JP6015295B2 - Heat treatment method for ERW welded pipe - Google Patents

Description

  The present invention relates to a heat treatment method for an electric resistance welded pipe in which heat treatment is performed by following the position of a welded part obtained by using a temperature distribution in the vicinity of the welded part when heat-treating a welded part of the electric resistance welded pipe.

  In the production of ERW steel pipes, the technology for detecting the position of welded parts that may be ERW welded (sometimes referred to as seam and seam welded parts) is the precision of bead cutting, heat treatment quality of welds, and welding. This is very important because it affects the accuracy of non-destructive inspection.

  In particular, the line pipe standard requires normalization to the inner surface for the purpose of improving weld performance, so it is important to accurately detect the weld when performing heat treatment after welding. It is.

  The welded portion of the ERW steel pipe is a straight line perpendicular to the pipe surface in the manufacturing process, and it is relatively easy to estimate the position of the welded part in the pipe thickness direction from the welded part on the outer surface of the steel pipe.

  However, when performing heat treatment after welding, it is difficult to specify the position of the welded part on the outer surface of the steel pipe because the weld bead is cut and the appearance of the welded part is not significantly different from the steel pipe base part. Several methods have been studied and proposed.

  Patent Document 1 relates to a method for detecting a seam portion of an ERW pipe, which is a method of measuring the temperature distribution on the circumference of the ERW pipe immediately after ERW welding and detecting the position of the seam portion by detecting a high-temperature zone due to welding. In order to solve the decrease in detection accuracy after the heat treatment process after welding, the position of the seam part is detected immediately after ERW welding, and marking is performed in advance according to the result, and marking part and non-marking are not performed. It is described that a marking position is detected based on a difference in emissivity from a portion, and a seam portion is detected during heat treatment or after heat treatment based on the marking position.

  Patent Document 2 relates to a seam position detection device for an electric resistance welded pipe, and detects the seam position when performing electric resistance welding by detecting the reflection intensity around the seam with an image sensor or the like while irradiating the seam with a light source. In a device that performs binarization processing on the reflected intensity distribution, a pair of light sources arranged symmetrically across the seam position is used to prevent the reflected intensity distribution from becoming an abnormal waveform that makes it difficult to identify the seam position. It is described that the distance is changed by moving the cross section in the horizontal direction, or the axial direction angle with respect to the steel pipe and the circumferential direction angle of the steel pipe cross section are changed.

Japanese Patent Laid-Open No. 03-264803 Japanese Patent Laid-Open No. 03-158706

  However, in the method of detecting the seam portion based on the marked mark described in Patent Document 1, the seam portion detecting device detects the seam portion that is at a high temperature immediately after welding, and performs marking based on the detection result. Since marking is performed using a device, both a seam detection device and a marking device are necessary, and the equipment load is large.

  Moreover, in the method using the reflection intensity of the bead cutting part described in Patent Document 2, the cutting blade moved up and down in the bead cantilever and the unstable cutting part, and the cutting width fluctuated and disturbed by chatter, etc. It is difficult to cope with the bead shape, the equipment load is small, and a method for detecting the seam portion after bead cutting with high accuracy has not been established.

  Therefore, when heat-treating the welded part after bead cutting, it is difficult to make the heat-treatment device follow the welded part with high accuracy, and heat treatment is widely performed around the welded part so that heat treatment can be reliably applied to the seam part after bead cutting. The amount of heat input from the heat treatment apparatus to the welded portion increased, and the heat treatment cost increased.

  Therefore, the present invention provides an electric resistance welded steel pipe that can accurately reduce the heat treatment cost by causing the heat treatment apparatus to follow the welded portion with high accuracy by using the surface temperature distribution in the vicinity of the welded portion after bead cutting and heat treatment. An object of the present invention is to provide a heat treatment method.

The object of the present invention can be achieved by the following means.
1. A method for heat treatment of an electric resistance steel pipe, when heat-treating a welded portion after bead cutting by the heat treatment apparatus in an electric resistance steel pipe production line in which a heat treatment apparatus having a plurality of dielectrics is arranged on the downstream side of the bead trimmer, The position of the welded portion on the outer surface of the steel pipe is obtained based on the steel pipe outer surface temperature distribution in the vicinity of the welded portion after bead cutting and after the heat treatment, and the dielectric of the heat treatment apparatus is controlled to follow the welded portion. A heat treatment method for ERW steel pipes.

  According to the present invention, since it is possible to estimate the position of the welded portion required when heat-treating the welded portion of the ERW pipe with high accuracy, the heat input fluctuation range from the heat treatment apparatus to the welded portion is reduced. With a width of about ± 3 mm, the heat input efficiency is improved, making it possible to produce thick-walled materials with minimal use of energy or equipment enhancement, which is extremely useful industrially.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining the principle of this invention, (a) is a schematic diagram of the ERW steel pipe manufacturing line provided with the line structure to which this invention is applied, (b) is a figure explaining the principle of this invention. The figure which shows typically the outer surface temperature distribution of the seam welding part vicinity measured with the sensor in front of the welding part heat processing apparatus of an ERW steel pipe manufacturing line. The figure which shows typically the outer surface temperature distribution of the seam welding part vicinity measured with the sensor after the welding part heat processing apparatus of an ERW steel pipe manufacturing line.

  The present invention is characterized in that the welded portion of the ERW steel pipe is obtained in the temperature distribution around the seam portion after heat treatment from the position information of the welded portion obtained from the temperature distribution around the seam portion after bead cutting. This will be described below.

  1A and 1B are diagrams for explaining the principle of the present invention. FIG. 1A is a schematic diagram of an ERW steel pipe production line having a line configuration to which the present invention is applied, and FIG. 1B is a diagram for explaining the principle of the present invention. Show.

  The illustrated ERW steel pipe production line performs heat treatment using the heat input at the time of ERW welding to the maximum, so that the squeeze roll 2, the bead trimmer 3 and the bead trimmer 3 for seam welding the hot-rolled steel sheet 1 are possible as much as possible. It is comprised by the welding part heat processing apparatus 4 arrange | positioned closely. The welded part heat treatment apparatus 4 includes a plurality of dielectrics 41 and a cooling device 42, and performs active cooling and heating such as annealing, normalization, quenching, and tempering on the welded part, and the figure shows a case where a quenching and tempering process is performed. Show. In the following description, the traveling direction of the ERW pipe after the ERW welding in the line is the Z axis, the traveling direction and the vertical direction of the ERW pipe are the Y axis, and the traveling direction of the ERW pipe and the horizontal right angle direction are the X axis. A fixed coordinate system is used.

  The welded part heat treatment apparatus 4 is provided with a plurality of inductors 41 in the tube traveling direction, and the inductors 41 can individually move in the tube traveling direction and in the circumferential direction perpendicular to the tube traveling direction. Between the bead trimmer 3 and the welded part heat treatment device 4, a sensor 5, for example a radiation thermometer, capable of measuring the weld temperature distribution is arranged, and a sensor having the same function as the sensor 5 on the downstream side of the welded part heat treatment device 4. 6 is placed. Sensors 5 and 6 are installed on the Z axis of the fixed coordinate system in the line.

  In the present invention, first, the sensor 5 measures the outer surface temperature distribution in the vicinity of the seam welded portion after bead cutting with the bead trimmer 3 after seam welding. FIG. 2 schematically shows the outer surface temperature distribution near the seam weld measured by the sensor 5.

  In the figure, the horizontal axis is the distance (mm) on the X axis of the fixed coordinate system of FIG. 1, and the position on the X axis of the sensor 5 in the line is the origin 0. The value (+) is the distance on the X axis on the left side of the direction of travel of the ERW steel pipe, and the value (-) is the distance on the X axis on the right side of the direction of travel of the ERW steel pipe. Indicates.

  In the outer surface temperature distribution shown in FIG. 2, the midpoint P of intersections A and B where the threshold T (° C.) selected from the outer surface temperatures of 150 to 50 ° C. and the outer surface temperature distribution curve intersect is obtained, and the seam estimated position P And The threshold value T is set to an arbitrary temperature within the range of the outer surface temperature of 150 to 50 ° C. in which the temperature change is rapid and the end of the heating region by welding can be easily specified.

  When bead cutting is performed at the seam welded portion, the seam welded portion having a high temperature is deleted. Therefore, the positions on the X coordinate axis where the maximum values C and D are at the outer surface temperature distribution are at the both ends in the width direction of the bead cutting trace. Position.

  Next, the sensor 6 measures the outer surface temperature distribution (hereinafter, the outer surface temperature distribution after the heat treatment) after heat treatment of the vicinity of the seam welded portion after bead cutting by the heat treatment apparatus 4. FIG. 3 schematically shows the outer surface temperature distribution after the heat treatment measured by the sensor 6.

  The initial maximum values on both sides of the outer surface temperature distribution after the heat treatment shown in FIG. 3 are E and F, and | C−P |: | D−P | = | EQ |: Q which becomes | FQ | is obtained and set as a seam estimated position Q. Similar to the maximum values C and D, the positions of the maximum values E and F on the X coordinate axis correspond to the positions at both ends in the width direction of the bead cutting trace.

  In the present invention, the seam estimation position P on the X axis at the position of the sensor 5 on the Z axis and the seam estimation position Q on the X axis at the position of the sensor 6 on the Z axis in the ERW steel pipe production line are connected. Assuming that there is a seam on the XZ plane line (line a in FIG. 1 (b)), each inductor 41 of the welded part heat treatment apparatus 4 is controlled to be positioned on the line, and the welded part is copied. .

In the case of the inductor at the position N on the Z axis (N = 1 to 5 because there are five inductors 41 in the ERW steel pipe production line shown in FIG. 1), X from the roll core (Z axis) to the line a The directional distance b (N) can be obtained by the equation (1) from the geometrical relationship in FIG. 1B (the squeeze roll position is the origin 0 of the XYZ coordinates).
(L (N) -L (P)) (QP) / (L (Q) -L (P)) + P (1)
In the equation, L (N), L (P), and L (Q) are the coordinate points on the Z axis of the positions N, P, and Q, and P and Q are the X-direction lengths at the coordinate points P and Q on the Z axis To do.

  In deriving the point Q, the absolute distance may be used on the premise that perfect tracking is performed, but the time variation of the bead cutting end position due to the wave out of the plate is large, In order to prevent feedback from becoming excessively sensitive from tracking errors, the ratio of the distance between the cutting parts was rounded in time.

  Thus, according to the present invention, since the position of the welded portion can be estimated with high accuracy, the heat input fluctuation range from the heat treatment apparatus to the welded portion is within about ± 3 mm, and the heat input efficiency is reduced. improves. A portion from the first welded portion of the ERW pipe through the sensor 5 on the Z-axis to the passage of the sensor 6 (length of about 6 m in a general ERW steel pipe production line) is the method of the present invention. However, in general, the precision of the welded portion in the heat treatment is not required at a portion where the allowance is discarded.

  Using the ERW steel pipe production line shown in FIG. 1, the seam portion was detected by the method of the present invention and the conventional method, and a plurality of steel pipes having different combinations of outer diameter and pipe thickness were produced. In the conventional method, the seam position in the outer surface temperature distribution after the heat treatment by the sensor 6 is set as the midpoint between the maximum values E and F.

  For the verification of the detection accuracy, the difference in the A1 penetration width on the left and right of the seam position in the cross section of the manufactured steel pipe was used. Table 1 shows the test results. According to the method of the present invention, compared to the conventional method, the difference between the A1 penetration widths on the left and right of the seam position is small, and the seam tracking accuracy of the dielectric of the heat treatment apparatus is better than the conventional method. The A1 penetration width is the width of the heat affected zone (expressed by Nital corrosion in the region heated above the Ac1 transformation point) from the center of the seam in the macro section of the seam cut out in the direction perpendicular to the weld line after heat treatment. And

DESCRIPTION OF SYMBOLS 1 Hot-rolled steel plate 2 Squeeze roll 3 Bead trimmer 4 Welding part heat treatment apparatus 41 Dielectric element 42 Cooling apparatus 5, 6 Sensor a Line b Distance

Claims (2)

A method for heat treatment of an electric resistance steel pipe, when heat-treating a welded portion after bead cutting by the heat treatment apparatus in an electric resistance steel pipe production line in which a heat treatment apparatus having a plurality of dielectrics is arranged on the downstream side of the bead trimmer, The seam estimation position P is obtained based on the steel pipe outer surface temperature distribution near the weld after bead cutting, and the seam estimation position Q is obtained based on the steel pipe outer surface temperature distribution near the weld after heat treatment. A position of a welded portion on the outer surface of the steel pipe is obtained using a line connecting the estimated position P and the estimated seam position Q, and a dielectric of the heat treatment apparatus is controlled to follow the welded portion. Heat treatment method. The traveling direction of the ERW steel pipe after the ERW welding in the ERW steel pipe production line is the Z axis, the advancing direction and the vertical direction of the ERW steel pipe are the Y axis, and the advancing direction of the ERW steel pipe is a horizontal perpendicular direction to the X axis,
When heat-treating the weld after bead cutting by the heat treatment device,
Obtaining the estimated seam position P based on the steel pipe outer surface temperature distribution near the weld after bead cutting, and obtaining the estimated seam position Q based on the steel pipe outer surface temperature distribution near the weld after heat treatment,
Assuming that there is a seam on the line a on the XZ plane connecting the obtained seam estimated position P and seam estimated position Q, the dielectric of the heat treatment apparatus is controlled to be positioned on the line a. The heat-treating method for an ERW steel pipe according to claim 1.