JP2000126881A - Manufacture of duplex stainless steel welded tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a duplex stainless steel welded tube at high speed and to obtain the stable quality of a weld zone. SOLUTION: In this method for manufacturing the duplex stainless steel welded tube by which a duplex stainless steel strip is continuously formed into a tubular shape with plural roll-forming stands, both edge parts to be butted of the formed tubular duplex stainless steel are heated and subjected to laser beam welding, fin pass rolls for holding the interval between both these edge parts at a prescribed distance and squeeze side rolls for pressurizing and butting both edge parts are provided, and also a lifting roll device 7 is arranged between the final fin pass roll 3a and the squeeze side rolls 6. The gap G in the height direction of both the edges is measured and butt welding is executed while adjusting the amount of lift with the lifting roll device 7 based on the measured results.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a duplex stainless steel pipe suitable for a line pipe or an oil country tubular good.

[0002]

2. Description of the Related Art Duplex stainless steel has a two-phase structure of a ferrite phase and an austenitic phase, and is used as a material for oil wells or seawater because of its excellent stress corrosion resistance and good toughness and weldability. Have been. Further, it is known that strength such as proof stress and tensile strength is larger than that of austenitic and ferritic. In general,
The duplex stainless welded steel pipe is formed by forming a material steel strip into an open pipe shape, and heating the opposing edges at both ends by high frequency welding by electric resistance welding (hereinafter, referred to as ERW method) or submerged arc welding (hereinafter, referred to as ERW method). (Referred to as SAW method).

However, since the SAW method uses a welding flux in the atmosphere, it is inevitable that gases such as O and N are mixed in from the atmosphere. For this reason, there has been a problem that oxides and nitrides are generated in the weld metal, and these lower the toughness level. As a countermeasure, the amount of oxygen in the weld metal is reduced by using a highly basic flux. The use of such a highly basic flux is also optimal from the viewpoint of corrosion resistance, that is, the prevention of non-uniformity in the concentration of components that can be a starting point of pitting corrosion. However, the high basic flux is not suitable for increasing the welding speed because the melting point of the flux is high. In addition, high-base flux has problems such as slag entrapment in the weld, welding defects such as undercut are likely to occur, and the high heat input welding method has a high degree of hot cracking. It also had the problem of becoming

On the other hand, the ERW method is advantageous in terms of high productivity, but generates an oxide on the surface of a steel sheet edge which is a joining surface due to heating during welding. In particular, since duplex stainless steel contains a large amount of Cr, it tends to remain in the weld as an oxide defect called a penetrator, and the toughness and corrosion resistance of the weld decrease.

[0005] For this reason, recently, from the viewpoint of improving the quality of the welded portion and the productivity of the duplex stainless steel pipe, a method using a laser beam (hereinafter referred to as a laser welding method).
However, Japanese Patent Application Laid-Open Nos. 8-155563 and 9-170
050 and JP-A-9-220682. In laser welding, the laser beam is focused by a lens or mirror to locally melt the object,
This is a method in which an inert gas is ejected at the same time to perform welding while sealing. Since the laser welding method is rapid heating and cooling, the solidification structure of the welded portion is fine, the strength and toughness levels are high, and the hot cracking resistance is good. In addition, unlike the SAW method, the laser welding method does not use flux, so that defects such as slag entrapment do not occur. Since the welding is performed in an inert gas atmosphere, the oxygen concentration in the welded portion is suppressed to the same level as the base metal and the quality is low. There is no deterioration. In addition, since both edges are heated (preheated) by an electric resistance heating method using a contact tip used in the ERW method or an annular induction heating method before laser welding, the production speed can be increased,
Higher productivity than other welding methods.

[0006]

However, when heating (preheating) the steel sheet edge by the electric resistance heating method or the like,
As will be described in detail later, since the thermal conductivity of high-alloy steel such as duplex stainless steel is smaller than that of carbon steel, a temperature distribution occurs in which only the vicinity of the edge of the steel plate becomes higher in temperature than carbon steel, which causes Only the outermost edge of the steel sheet softens, and when both edges are pressed and butted by a squeeze roll (hereinafter referred to as upset), the softened portion at the outermost edge is displaced by a slight external force in the vertical direction (slippage). 1) Because of deformation, so-called wraps shown in FIGS. 1A and 1B are very likely to occur as compared with carbon steel. For this reason, in order to prevent such lapping during the production of a duplex stainless steel welded pipe by the laser welding method, the preheating temperature of both edges of the steel sheet is lowered or the steel sheet is manufactured without preheating. However, this leads to an increase in manufacturing cost due to a reduction in manufacturing speed. The present invention has been made in view of such a situation, and an object of the present invention is to provide a method for producing a duplex stainless steel pipe suitable for a line pipe or an oil well pipe at a high productivity by a laser welding method. It is assumed that.

[0007]

Means for Solving the Problems The inventors of the present invention used a steel strip made of duplex stainless steel to form a cylindrical shape continuously by a plurality of roll forming stands, and used a laser beam to join the seam portion. In the method of manufacturing a welded pipe by using a method, both edges before laser welding are heated (preheated) by electric resistance heating method or induction heating method, measuring the height direction gap of both edges, By performing butt welding while adjusting the push-up amount using the push-up roll device arranged between the squeeze rolls,
It has been clarified that a high-speed production speed can be realized, a lap can be sufficiently suppressed, and a welded pipe having a stable welded portion quality can be manufactured without welding defects.

A specific configuration of the present invention is that a duplex stainless steel strip is continuously formed into a tubular shape by a plurality of roll forming stands, and both edge portions, which are butted portions of the formed tubular duplex stainless steel, are formed. A method for producing a duplex stainless steel welded pipe to be heated and laser-welded, comprising: a fin pass roll for maintaining a distance between the two edge portions at a predetermined distance; and a squeeze side roll for pressing and abutting the two edge portions. , Placing a lifting roll device between the final fin pass roll and the squeeze side roll,
Butt welding is performed by the push-up roll device while pushing up the edge portions from below.

Further, the heating temperature of the both edge portions before laser welding is set to 500 ° C. or more.

Further, a gap G in the height direction between the two edges is provided.
Is measured, and butt welding is performed while adjusting the amount of push-up by the push-up roll device according to the measurement result.

Further, a height direction gap G of the two edges is measured at an arbitrary point within the edge convergence area L expressed by the equation (1) so that the condition expressed by the equation (2) is satisfied. The amount of pushing up by the pushing up roll device is adjusted.

[0012]

(Equation 3) Here, L: edge convergence area on the upstream side of forming from the center of the squeeze side roll D: outer diameter of the welded pipe Df: flange outer diameter of the squeeze side roll B: flange outer diameter of the squeeze side roll from the distance between the centers of the squeeze side rolls Distance divided by 2

[0013]

(Equation 4) Here, G: height direction gap between both edges (mm) R: squeeze side roll upset amount (mm) t: steel strip thickness (mm) a: correction term depending on measurement position, edge convergence Area L
Divided by the distance from the center of the squeeze side roll to the gap measurement position

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described in detail below along with experimental results obtained. 1. Material steel strip The material steel strip is not particularly limited as long as it has excellent corrosion resistance made of a duplex stainless steel used for line pipes or oil country tubular goods, and is not particularly limited. For example, SUS329J3L or S
It is desirable to use a material steel strip that is a standard material such as US329J4L and has a ferrite ratio adjusted to approximately 50%.

2. Preheating temperature To heat (preheat) both edges before laser welding,
An electric resistance heating device using a contact tip and an annular induction heating device used in the ERW method are arranged in front of the squeeze side rolls, and the power supplied thereto is controlled to heat them to a desired temperature. In order to determine the effect of increasing the welding speed by preheating the steel plate edge before laser welding, the welding was performed by changing the preheating temperature from room temperature to near the melting point under a constant laser output of 20 kW, and the limit of penetration welding was possible. The speed was investigated.

A carbon steel strip having an outer diameter of 508 mm and a plate thickness of 12.7 mm is directly welded to both edges before laser welding by a contact shoe 4 of a high-frequency electric resistance welding (electric resistance welding) apparatus using a pipe mill shown in FIG. FIG. 3 shows a result of welding (preheating) to a desired temperature by energization and then welding with a laser beam device 5. As is apparent from FIG. 3, there is a tendency that the penetration limit welding speed increases as the preheating temperature increases.
However, if the preheating temperature is lower than 500 ° C., the rate of increase in the welding speed, which is determined by the ratio with the penetration limit welding speed when the laser is used alone (without preheating), is as low as 1.5 times or less, resulting in poor productivity. Therefore, in order to obtain high productivity, it is necessary to set the preheating temperature before the laser to 500 ° C. or higher.

However, when the preheating temperature of the steel sheet edge before laser welding is increased in the case of using a duplex stainless steel, lapping is very likely to occur during upset.
Therefore, in order to pursue a correlation between the lap phenomenon and the preheating temperature in the duplex stainless steel, the present inventors calculated the temperature distribution at the steel sheet edge when heated (preheated) by an electric resistance heating method or the like from numerical calculations. We calculated and considered the behavior of the steel sheet edge due to preheating.

Temperature Analysis First, it is assumed that the following three conditions are satisfied. 1) One-dimensional heat conduction 2) Physical properties are constant irrespective of temperature 3) Current distribution is constant irrespective of temperature Next, based on the basic equations shown in the equations (3) and (4), the temperature of the steel sheet edge is determined. Find the distribution.

[0019]

(Equation 5)

Here, T: temperature (° C.), t: time (s), α: thermal diffusivity (m ²⁾
/ S), Cp: specific heat (J / kg · ° C.), ρ: density (kg
/ M ³ ), σ: specific electric conductivity (Ω · m), j, j ₀ : electric density (A / m ² ), δ: penetration depth (m)

[0021]

(Equation 6)

From equations (3) and (4)

[0023]

(Equation 7)

The following equation is modified and substituted into equation (5). λ = Cp · ρ · α where λ: thermal conductivity (W / m · ° C.)

[0025]

(Equation 8)

By solving the equation (7) under the initial condition and the boundary condition, the temperature distribution at the steel sheet edge is obtained. In addition,
Here, it was solved by the forward difference method. FIG. 4 shows the temperature distribution from the steel sheet edge at the center of the sheet thickness of carbon steel and duplex stainless steel when the steel sheet's maximum edge temperature is 750 ° C. The physical properties of the steel used here are as shown in Table 1.

[0027]

[Table 1]

As shown in Table 1, high-alloy steel such as duplex stainless steel has a lower thermal conductivity than carbon steel.
As shown in FIG. 5, a temperature distribution occurs in which only the vicinity of the steel sheet's edge is higher than that of carbon steel.

FIG. 5 is a diagram showing the ratio of the strength of the steel sheet at that temperature to the strength of the steel sheet at room temperature (hereinafter, referred to as the steel sheet strength ratio) based on each temperature calculated by the above calculation.
As shown in FIG.
Compared with carbon steel, duplex stainless steel causes a sharp decrease in strength (softening) only near the edge of the steel plate. FIG. 6 shows the distribution of the strength ratio of the steel sheet in the duplex stainless steel in which the maximum edge temperature of the steel sheet was set to 500 ° C. by the same method. As is clear from FIG. 6, when the preheating temperature is lowered to about 500 ° C., local softening of the outermost edge of the duplex stainless steel as shown in FIG. 5 is not recognized.

From these results, when the preheating temperature is set to a high temperature of 500 ° C. or more using duplex stainless steel, the stress generated at the end face of the steel plate during upset is increased in the vertical direction in addition to the component perpendicular to the end face. Also, it is considered that the softened portion at the outermost edge shifts due to the stress in the vertical direction, deforms, and the abutting surface shifts (lapping occurs). This consideration is in good agreement with the phenomenon experienced in actual operation that the generation of lap can be suppressed by lowering the preheating temperature before laser welding in the production of duplex stainless steel pipes.

However, as described above, when the preheating temperature before laser welding is less than 500 ° C., the increase rate of the welding speed obtained by the ratio with the penetration limit welding speed when the laser is alone (no preheating) is as low as 1.5 times or less. The present inventors have studied a tube forming method capable of preventing lapping even in a state where the softened portion at the outermost edge at a preheating temperature of 500 ° C. or higher exists because of poor productivity.

3. Observation of Forming Conditions Behavior of Both Edges In general, the first cause of lap is that the edge wave 11 shown in FIG.
Although the edge wave 11 is slightly smaller than the thickness of the steel sheet,
The state of insertion of both edges of the steel sheet into the squeeze side roll 6 shown in FIG. 2 is due to the difference in the bent state of the two edges or the edge wave at both edges, etc. There are two cases in which the abutment surface is shifted in the vertical direction in addition to the vertical component, and the butt surface is displaced by the vertical stress.

FIG. 8 shows the results of measuring the fluctuation in the height direction of both edges of the open pipe when a welded pipe was manufactured under the following pipe forming conditions using a non-contact type laser displacement meter. FIG. In addition, the measurement of the gap G in the height direction of both edges was calculated as the difference between the measured values of both edges measured by the laser displacement meter. [Pipe making conditions] Welded pipe outer diameter x plate thickness 73.0mm x 1.2mm Material Cold rolled steel plate (equivalent to SPCC) Forming machine configuration Breakdown roll 3 stages Cage roll stand Fin pass roll stand 3 stages Squeeze roll stand 1 stage Required dimensions of the squeeze roll stand-Outer diameter of flange of squeeze side roll Df: 160m
m-Distance obtained by subtracting the flange outer diameter of the squeeze side roll from the center distance of the squeeze side roll and dividing by 2 B: 3 m
m

The squeeze side roll 6 is used as a squeeze roll mechanism. When mainly producing a large-diameter ERW pipe, two squeeze side rolls 6 are replaced with two squeeze top rolls. Used together with one roll of a squeeze bottom roll and two rolls of the squeeze side rolls 6 when mainly manufacturing a small-diameter ERW pipe. The restraint by the squeeze side roll is much larger than the restraint by the squeeze top roll.

As is apparent from FIG. 8, the influence of the position in the tube axis direction (longitudinal direction) on the edge fluctuation is almost equal to the area within the edge convergence area L of FIG. 9 expressed by the following equation (1). Shows a tendency to be constant. Thereby, the height direction gap G of both edges shows a monotonous decrease within L. The reason why the edge fluctuation becomes constant within the edge convergence region L is that the open pipe is sufficiently restrained by the forming rolls so that it is difficult to freely deform, and the whole pipe derived from the material of the raw material and the camper of the raw material. It is considered that disturbance such as self-excited vibration of the non-uniform open pipe can be eliminated. For this reason, as the position for measuring the height direction gap G of both edges, the edge fluctuation is constant as described above, and the appropriate position is within the edge convergence region L where the gap G monotonically decreases. Since the gap G shows a monotonous decrease within the edge convergence region L, a proper evaluation can be performed by multiplying the gap G by a value obtained by dividing the edge convergence region L by the measurement position. Although the number of measurement points of the gap G may be plural, one point is sufficient since the gap G monotonously decreases.

[0036]

(Equation 9)

Here, L: an edge converging area on the upstream side from the center of the squeeze side roll 6 shown in FIG. 9 D: an outer diameter of the welded pipe 12 'shown in FIG. 9 Df: a diameter of the squeeze side roll 6 shown in FIG. Flange outer diameter B: subtract the flange outer diameter of the squeeze side roll 6 from the center distance of the squeeze side roll 6 shown in FIG.
Distance divided by

FIG. 10 shows an outer diameter of 323.8 mm × a plate thickness of 6.2.
mm carbon steel pipe with the forming machine shown in FIG.
Lead is inserted into both edge butted portions at the time of cold, and the behavior of the edge is transferred to lead by rolling the lead at the steel plate edge. From the cross-sectional microscopic result of the transfer surface, both ends of the steel plate immediately before the center of the squeeze side roll 6 are obtained. It is the result of observing the behavior of the edge. As is clear from FIG. 10, immediately before the center of the squeeze side roll 6, that is, both edges of the steel sheet immediately before the upset are separated by a gap G in the height direction, one is strongly pushed from above to below, and the other is laterally pushed. It can be seen that the indentation is strong and both edges behave completely differently.

From these results, it can be seen that the stress generated at the end face of the steel plate at the time of upset acts not only in the direction perpendicular to the end face but also in the vertical direction, and because the stress directions are different at both edges. It can be assumed that slip deformation occurs on the surface and leads to wrap. In particular, when the outermost edge is extremely softened at a high temperature of 500 ° C. or higher, such as a duplex stainless steel, the softened portion easily shifts and deforms. It is thought that it is likely to occur.

Therefore, the present inventors have taken measures to prevent lapping during the high-temperature heating (preheating) of the duplex stainless steel.
As shown in FIG. 11, a push-up roll device 7 is arranged between the final fin pass roll 3a of the fin pass roll group and the squeeze side roll 6, and thereby tension is applied to both edges by pushing up both edges from below. We have devised that welding is performed while improving the butt situation while hanging. The structure of the push-up roll device 7 may be based on Japanese Patent Application Laid-Open Nos. 5-208213 and 9-1232 filed earlier by the present applicant. For example, as shown in FIG.
A pair of left and right push-up rolls 8 for pushing up the 2 'seam portion 12'a from the inside of the tube, an elevating device 9 for pushing up the push-up roll 8, and a push-up roll device 7 And a push-up height detector (not shown) for detecting the position in the height direction of the wheel 10 and the push-up roll 8 to be supported by the hand.

FIG. 13 shows an outer diameter of 323.8 mm × a plate thickness of 6.2.
4 shows the results of observing the behavior of both edges of a steel sheet within a both-edge convergence region L represented by the above-described formula (1) when a carbon steel pipe having a thickness of 2 mm is formed using the push-up roll device 7. FIG.
As is clear from, the behavior of both edges of the steel sheet immediately before the center of the squeeze side roll 6, that is, immediately before the upset, is corrected by using the push-up roll device 7,
The gap G in the height direction of both edges is also small, and it can be seen that both edges have almost the same behavior. in this way,
A push-up roll device 7 is arranged between the final fin pass roll 3a and the squeeze side roll 6, and both edges are pushed up from below by the push-up roll device 7 to perform butt welding while applying tension to both edges. By correcting the behavior of both edges of the steel sheet just before the upset so as to be substantially the same, it is possible to minimize the stress components generated on the both edge faces of the steel sheet during the upset other than in the direction perpendicular to the end face.

The push-up amount 14 are the Examples below, both edges heated temperature before laser welding in the case of using the two-phase stainless steel 5
When the pipe is formed at a temperature of not less than 00 ° C. and the push-up amount is changed variously, the height direction gap G of both edges of the steel sheet within the edge convergence region L expressed by the above-mentioned equation (1) and the squeeze side roll 6 It shows the effect of the upset amount R and the steel sheet thickness t obtained by the pipe circumference difference before and after passing on the presence or absence of lapping, and the horizontal axis represents the value obtained by the left side in the following equation (2): FIG. 5 is a diagram in which the vertical axis indicates whether or not a lap has occurred.

[0043]

(Equation 10)

G: height gap between both edges (mm) R: squeeze side roll up set amount (mm) t: steel plate thickness (mm) a: correction term of measurement position, edge Value obtained by dividing the convergence area L by the distance from the center of the squeeze side roll to the gap measurement position

The measurement of the gap G in the height direction at both edges is performed by measuring the position of the contact shoe 4 shown in FIG.
The position was controlled within the edge convergence region L obtained by the equation, and the vertical movement was measured on both sides by a contact displacement meter subjected to insulation treatment, and calculated from the difference between the measured values. FIG.
As is apparent from FIG. 4, the value obtained by the above equation (2) is 0.
Below 25, lap generation during pipe making is gone,
Therefore, it is understood that the push-up amount should be adjusted so as to satisfy the above equation (2).

The push-up roll mounted on the push-up roll device may be a single-stage type as shown in FIG. 11, or may be a multi-stage type as shown in FIG. By making the push-up roll a multi-stage type, the push-up reaction force acting at the time of push-up can be dispersed in each stage, and the roll mark on the inner surface of the tube and the collapse of the push-up roll by the push-up roll can be prevented. In addition, since the apparent push-up roll diameter can be increased, the edge is not locally stretched by the push-up.

[0047]

Next, an embodiment of the present invention will be described. Here, steels having the component compositions shown in Table 2 were melted, steel strips of various thicknesses and widths were produced by hot rolling, and these were used as welded pipe blanks.

[0048]

[Table 2]

After the above steel strip is formed into a tubular shape (or a cylindrical shape) by a forming machine shown in FIG. To the desired temperature, and output 2
Welding was performed using a 5 kW laser welding machine to produce welded pipes having different wall thicknesses and outer diameters. Here, as shown in FIG. 11, the push-up roll device 7 is installed between the last fin pass roll 3a of the fin pass roll group and the squeeze side roll 6. A mechanism for holding the push-up roll device 7 at a fixed position between the final fin pass roll 3 and the squeeze side roll 6 is disclosed in Japanese Patent Laid-Open No. 5-20 / 1993.
The technology according to No. 8213 can be adopted. Further, the position of the push-up is described in JP-A-9-19-1 already disclosed.
232 can be determined.

The measurement of the gap G in the height direction at both edges is performed as follows.
The position of the contact shoe 4 in FIG. 2 is controlled within the edge convergence region L determined by the above-described equation (1), and the vertical movement thereof is measured on both sides by a contact type displacement meter that has been subjected to insulation treatment. Calculated from the difference between the measured values of. In addition, the upset amount was determined by measuring the outer peripheral length of the pipe before and after passing through the squeeze side roll 6, and determining the difference.

As an index of the effect, the result of various welded pipes is indicated by x when lapping occurs during pipe making and welding failure occurs, and when good lapping does not occur and good welding can be performed. Are shown in Table 3. It should be noted that a lap where both edges do not completely abut can be visually confirmed, but if the lap is wrapped within a steel plate thickness as shown in FIG. Observation of arbitrary 50 points in the longitudinal direction by cross section polishing from the sample
As shown in FIG. 16, the step t between the inner and outer edges.
_{The case where G} exceeded 10% of the plate thickness t was regarded as the occurrence of lap. In addition, in order to make it easy to confirm the lap, the tube was formed without performing bead cutting on the inner and outer surfaces, which is usually performed. As a result, as shown in Table 3, it was confirmed that the one manufactured by the method of the present invention did not generate any lap, and it was possible to manufacture a welded pipe having stable welding quality.

[0052]

[Table 3]

[0053]

As described above, according to the present invention, the stabilization of the edge butting state during the pipe forming process allows
Duplex stainless steel pipes suitable for line pipes, oil well pipes, and the like can be manufactured with stable welding quality and high productivity.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing wrapping of a molding material edge portion by a conventional molding method.

FIG. 2 is a configuration diagram showing a production line for a welded pipe.

FIG. 3 is an explanatory diagram showing a relationship between a preheating temperature and a penetration limit welding speed.

FIG. 4 shows that the maximum edge temperature of a steel sheet is 750 by a heat conduction analysis.
FIG. 4 is a diagram showing a relationship between a distance from a steel plate edge and a temperature when the temperature is set to ° C.

FIG. 5 is a steel plate outermost edge temperature 75 obtained from heat conduction analysis.
It is a relation diagram of the ratio of the steel plate strength at 0 degreeC and the steel plate strength at room temperature, and the distance from the steel plate edge.

[FIG. 6] The steel plate outermost edge temperature 50 obtained from the heat conduction analysis.
It is a relation diagram of the ratio of the steel plate strength at 0 degreeC and the steel plate strength at room temperature, and the distance from the steel plate edge.

FIG. 7 is an explanatory diagram showing an edge wave generated in a formed material seam portion.

FIG. 8 is a diagram showing the relationship between the distance from the center of the squeeze side roll to the upstream side, edge fluctuation, and the gap between both edges.

FIG. 9 is an explanatory diagram showing a positional relationship when measuring a height-direction gap between both edges.

FIG. 10 is an explanatory view showing the behavior of both edges of a steel sheet near a squeeze side roll and the height gap between the two edges by a conventional forming method.

FIG. 11 is an explanatory diagram showing an embodiment of the present invention using a push-up roll device.

FIG. 12 is an explanatory view showing a configuration example of a push-up roll device used in the present invention.

FIG. 13 is an explanatory diagram showing the behavior of both edges of the steel sheet near the squeeze side roll and the height gap between the both edges by the forming method of the present invention.

FIG. 14 is an explanatory diagram showing the relationship between the height direction gap of both edges, the amount of upset, and the thickness of a steel sheet, which affects lap generation.

FIG. 15 is an explanatory view showing a multi-stage push-up roll device used in the present invention.

FIG. 16 is an explanatory diagram illustrating a method of determining the quality of a lap.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Breakdown roll group 2 Cage roll or cluster roll group 3 Fin pass roll group 3a Final fin pass roll 4 Contact shoe 5 Laser beam welding device 6 Squeeze side roll 7 Push-up roll device 8 Push-up roll 9 Lifting device 10 Wheel 12 Steel Strip (or steel plate) 12 'steel pipe G Gap between both edges R Upset amount by squeeze side roll t Steel strip or steel plate thickness t _G Step between both inner and outer edges L L From the center of squeeze side roll to upstream of forming Distance to the displacement gauge to be arranged a Correction term of the measurement position, which is the value obtained by dividing the edge convergence area L by the distance from the center of the squeeze side roll to the gap measurement position D Outer diameter of the welded pipe Df Flange of the squeeze side roll Outer diameter B Squeeze side roll from center distance Distance divided by 2 Pull the flange outer diameter of the side's roll

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Takashi Ariizumi, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Yukio Maho, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo F-term in Nippon Kokan Co., Ltd. (reference) 4E068 BA00 BE00 BG01 CJ01 DA15 DB01 4E081 AA12 BA03 BA19 CA19 DA11 DA31 EA14

Claims (4)

[Claims] 1. A duplex stainless steel strip is continuously formed into a tubular shape by a plurality of roll forming stands, and both edges, which are butted portions of the formed tubular duplex stainless steel, are heated and laser-welded. A method for manufacturing a duplex stainless steel welded pipe, comprising: a fin pass roll for maintaining a distance between the two edge portions at a predetermined distance; and a squeeze side roll for pressing and abutting the two edge portions, and a final fin pass roll. A method for manufacturing a duplex stainless steel welded pipe, comprising: arranging a push-up roll device between the squeeze side rolls and performing butt welding while pushing up the edges from below with the push-up roll device. . 2. The method for producing a duplex stainless steel welded pipe according to claim 1, wherein a heating temperature of the both edge portions before the laser welding is set to 500 ° C. or higher. 3. The method according to claim 1, wherein a height direction gap G between the two edges is measured, and the butt welding is performed while adjusting a pushing amount by the pushing roll device according to the measurement result. 3. The method for producing a duplex stainless steel welded pipe according to item 2. 4. A height direction gap G between the two edges at an arbitrary point within the edge convergence region L expressed by the equation (1) is measured so that the condition expressed by the equation (2) is satisfied. The method for producing a duplex stainless steel welded pipe according to any one of claims 1 to 3, wherein a push-up amount by the push-up roll device is adjusted. (Equation 1) Here, L: edge convergence area on the upstream side of forming from the center of the squeeze side roll D: outer diameter of the welded pipe Df: flange outer diameter of the squeeze side roll B: flange outer diameter of the squeeze side roll from the distance between the centers of the squeeze side rolls Subtracted by 2 and divided by 2 Here, G: height direction gap between both edges (mm) R: squeeze side roll upset amount (mm) t: steel strip thickness (mm) a: correction term depending on measurement position, edge convergence Area L
Divided by the distance from the center of the squeeze side roll to the gap measurement position