JPS6326342B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an ultrasonic flaw detection method for centrifugally cast tubes used in refurbished tubes and the like, and is capable of reliably determining the presence or absence of defects even if the cast structure is coarse. Centrifugally cast austenitic steel tubes have a coarse structure when cast, so ultrasonic flaw detection using the one-probe method, which is normally used to detect flaws inside steel materials, cannot be used. For this reason, a method is used to measure the magnitude of the sound waves that pass through the material and determine whether there are any parts (defects) in the sound wave transmission path that do not allow the sound waves to pass through. In this type of conventional ultrasonic flaw detection method for austenitic centrifugally cast tubes, as shown in FIG. The ultrasonic beam 6 transmitted from the transmitting probe 4 is transmitted within the thickness range of the centrifugal casting tube 2 and near the inner circumference in parallel to the tangential direction. The transmitted wave is received by the reception probe 5 to detect the wave height T, and the presence or absence of a defect is determined based on the amount of attenuation of the wave height T. Figure 2 shows the results of flaw detection on the re-formed tube using this method. Figure 2 shows the magnitude of ultrasonic transmission waves (hereinafter referred to as wave peak values) of various samples (tube numbers 1 to 7) sampled from refurbished tubes that have been used for several years using 1MHz longitudinal ultrasound. Table 1 shows the measurement results of the size of the cast structure and the size of defects (referred to as fissures) measured on the end face of the same sample.

【table】

[Table] Comparing Figure 2 and Table 1, the peak value T of the transmitted wave has no correlation with the presence or absence of fissures, but rather depends on the size of the cast structure. Therefore,
The amount of ultrasonic transmission depends not only on the presence or absence of defects but also on the attenuation of the ultrasonic waves, which depends on the size of the cast structure in the material.The conventional judgment based only on the size of the transmitted waves indicates that the cast structure is There was a risk that a coarse material with large attenuation would be judged as a defective product even though there was no defect. The present invention has solved the above problems, and its characteristics are that a pair of probes are arranged on both sides of the centrifugally cast tube, and one probe is located within the wall thickness range of the centrifugally cast tube. In an ultrasonic flaw detection method for centrifugally cast pipes, ultrasonic waves are transmitted so as to pass in parallel to the tangential direction near the inner periphery, and the transmitted waves are received by the other probe to determine the presence or absence of defects. Injecting ultrasonic waves into the centrifugally cast tube in the radial direction near the pair of probes, measuring reflected waves from the inner peripheral surface of the tube, and detecting the amount of attenuation of the transmitted ultrasonic waves by the casting structure from the reflected waves, From this, the peak value of the transmitted wave in the case where there is no defect is calculated, and the presence or absence of a defect is determined based on the ratio of the calculated peak value and the peak value of the transmitted wave. The present invention will be explained below. Figure 8 (and reference photo) shows the results of the penetrant test for pipe number 2. Arrow A in Figures 4 and 5 coincides with point A in the reference photo, and the clockwise direction of the reference photo is It is towards the right in the figure. According to this, since the fisher is oriented in the radial direction, it is thought that if the ultrasonic waves are passed in the radial direction, the effect of the fisher on the transmittance is small. Furthermore, the attenuation constant of ultrasonic waves generally depends on the size of the crystal. Therefore, we attempted to pass sound waves in a direction that would not affect the transmission of sound waves even if there was a fissure, and estimate the size of the crystal from the amount of attenuation. That is, as shown in FIG. 3, a probe 7 is placed near the transmitting probe 4 and the receiving probe 5, and the diameter of the probe 7 is An ultrasonic beam 8 is incident in the direction, and a reflected wave of the ultrasonic beam 8 from the tube inner circumferential surface 2a is received by a probe 7 to detect its wave height value _B1 . Then, using this wave height value _B1 , estimate the wave height value Te of the transmitted wave in the case where there is no defect, and from the ratio of this and the transmitted wave height value T of the ultrasonic beam 6, determine the ultrasonic beam originating from the casting structure. The amount of attenuation in step 6 is corrected and the presence or absence of a defect is determined. Figure 4 shows the wave height value B ₁ of the reflected wave for tube number 2.
The fifth figure shows the results of measuring the entire circumference of
The figure shows the result of measuring the peak value T of the transmitted wave for pipe number 2 over the entire circumferential direction, and the arrow A in Figures 4 and 5 is the same as point A in Figure 8 (reference photo). They match, and the clockwise direction in Figure 8 (reference photo) is the right direction in Figures 4 and 5. Comparing Fig. 8 (reference photo) with Fig. 5, it is found that the circumferential distribution of the size of the fissure corresponds to the distribution of the peak value T of the transmitted wave in Fig. 5. It can be seen that the peak value T of the transmitted wave is low in this part. Furthermore, by comparing Fig. 4 and Fig. 8 (reference photograph), it can be seen that the peak value _B1 of the reflected wave of the single search method does not depend on the size of the fissure. Further, Table 2 shows the results of measuring the peak value T of the transmitted wave and the peak value _B1 of the reflected wave for tube numbers 1 to 7 using the above method.

【table】

[Table] Next, the method of the above correction will be explained. The reflected wave peak value B ₁ detected by the one-search probe 7 can be expressed as B ₁ =C ₁ e ^-2at . Similarly, the peak value T of the transmitted wave can be expressed as T=C ₂ e ^-al . However, C ₁ , C ₂ = constant a = attenuation constant t = radial thickness of the cast tube 2 l = transmission length of the ultrasonic beam 6 to the cast tube 2 Based on both formulas, the reference tube (defective Measurement of _the peak values B _{1 and} T of the reflected wave and transmitted wave for the pipe ( _without Estimating the peak value Te of the transmitted wave when there is no defect, the following equation is obtained. Te=Toeln(B1n/B10)/2tl In Table 2 above, pipe number 6, which does not have a fuser and has a standard cast structure, is used as the standard, and in the same table, the peak value of the reflected wave is B ₁ , and the transmitted wave is The estimated peak value Te obtained when the peak value T is corrected and the ratio between the measured peak value T and the estimated peak value Te are also shown at the same time.
Looking at the ratio between the wave height value T and the estimated wave height value Te in this table, it is shown that the value is small for those with a large number of fissures (see Table 1), regardless of the tissue. Therefore, the influence of the casting structure can be effectively corrected,
It can be seen that the presence or absence of defects can be determined reliably. Next, we will discuss the use of a flaw detection system that focuses the ultrasonic beam on the inner surface of the tube, where defects are likely to occur. As mentioned above, the cast structure of the target pipe 2 is large, and therefore the sound waves that pass through the material are effectively limited to frequencies of 1 MHz or less. Furthermore, since the surface of the target tube is rough due to the cast structure, it is desirable to use a thick beam to be incident near the surface. Considering that defects are likely to occur on the inner wall, it is preferable that the ultrasonic beam 6 passes through approximately half or less of the wall thickness of the tube 2. Detection sensitivity is improved by using a lens system that satisfies the above three conditions. The above measurement results are for a 35mm transducer with a radius of 45
This was done with a mm line focus lens attached. FIG. 6 shows a block diagram of a flaw detection apparatus that specifically implements the present invention. In the same figure, PB1,
PB2 and PB3 are probes, and as shown in FIG.
PB1, PB2, and PB3 are capable of transmitting ultrasonic waves toward the casting tube 2 as transmitting probes, and also function as receiving probes, as shown in Table 3.
By combining PB1, PB2, and PB3 as transmitting or receiving probes, the objectives of Modes 1-5 can be fulfilled.

[Table] In mode 1, probe PB2 detects the peak value T of the transmitted wave due to the ultrasonic wave from probe PB1, and in mode 2, the wave reflected from the inner wall surface due to the ultrasonic wave from probe PB2. The high value _B1 is detected by the probe PB2. For modes 3 to 5, each probe PB1, PB
2. The ultrasonic waves transmitted from PB3 are reflected on the outer circumferential surface of the casting tube 2 and the reflected waves are detected by the same probe.
It is detected by PB1, PB2, and PB3.
From these peak values, it is possible to monitor the transmission and reception of sound waves and determine whether there are any abnormalities in the flaw detection system. A1, A2, A3 are preamplifiers, D1,
D2 and D3 are pulsars. Reference numeral 11 denotes a sensor selection circuit which selects the probe to be used so as to operate in each mode shown in Table 3 in a time-sharing manner using a command signal (clock pulse) from a computer 18, which will be described later.
PB1, PB2, PB3, preamplifier D1, D2,
Make selection D3. 12 is the main amplifier. 1
3 is an amplifier adjustment circuit, which adjusts the degree of amplification of the main amplifier 12 for each mode in order to match the output level of the main amplifier 12, since the magnitude of the transmitted wave or reflected wave differs depending on each mode. Outputs a signal to change accordingly. Reference numeral 14 denotes a peak hold circuit which peak-holds the maximum value of the wave height within a time period (gate) in which the transmitted wave or reflected wave of interest occurs in each mode. Reference numeral 15 denotes a gate generation circuit, which sets the time period in which the transmitted wave or reflected wave of interest occurs in each mode.
16 is an A/D converter which digitizes the information on the peak value. Reference numeral 17 denotes a synchronization separation circuit that discriminates to which mode the information digitized by the A/D converter 16 belongs. 18 is a computer and a probe
It outputs a command signal to drive PB1, PB2, and PB3, and records the obtained signal on a recording medium. In addition, it monitors whether flaw detection is being performed normally based on the signal magnitude of modes 3 to 5, and if it is normal, it calculates and outputs the peak value T ₀ of the transmitted wave after correcting the tissue size. . 19 is a memory. Reference numeral 20 denotes a display that displays the results of correcting the influence of the structure, that is, Tn/Te and the axial position of the cast tube 2. 21 is a synchronous separation circuit that synchronously separates analog signals. 22 is a monitor recorder. A position detector 23 detects the position of the movable body 10 with respect to the axial direction of the casting tube 2. In addition, the probe
The selection of PB1, PB2, and PB3 may be changed over using a switch such as a relay. In addition, a large number of A/D converters are used to convert the output of the synchronous separation circuit 21 into an A/D converter.
There is also a method of converting the data into D and inputting it to the computer 18. Therefore, if this flaw detection device is used, the magnitude of the reflected waves from the outer circumferential surface of the cast tube 2 of the ultrasonic waves emitted by each probe PB1, PB2, and PB3 can be monitored, and the ultrasonic waves can stably enter the material. This makes it possible to perform flaw detection while confirming whether or not the cast pipe is defective, which in combination with the ability to effectively correct the influence of the cast structure, allows for more reliable determination of the presence or absence of defects in the cast pipe. According to the present invention, ultrasonic waves are incident on a centrifugally cast tube in the radial direction to measure the reflected waves from the inner peripheral surface of the tube, and from the reflected waves the amount of attenuation of the transmitted ultrasonic waves due to the casting structure is detected. The wave height value of the transmitted wave is calculated in the case where there is no wave, and the presence or absence of a defect is determined from the ratio of the calculated wave height value and the wave height value of the transmitted wave, so the size of the transmitted wave largely depends on the casting structure. Nevertheless, the influence of the cast structure can be effectively corrected, and even if the cast structure is coarse, the presence or absence of defects can be reliably determined.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram showing the conventional method, Fig. 2 is a graph showing the measurement results of the transmitted wave peak value, Fig. 3 is a principle diagram showing an embodiment of the present invention, and Fig. 4 is a graph showing the reflected wave peak value. FIG. 5 is a waveform diagram showing the circumferential distribution of transmitted wave peak values. FIG. 6 is a block diagram showing a specific embodiment of the present invention. FIG. 7 is a portion of the probe. FIG. 8 is a diagram showing the results of penetrant testing for pipe number 2. 2...Centrifugal casting tube, 4...Transmission probe, 5...Reception probe, 8...Ultrasonic beam, PB1, PB2, PB3
...probe.

Claims (1)

[Claims] 1 A pair of probes are placed on both sides of the centrifugally cast tube, and ultrasonic waves are emitted from one probe so that it passes within the wall thickness range of the centrifugally cast tube and near the inner circumference in parallel to the tangential direction. In an ultrasonic flaw detection method for centrifugally cast tubes in which the transmitted wave is received by the other probe to determine the presence or absence of a defect, Inject ultrasonic waves and measure the reflected waves from the inner peripheral surface of the tube. From the reflected waves, detect the amount of attenuation of the transmitted ultrasonic waves due to the casting structure. From this, calculate the peak value of the transmitted waves when there are no defects. An ultrasonic flaw detection method for a centrifugally cast tube, in which the presence or absence of a defect is determined based on the ratio of the wave height value of the transmitted wave to the wave height value of the transmitted wave.