JP4772830B2 - Ultrasonic wall thickness measuring device for tubes - Google Patents

Description

  Inserted into pipes for inspection of corrosion depth, thickness reduction, and residual thickness of tubes with bending, such as heat exchanger tubes and boiler tubes, in chemical plants, petroleum plants, and paper plants using ultrasonic inspection methods Thus, the present invention relates to an apparatus for performing a detailed inspection.

  When heat exchanger tubes such as heat exchanger tubes and boiler tubes are used for a long time, corrosion thinning may occur. Therefore, it is necessary to check the soundness by periodically conducting the presence or absence of corrosion and measuring the wall thickness. Generally, heat exchange tubes are assembled densely, and it is difficult to visually check from the outer surface and to measure the wall thickness. Therefore, conventionally, an ultrasonic inspection is performed from the inner surface of the heat exchange tube using an internal insertion type ultrasonic inspection apparatus. For example, Patent Document 1 discloses an apparatus that performs ultrasonic inspection on a boiler tube having an inner diameter of about 40 mm. A feature of the device described in Patent Document 1 is a device that inserts an inspection device using a flow of fluid such as water. However, since the ultrasonic probe and the brush for holding the center are connected with a wire, the ultrasonic wave should be incident on the normal line with respect to the inner surface of the tube at the curved tube portion. Inclination occurs and stable inspection is not possible. In addition, since flowing water is used, in a tube having an inner diameter of about 20 mm, bubbles are generated when a brush is used, and the ultrasonic inspection is hindered. Patent Document 2 discloses an apparatus for inspecting a tube having an inner diameter of about 20 mm. However, an array probe is used, and an expensive phased array flaw detector is required. The use of a phased array flaw detector complicates the setting of inspection conditions. Patent Document 3 proposes an apparatus capable of inspecting a tube having an inner diameter of about 20 mm. However, since there is no mechanism for holding the tube from both sides of the probe at the center of the tube, stable inspection cannot be performed.

  In the prior art, there has been no device capable of collecting wall thickness data in detail at high speed in a curved tube having a minimum inner diameter of 20 mm with an internal insertion type ultrasonic inspection device.

  Conventionally, as an inspection device in a curved pipe section, there are only a low-speed device that can inspect only a tube with a low resolution or a tube with a large inner diameter by arranging a plurality of sensors in a circle, and it is detailed at high speed. There was no device capable of collecting wall thickness data.

According to the present invention, the thickness of the entire surface of the bent tube of the heat exchanger can be measured in detail and continuously at high speed, and a thickness distribution diagram and a cross-sectional view of an arbitrary orthogonal section can be displayed. .
JP 2003-172732 A JP-A-3-183944 JP 7-209257 A

  Heat exchanger tubes such as heat exchangers and boilers used in petroleum / chemical plants and paper manufacturing plants may cause corrosion thinning when used for a long time. Therefore, it is necessary to check the soundness by periodically conducting the presence or absence of corrosion and measuring the wall thickness. Generally, heat exchange tubes are assembled densely, and it is difficult to visually check from the outer surface and to measure the wall thickness. Therefore, ultrasonic inspection is conventionally performed from the inner surface of the heat exchange tube by filling the tube inner surface with water and using an in-tube ultrasonic inspection apparatus. In the prior art, as shown by the straight pipe portion 21 in FIG. 9, there is an apparatus capable of high-speed inspection in the internal insertion type ultrasonic inspection apparatus in the straight pipe portion, but heat exchange with a minimum inner diameter of 20 mm is possible. There was no device capable of collecting wall thickness data in detail at high speeds in the curved tube section. In order to enable the inspection to scan the entire surface at a high speed even in the curved pipe section, an ultrasonic probe is arranged at the center of the tube, and a reflection mirror having an angle of 45 degrees is moved while rotating at a high speed. The entire inner surface of the tube is scanned to measure the thickness of the tube, the corrosion depth of the inner surface, and the inner diameter of the tube. However, as shown by the curved pipe portion 22 in FIG. 9, by using water as the contact medium, a physical phenomenon in which the main beam is refracted by the difference in sound velocity between water and metal when ultrasonic waves enter the tube from water ( Snell's law) occurs, so when an inclination of only 3 degrees enters the tube, it becomes an inclination of 13 degrees, and the ultrasonic main beam reflected and returned from the outer surface of the tube is detached from the ultrasonic probe, As illustrated in FIG. 10, the inspection becomes impossible.

  In addition, when a center holding mechanism is provided before and after the center of the reflecting mirror as shown in FIG. Therefore, a large rotational torque is required, and it has been difficult to realize the above-described method with a small diameter pipe having an inner diameter of 20 mm or less.

  In order to enable high-speed inspection even in the curved pipe section, the ultrasonic probe is placed at the center of the tube, and the reflection mirror with a 45 degree angle is rotated at high speed to corrode the wall thickness and inner surface of the tube. Measure depth and tube inner diameter. At that time, a center holding mechanism is provided before and after the rotor including the reflecting mirror so that ultrasonic waves are always incident on the normal to the inner surface of the tube, particularly at a position equidistant from the center of the reflecting mirror. In order to obtain sufficient rotational torque and high-speed rotation even under rotational resistance due to pressing pressure during movement and pressure due to curvature, high-speed and detailed inspection is possible by transmitting rotational power from the outside with a flexible shaft. It was.

  According to the present invention, it is possible to continuously measure the wall thickness of the entire curved pipe portion of the heat exchanger tube of a small-diameter pipe, and to display a wall thickness distribution diagram and a cross-sectional view of an arbitrary orthogonal cross section.

  The details of the invention will be described with reference to the drawings. First, the internal insertion type ultrasonic inspection will be briefly described. As shown in FIG. 11, the ultrasonic main beam emitted straight from the probe 12 is reflected by the ultrasonic reflection mirror 3 in the direction of 90 degrees and covered. Perpendicular to the inner surface of the specimen, a part of it is transmitted to the inside of the subject without changing the angle, a part of the light is reflected and changed in direction, reflected again by the ultrasonic reflecting mirror 3 in the direction of 90 degrees, and returned to the probe 12. The S echo 27 from the inner surface shown in FIG. 16 is obtained after dividing the distance from the probe 12 to the reflecting mirror 3 and the reciprocating distance from the reflecting mirror 3 to the inner surface of the subject by the sound velocity of water as a transmission medium. Appears. The ultrasonic main beam transmitted to the inside of the subject is also reflected on the outer surface of the subject, transmitted to water as a transmission medium on the inner surface, and returned to the probe 12 in the same manner as when reflected on the inner surface. The first bottom surface B1 echo 29 appears after a time obtained by dividing the reciprocating distance from the inner surface of the subject to the outer surface by the sound velocity of steel as the subject material from the S echo 27 from the inner surface. Here, when the time difference between the first bottom surface B1 echo 29 and the S echo 27 from the inner surface is multiplied by the sound velocity of the steel, the reciprocating distance, that is, twice the wall thickness is obtained. Here, when there is thinning on the inner surface, as shown in FIG. 17, S 'echo from the inner surface appears when the inner surface is thinned behind the S echo 27 from the inner surface, and there is thinning on the outer surface. In this case, as shown in FIG. 17, the first bottom B1 echo 30 at the time of thinning of the outer surface appears prior to the first bottom B1 echo 29. By multiplying these time differences by the respective sound speeds and further halving them, the corrosion depth and thickness value can be obtained. To express.

  FIGS. 2 and 3 show an apparatus made to apply this to a small-diameter curved pipe portion. Here, the rotor 4 incorporating the ultrasonic reflection mirror 3 is held at both ends with bearings so that it can be rotated smoothly and stably, and a pair of center holding mechanisms 5 are equidistant from the center of the ultrasonic reflection mirror 3. The ultrasonic reflecting mirror 3 is always mounted at the center of the tube, and the ultrasonic main beam is designed to be perpendicular to the inner surface of the subject. The probe 12 transmits and receives signals to and from an external flaw detector using an ultrasonic signal cable 11 that passes through the ultrasonic signal cable protection hose 1. The ultrasonic signal cable protection hose 1 reduces the frictional resistance with the inner surface of the subject by the float 2. In addition, the ultrasonic signal cable protection hose 1 is used to feed water and eject the water from the rotor 4 to purge the bubbles adhering to the rotor 4 and the subject, thereby reducing noise. The rotor 4 can be rotated by the bearing 13, and the ultrasonic reflection mirror 3 is held at the center by the center holding mechanism 5 attached to the outside thereof. A flexible shaft 6 is connected to the rotor 4, and is coupled to a flexible shaft protection hose 8 by a coupling / transmission 7 to transmit high-rotation and high-torque power from an external motor. As for the position of the ultrasonic reflection mirror 3 itself in the circumferential direction, one rotation is detected by the rotation detection pin 9 or the rotation sensor 10, and the data collected during one rotation is equally divided on the circumference. It is the data of the lap.

  As an actual application example, a case where the inspection is performed by inserting into a bent pipe portion of a small-diameter thick wall pipe will be described with reference to FIG. The center holding mechanism 5 uses a brush or a magic tape in the case of a small diameter pipe. The motor of the power source is arranged outside the subject. Since the coupling / transmission 7 is a small-diameter pipe, the repetition rate of ultrasonic waves is relatively high, so that the transmission is operated 1: 1 without using a reduction gear. The ultrasonic repetition rate indicates how many times a second is measured, which is the number of times that 1 second is divided by the time it takes for the sound wave emitted from the probe to be reflected from the outer surface of the subject and returned. When the attenuation is small, the ultrasonic waves reciprocate several times inside, so in order to prevent erroneous measurement, set the number of times divided by the time of 2 to 3 reciprocations.

  FIG. 13 shows the result of measuring the thickness of an actual small-diameter thick tube using this apparatus.

  When the inner diameter is large, an arm with a spring as shown in FIG. 8, a center holding mechanism in which a roller is attached to an umbrella bone, or a large-diameter brush in FIG. 6 is used.

  FIG. 5 shows an apparatus made to apply this to a boiler tube, and FIG. 4 shows an example of application to a boiler tube. As described above, by using the present invention, a detailed corrosion inspection of the bent tube portion of the boiler tube can be performed at high speed. The radius of curvature that can be inspected is inversely proportional to the inner diameter, and a pipe with a larger inner diameter can be inspected with a smaller radius of curvature.

  When the inner diameter is large, it is possible to connect the submersible motor 19 to the flexible shaft 6 in FIG. 4, and in this case, access from one side is possible.

  At this time, in addition to using a battery as a power source of the motor, a method of using the supply DC cable 20 as the rotation detection pin 9 in the rotor 4 and passing it through the ultrasonic signal cable protection hose 1 together with the ultrasonic signal cable 11 Can also be selected.

  The bent portion as shown in FIG. 4 becomes a dead zone by the conventional method, and data is lost as indicated by 33 on the B scope and 34 on the C scope in FIG.

  An example of data obtained by the inspection to which the present invention is applied is shown in FIG. Thickness data is obtained as indicated by 35 on the B scope and 36 on the C scope.

  Regarding the detection of the rotational position in the circumferential direction, the inspection application range can be expanded by using an optical or magnetic rotation sensor 10 in addition to the rotation detection pin method that does not require an additional mechanism.

  FIG. 7 shows an apparatus improved to be applied to a curved pipe having a smaller radius of curvature in the present invention, and FIG. 6 shows an application example thereof.

  Rotation is transmitted by 6 flexible shafts from outside, the ultrasonic signal cable 11 can be attached to the flexible shaft protection hose 8, and the ultrasonic signal cable 11 can be used as a substitute for the rotation detection pin 9 in the rotor 4 part. Therefore, this device can also be accessed from one side.

  As described above, by using the present invention, detailed corrosion inspection of the bent portion of the heat exchanger can be performed at high speed. The radius of curvature that can be inspected is inversely proportional to the inner diameter, and a pipe with a larger inner diameter can be inspected even with a smaller curvature.

Example of application of the present invention to a small-diameter pipe bend Illustration of the present invention Sectional view of the rotary scanning unit and probe composed of a rotor and reflecting mirror Example of application of the present invention to a boiler tube Explanatory drawing of the motor built-in type of the present invention Example of application of the present invention to a pipe with a large curvature Illustration of an ultrasonic signal cable attached to a flexible shaft Illustration of the center holding mechanism when the inner diameter is large Illustration of conventional inspection method Examples that could not be solved by conventional inspection methods Explanatory drawing of inspection method in this invention Examples solved by the present invention Example of actual inspection using the present invention Example of boiler tube inspection using conventional inspection methods that could not be resolved Example of boiler tube that can be solved by the present invention Illustration of flaw detection waveform Explanatory drawing of flaw detection waveform when there is internal thinning Explanatory drawing of flaw detection waveform when there is external thinning

Explanation of symbols

1 Ultrasonic signal cable protection hose
2 Float
3 Ultrasonic reflection mirror
4 Rotor
5 Center holding mechanism
6 Flexible shaft
7 Coupling / Transmission
8 Flexible shaft protection hose
9 Rotation detection pin
10 rotation sensor
11 Ultrasonic signal cable
12 Ultrasonic probe
13 bearings
14 Heat exchanger tube (subject)
15 rollers
16 arms
17 spring
18 Flexible shaft protection tube
19 Underwater motor
DC power cable for 20 motors
21 Straight pipe (parts that can be inspected by conventional methods)
22 curved pipes (parts that cannot be solved by conventional methods)
23 Echo does not return from outer surface due to refraction of ultrasonic waves
Phenomenon in which echo does not return from inner surface due to inclination of inner surface of 24 ultrasonic waves
25 C-scope image of the area where corrosion was reduced in an actual tube
26 B-scope image of corrosion-thinned parts in an actual tube
27 S echo from inner surface
28 S 'echo from the inner surface during inner wall thinning
29 1st bottom B1 echo
30 1st bottom B'1 echo when the outer surface is thinned
31 Time difference of S from inner surface when inner surface is thinned
32B1 time difference from the outer surface when the outer surface is thinned
33 B-scope image of straight pipe and bent pipe connection measured by conventional method
34 C-scope image of straight pipe and bent pipe connection measured by conventional method
35 B-scope image of the connecting part of straight pipe part and curved pipe part measured by the present invention
36 C scope image of the connecting part of straight pipe part and curved pipe part measured by the present invention

Claims (3)

When inspecting from the inside of a tube with a rotating reflection mirror for ultrasonic inspection, ultrasonic waves are always incident on the normal to the inner surface of the tube. It has a whole surface scanning mechanism characterized by providing a center holding mechanism equidistant from the center of the ultrasonic reflection mirror and purging air bubbles adhering to the rotor and subject by sending water using an ultrasonic signal cable protection hose Ultrasonic wall thickness measuring device for tubes. The ultrasonic inspection apparatus according to claim 1, wherein the connected flexible shaft rotational scanning unit, rotational scanning unit ultrasonic wall thickness measuring device of the tube, characterized in that the rotating. The ultrasonic inspection apparatus according to claim 1, wherein the rotation by the connected motor scanning unit, rotational scanning unit ultrasonic wall thickness measuring device of the tube, characterized in that the rotating.

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