JP2013079843A - Method for inspecting metal drum and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for inspecting any sectional flaws of a metal drum from the outer surface side even when metal drums are piled and substantially 1/3 of the side face thereof are exposed to the outside.SOLUTION: A metal drum inspection method for detecting from the outer surface side any sectional flaws occurring on the inner surface side of a metal drum includes: projecting SH wave for a side plate of the metal drum in the circumferential direction of the side plate by ultrasonic flaw detection means attached to a side plate surface; and detecting thinned wall portions. Further, a method for detecting a bottom plate includes: projecting the SH wave in the horizontal direction along a bottom plate plane by the ultrasonic flaw detection means attached to a fitting edge portion of the bottom plate peripheral edge; and detecting the thinned wall portions.

Description

  The present invention relates to a drum can inspection method and apparatus for inspecting a drum can for defects.

  The drum can is used when temporarily storing and transporting a liquid such as petroleum. In addition, inspection methods that can detect cross-sectional defects such as corrosion or rust generated on the inner surface of drums that store low-level radioactive waste from the outer surface, such as wear due to physical factors, and identify the location of the occurrence. In addition, a drum can inspection method and apparatus capable of measuring the remaining thickness of the cross-sectional defect and obtaining the remaining life data have been proposed (for example, see Patent Document 1).

  In this drum can inspection method, a primary inspection is performed to detect a thinned portion generated on the inner surface of the drum can by a transverse wave ultrasonic wave and to estimate a range, and a vertical flaw detection is performed in a range obtained by the primary inspection by a longitudinal wave ultrasonic wave. This is an inspection method for performing a secondary inspection to detect the degree of thinning. In the primary inspection, transverse wave ultrasonic waves are propagated from the upper end to the lower end of the side plate of the drum can and from the lower end to the upper end, or the ultrasonic waves of the transverse wave are transmitted to the outer peripheral edges of the top and bottom plates of the drum can. It propagates from the center to the center.

  In addition, the drum inspection apparatus includes a primary inspection ultrasonic device that performs a primary inspection for detecting a thinned portion generated on the inner surface of the drum can by using ultrasonic waves of a transverse wave and estimating a range thereof, and a primary inspection by using ultrasonic waves of a longitudinal wave. A drum inspection apparatus including a secondary inspection ultrasonic device that performs a secondary inspection to detect the degree of thinning by performing a vertical flaw detection in a range obtained by inspection.

JP 2008-17596A

  However, for example, the current state of storage of drum cans containing low-level radioactive waste is a state in which a large number of drum cans are piled up, and about 1/3 of the side surface is substantially exposed. Therefore, this exposed surface is the actual work range, and the bottom surface is in a state where the work cannot be performed substantially. It is also piled up when storing specific waste.

  The present invention provides an inspection method and apparatus capable of detecting a cross-sectional defect of a drum can from the outer surface side even when it is in a piled state and substantially 1/3 of the side surface is exposed. For the purpose.

The drum can inspection method according to the invention described in claim 1 is a drum can inspection method for detecting a cross-sectional defect generated on the inner surface side of the drum can from the outer surface side,
The side plate of the drum can is subjected to a side plate inspection in which a SH wave is incident in a circumferential direction of the side plate from an ultrasonic flaw detector attached to the side plate surface to detect a thinned portion.

  A drum can inspection method according to a second aspect of the present invention is directed to a drum can inspection method according to the first aspect of the present invention, in which the SH wave is horizontally aligned along the bottom plate plane by ultrasonic flaw detection means attached to the fitting edge of the bottom plate periphery. Further, a bottom plate inspection for detecting a thinned portion by entering in the direction is further performed.

  A drum can inspection method according to the invention described in claim 3 is that the drum can of claim 1 or 2 is obtained by galvanizing both surfaces of an iron plate and applying a resin film on the surface of the galvanization. It is a feature.

The drum can inspection apparatus according to the invention described in claim 4 is a drum can inspection apparatus for detecting a cross-sectional defect generated on the inner surface side of the drum can from the outer surface side,
It is attached to the side plate surface of the drum can and includes side plate ultrasonic flaw detection means for detecting a thinned portion by causing SH waves to enter the circumferential direction of the side plate.

  The drum inspection apparatus according to the invention described in claim 5 is attached to the fitting edge portion of the bottom plate periphery of the drum can according to claim 4, and the SH wave is incident in the horizontal direction along the bottom plate plane to reduce the thickness. It further comprises a bottom plate ultrasonic flaw detection means for detecting the above.

  In the drum inspection apparatus according to the invention described in claim 6, the bottom plate ultrasonic flaw detection means according to claim 4 or 5 is provided with a contact piece that matches the curved surface of the mating edge of the bottom edge. It is a feature.

  The present invention provides an inspection method and apparatus capable of detecting a cross-sectional defect of a drum can from the outer surface side even when it is in a piled state and substantially 1/3 of the side surface is exposed. There is an effect that can be.

It is a front view of a drum can. It is a top view of a drum can. It is a diagram which shows the flaw detection waveform as a result of irradiating a SH wave horizontally toward the measurement line 1 toward R1-R9. It is a diagram which shows the flaw detection waveform as a result of irradiating SH wave horizontally from the survey line 2 toward S1-S9. It is a diagram which shows the flaw detection waveform as a result of irradiating SH wave horizontally from the measurement line 3 toward S1-S9. It is a diagram which shows the flaw detection waveform as a result of irradiating a SH wave horizontally from the new measurement line 200 mm away from the welding line A. It is a side plate development view showing a flaw detection position on the side plate. These are the diagrams which show the flaw detection waveform as a result of irradiating SH wave toward R1-R9 from the fitting part of a baseplate. It is explanatory drawing which shows the structure of SH wave flaw detector with which the acrylic jig | tool was mounted | worn. It is a diagram which shows the flaw detection waveform as a result of irradiating SH wave toward R1-R9 from the fitting part of the baseplate with the same sensitivity (40 dB) at the time of side plate search. It is a diagram which shows the flaw detection waveform as a result of having irradiated the SH wave toward R1-R9 from the fitting part of the baseplate in the case of raising a sensitivity.

  In the present invention, there is provided a drum can inspection method for detecting a cross-sectional defect occurring on the inner surface side of a drum can from the outer surface side. This is a method for performing a side plate inspection for detecting a thinned portion upon incidence. Thereby, even if it is in the state where it piles up and about 1/3 of the side surface has come out to the surface, the cross-sectional defect | deletion of the side wall surface of a drum can can be detected from an outer surface side.

  Further preferably, the bottom plate of the drum can further be subjected to a bottom plate inspection for detecting a thinning portion by injecting SH waves in the horizontal direction along the bottom plate plane from ultrasonic flaw detection means attached to the fitting edge of the bottom plate periphery. Thus, even when the state is a piled up state and approximately 1/3 of the side surface is exposed, the cross-sectional defect of the bottom plate portion of the drum can can be detected from the outer surface side.

  The inspection object of the present invention is a drum can. This drum was originally used for transporting crude oil and kerosene, but has recently been used for transporting chemical products and paints. It is also used for storing low-level radioactive waste or storing and storing specific waste.

  This drum can has a side plate corresponding to a side wall of a cylinder, and a top plate and a bottom plate above and below the side plate. The inside and outside of each wall surface of the drum can may be plated or coated with a resin film. For example, many drums are galvanized on both sides of the side plate, top plate, and bottom plate, and a resin film is provided on the surface of the galvanized layer. More specifically, the iron plate has a thickness of 1.6 mm, the galvanized layer has a thickness of 0.02 mm, and the resin film layer has a thickness of 0.03 mm. In addition, although an epoxy resin is used for a resin film layer, for example, it is not limited to this. In drums for storing low-level radioactive waste, open-type drums that can be removed are mainly used for the top plate.

  The drum can is formed as follows. First, after bending the steel plate into a cylindrical shape and welding both ends, the side plates are squeezed at both ends, and ring zones are formed at two locations inside the cylinder to face the force from the side of the cylinder. The top plate and the bottom plate are subjected to a pre-curl process in which the periphery of a steel plate punched into a circular tray is bent. After the surface of the side plate, the top plate and the bottom plate is treated and painted, the lower edge of the side plate and the peripheral edge of the bottom plate are wound and processed to form a drum can. By the tightening process, the lower edge portion of the side plate and the peripheral edge portion of the bottom plate are wound two to three times to form a fitting portion. In an open-type drum can, bending is performed so that the upper edge portion of the side plate and the peripheral portion of the top plate can be engaged with each other.

  The side plate of the drum can is formed into a cylindrical shape by welding, and what effect does the weld formed in the vertical direction of this top plate-bottom plate have on ultrasonic flaw detection across this weld? However, as described later, it was confirmed for the first time that ultrasonic waves were transmitted beyond the welded portion and the defect was detected by the present invention.

  Further, in the present invention, in order to detect cross-sectional defects such as corrosion on the wall surface other than the side plate, flaw detection means for the side plate and the bottom plate, which are likely to be corroded due to contact with internal waste, is performed. Note that the top plate may be removed and inspected for corrosion even after low-level radioactive waste is stored, but it can be detected from the outside by the same operation as the bottom plate. It is.

  In order to detect the bottom plate of the drum can even in the state where substantially 1/3 of the side surface in the piled state is on the surface, as will be described later, according to the present invention, from the fitting edge portion of the drum can It was confirmed for the first time that a wave was incident in the horizontal direction along the bottom plate plane, and ultrasonic waves were transmitted to the drum can bottom plate to detect defects.

  The ultrasonic flaw detection means of the present invention only needs to irradiate SH waves that are one of transverse waves. Specifically, as ultrasonic waves generally used for ultrasonic flaw detection, there are SV waves that are one type of longitudinal waves and transverse waves, and SH waves that are also one type of transverse waves. Longitudinal waves are waves that vibrate in the propagation direction, and do not vibrate in a direction perpendicular to the propagation direction.

  On the other hand, the SV wave is a transverse wave that vibrates in a direction perpendicular to the propagation direction, and a wave that vibrates in a direction perpendicular to the flaw detection surface. There is directionality because it is a transverse wave. The SH wave is a transverse wave having the same direction as the SV wave, but is a wave oscillating in a direction parallel to the flaw detection surface. Unlike the SV wave, the SH wave has a characteristic that allows the transverse wave to be strongly incident on the object even in a direction near a refraction angle of 90 °. Therefore, in the present invention, the SH wave is applied in consideration of the fact that the plate thickness of the target drum can is thin and that the ultrasonic wave is propagated to some extent.

  In the present invention, the frequency of the SH wave incident on the object is preferably selected from the range of 0.3 MHz to 0.8 MHz. If the frequency is less than 0.3 MHz, the wavelength will be large with respect to scratches / defects in the drum, and it will not be possible to inspect with sufficient accuracy. If the frequency is greater than 0.8 MHz, the attenuation will be large and will not propagate a sufficient distance. This is because the inspection cannot be performed with sufficient accuracy. A more preferable frequency is 0.4 MHz to 0.6 MHz, and a most preferable frequency is 0.5 MHz.

Example 1 (examination of drum can thinning exploration by lateral input of SH wave)
1. Inspection method In the local storage state of the drum can to be surveyed, about 1/3 of the side surface is the actual work range, and the bottom surface is in a state where the work is practically impossible. For this reason, the method of inputting the SH wave from the vertical direction with respect to the side surface of the drum can cannot be searched. To avoid this, devise a method in which the ultrasonic wave incident direction of the probe is horizontal along the circumference on the side plate and the bottom plate is incident from the fitting part, and an experiment to confirm the possibility of exploration is performed. It was.

2. Configuration of Drum Can FIG. 1 is a front view of the drum can. FIG. 2 is a plan view of the drum. The shape, dimensions, and inner diameter of the drum can are as follows. Drum can inner diameter (567 ± 3 mm), outer height (890 ± 5 mm), capacity (212L or more), plate thickness (1.6 mm).

3. Inspection device The ultrasonic flaw detector uses a low-frequency general-purpose ultrasonic probe UI-23LF manufactured by Ryoden Shonan Electronics Co., Ltd., and the frequency of the SH wave probe is 0.5 MHz.

4). Experimental procedure
(1) A through hole and a non-penetrating conical flaw were processed on the drum can side plate. Specifically, it is the through holes S1 to S9 indicated by black squares in the front view of the drum shown in FIG. Although not shown, non-through holes R1 to R9 are formed on the inner side of the drum can at about 700 mm away from the welding line A through the measurement line 2 on the back side of FIG.
(2) A through hole and a non-penetrating conical flaw were processed on the drum can bottom plate. Specifically, in the plan view of the drum shown in FIG. 2, there are non-through flaws A1 to A8 indicated by black circles and through holes B1 to B8 indicated by black squares.

5. Measurement of side plate Drum can side plate was measured. In order to verify whether the ultrasonic wave propagates through the welded part A, two of the survey line 1 and the survey line 2 are set with the welded part A interposed therebetween. As shown in FIG. 1, the survey line 1 is formed with a through hole S1 of the drum can side plate, and is a point of about 95 mm from the weld line A on the surface. The measurement line 2 is arranged on the opposite side of the measurement line 1 with respect to the surface welding line A, and is about 410 mm from the welding line A. Moreover, the survey line 3 which was 218 mm away from S9 was set.

  For each survey line, the ultrasonic probe 11 as the side plate ultrasonic flaw detection means is fixed to the side plate through a contact medium exclusively for transverse waves and irradiated with SH waves at a total of three locations between the end and the rim or between the rims. did.

The conditions for ultrasonic flaw detection on the side plate were as follows.
Gain: 40.0 dB Test frequency: 0.5 MHz
Measurement range: 1000 mm Refraction angle: 90.0 °
Speed of sound: 3.22 km / s

(5-1) Measurement at Survey Line 1 FIG. 3 is a diagram showing a flaw detection waveform as a result of irradiating SH waves from the survey line 1 toward the non-through holes R1 to R9. Fig. a shows the result of installing an ultrasonic probe between the upper end of the survey line 1 and the first rim, and Fig. b shows the result of installing the ultrasonic probe between the first rim and the second rim on the survey line 1. The figure c shows the result of installing an ultrasonic probe between the second rim on the survey line 1 and the lower end.

  As shown in FIGS. a to c, the broken line portion is displayed as a reflection echo, and the height is displayed as a reflection echo height of 0 to 100%. The number below is the distance from the probe (mm). As shown in each figure, it was shown that the ultrasonic wave of the SH wave is transmitted beyond the weld line A to detect the non-through hole.

(5-2) Measurement at Survey Line 2 FIG. 4 is a diagram showing a flaw detection waveform as a result of irradiating SH waves from the survey line 2 toward S1 to S9. The figure shows the result of installing an ultrasonic probe between the upper end on the survey line 2 and the first rim. As shown in the figure, the broken line portion is displayed as a reflection echo, and the height is displayed as a reflection echo height of 0 to 100%. The number below is the distance from the probe (mm). It was shown that SH wave ultrasonic waves are transmitted beyond the weld line A to detect non-through holes.

(5-3) Measurement at Survey Line 3 FIG. 5 is a diagram showing a flaw detection waveform as a result of irradiating SH waves from the survey line 3 toward S1 to S9. Fig. a shows the result of installing an ultrasonic probe between the upper end of the survey line 1 and the first rim, and Fig. b shows the result of installing the ultrasonic probe between the first rim and the second rim on the survey line 1. The figure c shows the result of installing an ultrasonic probe between the second rim on the survey line 1 and the lower end.

  As shown in FIGS. a to c, the broken line portion is displayed as a reflection echo, and the height is displayed as a reflection echo height of 0 to 100%. The number below is the distance from the probe (mm). As shown in each figure, it was shown that the ultrasonic wave of the SH wave is transmitted beyond the weld line A to detect the non-through hole.

(5-4) Measurement on a new survey line The reflected echo that crossed the weld line A was further verified. The ultrasonic probe 11 was fixed to the side plate via a contact medium dedicated to transverse waves on a measurement line 200 mm away from the through hole S1 with the welding line A as the center, and SH waves were irradiated. FIG. 6 is a diagram showing a flaw detection waveform as a result. As shown in the figure, the broken line portion is displayed as a reflection echo, and the height is displayed as a reflection echo height of 0 to 100%. The number below is the distance from the probe (mm).

  As shown in FIG. 6, it is shown that there are clear flaws at points of 200, 340, 380, and 635 mm. Here, the 200 mm reflection echo is from the weld. In actual measurement, if two circles with the radius of the value of the reflected echo obtained by measurement from two places are drawn on the drum can surface, there will be a flaw at the intersection.

  It was confirmed that 340 mm was a S2 flaw and 380 mm was a S3 flaw. Further, although it was unknown whether 635 mm was an echo indicating a flaw or noise, it was confirmed that 635 mm was an unnamed flaw. As described above, it was confirmed that the horizontal exploration was sufficiently possible for the side plate.

(5-5) Confirming the propagation range on the side plate Place the probe from the survey line 2 to the non-through hole R1. In this case, since there is no sensitivity at the position where the probe 11 is attached to the upper end, since R1 is found at a position of 200 mm at a survey point 52 mm lower than the upper end, the SH wave when inputting laterally to the side plate It was confirmed that the propagation angle was about 29 degrees. Note that this angle is large considering that the same angle when inputting in the vertical direction is about 18 degrees. The following two causes were considered.

(1) In the case of longitudinal input, the tangent line between the flat probe and the cylindrical side plate is vertically aligned and perpendicular to the direction of vibration of the SH wave, so input loss increases. In the lateral input, the input loss is small because the tangent line is parallel to the vibration direction.
(2) Longitudinal input has a large propagation loss because the curvature increases along the vibration direction.

(5-6) Flaw detection position on the side plate It was confirmed that on the side plate, the SH wave propagates beyond the weld line, and the SH wave propagation angle is about 29 degrees. Therefore, even if it is in a piled state and substantially 1/3 of the side surface is on the surface, defects on the side plate are detected from the outer surface side by flaw detection at at least three locations on one survey line. I found out that I can do it. Specifically, FIG. 7 is a developed side plate showing a flaw detection position on the side plate. As shown in the figure, the SH wave is incident in the circumferential direction of the side plate at the center height position of the side plate of the drum can to detect the thinned portion, and the upper and lower ends on the same line of measurement are circular on the opposite side to the center portion. The entire surface of the side plate can be measured by detecting the thinned portion by entering in the circumferential direction.

6). Measurement at the bottom slope
(6-1) Measurement at bottom slope 1
In the plan view shown in FIG. 2, the ultrasonic probe 21 as the bottom plate ultrasonic flaw detector is fixed to the side plate via a contact medium exclusively for the transverse wave at the position corresponding to 6 o'clock, and the SH wave was irradiated. The ultrasonic flaw detector 21 was irradiated while being brought into contact with the fitting portion of the bottom plate.

The conditions for ultrasonic flaw detection on the bottom plate were as follows.
Gain: 40.0 dB Test frequency: 0.5 MHz
Measurement range: 2730 mm Refraction angle: 90.0 °
Speed of sound: 3.22 km / s

  FIG. 8 is a diagram showing a flaw detection waveform as a result of irradiating SH waves from the fitting portion of the bottom plate toward R1 to R9. As shown in the figure, the broken line portion is displayed as a reflection echo, and the height is displayed as a reflection echo height of 0 to 100%. The number below is the distance from the probe (mm). It was shown that even when ultrasonic waves are irradiated from the fitting portion, ultrasonic waves of SH waves are transmitted to detect at least four through holes and non-through holes.

  In the measurement shown in FIG. 8, the contact area of the flaw detector is small, and since the contact is made in a straight line with respect to the curve of the drum, the input is small, and since the input is at the fitting portion, the folded iron plate It was shown that the attenuation at is large. In order to improve this, we decided to make an acrylic resin jig that matched the curve of the drum and tried the experiment again.

(6-2) Measurement at Sokosaka 2 (Effectiveness of acrylic jig)
FIG. 9 is an explanatory view showing a configuration of an SH wave flaw detector to which an acrylic jig is attached. FIG. 9A is a plan view, FIG. 9B is a front view, and FIG. 9C is a side view. For the purpose of complementing that the contact area is small from the mating part, an acrylic jig matched with the curvature of the side surface of the bottom plate was manufactured, and measurement was performed using this jig. Specifically, as shown in FIG. 9, the SH wave probe 21 was attached to the recess 93 of the acrylic jig 91. At this time, the ultrasonic wave oscillating surface 22 of the SH wave probe 21 is fitted into the concave portion 93 so as to come into contact with the bottom surface of the concave portion 93 formed on the upper surface of the curved surface 92 in accordance with the curvature of the side surface of the drum can bottom plate. The SH wave probe 21 was attached.

  FIG. 10 is a diagram showing a flaw detection waveform as a result of irradiating SH waves from the mating portion of the bottom plate toward R1 to R9 with the same sensitivity (40 dB) as in the side plate search. As shown in the figure, a plurality of reflected echoes and reflected echoes from the facing end were confirmed. Since the SH wave is incident at an angle, it is necessary to shift the positions of the acrylic jig 91 and the SH wave probe 21 to find the optimum relationship, but this jig can be brought into contact with the fitting portion appropriately. The sensitivity was better than using the probe alone. Note that the contact piece is not limited to the acrylic jig shown in FIG. 9, and any contact piece may be used as long as the ultrasonic wave from the SH wave probe is incident from a curved surface matching the curvature of the bottom plate side surface. .

(6-3) Measurement at the bottom slope 3 (correspondence between the reflection echo on the bottom plate and the actual flaw)
The length to the entrainment part and end part of the fitting part was measured. The entrainment part was 40 mm, and it was 620 mm up to the end of the facing surface. In the measurement screen of FIG. 10, there was an echo at 615 mm, but it seemed to be a looseness error in measuring the tape measure. Therefore, the sensitivity was increased and the echo position was confirmed (+10 dB). FIG. 11 is a diagram showing a flaw detection waveform as a result of irradiating SH waves from the mating portion of the bottom plate toward R1 to R9 when sensitivity is increased.

  As shown in the figure, a plurality of reflected echoes were confirmed at 145, 180, 200, 220, 240, 265, and 300 mm. Compared with the actual one, it was confirmed that 145 mm was B6 (error 5 mm), 180 mm was B5, 200 mm was B4, 220 was B3, 240 was B2, and 265 was B1. Although 300 could not be confirmed directly, it was thought to be A1.

  As described above, it was confirmed that the entire flaw bottom surface can be flawed by moving the ultrasonic flaw detector 21 about one third round along the fitting portion on the bottom surface.

7). Summary As described above, by inspection of the side plate, the ultrasonic wave detecting means attached to the side plate surface is irradiated with the SH wave in the circumferential direction of the side plate to detect the thinned portion, so that the ultrasonic wave exceeds the welded portion of the drum can side plate. Sound waves can be transmitted and defects can be detected. As a result, even if the surface is piled up and substantially 1/3 of the side surface is exposed, the cross-sectional defects of the drum can can be detected from the outer surface side. It was confirmed that it could be detected. By using this side plate inspection as a preliminary inspection for precise inspection, the inspection time can be shortened. In other words, it is not necessary to conduct a precise inspection for drums that do not have defects detected, and for drums that are suspected of having defects detected, the distance of the defect position can be measured by reversing the circumferential direction. A precise inspection is performed to identify the position of the defect. Thereby, shortening of inspection time and reduction of inspection cost are achieved.

  Even from the mating edge of the drum can by detecting the thinned portion by injecting the SH wave into the horizontal direction along the bottom plate plane from the ultrasonic flaw detector attached to the fitting edge of the bottom plate periphery by the bottom plate inspection. The ultrasonic waves are transmitted to the drum can bottom plate, so that the defect can be detected. As a result, the cross section of the drum can bottom plate can be obtained even in a state where about 1/3 of the side surface is exposed. It was confirmed that the defect could be detected from the outer surface side. Similar to the above-described side plate inspection, the bottom plate inspection is used as a preliminary inspection for precise inspection, thereby reducing the inspection time and the inspection cost.

Claims (6)

A drum can inspection method for detecting a cross-sectional defect occurring on the inner surface side of a drum can from the outer surface side,
A drum can inspection method for performing side plate inspection on a side plate of the drum to detect a thinned portion by introducing SH waves in the circumferential direction of the side plate from an ultrasonic flaw detector attached to the side plate.   The bottom plate of the drum can is further subjected to a bottom plate inspection in which a SH wave is incident in a horizontal direction along the bottom plate plane from an ultrasonic flaw detector attached to a fitting edge of the bottom plate periphery to detect a thinned portion. The drum can inspection method according to claim 1.   The drum can inspection method according to claim 1 or 2, wherein the drum can is obtained by galvanizing both surfaces of an iron plate and applying a resin film to the surface of the galvanized surface. A drum inspection apparatus for detecting a cross-sectional defect generated on the inner surface side of a drum can from the outer surface side,
A drum inspection apparatus, comprising: a side plate ultrasonic flaw detection unit which is attached to a side plate surface of the drum can and detects a thinning portion by causing an SH wave to enter the circumferential direction of the side plate.   5. A bottom plate ultrasonic flaw detection unit, which is attached to a mating edge portion of a peripheral edge of the bottom plate of the drum, and detects a thinning portion by causing SH waves to enter the horizontal direction along the bottom plate plane. The drum inspection apparatus described in 1.   The drum inspection apparatus according to claim 4 or 5, wherein the bottom plate ultrasonic flaw detection means includes an abutting piece that matches a curved surface of a mating edge portion of the bottom surface periphery.

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