ (2)

Therefore, in the present invention, the reducing high-temperature combustion flame satisfies the condition of z <4x + y in the above reaction formula (1), and the CO: 1 to 5% by volume and H: 1 to 10% by volume. It is preferable to contain one or two of the following. The lower limit of the content of CO and the content of H in the reducing high-temperature combustion flame: 1 vol% is set to 1 vol% since an oxidation reaction at the butt end face cannot be sufficiently suppressed if the content is lower than 1 vol%. On the other hand, if the upper limit of the CO content is 5% by volume and the upper limit of the H content is 10% by volume, the H ₂ gas generated by the combustion reaction of the above formula (1) increases the combustion gas if it is higher than these. Since it exceeds the theoretical explosion limit of the composition and is not preferable from the viewpoint of safety, it is set to 5% by volume and 10% by volume, respectively.

The non-oxidizing high-temperature plasma contains Ar alone or Ar as a main gas, and at least one or more of N ₂ , H _2, and He is added to increase the thermal conductivity, enthalpy, and heat transfer coefficient of the plasma. It is preferable to use a mixed gas prepared as described above.
H _{2 in} the main gas of Ar has an action of suppressing the oxidation reaction at the butted end faces, and in order to sufficiently obtain this action, the content of H ₂ is preferably set to 5% by volume or more. The upper limit of the content does not need to be particularly limited, but usually, if it exceeds 40%, the plasma becomes unstable, so the upper limit is preferably set to 40%.

N ₂ and He in the main gas of Ar are preferably added in an amount of 20% by volume or more or 10% by volume or more in order to improve the heat conduction and heat transfer coefficient of the plasma and increase the heating capability of the steel plate end face. The upper limits of these contents need not be particularly limited, but generally, if any of them exceeds 50%, the plasma becomes unstable, so that the upper limit is preferably set to 50%.

  Further, in the present invention, in addition to the action at the time of blowing the reducing high-temperature combustion flame to the butt end face, in addition to the action of suppressing the oxidation reaction at the butt end face, the butt end face that has already been generated using the shear force of this fluid. In order to further enhance the effect of promoting the emission of oxides from, it is set to 200 m / s or more. The upper limit of the flow velocity need not be particularly defined, but if it exceeds 600 m / s, the generation of spatter from the molten metal during electric resistance welding becomes remarkable, so the upper limit is more preferably set to 600 m / s.

  On the other hand, when the plasma is blown to the butt end face, if the flow rate is increased to obtain a fluid shear force for discharging the oxide, the entrainment of air around the butt end face increases and a non-oxidizing atmosphere is secured, and the oxidation reaction is started. It is difficult to control. Further, spatter of molten metal becomes remarkable, which causes an increase in weld defects due to scattered oxide of molten metal. For such a reason, the upper limit of the flow velocity at the time of blowing the plasma to the butt end face is set to 230 m / s. On the other hand, the lower limit of the flow velocity is to maintain the high-temperature atmosphere at the butt end face in a non-oxidizing atmosphere, to eliminate the cooling water of the squeeze roll or the power supply device used for the electric resistance welding, and to suppress the oxidation by the cooling water. , 30 m / s.

  The reducing high-temperature combustion flame can be generated, for example, by using an HVOF (High Velocity Oxygen Fuel) apparatus for thermal spraying that is widely used industrially.

  The combustion flame generated by this HVOF apparatus has a gas flow velocity higher than that of a combustion flame generated by a normal gas burner, and has a supersonic range of a flame length of 200 mm or more and a flame diameter of 15 mm or more. Therefore, it is a heat source that has a good seam copying property at the time of electric resistance welding and can relatively easily follow even when the thickness of the steel plate and the butt angle are changed.

  The reducing high-temperature plasma can be generated using, for example, a DC plasma for thermal spraying, a high-frequency plasma, or a hybrid plasma apparatus widely used industrially. These plasmas have a characteristic that the gas temperature is higher than the combustion flame generated by a normal gas burner and the like, and the flame length in a high temperature region is 100 mm or more and the flame diameter is 10 mm or more. Is a heat source that has a good seam copying property, and can relatively easily follow even when the thickness of the steel sheet and the butting angle change.

  Such a reducing high-temperature combustion flame or non-oxidizing high-temperature plasma generating device 8 is provided immediately above the butted end face 4 of the steel sheet 1 as shown in FIG. By spraying the butt end surface 4 over the entire range 14 (see FIG. 2) at least from the welding point 7 to a position away from the welding point 7 by 1/5 of the power supply distance, reduction of generated oxides or combustion flame fluid It is possible to reduce oxides that are discharged and cause welding defects. As a result, it becomes possible to manufacture an electric resistance welded steel pipe having good characteristics with almost no deterioration in the low-temperature toughness, corrosion resistance, and cold workability of the welded portion.

  Hereinafter, the present invention will be described in detail based on examples.

  In the process of manufacturing an electric resistance welded steel pipe, when performing electric resistance welding under the condition of water spray by cooling water of a squeeze roll using a 9Cr-2.5Ni-1.0Mo high Cr steel plate having a thickness of 5.3mm and a width of 275mm. Next, ERW welding was performed while spraying combustion flames having different compositions and reducing properties on the butt end faces while changing the spraying range, and the occurrence rate of welding defects in the welded portions was investigated. Table 1 shows the test conditions and results.

  The conditions of the electric resistance welding were as follows: welding speed: 33 m / min, welding heat input: 570 kW (the lower limit of two types of welding phenomena), power supply distance (distance between the coil end on the squeeze roll side and the welding point): 160 mm The upset amount: 3 mm (perimeter), the average apex angle: 7 °, and the spray amount of water applied to the welding point: about 400 l / min.

  In addition, a JP5000 thermal spray gun manufactured by Utech Japan Co., Ltd. was used as a combustion flame generator, and the raw materials of the combustion flame were kerosene and oxygen. FIG. 2 shows the arrangement of the torch of the combustion flame and the state of the spraying range of the combustion flame. In FIG. 2, when the torch angle (combustion flame blowing angle) 11 is φ °, the torch tip height (distance from the torch tip to the butt end face) 12 is H mm, and the frame diameter 13 is F mm, the combustion flame Is determined as F / sin (φ °). The most upstream position 15 and the most downstream position 16 in the welding direction of the combustion flame spraying range 14 are respectively located at a position H / tan (φ °) away from the tip of the torch to the welding downstream side and at the welding downstream from the tip of the torch. Side, and a position separated by H / tan (φ °) + F / sin (φ °).

  In the present embodiment, the height 12 of the torch tip is fixed at H = 10 mm, the frame diameter 13 is fixed at F = 15 mm, and the angle of the torch (combustion flame blowing angle) 11 is adjusted to spray as shown in Table 1. The most upstream position 15 and the most downstream position 16 of the range 14 in the welding direction were changed.

  As shown in Table 1, the most upstream position 15 and the most downstream position 16 in the welding direction in the spraying range are defined such that the welding point 7 is a reference (0), the upstream in the welding direction is +, and the downstream is-. Is defined. In this test, the position of the welding point 7 was a position 35 mm away from the position of the rotary shaft 17 of the squeeze roll 3 on the upstream side in the welding direction.

  The welding defect rate was determined by cutting out a Charpy test specimen from the welded portion of the ERW steel pipe after welding, forming a notch with a tip diameter of 0.25R and a depth of 0.5 mm at the weld butt, and using a 160 ° C oil. After conducting a Charpy test in the inside, a fracture surface of a portion where ductile fracture has occurred is observed and defined as a measured value of an area ratio of a penetrator (a welding defect caused by an oxide) to a welding area. The quality evaluation of the welded portion was judged as “poor” when the welding defect rate exceeded 0.05, and “good” when it was 0.05 or less.

In Table 1, No. 1 is an example of the present invention. As shown in FIGS. 1 to 8, a combustion flame in a reducing atmosphere and at a temperature of 1400 ° C. or higher is at least １ ／ of the power supply distance upstream from the welding point in the welding direction (in this embodiment, since the power supply distance is 160 mm, By spraying at a flow velocity of 200 m / s or more over the entire area up to a position distant by 1/5 (32 mm), the welding defect rate becomes 0.05 or less, and a good weld without welding defects is obtained. It turns out that it is possible.
On the other hand, No. Nos. 9 to 17 are comparative examples. Nos. 9 to 13 and 13 are the most upstream position or the most downstream position of the plasma spraying range. Nos. 14 and 15 are the reducing properties of the atmosphere; In Nos. 16 and 17, the temperature and flow velocity of the combustion flame were out of the specified range of the present invention, respectively.

  In the manufacturing process of the ERW steel pipe, when performing ERW welding using high Cr steel plates having the same size and the same components as in Example 1 under water spray conditions using cooling water of a squeeze roll, the gas composition of the butt end face is ERW welding was performed while spraying different plasmas while changing the spraying range, and the occurrence rate of welding defects in the welded portions was investigated. Table 2 shows the test conditions and results.

Note that the electric resistance welding conditions and the water spraying conditions were the same as in Example 1.
In addition, the plasma generator uses a PRAXAIR 2086A thermal spray gun, the Ar flow rate of plasma is fixed at 35 l / min, and the flow rate of one or more of H ₂ , He, and N ₂ is adjusted. Thus, the mixing ratio of each gas was changed. FIG. 2 shows the arrangement of the plasma torch and the state of the plasma spraying range. In this embodiment, as shown in Table 2, the plasma diameter 13 is fixed at F = 8 mm and the torch angle (plasma spray angle) 11 and the torch tip height 12 are adjusted in FIG. The most upstream position 15 and the most downstream position 16 in the welding direction 14 were changed.

  In addition, the definition of the most upstream position 15 and the most downstream position 16 in the welding direction of the spraying range, the position of the welding point 7, the welding defect rate, and the quality evaluation of the welded portion shown in Table 2 are the same as in Example 1. Define.

In Table 2, No. 1 is an example of the present invention. As shown in Nos. 1 to 6, a combustion flame in a non-oxidizing atmosphere and at a temperature of 1400 ° C. or higher is at least １ ／ of the power supply distance upstream from the welding point in the welding direction (in this embodiment, the power supply distance is 160 mm. By spraying the gas over the entire range up to a position distant by 1/5 (32 mm) at a flow rate of 30 to 230 m / s, the welding defect rate becomes 0.05 or less, and a good welding portion without welding defects is obtained. Is obtained.
On the other hand, No. Nos. 7 to 11 are comparative examples. Nos. 7 and 8 are the most upstream position and / or the most downstream position of the plasma spraying range. 9 is the plasma temperature; In Nos. 10 and 11, the flow rates of the plasma were out of the specified range of the present invention.

FIG. 3 is a schematic view for explaining a method for manufacturing an electric resistance welded steel pipe using a non-oxidizing high-temperature combustion flame or a non-oxidizing high-temperature plasma according to the present invention. It is a figure which shows arrangement | positioning of the torch of a combustion flame, and the state of the blowing range of a combustion flame.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Steel plate 2 High frequency coil 3 Squeeze roll 4 Butt end face 5 Weld seam 6 Power supply distance 7 Welding point 8 Non-oxidizing high-temperature combustion flame or non-oxidizing high-temperature plasma generating device 9 Non-oxidizing high-temperature burning flame or non-oxidizing high-temperature plasma 10 Transfer direction (reverse direction of welding direction)
11 Torch Angle 12 Torch Tip Height 13 Frame Diameter 14 Spraying Range 15 Most Upstream Position in Spraying Range 16 Most Downstream Position in Spraying Range 17 Rotary Axis Position of Squeeze Roll

Claims (4)

In the method for manufacturing an electric resistance welded steel pipe, a steel sheet is formed into a tubular shape, and when the butted end faces are subjected to electric resistance welding, the steel sheet covers the entire range from at least a welding point to a position upstream of the welding by a distance of 1/5 of a power supply distance. An electric resistance welded steel pipe excellent in weld quality, characterized in that a reducing high-temperature combustion flame having a temperature of 1400 ° C. or more is blown to the butt end face at a flow rate of 200 m / s or more. Production method. In the method for manufacturing an electric resistance welded steel pipe, a steel sheet is formed into a tubular shape, and when the butted end faces are subjected to electric resistance welding, the steel sheet covers the entire range from at least a welding point to a position upstream of the welding by a distance of 1/5 of a power supply distance. A non-oxidizing atmosphere and a non-oxidizing high-temperature plasma having a temperature of 1400 ° C. or more are blown to the butt end surface at a flow rate of 30 to 230 m / s, and the electric resistance is excellent in weld quality. Manufacturing method of steel pipe. The reducing high-temperature combustion flame contains one or two of CO: 1 to 5% by volume and H: 1 to 10% by volume, and is generated by a combustion reaction according to the following formula (1). The method for producing an electric resistance welded steel pipe according to claim 1, wherein the quality of the welded part is excellent.
_{C x H y M + (1/2} ) zO 2 → xCO 2 + (1/2) yH 2 O + M + ηCO + ξH
・ ・ ・ (1)
However, M: other components other than C and H in the fuel,
z <4x + y, x> 0, y> 0, z> 0, η> 0, ξ> 0 The non-oxidizing high temperature plasma, Ar alone gas or a superior weld quality according to claim 2, characterized in that a mixed gas of at least one or more of the Ar and N _2, H ₂ and He Manufacturing method of ERW steel pipe.

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