Creep Damage Detection Device and Creep Damage Detection Method

Abstract

To provide a creep damage detection device and a creep damage detection method capable of accurately evaluating creep damage in comparison with before.SOLUTION: A creep damage detection device includes: an ultrasonic probe; an ultrasonic flaw detector for driving the ultrasonic probe; and a signal processing device for signal-processing received ultrasonic signals. The creep damage detection device performs oblique angle flaw detection a plurality of times by tilting the ultrasonic probe at a first angle and a second angle different from the first angle with respect to an inspection target, extracts a defect indication position at the first angle and a defect indication position at the second angle with the signal processing device, and estimates the defect conditions of defect indications by comparing the signal levels of defect indication signals at a common position.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a creep damage detection device and a creep damage detection method.

Background Art

[0002] High Cr steels are widely used in actual operation as high-temperature and high-pressure piping materials in ultra-supercritical pressure (USC) thermal power plants with steam temperatures of 593°C or higher. The number of thermal power plants that have exceeded 30 years since the start of operation is increasing among those thermal power plants that employ these high Cr steels. In piping joints and the like that are exposed to high temperatures in such plants, creep damage may occur. It is important to ensure the safety of thermal power plants by detecting damage before pipe rupture and performing maintenance work such as replacement. For this reason, maintenance work such as planned replacement is carried out by evaluating the remaining life of pipes and the like based on the creep strength of high Cr steels investigated in advance and the management of actual operation time.

[0003] The method of replacing pipes after the elapse of a fixed period of time as described above requires replacement at a time obtained by multiplying the safety factor by the remaining life of the pipes. In the case of such maintenance, the actual usable period becomes short, which affects the power generation cost of thermal power plants. Therefore, there is a demand to use up the life of pipes in order to reduce the power generation cost.

[0004] Also, even if measures are taken by applying such a safety factor, damage may occur earlier than the calculated life due to variations in physical properties, and there is also a demand to know the accurate remaining life. In response to these demands, various methods for investigating the degree of damage or remaining life of piping joints have been proposed, including a method using ultrasonic waves (Patent Documents 1 and 2), a method of cutting out samples from the inspection target such as surface replicas for evaluation (Patent Documents 3 and 4), a method of measuring strain (Patent Documents 5 and 6), and many other methods.

[0005] For example, in Patent Document 1, the phased array ultrasonic testing method (PAUT) is used to obtain the height of the reflected echo, and by comparing this echo height with the corresponding data derived in advance, the number density of creep voids is obtained, and the creep damage amount is obtained from the number density of creep voids. If only creep voids can be reliably detected by PAUT, it is possible to accurately obtain the creep damage amount. However, if there are defects with higher echo heights, such as initial defects, the creep damage amount will be overestimated. To avoid such false detections, if there is information on the presence or absence of defects in the initial state before the operation of the thermal power plant, by taking the difference, it is possible to distinguish and detect only the damage caused by creep during operation. However, it is often the case that there is no inspection data in the initial state, and the inability to distinguish and detect creep damage and initial defects is an issue.

[0006] Also, in Patent Document 6, it is necessary to take a sample from the inspection object, the number of measurable times is limited, and although the local evaluation of the position where the sample is taken is accurate, it is also conceivable that it depends on the position where the sample is taken. As shown here, various proposed methods have their advantages and disadvantages, and it is considered that there is still no decisive method for evaluating creep damage.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0008] As described above, there has been a demand for the development of a creep damage detection device and a creep damage detection method that can accurately evaluate the creep damage of members exposed to high temperatures in thermal power plants and the like.

[0009] The present invention has been made in consideration of such conventional circumstances, and an object thereof is to provide a creep damage detection device and a creep damage detection method that can accurately evaluate creep damage as compared with the prior art.

Means for Solving the Problems

[0010] The creep damage detection device according to the embodiment includes an ultrasonic probe, an ultrasonic flaw detector for driving the ultrasonic probe, and a signal processing device for signal-processing the received ultrasonic signal, Perform multiple angle beam inspections on the inspection target at a first distance from the inspection target site and a second distance different from the first distance with the ultrasonic probe, and extract, with the signal processing device, the defect indication position at the first distance and the defect indication position at the second distance, perform calculations assuming that the defect indication signals at the common positions are spherical defects, and compare the change in the signal level of the extracted defect signals with the change in the signal level in the calculation result, characterized by estimating the defect state of the defect indication.

Effects of the Invention

[0011] According to the embodiment, it is possible to provide a creep damage detection device and a creep damage detection method that can accurately evaluate creep damage as compared with the prior art.

Brief Description of the Drawings

[0012]

Figure 1

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Figure 8

Mode for Carrying Out the Invention

[0013] Hereinafter, a creep damage detection device and a creep damage detection method according to an embodiment will be described with reference to the drawings.

[0014] In this embodiment, in particular, the above-described problem “There is often no inspection data in the initial state, and creep damage and initial defects cannot be distinguished and detected” can be solved. That is, in ultrasonic flaw detection, in order to distinguish between welding defects such as initial cracks and creep voids, ultrasonic flaw detection is performed under a plurality of flaw detection conditions, and by utilizing the difference in the reflectivity of ultrasonic waves due to the difference in the shape of creep voids and welding cracks, the signal level of the received signal varies depending on the flaw detection conditions. Creep voids are detected with high precision.

[0015] Hereinafter, the first embodiment will be described. In the first embodiment, the inspection target is the heat-affected zone of a welded joint. This inspection target may have initial defects in the welded metal part, and there may also be creep damage in the heat-affected zone of the weld. This embodiment relates to an ultrasonic flaw detection test that can accurately detect creep damage occurring in the heat-affected zone of the weld.

[0016] Figure 1(a) is a diagram showing an overview of the inspection being carried out in the first embodiment, and Figure 1(b) is a cross-sectional view taken along the A-A arrow in Figure 1(a) for explaining the flaw detection angle α. As shown in Figure 1, the creep damage detection device includes an ultrasonic probe 1, an ultrasonic flaw detector 2, a signal processing device 3, and a display device 10. Also, in Figure 1, 4 is the inspection object. The ultrasonic probe 1 is tilted by a first angle 102 with respect to the direction (y direction) of the weld line 4a of this inspection object 4 (in Figure 1, the first angle 102 is shown as 90 degrees). As shown in Figure 1(b), while obliquely flaw detecting the weld heat affected zone at the flaw detection angle α, the ultrasonic probe 1 is scanned in a direction parallel to the weld line 4a to investigate the presence or absence of significant defects.

[0017] Here, the flaw detection method at each single point without scanning is the so-called oblique angle flaw detection method. The flaw detection angle 104 (α, see Figure 3) is generally 30 to 70 degrees, and the distance from the ultrasonic incident point of the ultrasonic probe 1 to the weld heat affected zone is determined depending on the flaw detection angle 104 and the depth position of the region of interest of the inspection object.

[0018] The ultrasonic probe 1 transmits ultrasonic waves 101 by connecting to the ultrasonic flaw detector 2 and applying a pulsed voltage from the ultrasonic flaw detector 2. The ultrasonic waves 101 reflected by defects or the like are received by the ultrasonic probe 1 and transmitted to the ultrasonic flaw detector 2 as an electrical signal.

[0019] An example of the signal received by the ultrasonic probe 1 is shown in Figure 2. In Figure 2, the horizontal axis represents time and the vertical axis represents the ultrasonic signal level 105. After transmitting the ultrasonic waves 101, it is assumed that a reflected signal from a defect is obtained at time t1. In the ultrasonic flaw detector 2, the received electrical signal of the ultrasonic waves is transmitted to the signal processing device 3 as an analog-to-digital signal. In the signal processing device 3, the position of the defect, the ultrasonic signal level 105, etc. are stored as data from the ultrasonic signal. Also, the flaw detection result is displayed on the display device 10 as a defect indication. The position (X1, Y1, Z1) of the defect can be obtained by the following formula as shown in Figure 3 with reference to the ultrasonic incident point.

[0020] L1 = V × t1 / 2 L1: Propagation distance, V: Sound velocity of ultrasonic waves X1 = L1×sinα×cos(First Angle 102) Y1 = L1×sinα×sin(First Angle 102) Z1 = L1×cosα Also, let the ultrasonic signal level reflected by the defect be S1.

[0021] As shown in Figure 4, the defect is detected at the second angle 103 in the same way. The second angle 103 and the first angle 102 only differ in the rotation angle of the ultrasonic probe 1 (a scan generally called skew), but the method is the same. When detecting flaws at the second angle 103, the position (X2, Y2, Z2) of the defect can be obtained by the following formula based on the ultrasonic incident point.

[0022] L2 = V×t2 / 2 L2: Propagation distance, V: Sound speed of ultrasonic wave X2 = L2×sinα×cos(Second Angle 103) Y2 = L2×sinα×sin(Second Angle 103) Z2 = L2×cosα Also, let the ultrasonic signal level reflected by the defect be S2.

[0023] Here, a method for detecting the creep void 5 from the flaw detection results at the first angle 102 and the flaw detection results at the second angle 103 will be described with reference to Figure 5. As shown in Figures 1 and 4, it is assumed that there is one welding defect 6 each having a surface parallel to the creep void 5 and the weld line 4a in the inspection object 4. The first angle 102 is assumed to be incident perpendicular to the weld line 4a, and the second angle 103 is assumed to be incident at an angle not perpendicular to the weld line 4a.

[0024] As shown in FIG. 1, the ultrasonic wave 101 incident on the creep void 5 and the above-mentioned welding defect 6 at the first angle 102 (vertical) is reflected back in the incident direction. On the other hand, as shown in FIG. 4, the ultrasonic wave 101 incident on the creep void 5 at the second angle 103, like the first angle 102, is reflected back in the direction of incidence of the ultrasonic wave 101. However, the ultrasonic wave 101 incident on the welding defect 6 propagates in a direction different from the incident direction according to the principle of reflection, so the reflected wave cannot be received by the ultrasonic probe 1.

[0025] Therefore, in the flaw detection at the first angle 102, two defect indications (here, the reflected wave from the creep void 5: (X11, Y11, Z11) and the reflected wave from the welding defect 6 (X12, Y12, Z12)) are detected. In the flaw detection at the second angle 103, one defect indication (the reflected wave from the creep void (X21, Y21, Z21)) is detected.

[0026] Therefore, as shown in FIG. 5, first, flaw detection is performed at the first angle 102 (501), defect indications are extracted from this result (502), then flaw detection is performed at the second angle 103 (503), and defect indications are extracted from this result (504).

[0027] Next, in the signal processing device 3, first, the defect indication position (X11, Y11, Z11) obtained by flaw detection at the first angle 102 is compared with all the defect indication positions obtained by flaw detection at the second angle 103 (505). As a result of the comparison, if it can be determined that (X11, Y11, Z11) and (X21, Y21, Z21) are at the same or nearly the same position, then the signal levels S11 and S21 of the respective reflected waves (defect indication signals) are compared (506). On the other hand, if the result of the comparison determines that they are not at the same or nearly the same position, the process proceeds to the determination of the next indication (507).

[0028] As a result of the comparison between the signal levels S11 and S21 of the above-mentioned reflected waves, if it can be determined that the signal levels are the same or nearly the same, the detected indication is determined to be the creep void 5 (508). On the other hand, if the signal levels are different, it is determined to be another defect (509).

[0029] Also, regarding the comparison of the defect indication position and the signal level, it is conceivable to simply set a threshold for the deviation of each value and consider that they are the same if they are within the threshold. Since X11 and X21 are respectively based on the position of the ultrasonic probe 1, it is necessary to record and correct the scanning position of the ultrasonic probe 1. However, since it can be converted to the absolute coordinates on the inspection object 4 by simple calculation, it will not be described here.

[0030] Similarly, regarding the ultrasonic signal level, when the propagation distances are different, it shall be corrected according to the propagation distance. These corrections are made by installing the position of the ultrasonic probe 1 on the arc of the surface of the inspection object 4 centered on the defect detection target position (the position of the creep void 5) where a defect is assumed to occur as shown in FIG. 6, and making the ultrasonic wave 101 incident from these ultrasonic wave incident point groups 106, so that correction is not required. According to the first embodiment as described above, it is possible to distinguish and detect the creep void 5, the welding defect 6, etc.

[0031] (Second Embodiment) Next, the second embodiment will be described with reference to FIGS. 7 and 8. In FIG. 7, the parts corresponding to FIGS. 1 and 4 are denoted by the same reference numerals and redundant descriptions are omitted. In the first embodiment, the ultrasonic probe 1 is rotated at a plurality of angles on the surface of the inspection object 4 to perform flaw detection, and the flaw detection results under a plurality of conditions are obtained and compared to distinguish and detect the creep void 5 and the welding defect 6. In the second embodiment, instead of rotating the ultrasonic probe 1 on the surface of the inspection object 4, the ultrasonic probe 1 is arranged so as to be perpendicular to the weld line 4a which is the inspection object part, and at a plurality of positions where the distances from the weld line 4a are different, it scans in the direction perpendicular to the weld line 4a to change the distance from the inspection object area of the inspection object 4, thereby obtaining a plurality of flaw detection conditions and comparing the flaw detection results to distinguish and detect the creep void 5 and the welding defect 6.

[0032] That is, as shown in FIG. 8, first, flaw detection is performed at a first position 111 where the distance from the weld line 4a is a first distance (801), flaw indication extraction is performed from this result (802), then flaw detection is performed at a second position 112 where the distance from the weld line 4a is a second distance different from the first distance (803), and flaw indication extraction is performed from this result (804).

[0033] In the second embodiment, as an ultrasonic flaw detection method, an example in which a sector scan method using an array probe is applied is shown. When performing a sector scan at the first position, the flaw detection angle for obtaining the maximum signal level of the detected flaw indication is α1, the distance to the flaw indication is L1, and the ultrasonic signal level at that time is S1. Similarly, at the second position, the flaw detection angle for obtaining the maximum signal level of the detected flaw indication is α2, the distance to the flaw indication is L2, and the ultrasonic signal level at that time is S2.

[0034] Next, position comparison is performed based on the above results (805). If the positions are different, the process proceeds to the determination of the next instruction (806). If the positions are the same, the calculation of the signal level change is performed.

[0035] Here, assuming that the flaw indication is a spherical flaw, the reflection signal from the flaw is isotropic, and it is considered that the difference in ultrasonic signal level is only the attenuation depending on the propagation distance. Therefore, using the ultrasonic signal level S1 at the first position and the attenuation constant investigated in advance, the calculated value of the ultrasonic signal level at the second position is obtained by simulation and the simulation result is designated as S2' (807), and S2 and S2' are compared (808). A threshold is set for the deviation between the values of the flaws S2 and S2'. If the deviation is within the threshold, the detected indication is determined to be a spherical flaw, that is, a creep void 5 (809). On the other hand, if it exceeds the threshold, it is determined to be another flaw (810).

[0036] Here, an example of applying the sector scan method using array probes has been shown. However, it is also possible to apply multiple types of ultrasonic probes for angled inspection, and set the flaw detection angles of the ultrasonic probes that can obtain the maximum ultrasonic signal level at each inspection position as α1 and α2. Further, it is also possible to apply multiple types of ultrasonic probes for angled inspection, scan each probe in a direction perpendicular to the weld line at the flaw detection position, and set the distances to the flaw indication at the positions where the maximum ultrasonic signal level is obtained as L1 and L2. In addition, in the above embodiment, an example of arithmetic processing by simulation has been shown. However, an arithmetic operation for obtaining the intensity from the flaw detection angle may be used, or an arithmetic operation utilizing a database of angles and reflection intensities may also be used.

[0037] As described above, several embodiments of the present invention have been explained. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0038] 1... Ultrasonic probe, 2... Ultrasonic flaw detector, 3... Signal processing device, 4... Inspection object, 4a... Weld line, 5... Creep void, 6... Weld flaw, 10... Display device, 101... Ultrasonic wave, 102... First angle, 103... Second angle, 104... Flaw detection angle, 105... Ultrasonic signal level, 106... Ultrasonic wave incident point group, 111... First position, 112... Second position.

Claims

1. An ultrasonic probe, an ultrasonic flaw detector for driving the ultrasonic probe, and a signal processing device for signal-processing the received ultrasonic signal, performing multiple oblique-incidence flaw detections on the inspection target at a first distance and a second distance different from the first distance from the inspection target site to the ultrasonic probe, extracting, by the signal processing device, a defect indication position at the first distance and a defect indication position at the second distance, performing an operation assuming that the defect indication signals at the common positions are spherical defects, and comparing the change in the signal level of the extracted defect signals with the change in the signal level in the operation result to estimate the defect state of the defect indication, characterized in that it is a creep damage detection device.

2. Performing multiple oblique-incidence flaw detections on the inspection target at a first distance and a second distance different from the first distance from the inspection target site to the ultrasonic probe, extracting a defect indication position at the first distance and a defect indication position at the second distance, performing an operation assuming that the defect indication signals at the common positions are spherical defects, and comparing the change in the signal level of the extracted defect signals with the change in the signal level in the operation result to estimate the defect state of the defect indication, characterized in that it is a creep damage detection method.

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