JPH0552820A - Method for discriminating defect in electric resistance welded tube - Google Patents

Abstract

(57) [Summary] [Purpose] To accurately and quickly identify defects in the vicinity of welds in ERW pipes. [Structure] Ultrasonic flaw detection information (defect echo height, defect echo continuation length, beam path difference) and pipe manufacturing information (arcing result, welding heat input fluctuation, material of strip steel used,
(Inner surface shape of pipe manufacturing), the detected defects are classified into welding defects, material defects, and shape defects. Weld defects are further classified into cold welding, penetrator, and arcing. , Classify into inclusions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for discriminating a defect generated in the vicinity of a welded portion of an electric resistance welded steel pipe, and more particularly to an electric discharge method for discriminating a defect type with high precision by combining ultrasonic flaw detection information and pipe manufacturing information. The present invention relates to a method of discriminating defects in a sewn steel pipe.

[0002]

2. Description of the Related Art Generally, an electric resistance welded steel pipe is formed by passing a strip of steel through a forming roll group to form a cylindrical shape in which both edges are opposed to each other, and a welding current is passed in the vicinity of the opposite edges. A welding process in which heated edges are passed between squeeze rolls while they are being heated by resistance heat, and the edges that are in a heated state are butted against each other and welded together. Is manufactured through a series of steps including a step.

In the electric resistance welded steel pipe manufactured as described above, a defect is likely to occur in the vicinity of the welded portion, the defect is detected reversibly early in the middle of the finishing process, and the detection result is fed back to the welding process. It is used for quality control during welding. This defect detection is carried out by an ultrasonic flaw detector for electric resistance welded steel pipe that is guided along a predetermined path in the middle of the finishing process. Based on this, the types of detected defects are discriminated.

Various methods have been conventionally proposed for such defect discrimination. As a typical discrimination method,
There are two methods shown below. The first method disclosed in Japanese Patent Laid-Open No. Sho 60-98364 is to perform flaw detection by moving the electric resistance welded steel pipe and the probe relative to each other in the pipe axis direction at a constant speed, and at the same time, a defect echo reflected from the defect. Defects are discriminated by the combination of the defect continuation length measured from the ultrasonic pulse of 1 and the frequency bandwidth or the number of peaks of the frequency spectrum of the defect echo.

The second method disclosed in Japanese Patent Laid-Open No. 61-111461 is that the incident angle is 0 ° or more and 20 ° or less and the frequency is 25 MHz or more and 500 MHz or less with respect to the welded portion of the electric resistance welded steel pipe. The first ultrasonic wave of, the incident angle is 15 ° or more and 27 ° or less, the frequency is 2
The second ultrasonic wave of 10 MHz or more and 10 MHz or less is incident simultaneously or before and after, the cold welding defect, the penetrator and the inclusion are detected by the reflection echo of the first ultrasonic wave, and the penetrator and the penetrator are detected by the reflection echo of the second ultrasonic wave. Detect inclusions,
Only the cold welding defect is detected based on the difference between the detection results by the first and second ultrasonic waves.

[0006]

However, in any of the conventional discrimination methods described above, the defects are discriminated only based on the information in the ultrasonic flaw detection result, so that the discrimination accuracy is low and the defect detection environment is slightly deteriorated. There is a problem that accurate discrimination cannot be performed. According to the first method, it is possible to simply discriminate a defect based on the duration of the detected defect echo and the frequency bandwidth. However, in the case of paired flaw detection, ultrasonic flaw detection information such as echo height and beam path difference, and pipe manufacturing information such as welding heat input variation and strip steel material are essential for defect discrimination. Therefore, it is unlikely that the defect can be discriminated based on the above information alone. Also, the second
Similarly, in the method of (1), not only the information that is the basis for discrimination is insufficient, but also because high-frequency ultrasonic waves are used, the cost of the device increases, the attenuation is large, and the plate thickness of the electric resistance welded steel pipe to be discriminated is high. There are issues such as restrictions on

The present invention has been made in view of the above circumstances, and it is possible to discriminate the types of defects in the vicinity of a welded portion of an electric resistance welded steel pipe on the basis of a combination of ultrasonic flaw detection information and pipe manufacturing information, thereby obtaining a defect. An object of the present invention is to provide a defect discrimination method for an electric resistance welded steel pipe that can quickly obtain a highly accurate discrimination result even when the detection environment has various restrictions.

[0008]

A defect discrimination method for an electric resistance welded steel pipe according to the present invention is a method for discriminating a defect near a welded portion of an electric resistance welded steel pipe by an ultrasonic flaw detection method using a pair of probes. , Ultrasonic flaw detection information including defect echo height, defect echo continuation length, beam path difference, arcing detection result,
It is characterized in that the defect is discriminated by combining the fluctuation of the welding heat input, the material of the band steel used, and the pipe manufacturing information including the inner surface shape of the electric resistance welded steel pipe after bead cutting.

[0009]

According to the defect discrimination method of the electric resistance welded steel pipe of the present invention, first,
The presence or absence of defects is detected by ultrasonic flaw detection using a pair of probes. Then, the type of the detected defect is discriminated based on the combination of the ultrasonic flaw detection result information and the pipe manufacturing information. Depending on the difference in the height of the defect echo, the length of the defect echo, and the beam path length, the welding defect which is harmful and the material defect and the shape defect which are not so harmful are discriminated to some extent. Weld defects are identified by arcing detection results. Weld defects are identified by changes in welding heat input. Material defects and welding defects are specified according to the material of the steel strip used. Shape defects are identified by the inner surface shape of the electric resistance welded steel pipe after bead cutting.

[0010]

EXAMPLES Examples of the present invention will be specifically described below.

FIG. 1 is a schematic view showing a production line for electric resistance welded steel pipe. In this production line, from the upstream side to the downstream side, a forming roll group 1 for forming the strip steel K into a cylindrical shape, and both end edges of the strip steel K formed into a cylindrical shape are welded to each other to form an electric resistance welded pipe P.
Welding device 2, a pull-out roll group 3 that guides the electric resistance welded steel pipe P, a heat treatment device 4 that heat-treats the welded portion of the electric resistance welded steel pipe P, a water cooling tank 5 that cools the welded portion, and an outer diameter finish of the electric resistance welded steel pipe P. A sizer roll group 6 for performing the above and a cutting machine 7 for cutting the electric resistance welded steel pipe P are arranged in this order. In the pull-out roll group 3 between the welding device 2 and the heat treatment device 4, the electric resistance welded steel pipe P
There is provided a flaw detector 8 for performing ultrasonic flaw detection in order to detect defects near the welded portion. Further, in the vicinity of the upstream side of the flaw detection device 8, an inner bead monitoring device 9 for monitoring the inner surface shape of the electric resistance welded steel pipe P after cutting the bead generated by welding.
Are arranged. Further, the welding device 2 is connected to an arcing detector 10 that detects arcing (a phenomenon in which the welding current is temporarily short-circuited).

The manufacturing procedure of the electric resistance welded steel pipe P in the manufacturing line having such a configuration will be briefly described. The strip steel K, which is a raw material, is passed through the forming roll group 1 and formed into a cylindrical shape in which the edges on both sides in the width direction face each other, and then is fed to the welding device 2. The steel strip K fed to the welding device 2 is heated in the vicinity of the opposite end edge thereof by resistance heat accompanying the passage of a welding current and is sandwiched between a pair of squeeze rolls (not shown) to be in an heated state. The edges are abutted against each other to form an electric resistance welded steel pipe P, and the electric resistance welded steel pipe P is guided to the downstream side by the pullout roll group 3. The transferred electric resistance welded steel pipe P is first passed through the heat treatment device 4 to heat-treat the welded portion, and the water-cooled tank 5
To cool the weld, and then the sizer roll group 6
Is finished and rolled to have a predetermined outer diameter,
Finally, the cutting machine 7 cuts it into a predetermined length.

With respect to the electric resistance welded steel pipe P to be manufactured, a defect in the vicinity of the welded portion is detected in the manufacturing line, and its type is discriminated. FIG. 2 is a schematic diagram showing an implementation state of paired flaw detection using ultrasonic waves in the flaw detection device 8. Above the electric resistance welded steel pipe P, two probes 8a and 8b are arranged at equal intervals with the welded portion W interposed therebetween. Ultrasonic beams generated from the probes 8a and 8b are made incident on the electric resistance welded steel pipe P and propagated inside (A and B in the figure). If there is a defect, these ultrasonic beams are reflected by the defect to generate a defect echo. In the present embodiment, the defect echo is displayed on the screen of the cathode ray tube provided in the flaw detector 8. Further, in order to obtain pipe manufacturing information, the inner bead monitoring device 9 monitors the inner surface shape of the electric resistance welded steel pipe P, and the arcing detector 10 detects the presence or absence of arcing.

Next, the defect discriminating method which is the gist of the present invention will be described. In the present invention, the defect is discriminated based on the ultrasonic flaw detection information and the pipe manufacturing information. FIG. 3 is a schematic diagram showing the flow of this discrimination. Ultrasonic flaw detection information (defect echo height, defect echo continuation length, beam path difference) and pipe manufacturing information (detection result of arcing detector 10, welding heat input fluctuation, strip steel material used, inner bead monitoring device) 9), the detected defects are classified into welding defects, material defects, and shape defects. Further, welding defects are classified into cold welding, penetrator, and arcing. Classify into items. The ultrasonic flaw detection information used for defect discrimination and the types of defects that occur will be described below.

FIG. 4 shows a state in which the ultrasonic echoes A and B (see FIG. 2) generated from the respective probes 8a and 8b show defect echoes reflected by the defects on the screen of the cathode ray tube in the flaw detector 8. Is shown. In the figure, (a) shows a defect echo for the ultrasonic beam A from one probe 8a, and (b) shows a defect echo for the ultrasonic beam B from the other probe 8b. Defect echo height depends on the type of defect,
The difference (Δh) between both echoes also depends on the type of defect. In the example shown in FIG. 4, echo (a) is the H (High) level, echo
It can be said that (b) is at L (Low) level.

FIG. 5 shows the change over time in the height of the defect echo, and the time L that exceeds a certain predetermined echo height H is called the defect echo continuation length. Further, FIG. 6 shows each probe.
8a, the ultrasonic beam A generated from 8b, B is shows the route to reach the defect D, the ultrasonic beam A, beam path length of the B are each _{L a, L b, L a} -L The absolute value of _b is called the beam path difference.

FIG. 7 schematically shows types of defects. In the figure, D ₁ is a welding defect cold welding (due to insufficient heat input to the welding) or arcing (due to scale shortage at the welding point during welding, resulting in a temporary short circuit of the welding current).
Is shown. Further, D ₂ indicates a penetrator which is a welding defect (because of excessive welding heat input or particularly the material of the strip steel used in which the Mn / Si ratio is involved). Further, D ₃ indicates a hook crack which is a material defect (caused by inclusions on the metal flow M representing the flow state of the structure caused by rolling being cracked along the metal flow M by an upset generated in the welding process). .. Further, D ₄ indicates an inclusion which is a material defect. Further, D ₅ indicates a bead height which is a shape defect (due to insufficient adjustment when cutting the bead generated in the welding process with a tool).

Three kinds of ultrasonic flaw detection information (defect echo height, defect echo continuation length, beam path difference) and four kinds of pipe making information (detection result of arcing detector 10, welding heat input variation, use) Table 1 below shows specific discrimination criteria for defects by combining the material of the strip steel and the monitoring result of the inner bead monitoring device 9).

[0019]

[Table 1]

For example, in Table 1, two probes are used.
In both 8a and 8b, the defect echo height is H level, the defect echo continuation length is short, the beam path difference is not so large, and the welding heat input in the pipe manufacturing information is extremely low. The defect can be discriminated as cold welding among welding defects. Similarly, based on the combination of ultrasonic flaw detection information and pipe manufacturing information, it is possible to perform classification and type discrimination for other defects according to Table 1.

Next, an example in which the present invention is used to specifically discriminate a defect will be described. The discrimination results are shown in Table 2 below.

[0022]

[Table 2]

Defect discrimination was performed on 14 sample ERW steel pipes. The outer diameter of all sample ERW pipes is 22
The thickness was 9.1 mm and the wall thickness was 9.5 mm. As for the flaw detection conditions, the two probes had an incident angle of 22.5 °, a frequency of 5.0 MHz, and a flaw detection speed of 20 m / min. As for the level standard for the defect echo height, the sensitivity is set based on the N10 notch flaw defined by API, and the defect echo higher than the echo height from the artificial defect is at the H level, and half the level is at the L level. Was set. The defect echo continuation length was measured in 1 mm units along the tube axis direction, and the beam path was measured in 0.5 mm units. In addition, the arcing result was detected in dual time as the arcing occurred, and the welding heat input was measured in 0.1 sec.

With respect to all the samples of electric resistance welded steel pipe, the result of discrimination of defects shown in Table 2 was in agreement with the result of the cutting test. From the above, it was proved that the discriminating method of the present invention can discriminate defects accurately.

[0025]

As described above, in the defect discrimination method of the electric resistance welded steel pipe of the present invention, since the defect discrimination is performed by combining the ultrasonic flaw detection information and the pipe manufacturing information, the defect discrimination can be performed accurately and quickly. As a result, the quality of the electric resistance welded steel pipe in the production line can be greatly improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing a production line of an electric resistance welded steel pipe.

FIG. 2 is a schematic diagram showing an implementation state of ultrasonic flaw detection.

FIG. 3 is a schematic diagram showing a flow of performing defect discrimination by combining ultrasonic flaw detection information and pipe manufacturing information.

FIG. 4 is a schematic diagram showing a cathode ray tube display of a defect echo in ultrasonic flaw detection.

FIG. 5 is a schematic diagram for explaining a defect echo continuation length in ultrasonic flaw detection.

FIG. 6 is a schematic diagram showing a beam path length in ultrasonic flaw detection.

FIG. 7 is a schematic diagram showing various defects.

[Explanation of symbols]

 2 Welding device 8 Flaw detector 8a Probe 8b Probe 9 Inner bead monitoring device 10 Arcing detector K Strip steel P ERW pipe W Weld zone D Defect

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[Procedure amendment]

[Submission date] July 7, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

[Figure 6]

Claims (1)

[Claims] 1. A method for discriminating a defect in the vicinity of a welded portion of an electric resistance welded steel pipe by an ultrasonic flaw detection method using a pair of probes, wherein a difference in defect echo height, defect echo continuation length, and beam path difference is provided. Distinguishing the above defects by combining ultrasonic flaw detection information including arc detection information, arcing detection results, welding heat input fluctuations, strip material used, and pipe manufacturing information including the inner surface shape of ERW pipe after bead cutting A method for discriminating defects in electric resistance welded steel pipe.