JPS59108903A - Method for detecting seamed position of seam welded steel pipe - Google Patents

Abstract

PURPOSE:To detect the seamed position after annealing highly accurately without errors, by projecting laser light having a specified wavelength at a specified incident angle, and discriminating a seamed part and a parent material part based on the anisotropy of an equal intensity curve of a reflected light intensity distribution. CONSTITUTION:Laser light is projected at an incident angle of more than 70 deg. and less than 90 deg., with the wavelength of the laser light being more than 0.2mum and less than 0.7mum. The laser light 12 from a helium neon laser light source 30 is made to scan in the lateral direction in the vicinity of a seamed part 10b by a beam scanner 32. Reflected patterns 22 and 22' are obtained on a screen 16. The images of the reflected patterns 22 and 22' are picked up by a CCD camera 34. An operating device 38 judges whether the images are longer in the direction of a longitudinal axis 20 or in the direction of a lateral axis 18 on the screen 16. A laser light projecting angle is detected by a mirror rotating position detector 33. When the reflected patterns 22 and 22' are longer in the direction of the lateral axis 18, the patterns are judged to be the seamed position, and the result is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a seam position detection method of an electric resistance welded pipe, and particularly,
The seam position of an ERW tube is detected from the intensity distribution of reflected light when the surface of the ERW tube is irradiated with a laser beam, which is suitable for use in automating ERW tube welding and flaw detection work. Concerning improvements in detection methods.

Generally, in ERW steel pipes, the quality of the ERW steel pipes is ensured by performing ultrasonic flaw detection on the excess cutting part of the weld bead (hereinafter referred to as the seam part) after cutting the weld heat. Therefore, in such a process, technology to automatically detect the seam position is essential in order to have the ultrasonic flaw detector automatically follow the seam.For this reason, conventional methods such as electromagnetic methods and ultrasonic methods have been used. methods and optical methods have been proposed.

Among these methods, optical methods are generally used when there are abnormal points such as scratches or cutting marks on the surface of an object, and by projecting a laser beam onto the surface, a characteristic reflected light intensity corresponding to the shape and direction of the abnormal point can be detected. This method takes advantage of the fact that a distribution (hereinafter referred to as a reflection pattern) occurs.For example, as proposed in Japanese Patent Application No. 50-101835, an almost isodirectional reflection pattern is generated in the base material of an ERW tube. On the other hand, at the seam, the reflection pattern exhibits anisotropy due to cutting scratches left in the seam in the longitudinal direction of the steel pipe, which is used to distinguish between the seam and the base material. .

However, in the past, there were no particular limitations on the wavelength of the laser beam, the direction of incidence, the detection position of the reflection pattern, etc., so for example, for ERW steel pipes whose seams are annealed after bead cutting, the following problems arise: It had

(1) Regarding the properties of the seam after annealing, the directionality of cutting scratches is extremely unclear, and the difference in anisotropy of the laser beam reflection pattern is unclear.

(2) There are scales and scale drop-off marks on the seam after annealing, and the laser light reflection rate varies greatly depending on the location, making it difficult to detect the reflection pattern.

Therefore, in the conventional method, there is a high possibility of erroneously detecting the seam position, and it is not suitable for practical use as it is.

The present invention has been devised to solve the above-mentioned conventional problems, and provides an electric resistance welding machine that can detect the seam position after cutting an electric resistance welding tube bead, especially after annealing, with high precision and without error. An object of the present invention is to provide a method for detecting the seam position of a pipe.

The present invention provides a method for detecting the seam position of an ERW tube, in which the seam position is detected from the intensity distribution of reflected light when the surface of the ERW tube is irradiated with a laser beam. The angle of incidence in the plane containing the longitudinal center axis of the ERW tube is 70' or more and 90' or more.
The seam part and the base material part can be identified from the difference in anisotropy of the iso-intensity curve of the reflected light intensity distribution on the plane perpendicular to the specular reflection optical axis of the laser beam. By doing so, the above objective has been achieved.

The present invention will be described in detail below with reference to the drawings.

In the present invention, as shown in FIG.
4 is on the 100 DEF that includes the straight line CD coinciding with the central axis 10a of the electric resistance welded tube 10 in its plane. Further, the screen 16 for obtaining the reflection pattern is perpendicular to the specular reflection optical axis 14, and the axes 18 and 20 on the screen 16 both pass through the intersection B of the specular reflection optical axis 14 and the screen 16,
Each of the four planes CD E F is perpendicular to and parallel to the plane CDEr knee F〉. Therefore, the incident laser beam 12
is reflected to a point on the seam 101) of the screen 1
A reflective pattern 22 is produced on 6. In the figure, 24 is a normal line, and 10c is a base material portion.

In such an arrangement, the seam portion 10b has directionality in the longitudinal direction, and the root mean square roughness R is 0.0 in the longitudinal direction.
1 to 0.2 μm (=RL), 0.2 to 1 in the circumferential direction
．． 5 μm <= Rc). Here, the root mean square roughness R
Let the one-dimensional coordinate in the surface direction of the surface to be measured be χ, and the coordinate in the height direction be Z(χ). Also, according to BeCklla Old 1, on an irregular metal surface with a root mean square roughness R, a surface with a wavelength λ is When coherent light (laser light) is incident at an incident angle α, assuming a two-dimensional model l (χ) as the reflecting surface, it is diffused by g × 1 according to the value of 9 as shown in the following equation. It is inferred that a specular irregular state with small disturbance, a strong diffuse scattering state with 9〉〉1, and an intermediate state between these with 9α1.

(1= (4π RCO3α/λ) 2,
,, (3) Here, in order for the directionality in the longitudinal direction to appear in the reflection pattern, it is necessary that g >> 1 holds true for the circumferential direction roughness Rc of the seam portion, and 9
≧10, Rc=0.2μm1α−〇°, when the condition regarding the wavelength λ is determined, λ≦0.7μIll is obtained.

On the other hand, in order to emphasize only the directionality in the longitudinal direction of the seam, it is preferable to use the condition 7 in which the seam longitudinal direction roughness RL is ignored as much as possible. That is, the incident axis of the incident laser beam 12 and the seam portion 10
If the relationship with b is taken as shown in Figure 1 and g≦1, then R
When L=0.15 μm, COSθ/λ≦0.5 is obtained. Here, if it is 250.7 μm, θ≧70° can be obtained.

Also, when determining the conditions to prevent scattering from minute irregularities where Rc≦0.2μm, when g≦1, RL
= 0.2 μm, θ = 85° (maximum realizable angle), 220.2 μm) 1 is calculated as 1q.

By satisfying these conditions, it is possible to clarify the directionality of cutting scratches on the annealed ERW tube, and it is possible to clarify the difference in anisotropy of the laser beam reflection pattern. can.

Furthermore, if the air refractive index of the object is n, the angle of incidence of the light beam on the surface of the object is α, and the reflectance at that point is R, then when the polarization direction of the incident light beam is parallel to the object surface (the incident angle α If the value of is large, most of the reflected light component becomes this polarized light, and the film properties are not lost).As is clear from Fresnel's formula, the reflectance R(α, n) is as shown in Figure 2. Become. Further, the dependence of the reflectance ratio on α when the refractive index n is different is as shown in FIG. From these, the angle of incidence α〉70°
In the region, the reflectance R increases significantly and rapidly approaches 1, so the difference in reflectance due to the difference in refractive index (difference in object) becomes significantly smaller. Similarly, in Figure 1, 90
By setting °>θ≧70°, it is possible to prevent significant local variations in the reflection pattern intensity due to variations in reflectance on the seam portion 10b, and it is possible to obtain stable reflection pattern intensity.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In this embodiment, as shown in FIG. 4, the wavelength is 0,633 μn1.
a helium neon laser light source 30 that emits a laser beam; a beam scanner 32 that scans the laser light emitted from the helium neon laser beam a30 in the horizontal direction near the seam portion 10b of the electric resistance welded tube 10; A mirror rotational position detector 33 for detecting the rotational position of a reflection mirror used in the beam scanner 32, and a reflection pattern 22.22 of specularly reflected light 14.14- reflected at the reflection point A or /M. A screen 16 similar to that shown in FIG. a preprocessing circuit 36 for performing preprocessing on the CCD camera 3;
From a part of the iso-intensity curve of the reflection pattern 22.22' obtained based on 4, it is determined whether the reflection pattern 22.22- is longer in the direction of the vertical axis 20 or in the direction of the horizontal axis 18 on the screen 16. At the same time, the projection azimuth of the laser beam is detected by the output of the mirror rotation position detector 33, and if the foul pattern is long in the horizontal axis 18 direction, the position determined from the azimuth is determined to be the seam position. It is composed of an arithmetic unit 38 that outputs a determination result.

The action will be explained below.

Illuminated by a helium neon laser light source 30 q1.

The laser beam 12 with a wavelength of 0.633 μm1 is laterally scanned in the vicinity of the seam portion 10b by the beam scanner 32, and its reflection pattern 22, 22' is obtained on the screen 16. This reflection pattern 22 , 22 ′ is imaged by a CCD camera 34 and inputted to an arithmetic unit 38 via a preprocessing circuit 36 . The calculation device 38 determines whether the reflection pattern 22, 22' is longer in the vertical axis 20 direction or the horizontal axis 18 direction on the screen 16 from a part of the equal intensity curve. On the other hand, at the same time, the laser beam projection azimuth angle is detected by the output of the mirror rotation position detector 33, and if the reflection pattern is long in the horizontal axis 18 direction, the position determined from the azimuth angle is determined to be the seam position and output. do.

The seam position signal obtained in this way is, for example,
This is input to the position control device of the ultrasonic flaw detector and controlled so that the flaw detector head is always positioned on the seam.

In this example, when the incident angle θ is 60° and when the incident angle θ is 75°,
FIG. 5 shows a comparison of the reflection patterns when the angle is set to .degree.

In the case of the incident angle θ-60° shown on the left side of FIG. 5 (comparative example), the directionality of the reflection pattern with respect to the seam portion is unclear, and the fouling intensity is also not constant depending on the location. On the other hand, when the incident angle of the present light is θ-75°, a characteristic directional pattern G extending in the horizontal direction as shown in Fig. 5 appears in the reflection pattern on the seam, and the reflection intensity is almost constant. It becomes.

As described above, according to the present invention, the seam position after cutting the electric resistance welded tube bead, especially after annealing, can be detected with high precision and without error. Therefore, welding of ERW pipes, etc.
It has the excellent effect of being able to automate flaw detection work with high precision.

[Brief explanation of the drawing]

FIG. 1 is a perspective view for explaining the principle of the seam position detection method of an ERW pipe according to the present invention, FIG. 2 is a diagram showing the dependence of reflectance on the angle of incidence, and FIG. FIG. 4 is a diagram showing the dependence of the reflection ratio on the angle of incidence. FIG. A perspective view including a diblock diagram, FIG. 5 shows the incident angle of 6.
FIG. 3 is a diagram showing the difference in foul patterns between 0° (comparative example) and 75° (invention). DESCRIPTION OF SYMBOLS 10... ERW pipe, 10b... Seam part, 10c... Base material part, 12.12'... Incident laser beam, 14.14'... Specular reflection optical axis, 16... Screen, 22.22'...foul pattern. Agent Takaya Ron (and 1 other person) Figure 2 Figure 3

Claims (1)

[Claims] (1) In a seam position detection method for an ERW tube, in which the seam position is detected from the intensity distribution of reflected light when the surface of the ERW tube is irradiated with a laser beam, the wavelength of the laser light is set to 0.
．． 2μm1 or more and 0.7μ01 or less, irradiate from a direction such that the incident angle is 70° or more and less than 90° in a plane that includes the longitudinal center axis of the ERW tube, and perpendicular to the specular reflection optical axis of the laser beam. 1. A seam position detection method for an electric resistance welded pipe, characterized in that a seam portion and a base material portion are identified from the difference in anisotropy of isointensity curves of reflected light intensity distribution on a plane.