JPH0618485A - Ultrasonic angle beam flaw detecting method for steel pipe - Google Patents

Abstract

PURPOSE:To detect internal defects in a steel pipe accurately by making longitudinal wave ultrasonic waves incident on a material to be detected with respect to flaws so that the waves make a specified refractive angle to the material and the internal defects if any expanding over a surface inclined by a specified angle to the direction of the thickness of the material is inspected. CONSTITUTION:Ultrasonic waves 4 are made incident from the outer peripheral surface 3a toward the inner peripheral surface 3b of a steel pipe 3 so that 0.7-2 deg. of incident angle alpha is given through water used as a content medium 1 by an ultrasonic wave probe 2. The ultrasonic wave 4 is refracted at the outer peripheral surface 3a of a longitudinal seamless steel pipe 3 by 0-35 deg. of the refractive angle thetaL so that the wave mode is converted from the transverse wave to the longitudinal one. The ultrasonic wave 4 incident on the longitudinal seamless steel pipe 3 has 0-35 deg. of refractive angle thetaL, so that it is incident on an internal defect 5 expanding on a surface inclined to the thickness direction by 55-90 deg. in the direction orthogonal to the defect and the defect can be satisfactorily detected without pseudo-signals caused by noises.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flaw detection method for steel pipes.

[0002]

2. Description of the Related Art Ultrasonic flaw detection is performed in order to inspect a manufactured steel pipe for internal defects. For ultrasonic flaw detection of this steel pipe, a vertical flaw detection method that injects ultrasonic waves in the direction perpendicular to the surface of the steel pipe, that is, the thickness direction is used for defects extending parallel to the surface of the steel pipe. The oblique angle flaw detection method is used for the defects that spread on the inclined surface.

The above-described oblique angle flaw detection method for a steel pipe is a method in which ultrasonic waves are inclined to a certain extent from the thickness direction and are incident in the circumferential direction and the axial direction, and the ultrasonic waves are propagated to perform flaw detection on the entire surface of the steel pipe. The wave mode used in the bevel flaw detection method for this steel pipe is usually a transverse wave, and when propagating in the circumferential direction, the wall thickness / outer diameter (usually t / D) is 26.3%.
When testing a steel pipe that exceeds the limit, a longitudinal wave is incident at an oblique angle, is refracted, and is converted into a transverse wave by wave mode conversion.

When the ultrasonic waves are made to enter the steel pipe, a contact medium such as water or glycerin is interposed between the steel pipe and the ultrasonic probe in order to make the ultrasonic waves incident efficiently. ing. When the contact medium is water, the sound pressure round-trip passage rate, which indicates the ease of passage of transverse waves, is highest at a refraction angle of 37 to 38 °, as shown in the graph of FIG.
It sharply decreases at angles smaller than 37 °, becomes 0 at around 33 °, then rises again, and reaches a peak at 28 to 29 ° (a value less than 1/3 of the peak at 37 to 38 °). Also becomes smaller at 0 ° at a small angle.

On the other hand, when the refraction angle is 38 ° or more, it gradually decreases, then sharply decreases from about 75 ° and does not pass at 90 ° at all, so that the sensitivity of flaw detection changes depending on the refraction angle. In general, when performing oblique angle flaw detection using transverse waves, the refraction angle is 3
It is desirable to perform it at 5 ° or more.

Therefore, when an attempt is made to detect a defect that spreads on a surface inclined by at least 55 ° or more from the thickness direction, it is necessary for the ultrasonic waves to strike the surface at a right angle, so the refraction angle must be 35 ° or less. However, as described above, since the incidence efficiency of ultrasonic waves is deteriorated at this refraction angle, the echo height of the ultrasonic waves reflected from the defect is lowered.

FIG. 3 shows that ultrasonic waves are incident on the steel plate 22 from the ultrasonic transducer 21 at a refraction angle of 35 ° and reflected from a buttress-like defect 23 provided on the back surface of the steel plate 22 at an inclination angle β. FIG. 6 is a schematic diagram showing a test method for grasping how large the echo height is. The graph in FIG. 4 summarizes how the echo height changes when the tilt angle β is greatly changed by this test method. From this graph, at least 55 ° from the thickness direction
It can be seen that the sensitivity of the flaw detector must be considerably increased because the echo height is extremely reduced when flaw detection is performed on a defect extending to the inclined surface.

[0008]

However, in the conventional ultrasonic oblique-angle flaw detection using the conventional transverse wave, the method of increasing the sensitivity of the flaw detector has the following problems. That is, as can be seen from FIG. 4, the echo height when the surface where the flaw spreads faces the thickness direction and the echo height when the surface where the flaw spreads is inclined 60 degrees with respect to the thickness direction, Since there is a difference of about 20 dB (10 times faster), there is a problem in that even with defects of the same size at the same depth, the flaw evaluation greatly changes depending on the tilt angle.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and in ultrasonic oblique angle flaw detection of a steel pipe, the surface where the flaw spreads is 6 in the thickness direction.
It is an object of the present invention to provide an ultrasonic oblique angle flaw detection method in which the echo height from a defect does not decrease even when it is inclined by 0 degree or more.

[0010]

According to an ultrasonic oblique angle flaw detection method for a steel pipe according to the present invention, a longitudinal ultrasonic wave is incident on a material to be inspected so that a refraction angle is 0 to 35 degrees, and a thickness direction is applied. 55-9
This is to detect internal defects spread on a surface inclined by 0 degree.

[0011]

The ultrasonic bevel flaw detection method for a steel pipe according to the present invention comprises:
Longitudinal ultrasonic waves are incident on the material to be inspected so that the refraction angle is 0 to 35 degrees. The reason for doing this is as follows. That is, when an internal defect spreading on a surface inclined by 55 to 90 degrees from the thickness direction is detected, the refraction angle is 0.
Ultrasonic waves must be incident so that the angle is ˜35 degrees. In the case of the transverse ultrasonic wave, the ultrasonic wave is difficult to pass at such a refraction angle, and the flaw detection sensitivity is significantly lowered. Also, if you try to increase the sensitivity, it is easy to pick up noise,
It becomes difficult to distinguish defects from noise. Therefore, when the sound pressure reciprocating passage rate of the longitudinal wave ultrasonic wave which is another wave mode is examined, as shown in the graph of the relationship between the refracting angle and the sound pressure reciprocating passage rate in FIG. At ˜35 degrees, the sound pressure reciprocating passage rate of longitudinal ultrasonic waves is much higher than the sound pressure reciprocating passing rate of transverse ultrasonic waves. Therefore, the refraction angle is 0 to 3
Since it was found that higher sensitivity can be obtained by using longitudinal ultrasonic waves at 5 degrees, the longitudinal ultrasonic waves were used.

[0012]

EXAMPLE An ultrasonic bevel flaw detection method for a steel pipe according to an example of the present invention will be described with reference to FIG. In the ultrasonic bevel flaw detection method for steel pipes according to one embodiment of the present invention, water is used as the contact medium 1, and the ultrasonic probe 2 is used through the contact medium 1.
By setting the incident angle α to be 0 to 7.2 ° and moving from the outer peripheral surface 3a of the steel pipe 3 toward the inner peripheral surface 3b.
Incident. The ultrasonic wave 4 incident through the couplant 1 is
Outer peripheral surface 3a of seamless steel pipe 3 manufactured by the hot extrusion method
And refraction is performed so that the refraction angle θ _L becomes 0 to 35 °, and the wave mode is converted from the transverse wave to the longitudinal wave. The ultrasonic wave 4 incident on the seamless steel pipe 3 has a refraction angle θ _L of 0 to 35 °, and thus 55 to 90 ° from the thickness direction of the seamless steel pipe 3.
The internal defect 5 (an electric discharge flaw having an extension length of 1 mm) that spreads on the inclined surface is in a state of being hit from a direction orthogonal to the flaw, and the flaw can be satisfactorily detected without a pseudo signal due to noise.

[0013]

According to the present invention, it is possible to accurately detect defects in a steel pipe tilted from the wall thickness direction.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an ultrasonic oblique-angle flaw detection method for a steel pipe according to one embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the refractive index of transverse ultrasonic waves and the sound pressure round-trip passage rate.

FIG. 3 is a schematic diagram showing a test method for grasping the relationship between the inclination angle of a defect inclined from the thickness direction and the echo height of reflected ultrasonic waves.

FIG. 4 is a graph showing the relationship between the inclination angle of a defect and the echo height of reflected ultrasonic waves.

FIG. 5 is a graph showing the relationship between the refractive index of longitudinal ultrasonic waves and the sound pressure round-trip passage rate.

[Explanation of symbols]

 1 Contact medium 2 Ultrasonic probe 3 Steel tube 4 Ultrasonic wave 5 Internal defect

Claims (1)

[Claims] 1. A longitudinal ultrasonic wave is incident on a material to be inspected so that a refraction angle is 0 to 35 degrees, and an internal defect spreading on a surface inclined by 55 to 90 degrees from a thickness direction is inspected. Ultrasonic inspection method for steel pipes.