JPH046462A - Ultrasonic-wave flaw detecting method - Google Patents

Abstract

PURPOSE:To make it possible to detect a crack which is formed on the inner surface of a furnace wall pipe at the outside of a furnace from the inner side of the furnace by vertically sending an ultrasonic wave from the outer surface of the pipe at the opposite side of a part to be inspected from an ultrasonic wave probe, and detecting the flaw of the crack based on the attenuating amount of the ultrasonic wave. CONSTITUTION:A furnace wall pipe 2 is filled with, e.g. water 5, as a medium for transmitting an ultrasonic wave. A crack which is formed on the inner wall surface of the pipe at the outside of a furnace is detected. For this purpose, a vertical ultrasonic-wave probe 6 is brought into contact with the opposite side of a part to be inspected, i.e. the outer surface of the pipe on the inner side of the furnace. When the ultrasonic wave is inputted from the probe 6, the ultrasonic wave is propagated from the inner side of the furnace wall pipe 2 with respect to the furnace to the pipe wall on the outside of the furnace through the water 5 filled in the furnace wall pipe 2. Thus the ultrasonic wave reaches the part to be inspected. Then the ultrasonic wave which has reached the part to be inspected is reflected from the part to be inspected, propagated through the part in the reverse direction and returned to the probe 6. The crack is detected based on the attenuated amount of the returned ultrasonic wave.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic flaw detection method for detecting corrosion fatigue cracks occurring on the inner surface of a furnace wall tube of a thermal power boiler from inside the furnace.

[Prior Art] The furnace wall tube of a thermal power boiler generally has a structure as shown in FIG. In the figure, 1 is a reinforcement plate for the furnace wall, 2 is a furnace wall tube to which this reinforcement plate 1 is welded, 3 is a heat insulating material that covers the whole, and 4 is a welding point where the reinforcement plate 1 is welded to the furnace wall tube 2. .

When a boiler is used for a long period of time, cracks may develop on the inner surface of the tube near the welding point 4, so radiological inspections or tube removal surveys are carried out periodically.

[Problems to be Solved by the Invention] Periodic inspections for cracks that occur on the inner surface of the furnace wall tube 2 on the outside of the furnace are generally carried out by removing the heat insulating material 3 and placing an X on the part to be inspected.
Flaws were detected by touching a wire film and irradiating a radiation source from inside the furnace.

However, removing the heat insulating material 3 and restoring it after the flaw detection requires a large amount of man-hours because the flaw detection range is vast.

Furthermore, it is impossible to carry out the above-mentioned pipe removal investigation on all the furnace wall tubes, and the obtained results are statistical, and it is not possible to detect cracks in individual furnace wall tubes.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide an ultrasonic flaw detection method that can reduce the number of required man-hours.

[Means and effects for solving the problem, that is, the present invention is to fill the inside of the tube to be inspected with a medium for transmitting ultrasonic waves, such as water, and then transmit ultrasonic waves from the outer surface of the tube on the opposite side of the part to be inspected. This device uses a sonic probe to vertically inject ultrasonic waves and detect cracks based on the amount of attenuation.This method detects cracks that occur on the inner surface of the furnace wall tube outside the furnace from inside the furnace. This eliminates the need to remove and restore the heat insulating material, significantly reducing the number of man-hours required for periodic inspections.

[Example〕 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the flaw detection method. Since the structure around the part to be inspected is the same as that in FIG. 1, the same parts are given the same reference numerals and the explanation thereof will be omitted.

Therefore, when the boiler is stopped, the furnace wall tube 2 is filled with water 5 as a medium for transmitting ultrasonic waves, and in order to detect cracks that have occurred on the inner surface of the tube outside the furnace, 6th
As shown in the figure, the vertical ultrasonic probe 6 is brought into contact with the outside surface of the pipe on the opposite side of the part to be inspected, that is, inside the furnace.

When ultrasonic waves are applied by the vertical ultrasonic probe 6 in this state, the ultrasonic waves travel from the inside of the furnace wall tube 2 through the water 5 filled in the furnace wall tube 2 to the tube outside the furnace. It propagates through the wall and reaches the part to be inspected. The ultrasonic waves that reach the inspected area are reflected by the inspected area, propagate in the opposite direction through the above-mentioned area, and return to the vertical ultrasonic probe 6. Depending on the amount of attenuation of the returned ultrasonic waves, This is used to detect cracks.

Figure 2 shows the flaw detection situation when the furnace wall tube 2 is tested with a vertical ultrasonic probe 6. Here, a crack 7 has occurred in the inspected area, and the vertical ultrasonic probe The figure shows a state in which ultrasonic waves vertically incident from the probe 6 are scattered by this crack 7 in the inspected part. If there is no crack 7 in the part to be inspected, this phenomenon of scattering of ultrasonic waves will not occur.

FIG. 3(a) shows the waveform of the tube inner surface echo (S echo) when there is no crack. As described above, since there is no scattering, a tube inner surface echo with a high peak value can be obtained.

In contrast, if a crack 7 has occurred in the part to be inspected as shown in Fig. 2 above, scattering occurs due to the crack 7, so as shown in Fig. 3 (b). Therefore, the position of the crack 7 can be detected by inspecting the wave height value of the tube inner surface echo.

FIG. 4 is a graph of ultrasonic echo height [%] and crack depth [mm] obtained by actually investigating furnace wall tubes at five power plants using the flaw detection method described above. As shown in the figure, it has become clear that there is a correlation between the ultrasonic echo height and the crack depth, confirming that this flaw detection method is practically effective.

[Effects of the Invention] As described above, according to the present invention, after filling the inside of the tube to be inspected with a medium for transmitting ultrasonic waves, such as water,
By using an ultrasonic probe to vertically inject ultrasonic waves from the outer surface of the tube on the opposite side of the part to be inspected and detecting cracks based on the amount of attenuation, it was possible to detect cracks that occurred on the inner surface of the tube on the outside of the furnace wall tube. Since it is possible to detect cracks from inside the furnace, there is no need to remove and restore the heat insulating material, and it is possible to provide an ultrasonic flaw detection method that can significantly reduce the number of man-hours required for periodic inspections.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a flaw detection method according to an embodiment of the present invention, FIG. 2 is a cross-sectional view schematically showing vertical ultrasonic flaw detection, and FIG. 3 is a diagram showing ultrasonic flaw detection waveforms depending on the presence or absence of cracks. FIG. 4 is a diagram showing the correlation between the amount of attenuation of ultrasonic waves and the crack depth, and FIG. 5 is a diagram showing a schematic configuration around the furnace wall tube where ultrasonic flaw detection is performed. 1... Reinforcement plate, 2... Furnace wall tube, 3... Heat insulating material, 4...
... Welding point, 5... Vertical ultrasonic probe, 7... Crack. Applicant's representative Patent attorney Takehiko Suzue Crack depth (mm)

Claims (1)

[Claims] An ultrasonic device characterized in that the inside of a tube is filled with an ultrasonic transmission medium, and ultrasonic waves are vertically incident with an ultrasonic probe from the outer surface of the tube on the opposite side of the tube, facing the part to be inspected. Sonic flaw detection method.