JPS63290957A - Ultrasonic flaw detection method for stainless steel - Google Patents

Abstract

PURPOSE:To enable flaw detection of a ferrite-austenite two-phase stainless steel and austenitic stainless steel by setting the incident direction of ultrasonic waves having 2.5-4.5MHz flaw detection frequency and 40-50 angle of refraction at 0-15 deg. or 75-90 deg. direction with the rolling direction of a material. CONSTITUTION:The reason for limiting the flaw detection frequency of a probe lies in that sufficiently high S/N is obtainable in this range with the ferrite- austenite two-phase stainless steel and austenitic stainless steel. While the S/N is smaller with the two-phase stainless steel than with carbon steel, the sufficiently high S/N is obtainable in the 2.5-4.5MHz range. The reason for limiting the angle of refraction of the probe at 40-50 deg. lies in that the high S/N is obtainable at the angle of refraction within this range.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for ultrasonic flaw detection of welded parts of ferritic-austenitic duplex stainless steels and austenitic stainless steels.

Prior art and its problems As is well known, ultrasonic flaw detection of welded parts of steel plates, etc., is generally performed by the oblique angle method. For example, in the case of carbon steel, the flaw detection conditions include using a narrowband probe and narrowband amplifier, frequency 2 to 4) IH2, refraction angle approximately 70 degrees,
Uses transverse waves, beam path 1.5 skips (54-74mm)
) or 2.0 skips (75 to 95 mm).

However, when the material to be tested is ferritic-austenitic duplex stainless steel or austenitic stainless steel, due to the material properties, if the frequency band is narrow, the attenuation of the ultrasonic wave is large and the S/N ratio is poor, so the above-mentioned Welded parts of stainless steel plates and pipes such as SAW, DIG,
It has not been possible to directly apply the generally used narrowband ultrasonic flaw detection method to flaw detection (by MIG welding, etc.).

The present invention proposes a method that enables ultrasonic flaw detection of welded parts of stainless steel materials as described above.

Means for Solving the Problems This invention is an ultrasonic flaw detection method for Fe-1, austenitic duplex stainless steel, and austenitic stainless steel to which conventional general ultrasonic flaw detection methods cannot be applied.
Using a medium band probe (5 to 6 waves) and a wide band amplifier, the flaw detection frequency is 2.5 to 4.5 MHz, and the refraction angle is 40 to 40.
The present invention proposes a method in which the incident direction of ultrasonic waves is incident at 0 to 15 degrees or 75 to 90 degrees with respect to the rolling direction of the rolled material.

This invention will be explained in detail below.

First, the stainless steel that is the subject of this invention generally contains Cr2O to 30% and Ni4 to 8% 1M. 1-5%
, duplex stainless steel with a ferrite content of 40 to 60%, or austenitic stainless steel.

As a medium band type probe, an angle probe having a structure shown in FIG. 1 is often used. In the figure, (1) is a magnetic vibrator;
(2) is an acrylic resin wedge, (3) is a sound absorbing material, (4
) is the damper material, and (5) is the plug. In the case of this angle probe, a probe having frequency bands with different wave numbers can be obtained by adjusting the strength when adhering the vibrator (1) to the damper material (4).

In this invention, the reason why a medium band type probe with a wave number of 5 to 6 and a wide band type amplifier are adopted as the flaw detection probe is as follows.

FIG. 2(A) shows the wave number and frequency band of a medium band type probe. For comparison, the wave number and frequency band of a broadband type probe are shown in FIG.

In general, increasing the damping characteristics will broaden the band characteristics, so use a broadband high damping wideband probe (Figure B) for applications where resolution is important, and use a narrowband probe (Figure B) for applications where sensitivity is important. A feeler (Figure C) is used. □ However, when detecting monthly defects with large attenuation, a wide band is advantageous because high frequency components are attenuated, and conversely the S/N ratio may be better than a narrow band. Here, a medium-band type probe (see figure) takes advantage of the characteristics of both the broadband type (Figure B) and the narrow band type (Figure C).

Figures 3 (A) and (B) show the relationship between the beam path length and attenuation of duplex stainless steel when using a narrow band probe (conventional type) and a medium band probe (the present invention), respectively. It is a figure showing the relationship of S/N ratio. This figure shows a wall thickness of 1
The results were obtained by artificially forming a 1.6 mm diameter drill hole in a 0 mm welded part and using a refraction angle of 45 degrees.

That is, as is clear from Figure 3 (A) and (B),
In the case of conventional probes (narrowband probes and narrowband amplifiers), the attenuation is large and the S/N ratio is poor.

For corner flaw detection, the beam path cannot be long, usually 80mm.
This will be done below.

On the other hand, when a medium-band probe with a wave number of 5 to 6 is used in combination with a wide-band amplifier, the attenuation is relaxed, making it possible to detect defects in attenuated materials, and the beam path is as shown in the figure. (Flaws can be detected up to 130 mm with a good S/N ratio. Since there is excess material in the weld, the lower limit of the beam path is usually 40 mm.

Next, the flaw detection frequency of the probe is limited to 2.5 to 4.5 MHz because a sufficiently high S/N ratio can be obtained in this range for duplex stainless steel and the like.

FIG. 4 is a diagram showing the relationship between the frequency and S/N ratio of the probe for duplex stainless steel and carbon steel.

This figure shows the results of an investigation in which a drill hole of 1.6 mmφ was artificially formed in a welded part with a wall thickness of 10 mm, and the beam path length was 60 mm and the refraction angle was 45 degrees.

Although duplex stainless steel has a lower S/N ratio than carbon steel, it has a sufficiently high S/N ratio in the 2.5 to 4.5 MHz range.
It can be seen that the ratio can be obtained. Therefore, in the present invention, the above frequency range is adopted.

In addition, the refraction angle of the probe was limited to 40 to 50 degrees because
This is because a high S/N ratio can be obtained in this range of refraction angles.

Figure 5 shows the frequency set to 4HHZ under the test conditions in Figure 3.
This is the result of examining the S/N ratio by changing the refraction angle. From this figure, it can be seen that in the case of duplex stainless steel, the S/N ratio is high at a refraction angle of 40 to 50 degrees.

Furthermore, in this invention, the incident direction of the ultrasonic waves is limited to 0 to 15 degrees or 75 to 90 degrees with respect to the rolling direction of the monthly yield, because the rolling direction of the material has a degree of attenuation. Based on the knowledge that the ultrasonic wave propagation direction (incident angle) relative to the rolling direction was
As a result of investigating the relationship between the degree of attenuation and the degree of attenuation, as shown in Figure 6, it is best to inject the ultrasonic waves from a direction of 0 to 15 degrees or 75 to 90 degrees with respect to the rolling direction of the material in order to reduce the degree of attenuation. This is due to the fact that it was found to be important.

Example Using a medium-band probe and a wide-band amplifier with the structure shown in Fig. 1 and the waveform and frequency band shown in Fig. 2 (A), ferrite-austenite duplex stainless steel, carbon steel, 313304 The relationship between the beam path and the flaw detection sensitivity when testing each welded part (thickness 10 mm) is shown in the 7th table.
The relationship between the beam path and the S/N ratio is shown in FIG. 8 in comparison with a conventional probe (narrowband probe).

The types of plot marks in FIGS. 7 and 8 in this example are shown in the table below.

As is clear from the margins of FIGS. 7 and 8 below, according to the method of the present invention, good results were obtained in both flaw detection sensitivity and S/N ratio. These results confirmed the effectiveness of ultrasonic flaw detection of attenuating materials using the combination of the medium band type probe and wide band type amplifier of the present invention.

Effects of the Invention As is clear from the above explanation, according to the method of the invention, it is possible to detect flaws in ferrite-austenitic duplex stainless steel and austenitic stainless steel, to which conventional general ultrasonic flaw detection could not be applied. .

Furthermore, in the case of the combination of the medium band type probe and wide band type amplifier of the present invention, sufficient reception is possible even when the frequencies of the attenuating materials are different, so the attenuating materials can be inspected with high accuracy without compromising the S/N ratio. There are advantages.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of the structure of a medium band type probe used in the present invention. Figure 2 (8) is a diagram showing the wave number and frequency band of a medium band type probe, Figure 2 (B) is a diagram showing the wave number and frequency band of a broadband type probe, and Figure 2 (C) is a diagram showing the wave number and frequency band of a broadband type probe. FIG. 3 is a diagram showing wave numbers and frequency bands of a type probe. Figure 3 (A) is a diagram showing the relationship between the beam path length and attenuation of duplex stainless steel when using a narrow band probe (conventional probe) and a medium band probe (the present invention);
B) is a diagram showing the relationship between the beam path length and the S/N ratio of the same stainless steel. FIG. 4 is a diagram showing the relationship between probe frequency and S/N ratio in duplex stainless steel and carbon steel. FIG. 5 is a diagram showing the relationship between the refraction angle of the probe and the S/N ratio in the same as above. FIG. 6 is a diagram showing the relationship between the angle of incidence of ultrasonic waves and the degree of attenuation in the same as above. FIG. 7 is a diagram not showing the relationship between beam path length and flaw detection sensitivity in an embodiment of the present invention. FIG. 8 is a diagram showing the relationship between the beam path length and the S/N ratio in the same embodiment. 1...Magnetic vibrator 2...Wedge 3...
Sound-absorbing material 4... Damper material 5... Connection patent applicant Sumitomo Metal Industries, Ltd. (8p) Surface ¥ attack (UP) N/s a)Q Heam path (Parrot) No. (A) Heam Path length (CM) Figure 8 (B) Beam path (M) Beam path (wn)

Claims (1)

[Claims] In the ultrasonic flaw detection method of ferrite-austenitic duplex stainless steel and austenitic stainless steel, a medium band probe (wave number 5 to 6) and a wide band amplifier are used, the flaw detection frequency is 2.5 to 4.5 MHz, and the refraction Corner 40-50
The direction of incidence of ultrasonic waves is 0 to 15 degrees relative to the rolling direction of the material.
An ultrasonic flaw detection method for stainless steel characterized by incidence from a direction of 75 to 90 degrees.