JPH11230948A - Ultrasonic flaw detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the defect of a pipe to be inspected by correcting influence due to change in the external diameter of the pipe to be inspected. SOLUTION: For a flaw detection method, in a step S1, a simulated defect is machined to a test piece with the quality of a material and the roughness of the surface of a pipe that are the same as those of a pipe to be inspected, an ultrasonic flaw- detecting device is used, a simulated test corresponding to change in the external diameter of the pipe is made, and a transmission wave sensitivity value and the external diameter of the pipe are measured (S1a, S1b, and S1c). Then, the approximate line of the transmission wave sensitivity value and the external diameter of the pipe/the internal diameter of a tool (the reference of the external diameter of the pipe) is obtained for each of the simulated defect according to the obtained measurement result and is used as a reference line for judging a creep defect. In a step S2, when the flaw detection of an actual furnace pipe is performed, the external diameter of the pipe is measured, and at the same time the ultrasonic flaw-detecting device is used for measuring the transmission wave sensitivity value of an inspection site. In a step S3, the transmission wave sensitivity value and the external diameter of the pipe/the internal diameter of the tool are compared with the reference line for judgment, thus judging the creep defect of the pipe to be inspected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flaw detection method in which ultrasonic waves are projected onto a tube to be inspected and flaws are detected by receiving ultrasonic waves transmitted through the tube to be inspected.

[0002]

2. Description of the Related Art Conventionally, naphtha, butane,
The heating tube of the LPG cracking furnace or the heating tube of the reforming furnace at the hydrogen or ammonia plant is HK40 (0.40% C-25%
A plurality of high-carbon heat-resistant centrifugally cast pipes (hereinafter, referred to as “centrifugally cast pipes”) made of Cr-20% Ni-based material or the like are assembled by welding.

[0003] In this heating tube, gas and liquid are supplied to the inside of the tube filled with the catalyst, and the inside of the tube is brought into a high temperature and high pressure state by being heated from the outside of the tube by a burner of a furnace. Then, the substance inside the heating tube reacts and changes under high temperature and high pressure.

[0004] For this reason, in the above-mentioned heating tube, the creep fisher due to the hoop stress tends to spread radially from the inner surface to the outer surface of the tube as the use time elapses. In addition, a defect may occur in the circumferential direction of the inner surface of the pipe due to a temperature difference between the inside and the outside of the pipe (high temperature outside the pipe, low temperature inside the pipe). Therefore, it is indispensable for operation stability to grasp the secular change of the heating tube and estimate the remaining life. In the following,
These defects are called creep damage.

Therefore, the transmitting probe and the receiving probe are combined and scanned along the outer peripheral surface of the inspected tube by the water immersion method, and the inside of the thickness of the inspected tube is measured on the outer periphery of the inspected tube. An ultrasonic wave is incident on the tube to be inspected from the transmission probe by the oblique method so that the ultrasonic wave penetrates into a straight line connecting the two points, and a transmission echo of the ultrasonic wave is received by the reception probe. JP-A-54-128789 discloses a method for detecting a defect in the thickness of a tube to be inspected.

[0006]

However, a centrifugal casting tube used as a heating tube is formed by putting a solution of a steel alloy in a sand mold and sticking the solution to the outside by centrifugal force. for that reason,
Before use, the centrifugally cast tube has a rough casting surface in the form of sand of a sand mold. When used as a heating tube at a high temperature in a furnace, the layer having a rough casting surface causes oxidation thinning, and the tube outer diameter becomes smaller while the tube surface becomes smoother. Then, a phenomenon occurs in which the outer diameter of the pipe increases due to creep damage generated within the thickness of the pipe.

Therefore, in the conventional method of measuring only the attenuation (transmission amount) of ultrasonic waves and judging the presence or absence of creep damage from the secular change of the ultrasonic attenuation amount, the conventional method of measuring the outer diameter of the centrifugally cast pipe is not used. It has not been considered that the change in the incident angle and the output angle of the ultrasonic wave from a predetermined angle due to the change. In other words, in order to measure the attenuation of ultrasonic waves due to creep damage, it is assumed that measurement is performed under the same conditions, but the measurement conditions, especially the incident angle of ultrasonic waves, that is, the incident amount of ultrasonic waves changes. Therefore, accurate judgment was impossible.

Here, the relationship between the outer diameter of the centrifugally cast pipe and the attenuation of the transmitted wave will be specifically described with reference to FIGS. 2, 5, and 6, which are explanatory views of the present invention.

The ultrasonic flaw detector 2 shown in FIG. 2 relates to the present invention and will be described later in detail, but its basic structure is the same as that of the conventional one. The ultrasonic flaw detector 2
The transmitting probe 3 and the receiving probe 4 are arranged on the same circumference on the outer circumference of the inspected tube 1 at a predetermined directional angle and interval. The transmitting probe 4 can receive the transmitted echo of the transmitted ultrasonic wave 7. Needless to say, water 6 is filled in a portion corresponding to an ultrasonic path between the transmission probe 3 and the reception probe 4 and the inspection tube 1 because of the water immersion method. The outer diameter of the inspected tube 1 is a reference outer diameter D as a reference, and the directional angles of the transmitting probe 3 and the receiving probe 4 are directional angles i _{0 with} respect to the tube surface of the inspected tube. It is set so that accurate measurement can be performed in this state.

An ultrasonic wave 7 indicated by an arrow in FIG.
The tube 1 is refracted at the incident point A according to the law of reflection and refraction because of the water immersion method and the oblique angle method.
And the maximum depth 2 within the thickness of the tube 1 to be inspected.
Transmit at tangential direction at T / 3 (T: wall thickness of tube) and exit point B
Is refracted and emitted out of the thickness of the test tube 1 and received by the receiving probe 4. At this time, a defect (radial fisher) is present on the path of the ultrasonic wave 7 within the thickness of the tube 1 to be inspected.
Is present, the ultrasonic wave is scattered by the defect, detected as an attenuated transmission echo by the receiving probe 4, and the existence of the defect can be detected.

Here, as shown in FIG. 5, the ultrasonic flaw detector 2 is mounted on the pipe 11 to be inspected whose outer wall diameter has become D-.DELTA.D due to a decrease in the wall thickness of the pipe due to use. Is done. At this time, the directivity angles of the transmitting probe 3 and the receiving probe 4 are i ₁ (<i ₀ ), and an accurate measurement result cannot be obtained.

As shown in FIG. 6, the ultrasonic flaw detector 2 is mounted on the inspection pipe 12 whose outer diameter becomes D + ΔD by increasing the outer diameter by ΔD with use. At this time, the directivity angles of the transmitting probe 3 and the receiving probe 4 are i ₂ (> i ₀ ), and an accurate measurement result cannot be obtained.

From the above, the incident angle and the emission angle of the ultrasonic wave change due to the change in the outer diameter of the tube to be inspected, and the measurement conditions change. Therefore, the conventional method has a very large error and cannot detect a defect accurately. In addition, even in the same tube in the same furnace, there is a difference in the rate of oxidation thinning due to the temperature distribution, and the outer diameter of the tube differs for each inspection part. It is important to do.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an ultrasonic probe capable of examining a defect of a test tube by correcting the influence of a change in the outer diameter of the test tube. It is to provide a flaw detection method.

[0015]

According to a first aspect of the present invention, there is provided an ultrasonic flaw detection method in which a tube is disposed at a predetermined directional angle with respect to a tube surface whose outside diameter is a reference outside diameter. An ultrasonic flaw detector equipped with a transmitting probe and a receiving probe is mounted on a tube to be inspected, and a transmission echo of the tube to be inspected is measured by an ultrasonic water penetration method, and a defect in the tube to be inspected is detected. In the ultrasonic flaw detection method for determining, the transmitted echo of the test tube,
The defect in the inspected pipe is determined by comparing the outer diameter of the pipe with a determination reference value for each variation from the reference outer diameter.

With the above configuration, the transmitted echo of the inspected tube is measured using an ultrasonic flaw detector, the outer diameter of the tube is measured, and the transmitted echo of the inspected tube is measured as the reference outer diameter of the outer diameter of the tube. By comparing with the criterion value for each change amount from, the deviation of the directivity angles of the transmitting probe and the receiving probe is corrected, and the defect in the inspection tube is determined.

Specifically, first, a simulated defect is processed on a test piece having the same material and the same tube surface roughness as the tube to be inspected, and a simulated defect corresponding to a change in the outer diameter of the tube is obtained by using the ultrasonic flaw detector. Perform the test. Then, an approximation line between the transmitted echo and the amount of change in the tube outer diameter from the reference outer diameter is obtained for each simulated defect from the obtained measurement results, and is used as a determination reference value. When actually inspecting a tube to be inspected, measure the outer diameter of the tube, measure the transmitted echo of the inspection site using the ultrasonic inspection device described above, and measure the change in the outer diameter of the tube from the reference outer diameter. The creep damage of the pipe to be inspected is determined by comparing with the reference value.

As described above, by measuring the transmitted echo of the inspection site and measuring the outer diameter of the tube, the deviation of the directivity angles of the transmitting probe and the receiving probe due to the change in the outer diameter of the tube is corrected. Inspection can be performed. Further, since the amount of change in the pipe outer diameter required for this correction from the reference outer diameter can be obtained only by measuring the pipe outer diameter, the increase in the amount of work is also slight.

Therefore, the secular change of the heating tube can be accurately grasped, and the remaining life can be estimated with high accuracy.
Useless replacement of the heating tube can be prevented, and operation can be performed safely and economically.

According to a second aspect of the present invention, in order to solve the above-described problem, in addition to the configuration of the first aspect, the ultrasonic flaw detection method is applied to a test pipe having a tube outer diameter larger than the reference outer diameter. The judgment reference value is created by performing a simulation test in a state in which the inspected tube whose outer diameter is the reference outer diameter is separated from the ultrasonic inspection apparatus by a distance corresponding to a change amount of the outer diameter of the tube. It is characterized by.

According to the above configuration, in addition to the operation of the configuration of the first aspect, the inspection tube having an outer diameter equal to the reference outer diameter is separated from the ultrasonic flaw detector by a distance corresponding to a change amount of the outer diameter of the tube. By performing a simulation test in the separated state, the above-described determination reference value to be applied to a test pipe having a pipe outer diameter larger than the reference outer diameter is created.

Thus, it is possible to perform a simulation test in a state where it is difficult to prepare a test piece in a state where the outer diameter of the tube to be inspected is increased. Then, by performing a simulation test while gradually changing the distance between the tube to be inspected and the ultrasonic flaw detector, it is possible to create a determination reference value in a range of an arbitrary change amount. Further, the simulation test is simple in operation, and the accuracy of the obtained measurement result is high.

According to a third aspect of the present invention, in order to solve the above-described problem, in addition to the configuration of the first or second aspect,
The determination reference value to be applied to the inspected tube having a tube outer diameter smaller than the reference outer diameter is the inspected tube whose outer diameter is the reference outer diameter by a thickness corresponding to a change amount of the tube outer diameter, It is characterized in that it is created by performing a simulation test on the inspected tube whose surface has been cut down.

According to the above configuration, in addition to the operation of the first or second aspect, the pipe to be inspected whose outer diameter is the reference outer diameter is formed by a thickness corresponding to a change amount of the outer diameter of the pipe. It is created by performing a mock test on the cut test tube.

Thus, by performing a simulation test while gradually changing the thickness of the pipe to be inspected, a judgment reference value in an arbitrary range of change can be created. Further, the simulation test is simple in operation, and the accuracy of the obtained measurement result is high.

According to a fourth aspect of the present invention, in order to solve the above-described problems, in addition to the configuration of any one of the first to third aspects, the tube to be inspected is a high carbon heat resistant centrifugally cast tube. It is characterized by:

According to the above configuration, in addition to the operation according to any one of the first to third aspects, the transmission of the high carbon heat resistant centrifugally cast tube measured by the ultrasonic flaw detector by the ultrasonic water penetration method is used. A defect in the high-carbon heat resistant centrifugally cast tube is determined by comparing the echo with a judgment reference value for each change in the outer diameter of the high carbon heat-resistant centrifugally cast tube from the reference outer diameter.

Further, the criterion value applied to the high-carbon heat-resistant centrifugally cast tube is such that a high-carbon heat-resistant centrifugally cast tube having an outer diameter equal to the reference outer diameter is used for a tube outer diameter larger than the above-mentioned reference outer diameter. It is created by performing a simulation test in a state where it is separated from the ultrasonic flaw detector by a distance corresponding to the change amount of the outer diameter. Also, for a tube outer diameter smaller than the reference outer diameter,
A high-carbon heat-resistant centrifugally cast pipe having an outer diameter equal to the reference outer diameter is prepared by performing a simulation test by cutting the pipe surface by a thickness corresponding to the change in the outer diameter of the pipe.

The ultrasonic flaw detection method according to any one of claims 1 to 3 can be applied to a tube to be inspected whose tube outer diameter changes. Is large, and the effect of the correction is remarkable.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. In the following, the tube to be inspected will be described as a high carbon heat resistant centrifugally cast tube (hereinafter, referred to as “centrifugally cast tube”).

As shown in FIGS. 2 and 3, the ultrasonic flaw detector 2 used in the ultrasonic flaw detection method according to the present embodiment.
The transmission probe 3 and the reception probe 4 are attached to a jig 5.

The above-mentioned transmission probe 3 and reception probe 4
When the ultrasonic test equipment 2 is mounted on the test pipe 1 whose outer diameter is the reference outer diameter D, the ultrasonic test equipment 2 is arranged at a predetermined directivity angle and a predetermined interval on the same circumference of the test pipe 1. And jig 5
Attached to. The receiving probe 4 can receive a transmitted echo of the ultrasonic wave 7 transmitted from the transmitting probe 3 and transmitted through the thickness of the inspection tube 1.

The jig 5 is made of, for example, MMA (methyl methacrylate). And the transmitting probe 3
An opening 5a is formed in a portion corresponding to an ultrasonic path between the receiving probe 4 and the tube 1 to be inspected. Opening 5a
Since the ultrasonic flaw detector 2 is pressed against the tube 1 to be inspected and mounted, the outer diameter is formed in a shape suitable for the outer peripheral shape of the tube 1 having the reference outer diameter D. Therefore, hereinafter, the reference outer diameter D of the pipe 1 to be inspected may be referred to as “jig inner diameter”.

Also, since the water 6 is filled in the jig 5 due to the water immersion method, the jig 5 corresponds to an ultrasonic path between the transmission probe 3 and the reception probe 4 and the tube 1 to be inspected. Water 6 is retained in the part. Then, when the jig 5 is pressed against the pipe 1 to be inspected, the water 6 filled therein is prevented from leaking.
A seal 5b made of, for example, plate rubber or the like, which has elasticity, is provided at a contact portion that comes into contact with the tube 1 to be inspected. Further, the ultrasonic flaw detector 2 is provided with a water injection means and a water discharge means (not shown) for injecting and discharging the water 6 into the jig 5. Therefore, the measurement of the transmission echo by the ultrasonic flaw detector 2 includes mounting, water injection, measurement, and drainage in one.
This is done in cycles. This prevents the surrounding material such as the heat insulating material in the furnace from getting wet.

The ultrasonic wave 7 indicated by an arrow in the figure is projected from the transmitting probe 3 to which pulsed power is supplied by a flaw detector 21 (FIG. 4) described later, and the outer diameter of the ultrasonic wave 7 is outside the standard via the water 6. Since the light is incident on the test tube 1 having a diameter D at an incident angle i ₀ and is subjected to the water immersion method and the oblique method, the refraction angle θ at the incident point A on the outer peripheral surface of the test tube 1 according to the law of reflection and refraction. ₀ , refracts at the maximum depth d ₀ tangentially through the thickness of the tube 1 to be inspected, and has a refraction angle i ₀ with respect to the incident angle θ _{0 at} the emission point B on the outer peripheral surface of the tube 1 to be inspected. The beam is refracted and emitted out of the thickness of the test tube 1, and is received by the receiving probe 4 via the water 6. At this time, if a defect (radial fisher) exists on the path of the ultrasonic wave 7 in the thickness of the inspection target tube 1, the ultrasonic wave is scattered by the defect and the attenuated transmission echo is transmitted to the receiving probe 4. And the presence of a defect can be detected.

Further, the incident angle i ₀ of the ultrasonic wave 7 is
If the distance between the transmitting probe 3 and the receiving probe 4 is adjusted so as to receive the transmitted echo at the same time as the bottom surface reflection by the inner peripheral surface does not occur, the thickness of the tube 1 to be inspected can be reduced. The ultrasonic flaw detection depth d ₀ can be appropriately adjusted.

As shown in FIG. 4, the transmitting probe 3 and the receiving probe 4 are connected to a flaw detector 21 for supplying pulsed power, and the flaw detector 21 is connected to a recorder 22. I have. As the water injection means, for example, a jig 5
The jig 5 is connected to a water injection tank 23 so that the inside of the jig 5 can be filled with water 6. Similarly, a drain hole (not shown) is formed in the jig 5 and is connected to a drain tank 24 so that the water 6 filled in the jig 5 can be drained.

The measurement conditions of the specific examples described below are as follows. As the tube 1 to be inspected, a KHR24C centrifugally cast tube manufactured by Kubota Corporation (standard outer diameter 110 m)
m, wall thickness 12 mm). The roughness of the tube surface is such that the center line surface roughness is about 10 μm.

Further, the ultrasonic flaw detector 2 includes a transmitting probe 3
As V382 made by Panametrics (frequency 3.5 MHz)
z, transducer diameter 0.5 ", focus 3" LF), receiving probe 4
As V382 made by Panametrics (frequency 3.5 MHz)
z, vibrator diameter 0.5 ″, focal point FLAT). The transmitting probe 3 and the receiving probe 4 have a maximum outer diameter with respect to the test tube 1 having the reference outer diameter D. The depth d ₀ is 2T /
3, the mounting angle φ is set to 43 ° (FIG. 2).

Further, as the flaw detector 21, USL-38 and USL-48 manufactured by Kraut Kramer Co., Ltd. were used.
The recorder 22 measures the echo height of the received ultrasonic wave by CRT.
The sensitivity value when corrected so as to be 80% on the screen is recorded. According to this recording method, the smaller the amount of received ultrasonic waves, the higher the sensitivity value is set, and the same echo height is corrected. In other words, as creep damage progresses, the amount of ultrasonic waves received decreases, so that the set sensitivity value increases.

Here, the ultrasonic flaw detection method according to the present embodiment will be described with reference to the flowchart shown in FIG.

Step S1: A damage criterion for the inspected tube is created. First, as a preparation for performing a flaw detection of a pipe to be inspected in an actual furnace, a reference value for judging creep damage is obtained. Specifically, a simulated defect is machined on a test piece having the same material and tube surface roughness as the tube to be inspected, and a simulation test corresponding to a change in the tube outer diameter is performed using the ultrasonic flaw detector 2. The transmitted wave sensitivity value (corresponding to the amount of attenuation) is measured. Then, from the obtained measurement results, an approximate line of the transmitted wave sensitivity value and the tube outer diameter / jig inner diameter (change amount of the tube outer diameter from the reference outer diameter) is obtained for each simulated defect. If a damage criterion has already been created for pipes of the same material and pipe surface roughness, it goes without saying that step S1 can be omitted.

The simulation test includes a simulation test in which the pipe outer diameter is a reference outer diameter, a simulation test in which the pipe outer diameter is increased, and a pipe outer diameter in order to simulate a change in the pipe outer diameter of the inspected pipe. Three types of simulation tests are performed in a state in which is reduced.

First, a simulation test is performed in a state where the outer diameter of the inspected pipe is the reference outer diameter (S1a). The transmitted wave sensitivity value is measured for the test piece processed with the simulated defect and the unprocessed test piece by using the ultrasonic flaw detector 2. At this time, the positional relationship between the test piece (tube 1 to be inspected) and the ultrasonic flaw detector 2 is as shown in FIG. In order to equalize the roughness of the pipe surface, a rough layer on the pipe surface of a test piece, which is an unused pipe, is cut with a lathe and the outer diameter is set as a reference outer diameter D.

Secondly, a simulation test is performed for a state where the outer diameter of the inspected tube is increased (S1b). As in the simulation test in step S1a, the transmitted wave sensitivity value is measured for the test piece processed with the simulated defect and the unprocessed test piece. At this time,
As shown in FIG. 7, an elastic thin seal 5c made of, for example, plate rubber or the like having a uniform thickness is stuck on the seal 5b of the opening 5a of the ultrasonic flaw detector 2, and 2 is mounted on the test piece (tube 1 to be inspected). Thus, using the inspected tube 1 having the outer diameter D, it is possible to simulate and measure the inspected tube 12 (FIG. 6) in which the outer diameter of the tube has increased to D + ΔD. For example, it is possible to simulate various tube outer diameters by repeating the measurement while stacking and attaching the 1.5 mm thick seals 5c one by one.

In FIG. 7, one sticker 5c is attached.
Although only sheets are illustrated, the material, thickness, number of sheets, and the like of the seals 5b and 5c can be appropriately selected according to required measurement accuracy and the like.

Third, a simulation test is performed on a state where the outer diameter of the tube to be inspected is reduced (S1c). The above step S1a,
As in the simulation test of S1b, the transmitted wave sensitivity value is measured for the test piece processed with the simulated defect and the unprocessed test piece.
At this time, as shown in FIG. 5, the pipe surface of the pipe 1 to be inspected is cut by ΔD with a lathe to reduce the wall thickness and the outer diameter of the pipe to D-ΔD. For example, 0.1m
By repeating the measurement while shaving each m, various tube outer diameters can be simulated.

FIG. 8 shows the results of the above-described three types of simulation tests on a test piece obtained by processing a simulated defect of a slit (crack) of T / 2 and T / 3 in the thickness direction and an unprocessed test piece. The measured results of the transmitted wave sensitivity values and the approximate lines L2, L1, L0 obtained for each of the simulated defects are shown. As the approximation line in the present embodiment, a regression coefficient of the first order had the highest correlation, so a regression line was adopted.

Therefore, the ratio of the tube outer diameter to the reference outer diameter D, which is the ratio of the tube outer diameter to the jig inner diameter (FIG. 8), shows a good correlation (77% or more) with the transmitted wave sensitivity value. It can be seen that each of the approximation lines is sufficiently reliable as a criterion for creep damage in which the influence of the change in the pipe outer diameter is corrected.

Here, the meaning of the reference line will be described. For example, if the measured value of a certain inspection part is plotted on the approximate line L2, it is evaluated that the inspection part has the same attenuation as the simulated defect of the T / 2 slit. this is,
This does not mean that there is creep damage of the same size as the T / 2 slit at the inspection site. In other words, what is actually detected is not the attenuation of one crack, but the attenuation of an aggregate of a very small number of defects that have occurred innumerably, which is the attenuation of the simulated defect of the T / 2 slit. It means that they are comparable. He then assesses the level of Fisher's evolving defect cluster. Naturally, the defect is detected before a defect having the same size as the simulated defect occurs.

Step S2: The outer diameter of the tube to be inspected and the transmitted wave sensitivity value are measured. The outer diameter of the pipe to be inspected in the actual furnace is measured, and the transmitted wave sensitivity value is measured using the ultrasonic flaw detector 2.

Step S3: Damage to the tube to be inspected is determined (comparison with a reference). In step S2, the pipe outer diameter / the pipe outer diameter /
The inner diameter of the jig is calculated, and is compared with the approximated lines L2, L1, and L0 determined as reference lines for determination together with the transmitted wave sensitivity value.

That is, on the coordinate plane of the tube outer diameter / jig inner diameter and the transmitted wave sensitivity value, the position where the measured value of the tube to be inspected in the actual furnace is plotted with respect to the reference line, The state of the defect can be determined.

For example, FIG. 9 shows that, with respect to a damaged pipe extracted from an actual furnace, the pipe outer diameter and the transmitted wave sensitivity value are measured, and the pipe outer diameter / jig inner diameter is calculated from the obtained pipe outer diameter. And
This is graphed together with the approximate lines L2, L1, L0 (FIG. 8), which are reference lines. In addition, the presence or absence of a fisher confirmed by cross-sectional macro / micro structure observation is made to correspond.

In FIG. 9, the tube outer diameter has increased due to the occurrence of creep damage, and the ratio of tube outer diameter / jig inner diameter is distributed in the vicinity of 1.02. It can be seen that the transmission wave sensitivity value increases as the tube outer diameter / jig inner diameter increases, and the amount of transmitted echo decreases as the tube outer diameter increases. In addition, Fisher is detected at a portion where the transmitted wave sensitivity value is higher than the approximate line L1 of the T / 3 slit. As for the accuracy, Fisher is confirmed in 90% (7/8) or more of the parts exhibiting the transmitted wave sensitivity value higher than the approximate line L2 of the T / 2 slit.

Therefore, the damage to the inspected tube can be determined based on the reference line obtained by measuring the simulated defect, so that the heating tube can be replaced. For example,
The roughness of the tube surface and the transmitted wave sensitivity value of a predetermined inspection site are measured for one heating tube, and if even one of the tubes exceeds the reference line of T / 3 slit (approximate line L1), the heating tube is replaced. It can be performed.

As described above, according to the ultrasonic flaw detection method of the present embodiment, first, a simulated defect is processed on a test piece having the same material and the same tube surface roughness as the pipe to be inspected. Using the flaw detector 2, a simulation test is performed on the transmitted wave sensitivity value corresponding to the change in the tube outer diameter. Then, an approximate line between the transmitted wave sensitivity value and the variation of the tube outer diameter from the reference outer diameter (tube outer diameter / jig inner diameter) is obtained for each simulated defect from the obtained measurement results, and the creep damage determination is made. A reference line (judgment reference value for each change amount of the pipe outer diameter from the reference outer diameter) is obtained in advance. Then, when actually performing the flaw detection of the inspected tube, the outer diameter of the tube is measured, and the transmitted wave sensitivity value of the inspection site is measured using the ultrasonic flaw detector 2, and the determined reference line is determined. By performing the comparison, the creep damage of the inspected tube 1 can be determined. It has been confirmed that there is a good correspondence between the result of the ultrasonic inspection and the actual damage obtained by observing the cross-sectional micro / macro structure.

Thus, the damage of the pipe to be inspected can be accurately determined by correcting the influence of the change in the outer diameter of the pipe by using each of the approximation lines as the reference value for determining the creep damage. Therefore, the secular change of the heating tube can be accurately grasped, and the remaining life can be estimated with high accuracy. Therefore, unnecessary replacement of the heating tube can be prevented, and the operation can be performed safely and economically.

The present embodiment does not limit the scope of the present invention, and various changes can be made within the scope of the present invention. For example, when performing a simulation test in a state where the tube outer diameter of the tube to be inspected is increased, a seal may be attached to the test piece.
Further, the simulated defect may be other than the slits of T / 2 and T / 3 in the thickness direction, and can be appropriately selected by setting test conditions. Further, the regression coefficient of the approximate line to be obtained is not limited to the first order, and can be appropriately selected according to the correlation between the tube outer diameter / jig inner diameter and the transmitted wave sensitivity value.

Also, the centrifugally cast tube can be used even when not in use.
Outer diameter of pipe is not constant. However, the above-described criteria can be applied by converting the pipe outer diameter / jig inner diameter even when the reference outer diameter is different.

Further, the ultrasonic flaw detector 2 is provided with a seal 5b made of plate rubber or the like to prevent the leakage of the water 6, and the thickness of the seal 5b changes the incident state of the ultrasonic wave to the tube to be inspected. I do. According to the ultrasonic flaw detection method of the present embodiment, it is possible to correct the influence of the thickness of the seal 5b to be used and accurately determine the damage to the tube to be inspected.

[0062]

According to the ultrasonic flaw detection method of the first aspect of the present invention, as described above, the transmitting probe and the transmitting probe disposed at a predetermined directivity angle with respect to the pipe surface having the pipe outer diameter of the reference outer diameter are provided. An ultrasonic flaw detector equipped with a receiving probe is attached to a tube to be inspected, and a transmitted echo of the tube to be inspected is measured by an ultrasonic water penetration method to determine a defect in the tube to be inspected. In the method,
A defect in the inspected tube is determined by comparing the transmitted echo of the inspected tube with a determination reference value for each change amount of the tube outer diameter from the reference outer diameter.

Therefore, by measuring the transmitted echo of the inspection site and measuring the outer diameter of the tube, the deviation of the directivity angles of the transmitting probe and the receiving probe due to the change in the outer diameter of the tube is corrected to detect the flaw. Is achieved. In addition, since the amount of change in the pipe outer diameter required for this correction from the reference outer diameter can be obtained only by measuring the pipe outer diameter, there is an effect that the increase in the amount of work is small.

Therefore, the secular change of the heating tube can be accurately grasped, and the remaining life can be estimated with high accuracy.
It is possible to prevent wasteful replacement of the heating tube and to operate safely and economically.

According to the ultrasonic flaw detection method of the second aspect of the present invention, as described above, in addition to the configuration of the first aspect, the determination criterion applied to a pipe to be inspected having a tube outer diameter larger than the reference outer diameter The value is a configuration created by performing a simulation test in a state in which the inspected tube whose outer diameter is the reference outer diameter is separated from the ultrasonic inspection apparatus by a distance corresponding to the change amount of the outer diameter of the tube. .

Therefore, in addition to the effect of the configuration of claim 1, there is an effect that a simulation test can be performed on a state where it is difficult to prepare a test piece in a state where the tube outer diameter of the inspected tube is increased. . Then, by performing a simulation test while changing the distance between the inspection pipe and the ultrasonic flaw detector in a stepwise manner, there is an effect that a determination reference value in an arbitrary variation range can be created. Further, the simulation test has an effect that the operation is simple and the accuracy of the obtained measurement result is high.

As described above, the ultrasonic flaw detection method according to the third aspect of the present invention, in addition to the configuration according to the first or second aspect, is applicable to a pipe to be inspected having an outer diameter smaller than the reference outer diameter. The determination reference value is obtained by performing a simulation test on the inspected tube whose outer diameter is the reference outer diameter by a thickness corresponding to the amount of change in the outer diameter of the inspected tube with the tube surface being cut down. This is the configuration to be created.

Therefore, in addition to the effect of the structure of claim 1 or 2, the simulated test is performed by changing the thickness of the tube to be inspected in a stepwise manner to determine the range of any variation. This produces an effect that a value can be created. Further, the simulation test has an effect that the operation is simple and the accuracy of the obtained measurement result is high.

According to the ultrasonic flaw detection method of the fourth aspect of the present invention, as described above, in addition to the configuration of any one of the first to third aspects, the tube to be inspected is a high carbon heat resistant centrifugally cast tube. is there.

Therefore, in addition to the effect of any one of the first to third aspects, the high carbon heat resistant centrifugally cast tube has an effect that the aging of the tube outer diameter is large and the correction effect is remarkable. .

[Brief description of the drawings]

FIG. 1 is a flowchart schematically showing an ultrasonic flaw detection method according to an embodiment of the present invention.

FIG. 2 is an explanatory view schematically showing a configuration of an ultrasonic flaw detector used in the ultrasonic flaw detection method shown in FIG.

FIG. 3 is an explanatory view schematically showing the configuration of the ultrasonic flaw detector shown in FIG. 2 and FIGS. 5 to 7;

FIG. 4 is an explanatory diagram showing an outline of a usage state of the ultrasonic flaw detector shown in FIGS. 2 and 3;

FIG. 5 is an explanatory view showing a state where the ultrasonic flaw detector shown in FIGS. 2 and 3 is mounted on a test tube having a reduced tube outer diameter.

FIG. 6 is an explanatory view showing a state where the ultrasonic flaw detector shown in FIGS. 2 and 3 is mounted on a test tube having an increased tube outer diameter.

FIG. 7 is an explanatory diagram showing a state in which the ultrasonic flaw detector shown in FIGS. 2 and 3 is simulated mounted on a tube to be inspected having an increased tube outer diameter.

FIG. 8 is a graph showing measurement results of a tube outer diameter / jig inner diameter and a transmitted wave sensitivity value of a centrifugally cast tube on which a simulated defect has been processed, and an approximate line thereof.

FIG. 9 shows an approximation line between the tube outer diameter / jig inner diameter of the centrifugally cast pipe having a simulated defect processed and the transmitted wave sensitivity value, and the tube outer diameter / jig inner diameter of the actual furnace damaged tube and the transmitted wave sensitivity value. 6 is a graph showing the measurement results of FIG.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 tube to be inspected (high carbon heat resistant centrifugally cast tube) 2 ultrasonic flaw detector 3 transmission probe 4 receive probe 11 tube to be inspected (high carbon heat resistant centrifugal cast tube) 12 tube to be inspected (high carbon heat resistant centrifugal cast tube) ) I ₀ Direction angle D Reference outside diameter ΔD Change in tube outside diameter

Claims (4)

[Claims] 1. An ultrasonic flaw detector equipped with a transmitting probe and a receiving probe disposed at a predetermined directivity angle with respect to a tube surface whose tube outer diameter is a reference outer diameter is attached to a tube to be inspected. Then, in the ultrasonic flaw detection method for measuring a transmission echo of the test tube by an ultrasonic water penetration method and determining a defect in the test tube, An ultrasonic flaw detection method, wherein a defect in the inspection tube is determined by comparing with a determination reference value for each variation from a reference outer diameter. 2. The determination reference value applied to a test pipe having a pipe outer diameter larger than the reference outer diameter, the test pipe having an outer diameter equal to the reference outer diameter corresponds to a change amount of the pipe outer diameter. Only the distance you
The ultrasonic inspection method according to claim 1, wherein the ultrasonic inspection apparatus is created by performing a simulation test in a state where the ultrasonic inspection apparatus is separated from the ultrasonic inspection apparatus. 3. The determination reference value to be applied to a test pipe having a pipe outer diameter smaller than the reference outer diameter, the test pipe having an outer diameter equal to the reference outer diameter being equivalent to a change amount of the pipe outer diameter. Just the thickness
3. The method according to claim 1, wherein a simulation test is performed on the inspected tube whose surface is cut off.
The described ultrasonic flaw detection method. 4. The ultrasonic flaw detection method according to claim 1, wherein said tube to be inspected is a high carbon heat resistant centrifugally cast tube.