JPS63234157A - Ultrasonic oblique flaw detecting method for thick steel tube - Google Patents

Abstract

PURPOSE:To reduce the number of flaw detectors in use to half by detecting defective flaws in both internal and external surfaces of a thick steel pipe by one flaw detector which has a sending probe and a receiving probe arranged nearly at 180 deg.. CONSTITUTION:The sensing probe 2 and receiving probe 3 are arranged at an interval of nearly 180 deg. at the periphery of the thick steel tube 1 which has a >=0.2 thickness/external diameter rate. Further, the probe 2 is connected to the transmitting circuit 5 of the flaw detector 4, the probe 3 is connected to the receiving circuit 6 of the flaw detector 4, and the circuit 6 is connected to a signal processing circuit 7. Then an ultrasonic wave sent by the probe 2 is entered into the steel tube 1 to receives a reflected wave from the external surface defective flaw by the probe 3, and the longitudinal wave of the ultrasonic wave from the probe 2 is converted into a traversal wave to receive a reflected wave from the internal surface defective flaw by the probe 3. Consequently, the number of flaw detectors 4 in use is reduced to half.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention uses ultrasonic waves which are particularly effective for flaw detection of steel pipes with a wall thickness/outer diameter ratio (hereinafter referred to as t/D) of 0.2 or more. This relates to an oblique angle flaw detection method.

[Prior art]

Conventionally, when testing steel pipes using the ultrasonic angle angle flaw detection method, for those with t/D less than 0.2, only a replacement liquid (hereinafter referred to as S wave) is propagated into the steel pipe. Detecting flaws on the inner and outer surfaces of tubes.

However, when t/D exceeds 2, the ultrasonic waves no longer reach the inner surface of the steel pipe, making it impossible to detect internal defects.

Therefore, in the case of flaw detection of steel pipes with t/D of 0.2 or more, a longitudinal wave (hereinafter referred to as L wave) → SS mode conversion method has been developed and generally applied. In this case, since the difference in sensitivity between the inner surface defect signal and the outer surface defect signal is significant, in actual flaw detection, as shown in FIG. A flaw detection method using the L-wave → S-wave mode conversion method was adopted using the transmitting and receiving probe a, and for external flaw detection, the external flaw detector 4B and the Transmission 1. A combination method of ultrasonic angle flaw detection that uses a receiving probe to propagate only the S wave into the steel pipe, which is used when t/D is less than 0.2. (Tokuko 1984)
(Refer to Publication No.-17624). It can be seen that this ultrasonic angle flaw detection method requires a probe for external defects + a flaw detector for external surfaces, and a probe for internal defects + a flaw detector for internal defects.

[Problem that the invention seeks to solve]

In the ultrasonic angle flaw detection method for steel pipes with t/D of 0.2 or more, a probe and a flaw detector that detect flaws using L waves → S waves are used to detect flaws on the inner surface, and flaw detectors are used to detect flaws on the outer surface. Since ultrasonic flaw detection is performed using a combination method that uses a conventional flaw detection probe that uses only S waves and a flaw detector, it requires twice the number of probes and flaw detection as usual. A device is needed,
This required a large amount of equipment cost and installation space.

[Purpose and structure of the invention]

The purpose of this invention is to provide an ultrasonic angle flaw detection method for thick-walled steel pipes that can advantageously solve the above-mentioned problems. In the ultrasonic angle flaw detection method for thick-walled steel pipes 1 with a diameter of 0.2 or more, the transmitter probe 2 and the receiver probe 6 are placed at approximately 180 degrees, and defects and scratches on the inner and outer top surfaces of the thick-walled steel pipe are detected. An ultrasonic angle flaw detection method for thick-walled steel pipes, which is characterized by detecting flaws.

〔Example〕

Next, embodiments of the present invention will be described in detail.

FIG. 1 shows a state in which the present invention is being carried out to perform flaw detection on a thick-walled steel pipe, in which a transmitting probe 2 and a receiving probe 6 facing the outer surface of a thick-walled steel pipe 1 are The transmitting probes 2 are arranged around the thick-walled steel pipe 1 at intervals of approximately α=180, and the transmitting probes 2 are connected to the output part of the transmitting circuit 5 in the flaw detector 4. It is connected to the input part of the circuit 6, and the output part of the receiving circuit B is connected to the input part of the signal processing circuit 7 in the flaw detector 4.

= Figures A2 to 4 show an outer diameter of 57.
1 &, shows a flaw detection diagram when ultrasonic flaw detection was performed on a thick-walled steel pipe 1 with a thickness of 14.67 g (t/D = 0.257), where Ol is the incident angle, θa is the reception angle, OL is the L-wave refraction angle, θ is the S-wave refraction angle, G is the external defect, N
is an internal defect scratch.

Figure 2 shows the status of flaw detection for external surface flaws.
It is then propagated in the order of X-+Y-+ZΩ, and then reaches the external defect G at two points. A reflected wave is generated by this external defect G, and this reflected wave is transmitted from two points to Y.
The signal returns to the point and is then received by the receiving probe +6. This is the outer surface defect signal.

FIG. 6 and FIG. 4 show the inspection status of internal defects, and the ultrasonic waves emitted from the transmitting probe 2 are
After being propagated in the order of X (mode conversion) → X' → Y (mode conversion) → Z (mode conversion) → 2', it reaches the inner surface defect N. A reflected wave is generated from this inner surface defect NK, and this reflected wave propagates in the order of Z' → 2 (mode conversion) → Y → receiving probe 6, and is received by this receiving probe 6. The signal is an internal defect signal.

Regarding the internal defect signal, as shown in Figure 4, the signal transmitted from the transmitting probe 2 is in the order of Q→P-+X (mode conversion)→Y-+z (mode conversion)→2'. The reflected wave reaches the inner surface defect N and is received by the receiving probe 6 via Z' → 2 (mode conversion) → Y, so the above two reflected waves are received by the receiving probe 6. is received. That is, regarding the inner surface defect signal, FIGS. 6 and 4 have the same beam path, and the reception probe 3 receives a signal obtained by combining the reflected waves shown in FIGS. 6 and 4.

In FIGS. 2 to 4, when the transmitting probe 2 is set so that θL=45 degrees, θ8 becomes 22.8 degrees and θi becomes 10.2 degrees. Here, the transmitting probe 2 in FIGS. 2 to 4 is the same, and the receiving probe 3 is also the same.

Q with the sound pressure just before the transmitting probe 2 as 100%.

Based on the relationship between the sound pressure transmission rate at point Y and the sound pressure reflection rate at points X, Y, Z, It was found that the sound pressure from the inner surface defect was 6.84%, and the sound pressure from the inner surface defect was 6.87%, which was approximately equivalent to that obtained.

As a result of flaw detection of thick-walled steel pipes as shown in Table 1 using the ultrasonic angle flaw detection method of this invention, it was found that for thick-walled steel pipes of (1) to aυ in Table 1, the depth of internal and external surface defects was It was possible to detect a defect of about 0.3 parrot with a good signal/noise ratio (hereinafter referred to as S/N ratio). Also, Q21 in Table 1
- (For 151, 6% of pipe thickness - 5% of pipe thickness
It was possible to detect defects on the inner and outer surfaces with a good S/N ratio.

Table 1 [Effects of the Invention] According to the present invention, in the ultrasonic angle flaw detection method for thick-walled steel pipes 1 having a wall thickness/outer diameter ratio of 0.2 or more, the transmitting probe 2 and the receiving probe 6 are placed at approximately 180 degree positions to detect defects on the inner and outer surfaces of thick-walled steel pipes. Therefore, one flaw detector 4 having a transmitting probe 2 and a receiving probe 6 common to the inner and outer surfaces can It is possible to effectively detect defects on both the inner and outer surfaces of the thick-walled steel pipe 1, and therefore, the number of flaw detectors and flaw detectors used can be halved compared to the conventional case, resulting in lower equipment costs. At the same time, the space occupied by the equipment can be reduced.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the ultrasonic angle flaw detection method for thick-walled steel pipes according to the present invention, and Figs. 2 to 4 are explanatory diagrams of the flaw detection of internal and external defects according to the present invention. FIGS. 6 and 4 are explanatory diagrams showing a state in which defects are detected on the inner surface. FIGS. FIG. 5 is an explanatory diagram of a conventional ultrasonic angle flaw detection method for steel pipes. In the figure, 1 is a thick-walled steel pipe, 2 is a transmitting probe, 6 is a receiving probe, 4 is a flaw detector, 5 is a transmitting circuit, < is a receiving circuit, and 7
is a signal processing circuit.

Claims (1)

[Claims] In an ultrasonic angle angle flaw detection method for thick-walled steel pipes 1 with a wall thickness/outside diameter ratio of 0.2 or more, the transmitting probe 2 and the receiving probe 3 are placed at approximately 180 degrees, and the thick-walled steel pipe An ultrasonic angle angle flaw detection method for thick-walled steel pipes, which is characterized by detecting flaws on the inner and outer surfaces of the pipe.