JPH05288723A - Pitch-catch type ultrasonic flaw examination - Google Patents

Abstract

PURPOSE:To discriminate a direct propagation wave and a defect reflected wave distinctly from each other on the occasion of examination of a defect being parallel to the direction of propagation of an ultrasonic beam. CONSTITUTION:A transmission-side longitudinal wave angle probe 4a of a refractive angle 10 to 40 deg. is disposed on one of opposite blade groove end faces 2 of a blade groove tooth part 1 which has a defect 10 being parallel to the length direction, and a similar reception-side longitudinal wave angle probe 4b is disposed on the other, respectively. The defect is detected from a time difference between a propagation time of a wall surface reflected wave 8 once reflected on a blade groove wall surface 3 and then propagated as a longitudinal wave and a propagation time for which a wall surface defect reflected wave 9 once reflected on the blade groove wall surface 3 and then converted into a lateral wave is reflected by the defect 10, propagated to the blade groove wall surface 3, then converted in a mode into the longitudinal wave again and received.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pitch catch type ultrasonic flaw detection method suitable for nondestructive inspection of blade groove teeth of a turbine rotor.

[0002]

2. Description of the Related Art During operation of a turbine rotor, a defect that occurs in the serration type blade groove tooth portion is generated in parallel with the blade groove at approximately the center of the blade groove. Performs ultrasonic flaw detection by arranging the probe on the blade groove end surface which can only be approached by the ultrasonic probe. For example, as shown in the explanatory diagram of FIG. The transmitting side probe 4a 'and the receiving side probe 4a' are arranged respectively, and an ultrasonic beam is made incident on the defect 10 from the transmitting side probe 4a 'by a so-called pitch catch type, and the reflected wave is reflected. The reception side probe 4b 'has received and has detected a flaw. However, in this case, since the beam path difference between the defect reflected wave 11 and the direct propagation wave 7 propagating from the transmitting side probe 4a 'to the receiving side probe 4b' is almost the same, it is difficult to identify the defect. In addition, the reflected wave 12 whose mode has been converted into the transverse wave at the defect 10 is re-reflected by the blade groove wall surface 3 and received, or the ultrasonic wave which has passed as it is because the defect 10 is small is reflected by the blade groove wall surface 3 on the defect side and received. Various reflected waves are generated, and the defect reflected wave 11 cannot be specified. Therefore, as another flaw detection method, the blade groove end face 2 is inspected by the magnetic particle flaw detection method after the defect 10 has propagated to the blade groove end surface 2, or the magnetic pole flaw detection method is applied to the blade groove portion after extracting the moving blade. But
With this method, the inspection period and cost are enormous, and it is difficult to perform 100% inspection during the regular inspection period.

[0003]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above circumstances, and in the flaw detection of a defect parallel to the propagation direction of the ultrasonic beam, the direct propagation wave and the defect reflection wave are clearly defined. Pitch that can be identified and ultrasonic flaw detection method can be used from blade groove end face without extracting blade for flaw detection of turbine rotor blade groove tooth portion, which can shorten inspection period and cost. An object is to provide a catch type ultrasonic flaw detection method.

[0004]

To this end, the present invention provides a longitudinal wave bevel probe having a refraction angle of 10 to 40 ° on both scanning surfaces of a test body having a defect parallel to the propagation direction of an ultrasonic beam. The ultrasonic beam is placed and is reflected once by the wall surface of the test piece and propagates as a longitudinal wave, and the ultrasonic beam after being reflected once by the wall surface of the test object and converted into a transverse wave is reflected by a defect and tested. It is characterized in that the defect is detected by a time difference from a propagation time until the wave is propagated to the wall surface of the body and then converted into a longitudinal wave again to be received.

[0005]

In the pitch catch type ultrasonic flaw detection method of the present invention, a longitudinal wave bevel probe having a refraction angle of 10 to 40 ° is provided on both scanning surfaces of a test body having a defect parallel to the propagation direction of the ultrasonic beam. Ultrasonic waves are transmitted from the transmitting side probe, and the ultrasonic waves propagated in the test body are received by the receiving side probe, and are transmitted directly from the transmitting side probe to the receiving side probe. The delay time due to mode conversion of the reflected wave between the defect and the wall surface of the test body is measured based on the propagation time of the sound wave and the reflected wave that is reflected once as a longitudinal wave on the wall surface of the test body.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, an embodiment in which the pitch catch type ultrasonic flaw detection method of the present invention is applied to flaw detection of a turbine rotor blade groove tooth portion will be described. FIG. 1 is an explanatory diagram of an ultrasonic wave propagation path, and FIG. FIG. 3 is a perspective view of a flaw detection situation in an example, FIG. 3 is an explanatory diagram of a flawless portion flaw detection result in the above, and FIG. 4 is a defect portion flaw detection result.

First, the principle of the present flaw detection method will be described with reference to FIG. Generally, when a longitudinal wave is incident on the boundary surface at an angle other than 0 °, it becomes a reflected wave including mode conversion to a transverse wave, and it is often the case that the longitudinal wave becomes extremely small especially between the incident angles of 50 to 80 °. Are known. That is, in FIG. 1, a transmission side longitudinal wave bevel probe 4a applied to the blade groove end surface 2 of the blade groove tooth portion 1
The wall surface defect reflected wave 9 that is incident at a refraction angle θ is incident on the blade groove wall surface 3 at an incident angle of 90 ° -θ. By selecting the refraction angle θ so that this incident angle is 50 to 80 °, the wall surface defect reflected wave 9 between the blade groove wall surface 3 and the defect 10 is selected.
Many transverse waves are included in. Longitudinal wave velocity in steel 5900m / s
On the other hand, since the transverse sound velocity in steel is 3230 m / s and the propagation time is slow, the wall-defect reflected wave 9 including ultrasonic waves mode-converted into the transverse wave between the defect 10 and the blade wall surface 3 is the receiving side longitudinal wave oblique probe. On the CRT screen of the ultrasonic flaw detector, the direct propagation wave 7 directly propagating between the blade groove end faces 2 and the wall reflection received as a longitudinal wave after being reflected once by the blade groove wall surface 3 on the CRT screen of the ultrasonic flaw detector Since it appears as a delayed echo with respect to the wave 8, the presence or absence of a defect can be determined.

Explaining this phenomenon in more detail, since the blade groove tooth portion 1 to be inspected has a small cross-sectional area, the propagation path of the ultrasonic beam can be treated as a two-dimensional plane. Length of blade groove tooth portion 1 is L (m), width is W (m), sound velocity in longitudinal steel is C _L (m / s), transverse acoustic wave in steel is C _s (m / s), transverse wave reflection When the angle is φ (degrees) and the refraction angle is θ (degrees), the propagation time t ₁ (s) of the directly propagating wave 7 is
Is t ₁ = L / C _L. The propagation time t ₂ (s) of the wall reflected wave 8 is t ₂ = L / C _L · 1 / cos θ, and when L and θ are small, t ₂ ≈t ₁ , and the direct propagation wave on the time axis of the CRT screen. 7 and the wall reflected wave 8 appear at almost the same position. On the other hand, when the defect 10 is present, the wall defect reflected wave 9 is reflected once by the blade groove wall surface 3 and then the mode-converted component into a transverse wave (dotted line in the figure) is reflected by the defect 10 and propagates to the blade groove wall surface 3 as a transverse wave. After that, the mode is converted again to longitudinal waves and received. Assuming that the propagation time in the longitudinal wave is almost the same as the wall reflected wave 8, the propagation time difference Δt (s) between the wall defect reflected wave 9 and the wall reflected wave 8 is Δt = 2 · W · cos φ / C _s is there. Here _{^{φ = sin -1 {C s /}} C L sin (90-θ)}, a defect 1
If 0 exists, the wall surface defect reflected wave 9 appears as a defect echo at a position delayed by Δt from the wall surface reflected wave 8.

Next, a concrete example of the method of the present invention will be described with reference to FIGS. 2, the specimen 1 _0, with a mockup made serrations type wing Mizoha portion 1 of a turbine rotor in low carbon steel obtained by monitor. The length L is 33.4 mm, the width W of Tsubasamizoha part 1 of the specimen 1 ₀ is 2 mm. A transmission side longitudinal wave bevel probe 4a and a reception side longitudinal wave bevel probe 4b are respectively arranged on the blade groove end faces 2 on both sides, and are connected to the ultrasonic flaw detector 5 by a cable. The probes 4a and 4b are 5Z5 × 5LA
20 (longitudinal wave oblique angle, refraction angle 20 °, frequency 5 MHz, vibrator size 5 × 5 mm) was used. Specimen 1 ₀ 1mm deep by electric discharge machining, the slit-like defect length 5 mm 10
Is artificially made.

In such an apparatus, first, the longitudinal axis of a steel medium 1 is transmitted by a transmission pulse on the time axis of the CRT screen 6 of the ultrasonic flaw detector 5.
After setting the probe to 4 mm, set the probes 4a and 4b to the test piece 1 _0.
Is placed on the blade groove end face 2 of the sound part, the transmitted echo is detected, and the probes 4a and 4b are scanned and fixed at the position where the echo height of the wall reflected wave 8 is maximum. Next, the echo height is adjusted to 100% on the CRT screen 6. Then, as shown in the flaw detection result of FIG. 3, no delayed echo is recognized immediately after the wall surface reflected wave 8 in the sound blade groove tooth portion 1. On the other hand, defect 10
As shown in the flaw detection result of FIG. 4, a delayed echo of the wall surface defect reflected wave 9 appears immediately after the wall surface reflected wave 8, and it can be determined that there is a defect 10 in the blade groove tooth portion 1 having. The calculation results of the beam path lengths of the reflected waves 7, 8 and 9 are the beam path length t ₁ · C _L × 10 ⁻³ = 33.4 mm of the direct propagation wave 7 and the beam path length t ₂ · C _{L of the} wall reflected wave 8. × 10 ^-3 = 35.5 mm, beam path length of the wall defect reflected wave 9 (t ₂ · C _L + Δt · C _s ) ×
It is 10 ⁻³ = 41.8 mm. The appearance positions of the reflected waves 7, 8 and 9 in the calculation result and the flaw detection result are in good agreement, which shows that flaw detection can be correctly performed by the method of the present invention.

Thus, according to such an embodiment method,
Conventionally, it is possible to inspect the blade groove tooth portion for defects with the ultrasonic flaw detection method without removing the blade, which was previously inspected by the magnetic particle flaw detection method by removing the blade. In addition to significantly reducing the cost of inspection-related work such as re-installation of new rotor blades, the inspection period can be shortened, and 100% inspection can be carried out, ultimately leading to a highly reliable plant. Can be provided. Also, a blade root portion having a shape similar to that of the blade groove tooth portion can be inspected.

[0012]

In summary, according to the present invention, longitudinal wave bevel probes having a refraction angle of 10 to 40 ° are arranged on both scanning surfaces of a test body having a defect parallel to the propagation direction of the ultrasonic beam.
The propagation time of the ultrasonic beam that propagates as a longitudinal wave after being reflected once by the wall surface of the test body, and the ultrasonic beam that has been reflected once by the wall surface of the test body and then converted into transverse waves is reflected by a defect and the wall surface of the test body With the propagation time until it is received again after being converted to a longitudinal wave after being propagated up to, by detecting the above-mentioned defect by the time difference, in detecting the defect parallel to the propagation direction of the ultrasonic beam, the direct propagation wave The defect reflected wave can be clearly discriminated, and in the flaw detection of the turbine rotor blade groove tooth part, the ultrasonic inspection method can be used from the blade groove end surface without removing the blade, shortening the inspection period and reducing the cost. Since the pitch catch type ultrasonic flaw detection method capable of achieving the above is obtained, the present invention is extremely useful in industry.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an ultrasonic wave propagation path in an embodiment in which a pitch catch type ultrasonic flaw detection method of the present invention is applied to defect flaw detection of a turbine rotor blade groove tooth portion.

FIG. 2 is a perspective view of a flaw detection state in a specific example.

FIG. 3 is an explanatory diagram of a result of flaw detection on a sound portion in the above.

FIG. 4 is an explanatory diagram of a defect flaw detection result.

FIG. 5 is an explanatory view of a conventional pitch catch type ultrasonic flaw detection method.

[Explanation of symbols]

1 ₀ Specimen 1 Blade groove tooth portion 2 Blade groove end surface 3 Blade groove wall surface 4a Transmitting side longitudinal wave bevel probe 4b Receiving side longitudinal wave bevel probe 5 Ultrasonic flaw detector 6 CRT screen 7 Direct propagation wave 8 Wall reflected wave 9 Wall defect reflected wave 10 Defect

Claims (2)

[Claims] 1. A longitudinal wave bevel probe having a refraction angle of 10 to 40 ° is arranged on each of the scanning surfaces of a test body having a defect parallel to the propagation direction of an ultrasonic beam, and the probe is used once on the wall surface of the test body. The propagation time of an ultrasonic beam that propagates as a longitudinal wave after being reflected, and the ultrasonic beam that has been reflected once by the wall surface of the test object and then converted into a transverse wave is propagated to the wall surface of the test object and then propagates again as a longitudinal wave. A pitch catch type ultrasonic flaw detection method, characterized in that the defect is detected based on a time difference from a propagation time until the mode is converted and received. 2. The method according to claim 1, wherein longitudinal wave bevel probes each having a refraction angle of 10 to 40 are arranged on both blade groove end faces of the turbine rotor blade groove tooth portion having a defect parallel to the lengthwise direction. A pitch catch type ultrasonic flaw detection method, characterized in that the above defects are detected by means of: