JPS6126855A - Ultrasonic flaw detecting method of centrifugally cast iron pipe - Google Patents

Abstract

PURPOSE:To detect information with high accuracy by arranging at least four probes for the centrifugally cast iron pipe and varying an ultrasonic frequency for multifrequency flaw detection. CONSTITUTION:Four probes, i.e. transmitting probe 2A and receiving probe 3A, and transmitting probe 2B and receiving probe 3B are arranged diagonally at four corners of a rectangule on the outer peripheral surface of the pipe 1 to be inspected. Ultrasonic waves entering the pipe 1 to be inspected from the transmitting probes 2A and 2B pass through the thick part of the object pipe and are received by the receiving probes 3A and 3B or reflected by a defect 4 and received by the receiving probes 3B and 3A. Plural waveforms of different frequencies are added to the frequency of the ultrasonic waves to be transmitted to smooth a noise waveform due to the grain boundary of an austenite centrifugally case ion pipe. Those probes are used in combination for scanning and four flaw detection data are compared to detect the defect with high precision.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention detects with high accuracy internal defects that occur as a result of long-term use of centrifugally cast tubes such as heating tubes for steam catalytic reforming furnaces. This invention relates to a non-destructive testing method using ultrasonic flaw detection that makes it possible to perform

To explain the characteristics of this type of heating tube for steam catalytic reforming furnaces,
This pipe is mainly made of HK-40 due to the need for heat resistance, pressure resistance, and corrosion resistance.
It is manufactured by centrifugally casting austenitic heat-resistant cast steel such as (0.4%0125%Cr%2096JJi series) material and welding it to the desired length. In emergency situations, raw material gas and steam are pumped into a tube filled with catalyst and heated from outside the tube, so they are placed under high temperature and pressure. If it is used in this state for a long time (about 6 years or more), aging will occur, creep stress will occur due to stress, and defects will occur in the circumferential direction of the inner surface of the CV tube due to the temperature difference between external heating and internal cooling. There is a fear of being

Therefore, inspecting the occurrence of defects and understanding the remaining service life of the pipes is essential for operational safety.

(Prior technology) The reliability of the large number of welded joint centrifugally cast tubes installed vertically in the steam contact reforming furnace is questionable even after sampling and destructive inspection of unspecified defects that may occur due to aging. Therefore, it is necessary to perform individual non-destructive inspection in the installed state. In general, non-#J1f inspection methods for this purpose include radiographic inspection and ultrasonic flaw detection.
It is detected that the defect does not have a thickness greater than a certain level in the direction of radiation propagation, generally approximately 196 mm or more of the plate thickness, and a defect that extends perpendicular to the direction of radiation propagation.
<sOther defects.

For example, crack-like defects cannot be detected and the detection accuracy is poor.

Ultrasonic flaw detection is generally effective as a non-destructive test for internal defects in relatively homogeneous steel materials, and specific flaw detection methods include pulse reflection method, transmission method, resonance method, etc. Various configurations of the flaw detection target are known, such as those using one or two probes, and those in which the direction of ultrasonic waves incident on the object to be inspected is set vertically or at an oblique angle.

However, in the case of the centrifugally cast tube mentioned above.

Highly accurate flaw detection is not possible with conventional ultrasonic probes due to the material's high attenuation of ultrasonic waves and coarse crystal grains, which tend to produce forest-like echoes due to grain boundary reflection and complicate the received waveform. It was difficult.

(rIIJ Problems to be Solved by the Invention) The present invention aims to improve the flaw detection accuracy by reducing the influence of interference due to material factors regarding m-sonic flaw detection of centrifugally cast tubes having the above properties.

(Means, functions, and embodiments for solving the interpolation point) The present invention performs multi-frequency flaw detection using at least four probes on a centrifugally cast tube with coarse crystal grains and high attenuation of ultrasonic waves. The noise waveform caused by the influence of the material is smoothed out from the flaw detection data to improve the identifiability of defect reports, and to obtain highly accurate flaw detection results when scanning the entire circumference of the pipe to be inspected.

The structural features of the method of the present invention are as follows.

(1) At least four ultrasonic probes are placed around the circumference of the pipe to be inspected, and the CV deep flaw detection method is used for transmission and reflection methods to completely penetrate the thick part of the pipe to be inspected or reflect at internal defects. Transmission and reception can be carried out by intervening the area.

(b) Ultrasound uses multiple frequencies and combines the data to obtain highly accurate detection results.

In this case, flaw detection is performed using a plurality of transmitting probes, each using a different frequency. Alternatively, flaw detection is performed by transmitting ultrasonic waves of a plurality of frequencies using a single probe, for example, a ring-shaped probe.

) Scan the entire circumference.

FIG. 1 shows a probe arrangement for carrying out the method of the invention! The transmitting probe (2A) is shown so that the four probes occupy the positions of the four vertices of the quadrangle along the outer peripheral surface of the tube to be inspected (1).
and the receiving probe (6A), the transmitting probe C2B) and the receiving probe (6B) are arranged diagonally, and the light enters the tube to be inspected (1) from the transmitting probes (2A) and (2B). The ultrasonic waves pass through the thick part of the tube to be inspected and are received by the receiving probes (6A) and (3B), respectively. (6A).

By scanning these probes in combination and comparing the 94 flaw detection data, the shape of the defect (4) in the V* inspection tube (υ)
! ! 1, the presence of a defect can be inferred with higher accuracy in the case of the conventional two-probe probe. However, the transmitting probe (2A)
When the frequencies of the ultrasonic waves emitted by (2B) are the same, the crystal grains in the welded part of the austenitic cast steel pipe of the pipe to be inspected (1) are coarse, so scattering by grain boundaries is significant. It is difficult to identify defects.

The present invention goes further by changing the frequency of the ultrasonic waves that are transmitted through or reflected from the tube to be inspected, that is, performing flaw detection using a plurality of frequencies. Generally, the frequency of ultrasonic waves when inspecting this type of material is 0.5 to 5 MB.
2, so all you have to do is select all the appropriate multiple frequencies within this range depending on the condition of the tube to be inspected. In the austenitic centrifugally cast pipes, the scattering steepness of the grain boundaries differs greatly depending on the frequency # and L, and in some cases the phase is reversed depending on the frequency. Therefore, by adding multiple waveforms with different frequencies, the noise waveform due to grain boundaries is smoothed.On the other hand, since the flaw detection waveform from a defect does not depend on the same wave number, cumulative comparison of flaw detection data This improves the accuracy of defect detection.

When performing multi-frequency flaw detection, it is actually possible to arrange a plurality of sets of probes m, each having an appropriate flaw detection frequency, on the outer circumferential surface of the tube to be inspected.

Figure 2]←) shows one example, and the frequency
Transmission method receiving probe (2x) for transmitting probe (2x)
(3 Tentacle (6
Place Y).

Alternatively, an arrangement can be made in which probes that generate & types of orbits with %1 probes are used. The ring-shaped probe is a type of probe with multiple circumferences i1, and the diameter of each ring is determined so that the sound field is almost the same in the flaw detection area.

Furthermore, in these probe arrangements, the transmitting and receiving probes are exchanged, and the probe pairs shown in the table below are changed based on the probe (A) (Q medium) arrangement shown in Fig. Each flaw detection in the machining flaw detection direction can be carried out as shown by the arrows in the figure.

Transmitting probe: AAACCD Receiving probe: BCDDBB By rotating each pair of probes over the entire circumference, defects in the centrifugally cast tube can be determined to be even more sensitive.

(Effect of selling out) If the method of the present invention is applied as described above, the attenuation of the super-succulent wave,
In the case of austenitic heat-resistant cast steel centrifugally cast pipes with large scattering, defects that are difficult to detect using conventional ultrasonic flaw detection methods can be detected with high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a front view showing an example of the probe arrangement of the method of the present invention;
Figure 2 (4 is a side view of another probe arrangement. Figure 2 (, = 0 is a front view thereof, and Figure 5 is a front view of yet another probe arrangement. (1)... Tube to be inspected, (2A) (2E) (2X) (2M
)...Sending probe, C5A)C5B)C51)C51)
C5Y) C6Y) - 1 receiving probe, 0 bar B) (c)
(n)...Probe, (4)...Defect.

Claims (3)

[Claims] (1) At least four ultrasonic probes are placed around the circumference of the tube to be inspected, and the flaw detection area is sandwiched between the two probes so that transmission and reception can be performed by the transmission method and the reflection method, and An ultrasonic flaw detection method for centrifugally cast tubes, characterized in that the frequency of emitted and received ultrasonic waves can be changed to scan the entire circumference of the tube to be inspected, and defects are detected by relating each individual emitted and received flaw detection data. . (2) The ultrasonic flaw detection method for centrifugally cast tubes according to claim 1, wherein flaw detection is performed by transmitting ultrasonic waves of different frequencies from a plurality of transmitting probes. (3) The ultrasonic flaw detection method for centrifugally cast tubes according to claim 1, wherein flaw detection is performed by transmitting ultrasonic waves of different frequencies from one transmitting probe.