Corrosion diagnosis method and corrosion diagnosis system

Abstract

This invention provides a corrosion evaluation method that can accurately assess the level of corrosion. [Solution] The corrosion evaluation method of this disclosure includes: a creation step S1 for creating a master curve; a reference determination step S3 for determining the sound velocity and echo height ratio of the ultrasound from ultrasonic echoes obtained by sending and receiving ultrasound to a flange; a correction magnification determination step S4 for determining a correction magnification to match the reference surface echo height ratio determined in the reference determination step S3 to the representative echo height ratio used when creating the master curve; an inspection step S6 for determining the sound velocity and inspection surface echo height ratio from ultrasonic echoes obtained by sending and receiving ultrasound to an elbow pipe; a correction step S7 for correcting the echo height ratio determined in the inspection step S6 using the correction magnification determined in the correction magnification determination step S4; and an evaluation step S8 for evaluating the corrosion level from the corrected echo height ratio.

Description

Technical Field

[0001] The present disclosure relates to a corrosion diagnosis method and a corrosion diagnosis system. Background Art

[0002] Non-Patent Document 1 describes that "in this study, with the pump kept installed, an ultrasonic pulse is incident in the wall thickness direction from the outer surface of a gray cast iron component, and a method for simultaneously measuring the corrosion state on the inner surface and the wall thickness from the reflected wave is studied." Prior Art Documents Non-Patent Documents

[0003] Non-Patent Document 1 Ultrasonic Diagnosis of Graphitization Corrosion Occurring in Cast Iron Pump Parts, Turbo Machinery, Vol. 38, No. 1, pp. 54-63 Summary of Invention Problem to be Solved by the Invention

[0004] For gray cast iron, taking Japanese Industrial Standards (JIS) as an example, only the mechanical strength is specified, and there is no specification related to chemical components. Therefore, even for components made of the same "gray cast iron", the chemical components may differ due to factors such as differences in casting lots. As a result, the propagation characteristics of ultrasonic waves propagating inside the component may differ, so there is room for improvement in the evaluation accuracy of corrosion levels using ultrasonic waves. The problem to be solved by the present disclosure is to provide a corrosion evaluation method and a corrosion evaluation system that can evaluate a corrosion level with high accuracy. Means for Solving the Problem

[0005] The corrosion evaluation method of this disclosure includes: a reference surface transmission and reception step in which ultrasonic waves are irradiated onto a reference surface of a gray cast iron object to be inspected and ultrasonic echoes of the reference surface, which are reflected waves; a reference surface echo height ratio in which ultrasonic waves are represented in the ultrasonic propagation characteristics within the object to be inspected, determined from the ultrasonic echoes obtained in the reference surface transmission and reception step and the thickness of the object to be inspected in the portion forming the reference surface, determined from the ultrasonic echoes obtained in the reference surface transmission and reception step and the thickness of the object to be inspected in the portion forming the reference surface; a correction magnification determination step in which a correction magnification of the reference surface echo height ratio is determined so that the reference surface echo height ratio determined in the reference determination step matches a representative echo height ratio in which the reflective surface at the same thickness as the reference thickness of a predetermined master curve shows a healthy state; and a correction magnification determination step in which a correction magnification of the reference surface echo height ratio is determined so that the reference surface echo height ratio determined in the reference determination step matches a representative echo height ratio in which the reflective surface at the same thickness as the reference thickness of a predetermined master curve shows a healthy state; and an inspection surface provided on the object to be inspected that is not visible from the outside. The present invention includes: an inspection surface transmission and reception step in which ultrasonic waves are irradiated from the outer surface of the object to be inspected and ultrasonic echoes of the inspection surface, which are reflected waves; an inspection step in which the thickness of the portion of the object to be inspected that forms the inspection surface is determined from the time difference between a first bottom surface echo and a second bottom surface echo among the ultrasonic echoes of the inspection surface obtained in the inspection surface transmission and reception step and the speed of sound determined in the reference determination step, and an inspection surface echo height ratio which is the ratio of the echo heights of the inspection surface determined from the first bottom surface echo and the second bottom surface echo; a correction step in which the corrected echo height ratio is obtained by correcting the inspection surface echo height ratio determined in the inspection step with the correction magnification determined in the correction magnification determination step; and an evaluation step in which the corrosion level of the inspection surface is evaluated by determining the corrosion level using the master curve from the thickness determined in the inspection step and the corrected echo height ratio determined in the correction step. Other solutions will be described later in the embodiments for carrying out the invention. [Effects of the Invention]

[0006] This disclosure provides a corrosion evaluation method and a corrosion evaluation system that can accurately evaluate the corrosion level. [Brief explanation of the drawing]

[0007] [Figure 1] This flowchart shows the corrosion evaluation method disclosed herein. [Figure 2] This is a schematic diagram of a corrosion assessment map. [Figure 3] This diagram shows the received ultrasound echo and illustrates the echo height ratio. [Figure 4] This diagram shows a magnified view of the area near the standard evaluation site and the area irradiated with ultrasound within the object being inspected. [Figure 5] This figure shows the standard evaluation area of ​​the object being inspected, viewed from a different direction than in Figure 4, and magnified. [Figure 6] This is an enlarged view of section A in Figure 4. [Figure 7] This diagram shows the probe being brought into contact with the bottom surface of a depression. [Figure 8] This figure shows a probe in contact with the upper surface of a flange in another embodiment. [Figure 9] This diagram illustrates how to position the transducer when transmitting and receiving ultrasound in the reference plane transmission / reception step, and shows the transducer viewed from above. [Figure 10] This is an enlarged view of section B in Figure 4. [Figure 11] This diagram illustrates how to position the transducer when transmitting and receiving ultrasound waves during the inspection surface transmission / reception step, and shows the object being inspected viewed from an oblique angle. [Figure 12] In another embodiment, this diagram illustrates how the transducer is positioned when transmitting and receiving ultrasound waves in the inspection surface transmission / reception step, and is a view of the object to be inspected from an oblique direction. [Figure 13] This figure plots the wall thickness and corrected echo height ratio, determined by ultrasonic irradiation of the inspection surface, onto a corrosion evaluation map. [Figure 14] This is a contour map created by imaging each measurement area of ​​the inspection surface and combining them into a single image. [Figure 15] This is a block diagram of the corrosion assessment system of this disclosure. [Figure 16]This block diagram shows the specific hardware configuration of the corrosion evaluation system of this disclosure. [Modes for carrying out the invention]

[0008] The following describes embodiments for implementing this disclosure, with reference to the drawings. The following is merely an example of how to implement the invention related to this disclosure, and this disclosure is not limited to the following example. Within the description of one embodiment below, other embodiments applicable to that embodiment will also be described as appropriate. This disclosure is not limited to the following embodiment, and different embodiments can be combined or modified as appropriate without significantly impairing the effects of this disclosure. In addition, the same reference numerals will be used for the same components, and redundant explanations will be omitted. Furthermore, components having the same function will be given the same name. The illustrations are schematic, and for illustrative purposes, the actual configuration may be changed or some components may be omitted or modified between drawings without significantly impairing the effects of this disclosure. Also, the same embodiment does not necessarily need to have all the components.

[0009] Figure 1 is a flowchart of the corrosion evaluation method of this disclosure. The corrosion evaluation method of this disclosure can be performed, for example, using the corrosion evaluation system 500 described later. The corrosion evaluation method of this disclosure is a method for evaluating the corrosion level (corrosion status; degree of corrosion) of an inspection surface 1c (described later) that is not visible from the outside, using the sound velocity specific to the inspection object 1 and the echo height ratio of the ultrasonic echo described later, for an inspection object 1 made of gray cast iron (an example of cast iron). The evaluation can be performed with the inspection object 1 installed and non-destructively.

[0010] When ultrasonic waves are incident from one surface (for example, the outer surface 1d of a pipe (described later), which is the surface) using a probe 551 (described later) among the two opposing surfaces forming the inspection object 1 (structure), the ultrasonic waves propagate through the inside (solid) of the inspection object 1 and reach the other surface (for example, the inner surface of a pipe, which is the reflecting surface and the back surface, and is the inspection surface 1c described later). The ultrasonic waves are reflected on the back surface and reach the front surface. In this way, the incident ultrasonic waves repeatedly reflect between one surface and the other surface.

[0011] On the surface of gray cast iron (for example, the inner surface of a pipe made of gray cast iron), irregularities form on the corroded surface as corrosion progresses. Therefore, when reflected, the ultrasonic waves are scattered by the irregularities. As a result, in the received ultrasonic echo, the echo height ratio determined from the first bottom echo and the second bottom echo changes depending on the degree of the irregularities. Therefore, the degree of corrosion can be evaluated from the magnitude of the echo height ratio. Specifically, it can be evaluated that the fewer the irregularities and the larger the echo height ratio, the lower the corrosion level. On the other hand, it can be evaluated that the more the irregularities and the smaller the echo height ratio, the higher the corrosion level. It should be noted that on the surface of a casting immediately after casting (the inspection object 1 immediately after solidification), there are no irregularities that can be called corrosion, and the surface can be evaluated as sound. In addition, a surface that has been placed in an environment where corrosion is unlikely to occur, such as being difficult to contact with moisture and air for a long period of time, can also be evaluated as sound. Furthermore, for example, coating is applied to surfaces (such as the outer surface 1d described later (the joint surface 2d described later, etc.) and the inner surface (the inspection surface 1c described later), etc.) for surface protection. As a result, a coating film (not shown) is formed on the surface. Among these, on the outer surface 1d that does not come into contact with fluid such as liquid, the coating film is less likely to peel off than on the inspection surface 1c that comes into contact with fluid such as liquid in the elbow pipe 1a described later. In addition, even if the coating film peels off, corrosion is less likely to progress on the outer surface 1d that does not come into contact with the fluid than on the inspection surface 1c that comes into contact with the fluid. Thereby, the soundness of the outer surface 1d is maintained.

[0012] The extent of corrosion on the inspection surface 1c (described later) that is the object of evaluation, that is, the evaluation of the corrosion level, can be determined, for example, by using the master curves M1, M2, M3, M4, M5 (hereinafter appropriately referred to as "master curves M1, etc.") described later, details of which will be described later. The master curves M1, etc. are predetermined in, for example, a factory or the like. Therefore, the master curves M1, etc. are predetermined before the ultrasonic inspection of the inspection object 1. However, in the example of the present disclosure, for convenience of explanation, the creation of the corrosion evaluation map 100 including the master curves M1, etc. is performed as part of the corrosion evaluation method of the present disclosure. The master curves M1, etc. are normally created only once, and thereafter, when performing corrosion evaluation, the initially created master curves M1, etc. are used to evaluate the corrosion level. That is, even if the lot, type, structure, manufacturer, etc. of the inspection object 1 to be subjected to ultrasonic inspection change, the same master curves M1, etc. are used.

[0013] The conditions (the lot at the time of casting, the wall thickness of the test member which is the wall thickness of the portion through which ultrasonic waves propagate (reference wall thickness), etc.) of the test member (a sample for determining a master curve linked to the corrosion level, also referred to as a test material) when creating the master curves M1, etc. are different from the conditions (the lot at the time of casting, the wall thickness of the inspection object 1, etc.) of the inspection object 1. The conditions referred to herein are ultrasonic propagation conditions (sound velocity, the aforementioned echo height ratio, etc.). That is, as described above, the state of the casting may differ depending on the lot of the material used during casting. In other words, different lots may have different compositions, which may lead to different ultrasonic propagation conditions. For this reason, the ultrasonic propagation conditions change, and even if exactly the same ultrasonic inspection is performed, different results may be obtained. Therefore, in the example of the present disclosure, by matching the conditions of the inspection object 1 with the conditions of the test material when creating the master curves M1, etc., the evaluation accuracy using the master curves M1, etc. can be improved.

[0014] The corrosion evaluation method of this disclosure includes a creation step S1, a reference surface transmission / reception step S2, a reference determination step S3, a correction magnification determination step S4, an inspection surface transmission / reception step S5, an inspection step S6, a correction step S7, an evaluation step S8, and an imaging step S9. However, these steps do not necessarily have to be performed in this order. For example, after the reference surface transmission / reception step S2 and the inspection surface transmission / reception step S5 are performed consecutively, the reference determination step S3, correction magnification determination step S4, inspection step S6, correction step S7, etc., may be performed using the obtained first bottom surface echo and second bottom surface echo. Also, as described above, the creation step S1 is usually performed only once on the first measurement, so in subsequent measurements, the creation step S1 is not performed. Therefore, for example, in an actual inspection site, usually only the reference surface transmission / reception step S2 and subsequent steps are performed.

[0015] Step S1 is the step of creating a master curve M1, etc. In the example of this disclosure, a corrosion evaluation map 100 including the master curve M1, etc. is created. The specific contents of the corrosion evaluation map 100 and the method of creating it will be used to explain the specific contents of the master curve M1, etc. and the method of creating it.

[0016] Figure 2 is a schematic diagram of the corrosion evaluation map 100. The corrosion evaluation map 100 is output to an output device 510 (described later), such as a display device, for visual evaluation of the frequency distribution of corrosion levels. This allows the user to visually evaluate the corrosion level. In the example of Figure 2, the corrosion evaluation map 100 is a graph in a Cartesian coordinate system with wall thickness as one axis (horizontal axis in the illustrated example) and echo height ratio as the other axis (vertical axis in the illustrated example). Wall thickness is the thickness of the object to be inspected 1, such as a pipe, and is the length of the part over which the irradiated ultrasonic waves propagate in the shortest possible time. The corrosion evaluation map 100 includes the master curves M1, M2, M3, M4, M5 (master curves M1, M2, M3, M4, M5) used to evaluate the corrosion level.

[0017] In Figure 2, the patterns enclosed in squares represent patterns corresponding to the corrosion level and are the patterns used in the contour plot described later. The corrosion evaluation map 100 is a map recorded in association with the wall thickness of the object to be inspected, such as a pipe, and the echo height ratio in the received ultrasonic echo. The master curve M1, etc., is a function of wall thickness and echo height ratio. The echo height ratio will be explained with reference to Figure 3.

[0018] Figure 3 shows the received ultrasound echo and illustrates the echo height ratio. The horizontal axis represents the elapsed time from the start of irradiation, and the vertical axis represents the echo intensity (peak intensity). When ultrasound is irradiated onto object 1, multiple bottom echoes (waves), such as the first bottom echo, second bottom echo, and third bottom echo, are observed in the received ultrasound echo, as shown in Figure 3.

[0019] The first bottom echo is the ultrasonic waves that were incident on the object under inspection 1 and reflected off the inspection surface 1c (for example, the inner surface of the elbow pipe 1a described later). These waves are the waves that travel back and forth from the transducer 551 (described later) through the inside of the object under inspection 1 and return to the transducer 551. Furthermore, the ultrasonic waves that enter the inside of the object under inspection 1 are almost entirely reflected because the difference in acoustic impedance is large due to the outside being the atmosphere. However, the ultrasonic waves that reach the surface 1b are coated with a couplant described later, which has a relatively small difference in acoustic impedance with the outside. As a result, some of the ultrasonic waves propagate to the outside and reach the transducer 551 located outside the object under inspection 1. The peak of the first bottom echo is observed at time T1. The second bottom echo is the ultrasound that has been reflected again from the incident surface of the ultrasound (the contact surface of the transducer 551) and reflected again from the inspection surface 1c. Therefore, the second bottom echo is the wave that has traveled back to the transducer 551 after two round trips inside the object 1 being inspected. The peak of the second bottom echo is observed at time T2. The third bottom echo is the ultrasound that has been reflected again from the incident surface of the ultrasound (the contact surface of the transducer 551) and reflected again from the inspection surface 1c. Therefore, the third bottom echo is the wave that has traveled back to the transducer 551 after three round trips inside the object 1 being inspected. The peak of the third bottom echo is observed at time T3.

[0020] The echo height is the echo height at which the echo intensity is maximum for each echo (first bottom echo, second bottom echo, third bottom echo, etc.). The echo height ratio is the value obtained by dividing the echo heights of adjacent echoes; for example, it is the value obtained by dividing the echo height H2 of the second bottom echo observed after the first bottom echo observed by the echo height H1 of the first bottom echo (H2 / H1).

[0021] Returning to Figure 2, as described above, as corrosion progresses on the surface of the inspection surface 1c, the surface becomes more uneven. Therefore, as described above, the echo height ratio decreases. If the inspection surface 1c is, for example, the inner surface of the elbow pipe 1a, the wall thickness is, as described above, for example, the wall thickness of the elbow pipe 1a, and the shortest distance between the ultrasonic incident site on the outer surface of the elbow pipe 1a and the inspection surface 1c. Figure 2 illustrates several master curves M1 etc. (graphs, relationships, correlations). Master curves M1 etc. are empirical formulas that show that the echo height ratio decreases as the wall thickness increases.

[0022] In step S1 of the creation of Figure 1, a test member made of gray cast iron (not shown) from a different lot than the object under inspection 1 is used, and the wall thickness and echo height ratio are measured according to the actual level of corrosion to create a master curve M1, etc. A different lot means that the crucible in which the molten material was placed during casting is different, and the details are specified in JIS G 5501. Note that the term "lot" as used in this specification corresponds to the term "batch" as used in the JIS standard. It is not necessary to perform five corrosion experiments to create five master curves M1, etc. For example, corrosion experiments may be performed to obtain the least corroded (i.e., sound) master curve M1 and the most corroded master curve M5, and master curves M2, M3, and M4 may be placed between master curve M1 and master curve M5 at equal intervals, for example.

[0023] Master curves such as M1 are created, for example, by conducting corrosion experiments using test specimens with varying wall thicknesses (thickness of the test specimen) in a factory setting, and plotting the results according to the degree of corrosion. In other words, master curves such as M1 are created for each corrosion level of the test specimen. This allows for the evaluation of corrosion levels using a predetermined, unified index.

[0024] In Figure 2, depending on the wall thickness, for example, if the echo height ratio is greater than that of master curve M1, no problematic corrosion has occurred, and the inspection surface 1c can be evaluated as sound. If the echo height ratio is between master curve M1 and master curve M2, the corrosion level can be evaluated as 1. If the echo height ratio is between master curve M2 and master curve M3, it can be evaluated as corrosion level 2, which is more advanced than corrosion level 1. If the echo height ratio is between master curve M3 and master curve M4, it can be evaluated as corrosion level 3, which is more advanced than corrosion level 2. If the echo height ratio is between master curve M4 and master curve M5, it can be evaluated as corrosion level 4, which is more advanced than corrosion level 3. If the echo height ratio is less than that of master curve M5, it can be evaluated as corrosion level 5, which is more advanced than corrosion level 4. Therefore, corrosion levels 1 to 5 are determined to the extent of the relationship with master curve M1, etc., including master curve M1, which is in a sound state for ultrasonic reflection.

[0025] The corrosion evaluation map 100 includes a soundness relationship, which is the relationship between the thickness and the echo height ratio when the inspection surface 1c (ultrasonic reflection surface) is in a sound state. The soundness relationship is the relationship between the thickness and the echo height ratio when the inspection surface 1c is evaluated as being in a sound state where it is not corroded, and is, for example, a function (correlation). By including such a relationship, the inspection accuracy can be improved by using the measurement results (sound velocity and echo height ratio) using the standard evaluation part 2 of the sound state and the said soundness relationship.

[0026] In the example in Figure 2, the healthy state relationship is represented by the master curve M1. That is, the master curve M1 is the result obtained by conducting experiments in advance, for example, in a factory, as described above, and is a function obtained by actually performing ultrasonic inspection on a surface that has been previously identified (confirmed) as healthy. Note that the master curves M1, etc., are all related to each other. For example, the master curve M2 can be considered as a graph in which the echo height ratio is smaller by a predetermined percentage than that of the master curve M1. Also, for example, the master curves M2, M3, and M4 may be graphs that equally divide the space between the master curve M1 and the master curve M5, as described above.

[0027] Returning to Figure 1, the reference surface transmission / reception step S2 is a step in which ultrasonic waves are irradiated onto the reference surface of the object to be inspected 1, which is made of gray cast iron, and ultrasonic echoes of the reference surface, which are reflected waves. The reference surface here is the joint surface 2d described later. Irradiation can be performed by irradiating ultrasonic waves onto the reference evaluation part 2 which has the reference surface. Specifically, irradiation is performed by using a transducer 551 to incident ultrasonic waves from the upper surface 2e of the flange 2a (an example of the reference evaluation part 2) facing the joint surface 2d. The ultrasonic echoes received by the transducer 551 have a shape that is generally as shown in Figure 3 above, although the echo height ratio and the time difference between adjacent ultrasonic echoes (difference between time T1 and time T2, etc.) differ.

[0028] Figure 4 is a magnified view of the vicinity of the reference evaluation area 2 and point 1f, which is the ultrasonic irradiation area, within the object to be inspected 1. Figure 5 is a magnified view of the reference evaluation area 2 of the object to be inspected 1, viewed from a different direction than in Figure 4. The object to be inspected 1 is a pipe such as an elbow pipe 1a (discharge elbow), a gray cast iron base, etc., but is not limited to these. In the illustrated example, the object to be inspected 1 is an elbow pipe 1a. Also, the reference evaluation area 2 is not limited to the flange 2a in the illustrated example. The reference evaluation area 2 can be any part that can be evaluated as not having corrosion that would affect the accuracy of the corrosion level evaluation. For example, it may be a measuring area pre-installed in the object to be inspected 1 for measuring (actual measurement) the sound velocity and echo height of the object to be inspected 1, a fastening part for suspending the object to be inspected 1, a rib, etc.

[0029] The object to be inspected 1 includes a reference evaluation area 2 for measuring (determining) the sound velocity and echo height ratio on the object to be inspected 1 itself, which has an inspection surface 1c. The reference evaluation area 2 is a part on which a person observing the object to be inspected 1 from the outside can measure the thickness of the ultrasonic surface. In addition, the joint surface 2d (an example of a reference surface) is a surface on which a person observing the object to be inspected 1 from the outside can measure the thickness of the part of the object to be inspected 1 that has the joint surface 2d (for example, the thickness of the flange 2a). By using such surfaces, when ultrasonic waves are irradiated onto the reference evaluation area 2, the actual characteristics of the object to be inspected 1 (sound velocity and echo height ratio) can be determined from the obtained ultrasonic echoes (first bottom surface echo and second bottom surface echo, etc.).

[0030] In the example of this disclosure, the reference evaluation part 2 is a flange 2a formed integrally with the elbow pipe 1a. Two opposing flanges 2a are joined together by bolts 2b and nuts 2c. The joint surfaces 2d of the flanges 2a are usually smooth, for example by machining, to eliminate gaps. Also, when joined, moisture, air, etc. are unlikely to come into contact with the joint surface 2d, and the joint surface 2d is not corroded and can be considered sound. The bolts 2b are inserted into insertion openings (not shown) formed in the flange 2a. The bolts 2b and nuts 2c are arranged continuously at predetermined intervals in the circumferential direction of the flange 2a. The two flanges 2a can be seen from the outside by a person, for example, a worker. Therefore, the thickness of the flanges 2a (length in the direction of bolt insertion and length in the direction of ultrasonic propagation) can be measured from the outside.

[0031] Figure 6 is an enlarged view of section A in Figure 4. In the flange 2a, bolts 2b and nuts 2c are arranged circumferentially at predetermined intervals, and recesses 3 are formed between adjacent bolts 2b and nuts 2c. The upper surface 2e of the flange 2a (the side facing the joint surface 2d, the opposite side of the joint surface 2d) and the joint surface 2d may not be parallel. Therefore, the bottom surface 3a of the recess 3 is a smooth surface and is parallel to the joint surface 2d. The recess 3 can be formed on the upper surface 2e, for example, by machining, creating a cylindrical recess.

[0032] A probe 551 is positioned in the recess 3 to inject ultrasonic waves into the interior of the flange 2a, i.e., into the object to be inspected 1. Therefore, by pressing the probe 551 against the bottom surface 3a of the recess 3, ultrasonic waves are injected into the flange 2a. A paste (e.g., glycerin paste) may be placed between the probe 551 and the bottom surface 3a (the injection site of the ultrasonic waves) to fill the gap. The ultrasonic waves injected into the interior of the flange 2a from the bottom surface 3a are reflected at the joint surface 2d between the flanges 2a, and the probe 551 receives the reflected waves from the joint surface 2d. As described above, since the flange 2a is visible from the outside, the distance between the bottom surface 3a of the recess 3 and the joint surface 2d can be measured using a measuring device such as a caliper gauge. Therefore, the speed of sound of the ultrasound in the object being inspected 1 can be calculated (determined) from the time from when the ultrasound is incident until it is received (or the time difference between the first bottom surface echo and the second bottom surface echo), and the distance between the bottom surface 3a and the joint surface 2d.

[0033] The upper surface 2e and the joint surface 2d may be parallel. In this case, the probe 551 may be pressed (brought into contact) with the upper surface 2e without the recess 3.

[0034] Figure 7 shows the probe 551 in contact with the bottom surface 3a of the recess 3. As described above, the top surface 2e of the flange 2a and the joint surface 2d are not parallel, and the thickness of the flange 2a varies depending on the distance from the inspection surface 1c. On the other hand, the bottom surface 3a and the joint surface 2d are parallel. Therefore, the ultrasonic wave UL irradiated from the probe 551 onto the joint surface 2s propagates through the inside of the flange 2a from the bottom surface 3a to the joint surface 2d in the shortest possible distance. The ultrasonic wave UL reflected from the joint surface 2d also propagates through the inside of the flange 2a in the shortest possible distance and reaches the probe 551. The "thickness" of the part to which the probe 551 is applied is the thickness of the part to which the ultrasonic wave propagates in the shortest distance. Therefore, in the example of Figure 7, the thickness of the part to which the probe 551 is applied is the distance between the bottom surface 3a and the joint surface 2d.

[0035] For example, when casting using a mold, the flange 2a may be given a slope to make it easier to remove the flange 2a from the mold. In this case, the top surface 2e and the joint surface 2d are not parallel. Therefore, depending on how the transducer 551 is applied, the ultrasonic waves may not propagate in the shortest possible path inside the flange 2a, and variations in the direction of ultrasonic wave propagation may occur. These variations can change the shape of the observed first bottom surface echo and second bottom surface echo, particularly the time difference between the first and second bottom surface echoes, and thus the speed of sound may change. Also, the reflection pattern of the ultrasonic waves reflected at the joint surface 2d may differ, for example, the amount of scattered ultrasonic waves may change, and thus the height of the ultrasonic echo may also change. Therefore, the echo height ratio may also change. For this reason, depending on how the transducer 551 is applied, the speed of sound and the echo height ratio may change.

[0036] Therefore, in the example of this disclosure, in the reference surface transmission / reception step S2, the transducer 551 that transmits and receives ultrasonic waves is brought into contact with the bottom surface 3a parallel to the joint surface 2d (an example of a reference surface), and ultrasonic waves are transmitted and received, thereby irradiating the joint surface 2d via the bottom surface 3a. The bottom surface 3a is the surface that forms the bottom of the depression 3 formed on the upper surface 2e, which is a part that is not parallel to the joint surface 2d that forms the surface 1b of the object to be inspected 1, as described above. In this way, ultrasonic waves can be propagated in the shortest possible distance inside the object to be inspected 1, and since anyone can transmit and receive ultrasonic waves in the same direction regardless of who performs the inspection, the calculation accuracy of the calculated sound velocity and echo height ratio can be improved.

[0037] The position and depth of the recess 3 are not particularly limited. However, it is preferable that the recess 3 is formed such that the distance L1 (measured distance) between the bottom surface 3a and the joint surface 2d is approximately the same as the wall thickness L2 of the object to be inspected 1 in the portion forming the inspection surface 1c (e.g., the inner surface of an elbow pipe). For example, the wall thickness L2 (e.g., the wall thickness of an elbow pipe 1a) can be determined from design drawings, specifications, etc. It is preferable that the position and depth of the recess 3 be designed so that the distance L1 is approximately the same as the design value, specification value, etc. "Approximately the same" here means, for example, within ±10% of the design value, specification value, etc.

[0038] Figure 8 shows a different embodiment in which the transducer 551 is in contact with the upper surface 2e of the flange 2a. In Figure 8, the propagation axis U, which indicates the propagation direction of the ultrasonic waves transmitted and received by the transducer 551, is shown as a dashed line. In Figure 8, for illustrative purposes, the transducer 551 is shown tilted more as it moves away from the surface 1b, but in reality, the direction of the propagation axis U can be changed by changing the direction of the force applied while the transducer 551 is in close contact with the surface 1b. This point is similar in Figure 9, which will be described later.

[0039] When the upper surface 2e and the joint surface 2d are not parallel, it is preferable that a recess 3 is formed as shown in Figure 7. However, in the case of an existing inspection object 1, such as an inspection object 1 installed without a recess 3, a recess 3 may not be formed. In such cases, the configuration shown in Figure 8 is preferable. Furthermore, in the inspection surface transmission and reception step S5 described later, when the probe 551 is pressed against a surface 1b that is not parallel to the inspection surface 1c, or a surface 1b that has curvature, the configuration shown in Figure 8 is also preferable.

[0040] In the example shown in Figure 8, during the reference surface transmission / reception step S2 and the inspection surface transmission / reception step S5 described later, the ultrasonic transducer 551 is pressed against the surface 1b of the object to be inspected 1. Specifically, the transducer 551 is pressed against the upper surface 2e of the flange 2a, which is part of the object to be inspected 1. At this time, a gap-filling paste (for example, a couplant such as glycerin paste) is placed between the transducer 551 and the upper surface 2e (surface 1b). This makes it easier for the ultrasonic waves emitted from the transducer 551 to enter the object to be inspected 1. At the same time, the reflected ultrasonic waves are made easier for the transducer 551 to receive by emitting them out of the object to be inspected 1.

[0041] As described above, the upper surface 2e (the surface opposite to the bonding surface 2d) and the bonding surface 2d may not be parallel. Therefore, in the example of this disclosure, with the probe 551 pressed against the surface 1b, ultrasonic waves are transmitted and received while changing at least one of the incident conditions: the direction relative to the normal L of the surface 1b, or the angle θ relative to the direction of the normal L of the surface 1b. This allows the ultrasonic inspection to be performed while "searching" for the appropriate direction. By transmitting and receiving in this manner, ultrasonic echoes corresponding to the incident conditions at that time are observed. Of the obtained ultrasonic echoes, the ultrasonic echo that is considered most appropriate, i.e., that reflects the true sound velocity and echo height ratio, can be used to determine the sound velocity and echo height ratio. The angle θ is the angle between the normal L and the propagation axis U.

[0042] For example, by tilting the transducer 551 in the same direction but changing the angle θ, ultrasonic echoes corresponding to each angle θ can be observed. Similarly, by tilting the transducer 551 in different directions while keeping the angle θ the same, ultrasonic echoes multiplied by each direction can be observed. In the example shown in Figure 8, the transducer 551 is tilted at different angles θ in the left-right direction on the plane of Figure 8.

[0043] For example, under the incidence conditions (e.g., angle θ) where the time difference between adjacent ultrasonic echoes (e.g., the time difference between peaks) is shortest, it can be assumed that the ultrasound propagated along the shortest path. In this case, the portion corresponding to the shortest path is the thickness, as described above. Therefore, the incidence conditions in this case can be considered to reflect the true sound velocity and echo height ratio. The incidence conditions to be adopted should be determined appropriately according to the accuracy required by the user, but the reference surface transmission / reception step S2 and the inspection surface transmission / reception step S5 are performed under the same incidence conditions.

[0044] In another embodiment, in the reference determination step S3 and the inspection step S6, the sound velocity and echo height ratio are determined by estimating the plausible sound velocity and echo height ratio for each of the sound velocity and echo height ratios determined based on each ultrasonic echo acquired while varying the incident conditions, using statistical methods. In this way, the true sound velocity and echo height ratio can be estimated.

[0045] Statistical methods, though not limited to this, include extreme value analysis. Specifically, by estimating the value that minimizes the time difference between adjacent echoes from waveform information (first bottom echo and second bottom echo) obtained by changing the incidence conditions, and then estimating the sound velocity and echo height ratio based on the estimated time difference, these can be used as the true sound velocity and echo height ratio.

[0046] Figure 9 is a diagram illustrating how the transducer 551 is positioned when transmitting and receiving ultrasound in the reference plane transmission / reception step S2, and shows the transducer 551 viewed from above. In Figure 9, the transducer 551 is shown tilted at a predetermined angle θ on the lower side of the transducer in the plane of the paper. In the example shown in Figure 9, the transducer 551 is moved in a circular motion, for example by the user, while maintaining the angle θ with respect to the normal L (Figure 8) (i.e., at a constant angle θ). As a result, the ultrasound echo is observed while the direction of the propagation axis U is oriented in various directions. In this way, the ultrasound echo is observed while changing the incidence conditions in multiple directions with respect to the direction of the normal L.

[0047] In the example shown in Figure 9, the probe 551 is tilted and measured over its entire circumference, but it may also be measured over only a portion of the circumference. For example, the length may be, for example, 10% to 100%, preferably 30% to 100%, more preferably 50% to 100%, and particularly preferably 75% to 100% of the total circumferential length.

[0048] Furthermore, if the surface to which the probe 551 is applied is parallel to the joint surface 2d, such as the bottom surface 3a, it is not necessary to change the incidence conditions as shown in Figures 8 and 9. However, if it is not parallel, it is preferable to change the incidence conditions as shown in Figures 8 and 9 for inspection.

[0049] Returning to Figure 1, the reference determination step S3 is a step in which the sound velocity within the object to be inspected 1 and the reference surface echo height ratio are determined from the ultrasonic echo obtained in the reference surface transmission / reception step S2 and the thickness of the object to be inspected 1 in the portion forming the joint surface 2d. The reference surface echo height ratio is an echo height ratio that indicates the ultrasonic propagation characteristics within the object to be inspected 1, and is the echo height ratio of the joint surface 2d determined from the first bottom surface echo and the second bottom surface echo in the ultrasonic echo. As described above, the received first bottom surface echo and second bottom surface echo are, for example, roughly the echoes shown in Figure 3 above, although their echo height ratios etc. are different. Therefore, for the sake of simplicity, the reference determination step S3 will be explained using the ultrasonic echo used in the creation step S1.

[0050] In the received first ultrasonic echo, the time difference between the peak time T1 of the first bottom echo and the peak time T2 of the second bottom echo is the time required for the ultrasonic waves to propagate within the flange 2a. Therefore, the speed of sound of the ultrasonic waves inside the object under inspection 1 can be calculated from this time difference and the wall thickness (distance) of the flange 2a measured by visually inspecting the flange 2a from the outside. However, the time used to calculate the speed of sound does not have to be the time difference between the two peak times T1 and T2; for example, it may be the time difference between the rise time of the first bottom echo and the rise time of the second bottom echo. However, in this disclosure, the calculation of the speed of sound is performed using a unified method in either case.

[0051] The more specific method for calculating the speed of sound is as follows. As described above, the thickness of the object under inspection 1 at the joint surface 2d is measured. Furthermore, the thickness of the object under inspection 1 at the joint surface 2d, the time difference between the first bottom surface echo and the second bottom surface echo (for example, the time difference between time T1 and time T2), and the speed of sound are correlated. That is, the speed of sound can be calculated from the thickness and the time difference. Therefore, it can be calculated from the measured thickness and the time difference between time T1 and time T2 based on the observed ultrasonic echo.

[0052] Another calculation method is as follows: When using a transducer 551 that allows setting the sound velocity of the ultrasonic waves transmitted and received from the transducer 551, the ultrasonic waves may be transmitted and received while changing the sound velocity, and the sound velocity at which the thickness calculated from the received ultrasonic echo matches the measured thickness may be determined (set) as the sound velocity to be used for the object to be inspected 1.

[0053] Furthermore, using the method described in creation step S1 above, the reference plane echo height ratio (H2 / H1) of adjacent ultrasound echoes can be determined as an example of the echo height ratio.

[0054] The correction factor determination step S4 is a step in which the correction factor of the reference surface echo height ratio is determined so that the reference surface echo height ratio determined in the reference determination step S3 matches the representative echo height ratio. The representative echo height ratio is an example of an echo height ratio, and is the echo height ratio that indicates a healthy reflective surface at the same thickness as a reference thickness such as a predetermined master curve M1. The representative echo height ratio, along with the thickness, is a variable that constitutes the master curve M1. In other words, the master curve M1 is a function consisting of thickness (for example, horizontal axis) and representative echo height ratio (vertical axis), as explained with reference to Figure 2 above.

[0055] The correction magnification determination step S4 allows the ultrasonic propagation characteristics (echo height ratio) in the actual object being inspected 1 to be matched with the ultrasonic propagation characteristics (echo height ratio) used when creating the corrosion evaluation map 100. This enables highly accurate evaluation of the corrosion level using existing master curves such as M1.

[0056] In the correction magnification determination step S4, "match" does not need to be a strict match. That is, a slight deviation is acceptable as long as it does not affect the evaluation result of the corrosion level. Therefore, in the correction magnification determination step S4, the correction magnification should be determined so that the reference plane echo height ratio determined in the reference determination step S3 falls within a predetermined range based on the representative echo height ratio of the ultrasonic echo when the master curve M1 (healthy state relationship) was created. The specific numerical range of this predetermined range is not particularly limited, but for example, it can be set to within ±10% of the representative echo height ratio, centered on that representative echo height ratio.

[0057] While correcting for a strict match (perfect equality) significantly improves accuracy, it also drastically increases the computational effort. Therefore, the computational effort can be reduced by, for example, ensuring that the value falls within a predetermined range that does not affect the corrosion level evaluation results.

[0058] As described above, since the joint surface 2d is not corroded, the joint surface 2d (ultrasonic reflection surface) can be said to be in a sound condition, similar to the master curve M1. In other words, the ultrasonic propagation conditions (echo height ratio) used for the master curve M1 and the ultrasonic propagation conditions obtained using the sound joint surface 2d at the flange 2a (reference evaluation area 2) of the object under inspection 1 can be evaluated as being basically the same. Therefore, as described in this disclosure, a correction factor (correction value) is determined so that the reference surface echo height ratio determined in the reference determination step S3 matches the representative echo height ratio when the master curve M1 (corrosion evaluation map 100) was defined. For example, suppose the reference surface echo height ratio is R1 and the representative echo height ratio is R2, and there is a relationship R2 = 1.1 × R1. In this case, if R1 is to be matched to R2, the correction factor for R1 can be calculated to be 1.1.

[0059] In another embodiment, the correction factor can be determined using a master curve M1 as follows. In the reference determination step S3, the thickness of the object to be inspected 1 (flange 2a) that forms the joint surface 2d, which is the reference surface, is determined. From the determined thickness and the master curve M1, which is known to be sound, the echo height ratio (representative echo height ratio; R2 above) can be determined. Then, the correction factor can be determined by comparing the representative echo height ratio determined using the master curve M1 with the reference surface echo height ratio (R1 above) determined in the reference determination step S3.

[0060] Step S5, which involves transmitting and receiving an inspection surface, is a step in which ultrasonic waves are irradiated from the outer surface 1d of the object to be inspected 1 toward the inspection surface 1c and the ultrasonic echo of the inspection surface 1c, which is the reflected wave. The inspection surface 1c is a surface provided on the object to be inspected 1 (the surface 1b of the object to be inspected 1) that is not visible from the outside of the object to be inspected 1 when it is installed. In the example of this disclosure, the inspection surface 1c is, for example, the inner surface of an elbow pipe 1a (the surface that comes into contact with the fluid flowing inside the elbow pipe 1a).

[0061] On the outer surface 1d of the object to be inspected 1, facing the inspection surface 1c, for example, probes 551 are pressed against each of several locations, and ultrasonic waves are transmitted and received at each location. Between the probes 551 and the outer surface 1d (the site where the ultrasonic waves enter; surface 1b), for example, a gap-filling paste (for example, a couplant such as glycerin paste) is placed, as described above. Through transmission and reception, the ultrasonic waves transmitted from each location travel to the inspection surface 1c, for example, in the shortest possible direction, and are reflected by the inspection surface 1c. The reflected waves are received by the probes 551. In this way, the distribution of corrosion levels can be evaluated over a wide area of ​​the inspection surface 1c.

[0062] Figure 10 is an enlarged view of part B in Figure 4. Points 1f are displayed on the outer surface 1d of the object to be inspected 1, for example, at predetermined intervals. The display can be performed, for example, by attaching a transparent film with points 1f printed on it to the outer surface 1d. When using a film, it is preferable to place the above-mentioned couplants between the film and the object to be inspected 1, and between the film and the transducer 551. Multiple points 1f are displayed along with numbers indicating the position of point 1f. Point 1f is the point to which the transducer 551 is pressed, and is the incident site (irradiation site) of the ultrasound. Therefore, point 1f can be called a measurement point. By pressing the transducer 551 against each point 1f and incident ultrasound, the inspection surface 1c (inner surface, back surface) which is, so to speak, on the back side of the outer surface 1d can be ultrasonically inspected.

[0063] In the inspection surface transmission / reception step S5, ultrasound can be transmitted and received in the same manner as in the reference surface transmission / reception step S2. Therefore, the matters described in the reference surface transmission / reception step S2 can also be applied to the inspection surface transmission / reception step S5. When using a transducer 551 that allows setting the sound velocity of the ultrasound transmitted and received from the transducer 551, ultrasound with the sound velocity set as described above (the sound velocity used for the object under inspection 1) is transmitted and received. As a result, ultrasound echoes including the first bottom echo and the second bottom echo are observed.

[0064] Even if there are differences in the degree of corrosion (i.e., corrosion level), if the inspection surface 1c is corroded, the distance between the outer surface 1d and the inspection surface 1c is not constant due to the irregularities of the inspection surface 1c. Also, depending on the object to be inspected 1, the actual dimensions (e.g., the wall thickness of the elbow pipe 1a) may differ from the dimensions on the design drawing. Therefore, the distance between the outer surface 1d and the inspection surface 1c is unknown at the time of the inspection surface transmission / reception step S5. However, the sound velocity and echo height ratio at the object to be inspected 1 when transmitting and receiving ultrasonic waves in the inspection surface transmission / reception step S5 have already been determined in the above-mentioned standard determination step S3, which was measured on a flange 2a made of cast iron from the same lot. Therefore, using the sound velocity determined in the above-mentioned standard determination step S3, the distance between the outer surface 1d and the inspection surface 1c and the echo height ratio are determined in the following inspection step S6.

[0065] Figure 11 is a diagram illustrating how the probe 551 is applied when transmitting and receiving ultrasonic waves in the inspection surface transmission / reception step S5, and is a view of the object to be inspected 1 from an oblique direction. In Figure 11 and Figure 12 described later, some components such as bolts 2b and nuts 2c are not shown. When ultrasonic waves are irradiated onto the above-mentioned reference evaluation area 2 (flange 2a), the probe 551 is pressed against, for example, the bottom surface 3a and top surface 2e of the recess 3, which are smooth surfaces (flat surfaces). However, in the case of elbow piping, etc., where the outer surface 1d is a curved surface (a surface with curvature; a surface that is curved in three dimensions), it is difficult to press against the surface because the surface to be pressed is curved. Therefore, as explained with reference to Figures 8 and 9 above, it is preferable to tilt the probe 551 in multiple directions to transmit and receive ultrasonic waves in the inspection surface transmission / reception step S5.

[0066] In the example shown in Figure 11, the propagation axis U (not shown in Figure 11) of the transducer 551 is tilted in a total of four directions: downward, upward, left, and right, with respect to, for example, the normal L (not shown in Figure 11) to the curved surface being pressed. That is, the transducer 551 is swiveled in a cross shape. As a result, even if it is not possible to consciously orient the propagation axis U in the direction that results in the shortest distance between the outer surface 1d and the inspection surface 1c, by orienting it in multiple directions, the direction of extension of the propagation axis U can be directed in the direction that results in the shortest distance. Therefore, an appropriate wall thickness and echo height ratio can be determined.

[0067] Figure 12 is a diagram illustrating how the transducer 551 is positioned when transmitting and receiving ultrasound in the inspection surface transmission / reception step S5 in another embodiment, and is a view of the object to be inspected 1 from an oblique direction. In order to estimate the true thickness and echo height ratio, it is preferable to have a large amount of data on the thickness and echo height ratio determined by changing the irradiation conditions. Therefore, in the example of Figure 12, the propagation axis U (not shown in Figure 11) is tilted in a total of eight locations, in addition to the downward, upward, left, and right directions shown in Figure 10, as well as the left-downward, left-upper, right-downward, and right-upper directions. That is, the transducer 551 is generally swung in all directions. This increases the amount of data acquired (ultrasonic echoes including the first bottom surface echo and the second bottom surface echo), and improves the accuracy of estimating the thickness and echo height ratio.

[0068] The direction of the oscillating operation is not limited to the directions shown in Figures 11 and 12 above. For example, using the position where the probe 551 was first applied as a reference, the oscillating operation may be performed in multiple directions, such as oscillating upwards, returning to the reference position, and then oscillating downwards and returning to the reference position.

[0069] Multiple measurement data points for each point 1f obtained by the methods shown in Figures 11 and 12 are processed, for example, by the statistical method described above. This determines the sound velocity and echo height ratio for each point 1f.

[0070] Returning to Figure 1, inspection step S6 is a step in which the thickness of the object to be inspected in the portion forming the inspection surface 1c is determined from the time difference between the first bottom surface echo and the second bottom surface echo of the ultrasonic echo of the inspection surface 1c obtained in inspection surface transmission / reception step S5, and the sound velocity determined in reference determination step S3. The time difference is the time it takes for the ultrasonic waves to travel back and forth once within the object to be inspected 1. Therefore, by multiplying the time difference by half and the sound velocity, the thickness of, for example, the elbow pipe 1a can be determined. The thickness is, for example, the propagation distance of the ultrasonic waves from point 1f, which is the irradiation site of the ultrasonic waves, to the inspection surface 1c.

[0071] In conjunction with this, inspection step S6 is a step in determining the inspection surface echo height ratio, which is the echo height ratio of the inspection surface 1c determined from the first bottom surface echo and the second bottom surface echo obtained in inspection surface transmission / reception step S5. The echo height ratio can be determined in the same manner as described in the criterion determination step S3 above. That is, the echo height ratio can be determined by calculating the ratio of the heights of adjacent first bottom surface echoes and second bottom surface echoes in the ultrasonic echoes observed in inspection surface transmission / reception step S5.

[0072] The correction step S7 is a step in which the inspection surface echo height ratio determined in the inspection step S6 is corrected by the correction magnification determined in the correction magnification determination step S4 to determine the corrected echo height ratio. Specifically, the corrected echo height ratio can be determined by multiplying the echo height ratio determined in the inspection step S6 by the correction magnification determined in the correction magnification determination step S4.

[0073] The correction factor is used to match the ultrasonic propagation characteristics in the actual object being inspected 1 with the ultrasonic propagation characteristics used when creating the corrosion evaluation map 100. By multiplying by the correction factor, the corrosion level can be evaluated from the actual echo height ratio determined in inspection step S6 using a predetermined, uniform master curve M1 or the like.

[0074] Evaluation step S8 is a step in which the corrosion level of the inspection surface 1c is evaluated by determining the corrosion level using a master curve M1, etc., based on the wall thickness determined in inspection step S6 and the corrected echo height ratio determined in correction step S7. This evaluates the corrosion level of the inspection surface 1c. Specifically, the determination method is such that, for example, the corrosion level can be determined by calculation, for example, based on the position of a predetermined master curve M1, etc., and the position of the corrected echo height ratio in the wall thickness of the part forming the inspection surface 1c.

[0075] Figure 13 shows the thickness and corrected echo height ratio determined by ultrasonic irradiation of the inspection surface 1c plotted on the corrosion evaluation map 100. As described above, the corrosion level can be determined by calculation, for example. However, by plotting the echo height ratio (corrected echo height ratio) on the corrosion evaluation map 100 shown in Figure 2 above, and outputting the resulting corrosion evaluation map 100 to an output device 510 such as a display device, the user can visually grasp the corrosion level. It would be even easier to understand if the image 101 described later were also displayed in real time. Furthermore, the output of the resulting corrosion evaluation map 100 may be performed after each inspection and plotting, or it may be output all at once after all inspections and plotting.

[0076] In Figure 13, the corrected echo height ratio is plotted as white circles on the vertical axis (echo height ratio) according to the wall thickness on the horizontal axis. The plot is performed for each point 1f as shown in Figure 10 above. Therefore, in this disclosure, where measurements were taken for 100 points 1f, there are 100 plots, and the measurement position corresponds to the plot.

[0077] For example, if calculations show that the inspection surface 1c irradiated with ultrasound through point 1f corresponding to plot P is not corroded and is evaluated as sound, then plot P lies in a region above the master curve M1, which indicates the sound state relationship. This region is a region that can be evaluated as sound. On the other hand, if calculations show that the inspection surface 1c irradiated with ultrasound through point 1f corresponding to plot Q is evaluated as significantly corroded, then plot Q lies in a region below the master curve M5, which indicates the most advanced corrosion. This region is the corrosion level 5 region, which can be evaluated as the most advanced corrosion.

[0078] Returning to Figure 1, the imaging step S9 is a step to create an image 101 that associates the corrosion level evaluated in the evaluation step S8 with the inspection surface 1c. Image 101 is an image obtained by imaging each measurement site (the position of the inspection surface 1c corresponding to point 1f) of the inspection surface 1c. At least one image (for example, one image) can be obtained. Image 101 is, for example, a monochrome or color contour map.

[0079] Figure 14 is a contour map of the inspection surface 1c, where each measurement area is imaged to form a single image 101. In image 101, the intersection points of a straight line extending vertically and a straight line extending horizontally correspond to the irradiation area (inspection area) on the inspection surface 1c when ultrasound is irradiated from point 1f. Figure 14 also shows parts 1p and 1q of the inspection surface 1c corresponding to plots P and Q explained with reference to Figure 13.

[0080] The generated contour map is output to, for example, an output device 510 (described later). The output device 510 is, for example, a monitor, display, server, printer, tablet, etc. This makes it easier for the user to visually grasp the state of corrosion (corrosion level) of the inspection surface 1c.

[0081] The corrosion evaluation method of this disclosure has been described above. The corrosion evaluation method of this disclosure is performed for each object to be inspected (for each lot). If the lot is the same but corrosion evaluation is performed on different parts of the same object to be inspected, or if the object to be inspected is different, the corrosion evaluation can be performed using the sound velocity, reference surface echo height ratio, and correction factor that have already been acquired. However, if a corrosion evaluation is performed for the second time or later after a corrosion evaluation has already been performed, it is preferable to reacquire the sound velocity, reference surface echo height ratio, and correction factor, as changes in sound velocity, etc., due to aging and temperature may occur.

[0082] Figure 15 is a block diagram of the corrosion evaluation system 500 of this disclosure. As described above, the corrosion evaluation system 500 can perform the corrosion evaluation method of this disclosure. Therefore, the corrosion evaluation system 500 is a device that evaluates the corrosion status of an inspection surface 1c that is not visible from the outside of an inspection object 1 made of gray cast iron, using the sound velocity specific to the inspection object 1 and the echo height ratio of the ultrasonic echo. The matters described in the above corrosion evaluation method can be similarly applied to the corrosion evaluation system 500 described below.

[0083] The corrosion evaluation system 500 comprises a standard determination unit 501, a correction magnification determination unit 502, an inspection unit 503, a correction unit 504, an evaluation unit 505, an imaging unit 506, and a storage unit 507. Although not shown in the figures, the corrosion evaluation system 500 may also include a creation unit that performs the creation step S1 described above. Furthermore, at least some of the functions of the functional units constituting the corrosion evaluation system 500 may be configured separately from the remaining functional units. Specifically, for example, the storage unit 507 (e.g., master curve M1) may be located in a server (not shown) connected to the corrosion evaluation system 500, for example, which is located at a remote location relative to the corrosion evaluation system 500 installed at the inspection site.

[0084] The reference determination unit 501 is a functional unit that determines the sound velocity within the object to be inspected 1 and the reference surface echo height ratio from the ultrasonic echo and the wall thickness. The ultrasonic echo is the ultrasonic echo of the joint surface 2d, which is the reflected wave obtained by irradiating the joint surface 2d (an example of a reference surface) of the object to be inspected 1 made of gray cast iron with ultrasonic waves. The wall thickness is the thickness of the flange 2a (part of the object to be inspected 1) that forms the joint surface 2d. The reference surface echo height ratio is the echo height ratio that indicates the ultrasonic propagation characteristics within the object to be inspected 1, and is the echo height ratio of the joint surface 2d determined from the first bottom surface echo and the second bottom surface echo in the ultrasonic echo.

[0085] The reference determination unit 501 can, for example, execute the reference determination step S3 described above. The ultrasonic echo may be acquired, for example, by the user holding the transducer 551 and applying it to the surface 1b (bottom surface 3a, top surface 2e, etc.), or it may be acquired automatically by applying the transducer 551 to the surface 1b using an arbitrary actuator (not shown).

[0086] The correction magnification determination unit 502 is a functional unit that determines the correction magnification of the reference surface echo height ratio so that the reference surface echo height ratio determined by the reference determination unit 501 matches the representative echo height ratio. The representative echo height ratio is the echo height ratio that indicates a healthy state of the reflective surface at the same thickness as a reference thickness such as a predetermined master curve M1. The correction magnification determination unit 502 can, for example, execute the correction magnification determination step S4 described above.

[0087] The inspection unit 503 is a functional unit that determines the wall thickness from the time difference and the sound velocity determined by the reference determination unit 501, and also determines the inspection surface echo height ratio. The time difference is the time difference between the first bottom echo and the second bottom echo of the ultrasonic echo of the inspection surface 1c, which is the reflected wave obtained by irradiating ultrasonic waves from the outer surface 1d of the object to be inspected 1 toward the inspection surface 1c. The inspection surface 1c is a surface of the object to be inspected 1 that is subject to inspection for evaluation of the corrosion level, and is a surface that cannot be seen from the outside. The wall thickness is the thickness of the object to be inspected 1 in the portion that forms the inspection surface 1c. The inspection surface echo height ratio is the echo height ratio of the inspection surface 1c determined from the first bottom echo and the second bottom echo. The inspection unit 503 can, for example, perform the inspection step S6 described above.

[0088] The correction unit 504 is a functional unit that determines the corrected echo height ratio by correcting the inspection surface echo height ratio determined by the inspection unit 503 with the correction magnification determined by the correction magnification determination unit 502. The correction unit 504 can, for example, execute the correction step S7 described above.

[0089] The evaluation unit 505 is a functional unit that evaluates the corrosion level of the inspection surface 1c by determining the corrosion level using a master curve M1 or the like, based on the wall thickness determined by the inspection unit 503 and the corrected echo height ratio determined by the correction unit 504. The evaluation unit 505 can, for example, perform the evaluation step S8 described above.

[0090] The imaging unit 506 is a functional unit that creates an image 101 relating the corrosion level evaluated by the evaluation unit 505 with the inspection surface 1c. The imaging unit 506 can, for example, perform the imaging step S9 described above.

[0091] The memory unit 507 is a functional unit that pre-stores the master curve M1, etc. The memory unit 507 also stores information calculated by the corrosion evaluation system 500, information acquired by the corrosion evaluation system 500, etc.

[0092] Figure 16 is a block diagram showing the specific hardware configuration of the corrosion evaluation system 500 of this disclosure. The corrosion evaluation system 500 is a device that controls the operation, driving, etc., of the corrosion evaluation system 500, and executes at least a part of the corrosion evaluation method. The corrosion evaluation system 500 is configured to include, for example, a CPU (Central Processing Unit) 1001, RAM (Random Access Memory) 1002, ROM (Read Only Memory) 1003, I / F (Interface) 1004, bus 1005, etc. The CPU 1001, RAM 1002, ROM 1003, and I / F 1004 are connected, for example, via bus 1005. The corrosion evaluation system 500 is realized when a predetermined control program (for example, the corrosion evaluation method of this disclosure) stored in ROM 1003 is loaded into RAM 1002 and executed by CPU 1001. Signals and information are exchanged between the corrosion evaluation system 500 and various devices (probe 551, output device 510, server, PC, etc.) and external networks via the I / F 1004 in terms of hardware. [Explanation of symbols]

[0093] 1. Objects to be inspected 100 Corrosion Assessment Map 101 images 1a Elbow piping 1b surface 1c. Inspection surface (ultrasound reflective surface, inner surface) 1d external surface 1f point (the site of ultrasound irradiation; the entry point) 1p portion 1q part 2. Criteria for evaluation 2a Flange 2b Bolt 2c nut 2D bonding surface (reference evaluation surface; ultrasonic reflection surface) 2e Top side 3. Indentation 500 Corrosion Assessment System 501 Standard Determination Department 502 Correction magnification determination section 503 Inspection Department 504 Correction Unit 505 Evaluation Department 506 Image Processing Unit 507 Storage section 510 Output device 551 Probe L1 distance L2 wall thickness M1 Master Curve (Relationship to Healthy State) M2 Master Curve M3 Master Curve M4 Master Curve M5 Master Curve S1 Creation Steps S2 Reference plane transmission / reception step S3 Criteria Determination Step S4 Correction Magnification Determination Step S5 Inspection surface transmission / reception step S6 Inspection Step S7 Correction Step S8 Evaluation Steps S9 Imaging step

Claims

1. A reference surface transmission and reception step involves irradiating the reference surface of a gray cast iron object to be inspected with ultrasonic waves and receiving the ultrasonic echo of the reference surface, which is the reflected wave. A reference determination step in which the ultrasonic echo obtained in the reference surface transmission and reception step and the thickness of the object to be inspected in the portion forming the reference surface are used to determine the sound velocity within the object to be inspected and the reference surface echo height ratio, which is an echo height ratio indicating the ultrasonic propagation characteristics within the object to be inspected and is the echo height ratio of the reference surface determined from the first bottom surface echo and the second bottom surface echo in the ultrasonic echo, A correction factor determination step is to determine a correction factor for the reference surface echo height ratio so that the reference surface echo height ratio determined in the reference determination step matches the representative echo height ratio, which is the echo height ratio that indicates a healthy state of the reflective surface at the same thickness as the reference thickness of the predetermined master curve. A surface transmission and reception step involves irradiating ultrasonic waves from the outer surface of the object to be inspected toward an inspection surface provided on the object to be inspected that is not visible from the outside, and receiving the ultrasonic echo of the inspection surface, which is the reflected wave. An inspection step in which the thickness of the object to be inspected in the portion forming the inspection surface is determined from the time difference between the first bottom surface echo and the second bottom surface echo of the ultrasonic echo of the inspection surface obtained in the inspection surface transmission and reception step, and the sound velocity determined in the reference determination step, and an inspection surface echo height ratio, which is the echo height ratio of the inspection surface determined from the first bottom surface echo and the second bottom surface echo, A correction step to determine a corrected echo height ratio obtained by correcting the inspection surface echo height ratio determined in the inspection step using the correction magnification determined in the correction magnification determination step, The evaluation step includes determining the corrosion level of the inspection surface using the master curve based on the thickness determined in the inspection step and the corrected echo height ratio determined in the correction step, thereby evaluating the corrosion level of the inspection surface. A corrosion evaluation method characterized by the following.

2. A corrosion evaluation method according to claim 1, Furthermore, the evaluation step includes an imaging step to create an image that associates the corrosion level determined in the evaluation step with the inspection surface. A corrosion evaluation method characterized by the following.

3. A corrosion evaluation method according to claim 1, The aforementioned reference surface is a surface on which a person observing the object to be inspected from the outside can measure the thickness of the portion of the object to be inspected that includes the reference surface. A corrosion evaluation method characterized by the following.

4. A corrosion evaluation method according to claim 1, In the aforementioned reference surface transmission / reception step and the aforementioned inspection surface transmission / reception step, a transducer that transmits and receives ultrasonic waves is pressed against the surface of the object to be inspected, With the probe pressed against the surface, ultrasonic waves are transmitted and received while changing at least one of the incident conditions: the direction relative to the normal direction of the surface, or the angle relative to the normal direction of the surface. A corrosion evaluation method characterized by the following.

5. A corrosion evaluation method according to claim 4, Based on the ultrasonic echoes acquired while varying the incidence conditions, the sound velocity and echo height ratio are determined, and a statistical method is used to estimate the most likely sound velocity and echo height ratio for each of these values, thereby determining the sound velocity and echo height ratio. A corrosion evaluation method characterized by the following.

6. A corrosion evaluation method according to claim 1, In the reference surface transmission and reception step, a transducer that transmits and receives ultrasonic waves is brought into contact with the bottom surface of a depression formed in a portion of the surface of the object to be inspected that is not parallel to the reference surface, but is parallel to the reference surface, and ultrasonic waves are transmitted and received, thereby irradiating the reference surface via the bottom surface. A corrosion evaluation method characterized by the following.

7. A reference determination unit that determines the speed of sound within the object to be inspected and the reference surface echo height ratio, which is the echo height ratio of the reference surface determined from the first bottom surface echo and the second bottom surface echo in the ultrasonic echo, based on the ultrasonic echo of the reference surface, which is the ultrasonic propagation characteristics within the object to be inspected, which is the echo height ratio of the reference surface determined from the first bottom surface echo and the second bottom surface echo in the ultrasonic echo, A correction magnification determination unit determines a correction magnification for the reference surface echo height ratio so that the reference surface echo height ratio determined by the reference determination unit matches the representative echo height ratio, which is the echo height ratio that indicates a healthy state of the reflective surface at the same thickness as the reference thickness of the predetermined master curve. An inspection unit determines the thickness of the portion of the object to be inspected that forms the inspection surface, based on the time difference between a first bottom surface echo and a second bottom surface echo of the ultrasonic echo of the inspection surface, which is the reflected wave obtained by irradiating an inspection surface provided on the object to be inspected that is not visible from the outside of the object to be inspected with ultrasonic waves, and the sound velocity determined by the reference determination unit, and also determines the inspection surface echo height ratio, which is the echo height ratio of the inspection surface determined from the first bottom surface echo and the second bottom surface echo. A correction unit that determines a corrected echo height ratio obtained by correcting the inspection surface echo height ratio determined by the inspection unit using the correction magnification determined by the correction magnification determination unit, The system includes an evaluation unit that evaluates the corrosion level of the inspection surface by determining the corrosion level using the master curve based on the thickness determined by the inspection unit and the corrected echo height ratio determined by the correction unit. A corrosion evaluation system characterized by the following features.

Images