A special test block for the detection of under-deposit reheating cracks and a method for manufacturing the same

Abstract

The present application relates to a kind of special test block for welding layer under reheating crack detection and its manufacturing method.The special test block includes base material and the surfacing layer covering its surface, and the thickness of base material is more than 2 times the thickness of surfacing layer;3 flat-bottomed holes are arranged along the width direction of test block on one side of surfacing layer, and 3 flat-bottomed holes are arranged on the same side and in the same direction of base material and surfacing layer opening;6 holes correspond to 1 / 4, 1 / 2, 3 / 4 surfacing layer thickness respectively, and are arranged in equal interval along the length direction of test block, and are sequentially arranged in thickness direction.The present application can simulate reheating crack tip diffraction, fully cover crack area, and improve the detection rate and detection accuracy of crack under surfacing layer.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing technology for nuclear power equipment, and in particular to a special test block for detecting reheat cracks under weld overlays and its manufacturing method. Background Technology

[0002] During manufacturing and long-term service, reheat cracks are highly susceptible to develop beneath the interface between the austenitic stainless steel weld overlay and the low-alloy steel base material in core nuclear-grade components such as reactor pressure vessels and steam generators of nuclear power units. These cracks are typical planar hazardous defects, characterized by their concealed initiation location, irregular propagation direction, and difficulty in detection. They directly threaten the operational safety of nuclear power units. Therefore, mandatory testing standards for nuclear island equipment explicitly require full-range, high-reliability ultrasonic testing of reheat cracks beneath the weld overlay.

[0003] The accuracy and reliability of ultrasonic testing depend entirely on the precision of the calibration test block's simulation of defect characteristics. Currently, the nuclear power industry commonly uses ASME standard-specified weld overlay test blocks for ultrasonic testing of weld overlays. These test blocks employ a hybrid reflector design of "flat-bottomed holes + long horizontal holes": one type consists of flat-bottomed holes distributed at different depths within the weld overlay, used for the detection and calibration of volumetric defects within the weld overlay; the other type consists of long horizontal holes distributed at different depths within the base material, used for the detection and calibration of defects in the base material and the bonding surface.

[0004] The existing ASME standard test blocks, by their very design, are fundamentally inadequate for detecting reheat cracks beneath the weld overlay, exhibiting the following fatal flaws: First, they cannot simulate the core acoustic characteristics of reheat cracks. As a planar defect, the core ultrasonic response of a reheat crack is a tip-diffraction echo. However, the existing test blocks have hemispherical ends with elongated horizontal holes, lacking a stable tip structure, and can only generate conventional reflected echoes, failing to produce the tip diffraction effect consistent with real reheat cracks. Furthermore, the conventional flat-bottomed holes are designed only for volumetric defects, failing to create a regular tip structure suitable for crack simulation. This results in severely inaccurate detection sensitivity settings, leading to extremely high false positive and false negative rates for reheat cracks, completely failing to meet the accuracy requirements for detecting cracks beneath the weld overlay. Second, there is no specific coverage design for reheat cracks. The reflector arrangement of the existing test blocks is not designed for the initiation patterns of reheat cracks beneath the weld overlay, failing to effectively cover the typical crack initiation and propagation area of ​​2mm-4mm below the fusion surface, creating a serious blind spot in detection calibration. Third, inconsistent calibration standards lead to significant systematic errors. Existing test blocks use a mix of reflectors with completely different acoustic properties—flat-bottomed holes and long horizontal holes—resulting in inconsistent calibration standards for cracks of different depths. This greatly amplifies the systematic errors in the test results, making it impossible to accurately quantify reheat cracks. Fourth, there are no dedicated test blocks specifically designed for reheat crack detection under weld overlays. Currently, no dedicated test blocks have been developed specifically for this purpose. On-site testing can only use ASME standard test blocks that are compatible with volumetric defects, failing to address the core issue of crack detection calibration failure and becoming a key technical bottleneck restricting the safety testing of nuclear-grade equipment. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention proposes a special test block for detecting reheat cracks under weld overlay and its manufacturing method, which can simulate the diffraction of reheat crack tips, fully cover the crack area, and improve the detection rate and accuracy of cracks under weld overlay.

[0006] Specifically, the present invention proposes a special test block for detecting reheat cracks under a weld overlay, which has the same structure as the weld overlay. The special test block includes a base material and a weld overlay covering the surface of the base material, wherein the thickness of the base material is greater than twice the thickness of the weld overlay. On one side of the weld overlay, three flat-bottomed holes are formed along the width direction of the special test block, including a first flat-bottomed hole, a second flat-bottomed hole, and a third flat-bottomed hole; on the same side of the base material and the opening of the weld overlay, three flat-bottomed holes are formed along the width direction of the special test block, including a fourth flat-bottomed hole, a fifth flat-bottomed hole, and a sixth flat-bottomed hole. The distance between the first flat-bottomed hole and the surface of the weld overlay is 1 / 4 of the weld overlay thickness; the distance between the second flat-bottomed hole and the surface of the weld overlay is 1 / 2 of the weld overlay thickness; the distance between the third flat-bottomed hole and the surface of the weld overlay is 3 / 4 of the weld overlay thickness; the fourth flat-bottomed hole is abutted against the bonding surface of the base material and the weld overlay; the distance between the fifth flat-bottomed hole and the bonding surface is a first preset value; and the distance between the sixth flat-bottomed hole and the bonding surface is a second preset value. The first to sixth flat-bottomed holes are arranged in parallel at equal intervals along the length of the special test block and are arranged sequentially along the thickness of the special test block.

[0007] According to one embodiment of the present invention, the first to sixth flat-bottomed holes are all cylindrical blind holes, and the bottom surface of each flat-bottomed hole is perpendicular to the central axis of the corresponding hole, and the hole wall intersects with the bottom surface to form an annular ridge.

[0008] According to one embodiment of the present invention, the distance between two adjacent flat-bottomed holes in the length direction of the special test block is 23mm to 27mm, the central axis of each hole is parallel to the detection surface of the special test block, and the central axes of each hole are parallel to each other.

[0009] According to one embodiment of the present invention, the diameter of each of the flat-bottomed holes ranges from 1 mm to 3 mm, and the minimum drilling depth is 38 mm.

[0010] According to one embodiment of the present invention, the inner wall roughness Ra of each of the flat-bottomed holes is ≤1.6μm, the hole diameter tolerance is ±0.025mm, the hole depth tolerance is ±0.1mm, and the parallelism between the hole axis and the test surface of the special test block is ≤0.05mm / m.

[0011] According to one embodiment of the present invention, the surface roughness Ra of the special test block is ≤3.2μm, the parallelism between the test surface and the bottom surface is ≤0.03mm, and the perpendicularity between adjacent side surfaces is ≤0.05mm.

[0012] According to one embodiment of the present invention, the special test block is a homogeneous composite structure that has undergone overall stress-relieving heat treatment.

[0013] The present invention also provides a method for manufacturing a special test block, the special test block being suitable for detecting reheat cracking under weld overlay, the manufacturing method comprising the following steps: S11. Select a metal material with the same material and heat treatment state as the base material of the nuclear grade equipment to be tested as the base material of the test block. The thickness of the base material after cutting is greater than twice the design thickness of the weld overlay layer to be simulated. S12, on one side of the base material, a weld overlay layer is formed by welding with welding materials, welding process and post-weld heat treatment process that are completely consistent with the nuclear grade equipment to be inspected. The forming thickness of the weld overlay layer is consistent with the design thickness of the weld overlay layer of the nuclear grade equipment to be inspected. S13, the test block blank after the welding is completed is subjected to overall stress relief heat treatment. After the heat treatment is completed, the test surface, corresponding bottom surface and each side surface of the test block are machined so that the external dimensions and geometric tolerances of the special test block meet the basic accuracy requirements of ASME standard test blocks. S14, on the side of the weld overlay layer of the special test block, a first flat-bottomed hole, a second flat-bottomed hole, and a third flat-bottomed hole are sequentially machined along the width direction of the special test block. On the same side of the base material and the weld overlay layer opening, a fourth flat-bottomed hole, a fifth flat-bottomed hole, and a sixth flat-bottomed hole are sequentially machined along the width direction of the special test block. The distance between the first flat-bottomed hole and the surface of the weld overlay layer is 1 / 4 of the weld overlay layer thickness; the distance between the second flat-bottomed hole and the surface of the weld overlay layer is 1 / 2 of the weld overlay layer thickness; the distance between the third flat-bottomed hole and the surface of the weld overlay layer is 3 / 4 of the weld overlay layer thickness; the fourth flat-bottomed hole is abutted against the fusion surface of the weld overlay layer and the base material; the distance between the fifth flat-bottomed hole and the fusion surface is a first preset value; and the distance between the sixth flat-bottomed hole and the fusion surface is a second preset value. The six flat-bottomed holes are evenly spaced along the length direction of the special test block. S15, Perform full-range ultrasonic testing on the processed special test block.

[0014] According to one embodiment of the present invention, each of the flat-bottomed holes is machined into a cylindrical blind hole using deep hole drilling technology. The bottom surface of the hole is perpendicular to the central axis of the corresponding hole, and the hole wall intersects with the bottom surface to form an annular ridge line for simulating the crack tip. The diameter tolerance of each flat-bottomed hole is controlled within ±0.025mm, the hole depth tolerance is controlled within ±0.1mm, the parallelism between the hole axis and the test surface of the test block is ≤0.05mm / m, and the roughness Ra of the inner wall of the hole is ≤1.6μm.

[0015] The present invention also provides another method for manufacturing a special test block, the special test block being suitable for detecting reheat cracking under weld overlay, the manufacturing method comprising the following steps: S21, Select an ASME standard test block with first to fourth transverse holes suitable for reheat crack detection under weld overlay. The standard test block includes a base material and a weld overlay covering the surface of the base material, and a fusion surface is formed between the base material and the weld overlay. S22, the ends of the first to fourth transverse holes on the standard test block are processed into the first to fourth flat-bottomed holes, so that the hole walls of the first to fourth flat-bottomed holes intersect with the bottom surface to form an annular ridge line for simulating the crack tip. S23, on the same side of the base material and the weld overlay opening, a fifth flat-bottomed hole and a sixth flat-bottomed hole are machined. The distance between the fifth flat-bottomed hole and the fusion surface is a first preset value, and the distance between the sixth flat-bottomed hole and the fusion surface is a second preset value. All flat-bottomed holes are arranged at equal intervals along the length of the special test block. S24, Perform full-range ultrasonic testing on the processed test block.

[0016] This invention provides a special test block for detecting reheat cracks under weld overlay and its manufacturing method. It adopts a fully flat-bottomed hole structure, accurately simulates the diffraction of the reheat crack tip, fully covers the crack area, and unifies the calibration benchmark, effectively improving the detection rate and accuracy of cracks under weld overlay.

[0017] It should be understood that the above general description and the following detailed description of the present invention are exemplary and illustrative, and are intended to provide further explanation of the present invention. Attached Figure Description

[0018] The accompanying drawings are included to provide further explanation of the invention; they are incorporated into and constitute a part of this application. The drawings illustrate embodiments of the invention and, together with this specification, serve to explain the principles of the invention. In the drawings: Figure 1 A schematic diagram of a special test block for detecting reheat cracks under a weld overlay is shown according to an embodiment of the present invention.

[0019] Figure 2 for Figure 1 The top-view perspective view of the special test block shown.

[0020] Figure 3 A flowchart illustrating a method for manufacturing a special test block according to an embodiment of the present invention is shown.

[0021] Figure 4 A flowchart illustrating a method for manufacturing a special test block according to an embodiment of the present invention is shown.

[0022] Figure 5 A schematic diagram of an ASME standard test block with transverse elongated holes, suitable for reheat crack detection under weld overlay, is shown according to an embodiment of the present invention.

[0023] Figure 6 for Figure 5 The top-view perspective view of the special test block shown. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0026] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0027] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this application. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0028] In the description of this application, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0029] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application. In addition, although the terminology used in this application is selected from commonly known and used terms, some terms mentioned in this application's specification may have been chosen by the applicant according to his or her judgment, and their detailed meanings are explained in the relevant sections of this description. Moreover, this application should be understood not only through the actual terms used, but also through the meaning implied by each term.

[0030] Figure 1 A schematic diagram of a special test block for detecting reheat cracks under a weld overlay is shown according to an embodiment of the present invention. Figure 2 for Figure 1 The figure shows a top-view perspective view of the dedicated test block. As shown, this invention provides a dedicated test block 100 for detecting reheat cracks under the weld overlay. The weld overlay structure of the test block is consistent with that of the AP100 reactor pressure vessel to ensure that the acoustic propagation characteristics of the test block match those of the workpiece to be tested on-site, thereby improving the accuracy of the testing and calibration. The dedicated test block 100 includes a base material 110 and a weld overlay 120 covering the surface of the base material. The thickness of the base material 110 is greater than twice the thickness of the weld overlay 120 (Cladding Thickness, CT) to avoid interference from the ultrasonic reflection echo from the bottom surface of the test block on the weld overlay 120 and the defect echo near the bonding surface, thus ensuring the accuracy of the identification of effective signals during the testing process.

[0031] Three flat-bottomed holes are formed along the width of the special test block 100 on one side of the weld overlay 120, namely the first flat-bottomed hole 131, the second flat-bottomed hole 132, and the third flat-bottomed hole 133. On the same side of the base material 110 and the weld overlay 120, three flat-bottomed holes are formed along the width of the special test block 100, namely the fourth flat-bottomed hole 134, the fifth flat-bottomed hole 135, and the sixth flat-bottomed hole 136. The first to third flat-bottomed holes in the weld overlay 120 and the fourth to sixth flat-bottomed holes in the base material 110 correspond to the full thickness range of the weld overlay 120, the interface area between the weld overlay 120 and the base material 110, and the area of ​​the base material 110 near the interface, respectively. In other words, the first to sixth flat-bottomed holes cover the main initiation and propagation areas of reheat cracks under the weld overlay, enabling system calibration for defect detection at different depths.

[0032] For example, the distance between the first flat-bottomed hole 131 and the surface of the weld overlay 120 is 1 / 4 of the weld overlay 120 thickness; the distance between the second flat-bottomed hole 132 and the surface of the weld overlay 120 is 1 / 2 of the weld overlay 120 thickness; and the distance between the third flat-bottomed hole 133 and the surface of the weld overlay 120 is 3 / 4 of the weld overlay thickness. The fourth flat-bottomed hole 134 is abutted against the mating surface of the base material 110 and the weld overlay 120; the distance between the fifth flat-bottomed hole 135 and the mating surface is a first preset value; and the distance between the sixth flat-bottomed hole 136 and the mating surface is a second preset value. This depth setting can completely cover the upper surface layer, middle layer, and near-matting surface layer of the weld overlay 120, as well as the different depth positions of the fused mating surface and near-matting surface of the base material 110, providing corresponding amplitude calibration benchmarks for reheat crack detection at different depths, and can also be used to determine the distance-amplitude curve of the ultrasonic testing system. Figure 1 As shown, the first preset value is preferably 2mm, and the second preset value is preferably 4mm.

[0033] The first to sixth flat-bottomed holes 131 to 136 are arranged in parallel at equal intervals along the length of the special test block and sequentially along the thickness of the special test block. This arrangement ensures that the ultrasonic echo signal of each flat-bottomed hole is not interfered with by adjacent holes, and at the same time facilitates the testing personnel to quickly locate the calibration hole at the corresponding depth during the scanning process, thereby improving the efficiency and consistency of the calibration operation.

[0034] In some examples, all six flat-bottomed holes are cylindrical blind holes, with the bottom surface of each hole perpendicular to the central axis of the corresponding hole. The hole wall intersects the bottom surface to form a ring-shaped ridge. The cylindrical blind hole structure can form a stable and repeatable ultrasonic reflector. The flat bottom surface perpendicular to the hole axis can provide a stable vertical reflected echo, while the ring-shaped ridge can simulate the reflection characteristics of the crack tip, providing a stable simulation benchmark for the detection and quantification of reheat cracks.

[0035] In some examples, the distance between two adjacent flat-bottomed holes along the length of the dedicated test block 100 is 23mm to 27mm. The central axis of each hole is parallel to the detection surface (surface of the weld overlay) of the dedicated test block 100, and the central axes of each hole are parallel to each other. This spacing range allows for the reasonable arrangement of all calibration holes within the limited size of the test block, while avoiding superposition interference from the reflected signals of adjacent holes. The parallel hole axes ensure that the reflection conditions of each flat-bottomed hole are consistent, ensuring that the echo amplitude of calibration holes at different depths is only affected by depth and hole diameter, eliminating detection errors caused by angular deviations. In this example, the distance between two adjacent flat-bottomed holes along the length of the dedicated test block 100 is 25mm.

[0036] In some examples, the diameter of each flat-bottomed hole ranges from 1mm to 3mm, with a minimum drilling depth of 38mm. This design for the diameter range of 1mm to 3mm is compatible with the 70° point focusing probe 140 required by the weld overlay 120 inspection specification. This allows the ultrasonic waves incident on the annular ridge formed by the perpendicular intersection of the flat-bottomed hole wall and the bottom surface, used to simulate crack tips, to generate an effective signal with stable amplitude and acoustic characteristics highly matched to the diffraction echo of a real reheat crack tip, thus ensuring the accuracy of the inspection sensitivity calibration from the root. At the same time, this diameter range is compatible with the conventional reflector diameter specifications of the ASME standard weld overlay 120 test block, fully retaining the original standard test block's function of detecting and calibrating volumetric defects within the weld overlay 120 without changing the existing mature inspection process logic, significantly reducing the threshold for field application of this invention. Furthermore, this aperture range balances the feasibility of precision machining with the simulation accuracy of micro-cracks, effectively avoiding the problems of drastically increased machining difficulty and inability to guarantee the regularity of the annular ridge line due to excessively small apertures, or the distortion of crack simulation due to excessively large apertures. The design of a minimum drilling depth of 38mm conforms to the ASME standard's minimum hole depth requirement for the 120 weld overlay test block, ensuring compatibility with existing inspection and scanning processes. On the other hand, sufficient drilling depth ensures that the ultrasonic beam can completely and stably cover the annular ridge line at the bottom of the hole during scanning, avoiding limited effective scanning range due to insufficient hole depth, ensuring the stability and repeatability of diffraction echoes, eliminating detection errors caused by manual scanning operations, and matching the thickness design of the base material 110 of the nuclear-grade component under inspection. This ensures that the ultrasonic propagation path within the test block is consistent with the actual component under inspection, further reducing systematic errors in inspection and calibration.

[0037] In some examples, the inner wall roughness Ra of each flat-bottomed hole is ≤1.6μm, the hole diameter tolerance is ±0.025mm, the hole depth tolerance is ±0.1mm, and the parallelism between the hole axis and the test surface of the special test block 100 is ≤0.05mm / m. Strict control over the machining accuracy and surface roughness of the holes ensures stable and consistent ultrasonic reflection characteristics for each flat-bottomed hole, eliminates echo amplitude fluctuations caused by machining deviations, and ensures the repeatability and reliability of the test calibration results.

[0038] In some examples, the surface roughness Ra of the special test block 100 is ≤3.2μm, the parallelism between the test surface and the bottom surface is ≤0.03mm, and the perpendicularity between adjacent sides is ≤0.05mm. Controlling the surface roughness ensures good acoustic coupling between the ultrasonic probe and the test block surface, reducing detection errors caused by coupling loss. Strict dimensional and positional tolerances ensure that the test block is placed stably during the testing process, the scanning path is stable, and detection deviations caused by deformation of the test block body are avoided.

[0039] In some examples, the dedicated test block 100 is a homogeneous composite structure that has undergone overall stress-relieving heat treatment. The dedicated test block 100 undergoes overall stress-relieving heat treatment, and after the heat treatment, the longitudinal wave velocity deviation between the base material 110 and the weld overlay does not exceed ±5%, and the ultrasonic attenuation coefficient deviation does not exceed ±5%. Stress-relieving heat treatment eliminates residual stress generated during the test block's processing, preventing deformation during use. Simultaneously, it controls the acoustic characteristic deviation between the base material and the weld overlay within a limited range, ensuring that the acoustic propagation characteristics of the test block match those of the AP100 weld overlay workpiece to be tested on-site, and ensuring that the calibration results can be directly applied to on-site testing.

[0040] This invention also provides a dedicated scanning method for test blocks, which is fully compatible with the structural design of the test blocks and the functional positioning of simulated defects. It can give full play to the simulation effect of flat-bottomed holes on weld overlay cracks and provide a stable and repeatable calibration benchmark for ultrasonic detection of reheat cracks under AP100 weld overlay.

[0041] Specifically, the detection surface of the special test block is the upper surface of the weld overlay. The central axes of all flat-bottomed holes are parallel to this detection surface and extend along the width of the test block. Adjacent flat-bottomed holes are evenly spaced along the length of the test block, and the burial depth is gradient-distributed along the thickness of the test block. This structure matches the scanning method parallel to the axis of the flat-bottomed holes. Before scanning, the test block is placed stably with the weld overlay facing upwards and the detection surface horizontal. Stains and foreign objects on the detection surface are cleaned to ensure acoustic coupling. Then, based on the diameter and burial depth range of the flat-bottomed holes in the test block, an ultrasonic probe with a matching center frequency is selected. The central axis of the probe's sound beam is incident perpendicular to the detection surface, and the scanning movement direction of the probe is completely parallel to the direction of the central axis of the flat-bottomed holes (e.g., ...). Figure 2 (As shown by the vertical double-headed arrow in the middle), ensuring that the sound beam can stably cover the bottom structure of the flat-bottomed hole throughout the entire scanning process.

[0042] The scanning operation can be carried out sequentially on a single flat-bottomed hole basis. For each flat-bottomed hole, the horizontal projection area corresponding to the hole is marked on the inspection surface according to the design parameters of the test block. The probe is placed at the starting end of the projection area, and a uniform linear scan is performed along a direction parallel to the axis of the flat-bottomed hole. Throughout the scan, the probe and the inspection surface are kept stably coupled, and the incident direction of the sound beam is always perpendicular to the inspection surface, so that the sound beam continuously covers the bottom area of ​​the flat-bottomed hole. During the scan, the focus is on collecting the diffraction wave signal generated by the tip effect at the annular ridge where the bottom surface of the flat-bottomed hole intersects with the hole wall. It is not necessary to collect the specular reflection echo of the bottom surface of the flat-bottomed hole. The annular ridge of the flat-bottomed hole can realistically simulate the tip structure of the reheat crack in the weld overlay. The diffraction wave generated by the ultrasonic beam is completely consistent with the acoustic characteristics of the diffraction wave at the tip of the weld overlay crack in the workpiece under inspection. It can be directly used for sensitivity calibration of the detection system, verification of defect location accuracy, and identification of diffraction wave signal characteristics. Compared to the traditional transverse scanning method perpendicular to the axis of the flat-bottomed hole, the linear scanning method parallel to the hole axis ensures that the ultrasonic beam maintains a perpendicular incident relationship with the annular ridgeline at the bottom of the flat-bottomed hole throughout the entire scanning stroke. This fully stimulates the tip diffraction effect at the ridgeline, resulting in diffraction wave signals with higher signal-to-noise ratio and clearer characteristics, thus fully utilizing the test block's function of simulating defects. The design of the test block's base material thickness being greater than twice the thickness of the weld overlay avoids interference from ultrasonic reflection echoes from the bottom surface of the test block on the diffraction wave signals of the flat-bottomed hole ridgeline, further improving the accuracy of effective signal identification during the scanning process.

[0043] For the first, second, and third flat-bottomed holes 133 within the weld overlay, parallel scanning operations were sequentially performed to acquire diffraction wave signals simulating cracks at the upper surface, middle layer, and near the fusion surface of the weld overlay, respectively, completing the calibration of the detection system across the entire thickness range of the weld overlay. For the fourth flat-bottomed hole 134, which is attached to the bonding surface between the base material and the weld overlay, and the fifth and sixth flat-bottomed holes 136, which are located near the bonding surface of the base material, parallel scanning was sequentially performed to acquire diffraction wave signals simulating cracks at the fusion surface and in the near-fusion surface region of the base material, completing the calibration and location verification of the detection system for areas prone to reheat cracking under the weld overlay. Throughout the scanning process, the scanning method parallel to the hole axis ensures that the relative angle between the sound beam and the annular ridge of each flat-bottomed hole remains consistent, eliminating diffraction wave signal fluctuations caused by scanning angle deviations. This ensures that the simulated signals of flat-bottomed holes at different burial depths and positions are consistent and comparable. At the same time, the strict control of the flat-bottomed hole form and position tolerances, machining accuracy, and surface roughness of the test block can further reduce human operation errors during the scanning process, ensuring the repeatability and reliability of the calibration results.

[0044] Figure 3A flowchart illustrating a method for manufacturing a dedicated test block according to an embodiment of the present invention is shown. As shown, the present invention also provides a method for manufacturing a dedicated test block. This dedicated test block is suitable for detecting reheat cracks under the weld overlay. The manufacturing process ensures that the structure, material properties, and acoustic performance of the test block are highly matched with the weld overlay structure of the nuclear-grade equipment to be inspected, providing a stable and reliable calibration benchmark for on-site testing. The method for manufacturing this dedicated test block includes the following steps: S11. A metal material of the same material and heat treatment state as the base material of the nuclear-grade equipment to be inspected is selected as the base material for the test block. The thickness of the base material after cutting is greater than twice the design thickness of the weld overlay to be simulated. Using the same base material and heat treatment state as the equipment to be inspected ensures that the acoustic propagation characteristics of the test block base material are completely matched with the workpiece to be inspected on site, avoiding deviations in ultrasonic testing calibration due to material differences. Setting the base material thickness to be greater than twice the weld overlay thickness can prevent the ultrasonic reflected echo from the bottom surface of the test block from interfering with the simulated defect signals near the weld overlay and fusion surface during subsequent testing, ensuring the recognition accuracy of the effective signal.

[0045] S12 involves depositing a weld overlay on one side of the base material using welding materials, welding processes, and post-weld heat treatment processes identical to those used in the nuclear-grade equipment under inspection. The thickness of the weld overlay is consistent with the design thickness of the weld overlay on the nuclear-grade equipment under inspection. Complete replication of the welding process and parameters of the equipment under inspection ensures that the microstructure, acoustic properties, and interface bonding of the weld overlay on the test block are consistent with those of the workpiece under inspection on-site. This eliminates problems such as ultrasonic attenuation and sound velocity deviation caused by differences in welding processes, guaranteeing a high degree of consistency between the simulated defect signals and the signal characteristics of actual cracks on-site.

[0046] S13 involves performing overall stress-relieving heat treatment on the weld-overlayed test block blank. After heat treatment, the test surface, corresponding bottom surface, and all sides of the test block are machined to ensure that the dimensions and form and position tolerances of the special test block meet the basic accuracy requirements of ASME standard test blocks. Overall stress-relieving heat treatment eliminates residual stress generated during weld overlay and early processing, preventing deformation of the test block during subsequent processing and long-term use. It also further homogenizes the microstructure of the base material and the weld overlay layer, ensuring the uniformity of acoustic performance. The machining accuracy requirements meeting ASME standards ensure the flatness of the test surface of the test block, providing a stable reference for subsequent probe coupling and flat-bottom hole machining, while also meeting the industry specifications for nuclear-grade testing test blocks.

[0047] S14, on the side of the weld overlay layer of the special test block, the first flat-bottomed hole 131, the second flat-bottomed hole 132, and the third flat-bottomed hole 133 are sequentially machined along the width direction of the special test block. On the same side of the base material and the weld overlay layer opening, the fourth flat-bottomed hole 134, the fifth flat-bottomed hole 135, and the sixth flat-bottomed hole 136 are sequentially machined along the width direction of the special test block. The distance between the first flat-bottomed hole 131 and the surface of the weld overlay layer is 1 / 4 of the weld overlay layer thickness, the distance between the second flat-bottomed hole 132 and the surface of the weld overlay layer is 1 / 2 of the weld overlay layer thickness, the distance between the third flat-bottomed hole 133 and the surface of the weld overlay layer is 3 / 4 of the weld overlay layer thickness, the fourth flat-bottomed hole 134 is close to the fusion surface of the weld overlay layer and the base material, the distance between the fifth flat-bottomed hole 135 and the fusion surface is a first preset value, and the distance between the sixth flat-bottomed hole 136 and the fusion surface is a second preset value. The six flat-bottomed holes are evenly spaced along the length direction of the special test block. The gradient-set burial depth parameter allows the six flat-bottomed holes to completely cover the full thickness of the weld overlay, the fusion surface, and the base material area near the fusion surface. This area is the main initiation and propagation zone for reheat cracks under the weld overlay, providing a corresponding calibration benchmark for crack detection at different depths. The equidistant arrangement avoids interference between ultrasonic reflection signals from adjacent holes and facilitates rapid location of corresponding holes during inspection, ensuring consistency and convenience in calibration operations. The first preset value is preferably 2 mm, and the second preset value is preferably 4 mm.

[0048] S15. Perform full-range ultrasonic testing on the processed special test blocks. Full-range ultrasonic testing can verify that there are no original defects in the base material and weld overlay of the test block that would affect its use. At the same time, it can confirm that the processing position and dimensional accuracy of each flat-bottom hole meet the design requirements, verify that each flat-bottom hole can generate stable simulated defect signals, and ensure that the performance of the test blocks leaving the factory is consistent with the design expectations and meets the requirements for nuclear-grade testing.

[0049] In some examples, each flat-bottomed hole is machined into a cylindrical blind hole using precision deep hole drilling. The bottom surface of the hole is perpendicular to the central axis of the corresponding hole, and the hole wall intersects with the bottom surface to form an annular ridge line used to simulate crack tips. Using precision deep hole drilling ensures the machining accuracy of small-sized blind holes and avoids problems such as hole position deviation and hole wall deformation during machining. The flat bottom surface and annular ridge line, perpendicular to the hole axis, stably simulate the structural characteristics of crack tips, enabling the flat-bottomed holes to generate diffraction wave signals consistent with actual crack tips, meeting the calibration requirements of ultrasonic diffraction testing.

[0050] In some examples, the diameter tolerance of each flat-bottomed hole is controlled within ±0.025mm, the depth tolerance within ±0.1mm, the parallelism between the hole axis and the test surface of the test block is ≤0.05mm / m, and the inner wall roughness Ra is ≤1.6μm. Strict control of dimensional tolerances, form and position tolerances, and surface roughness ensures stable and consistent acoustic reflection characteristics of each flat-bottomed hole, eliminates signal fluctuations caused by machining deviations, and guarantees the repeatability and reliability of the test block calibration results.

[0051] Figure 4 A flowchart illustrating a method for manufacturing a special test block according to an embodiment of the present invention is shown. Figure 5 A schematic diagram of an ASME standard test block with transverse elongated holes, suitable for reheat crack detection under weld overlay, is shown according to an embodiment of the present invention. Figure 6 for Figure 5 The diagram shows a top-view perspective view of the special test block. (See diagram below.) Figure 4 As shown, the present invention also provides a method for manufacturing a special test block, which is suitable for detecting reheat cracks under the weld overlay. This method is based on the mature ASME standard test block and is adapted to meet the requirements of nuclear-grade testing specifications. It can shorten the manufacturing cycle and reduce the process difficulty while ensuring that the test block meets the requirements of nuclear-grade testing specifications, so that the test block can be adapted to the detection and calibration requirements of reheat cracks under the weld overlay.

[0052] S21, Select an ASME standard test block with transverse elongated holes suitable for detecting reheat cracking under weld overlay. (Reference) Figure 5 and Figure 6 The standard test block 200 includes a base material 210 and a weld overlay 220 covering the surface of the base material 210, forming a fusion surface between the base material 210 and the weld overlay 220. The weld overlay 220 has a first transverse elongated hole 231, a second transverse elongated hole 232, and a third transverse elongated hole 233, and the base material 210 has a fourth transverse elongated hole 234. The positions of each transverse elongated hole are... Figure 1 The first to fourth flat-bottomed holes of the special test block are located in the same position. By selecting a standard test block 200 that conforms to ASME specifications, it can be ensured that the material, welding process, and heat treatment state of the base material 210 and the weld overlay 220 of the test block meet the general requirements for nuclear-grade equipment testing. It also has a good match with the weld overlay structure and acoustic characteristics of the nuclear-grade equipment to be tested, eliminating the need to redo the base material preparation and weld overlay operations. This avoids the process deviations that may occur during the new preparation process, and at the same time, it makes the modified test block compatible with the existing conventional calibration procedures for nuclear-grade ultrasonic testing.

[0053] S22, the ends of all the transverse holes on the standard test block 200 are machined into flat-bottomed holes, so that the hole wall of the flat-bottomed hole intersects with the bottom surface to form an annular ridge line for simulating the crack tip, thereby transforming the first to fourth transverse holes 231 to 234 into... Figure 1The first to fourth flat-bottomed holes in the sample. Since the transverse elongated holes on the ASME standard test block 200 can meet the calibration requirements of conventional ultrasonic testing, machining the ends into flat-bottomed holes can form an annular ridge structure that can simulate the tip of reheat cracks in the weld overlay while retaining the original standard function of the test block. When excited by an ultrasonic beam, this structure can generate a diffraction wave signal consistent with the actual crack tip, which can meet the calibration requirements of diffraction ultrasonic testing of reheat cracks under the weld overlay. There is no need to additionally machine new simulated defect holes in the weld overlay, simplifying the processing procedure.

[0054] S23, on the same side as the openings in the base material 210 and the weld overlay 220, a fifth and a sixth flat-bottomed hole are machined. The distance between the fifth flat-bottomed hole and the fusion surface is a first preset value, and the distance between the sixth flat-bottomed hole and the fusion surface is a second preset value. The original ASME standard test block 200's transverse elongated holes mostly cover the interior of the weld overlay and the fusion surface. However, reheat cracks under the weld overlay are prone to initiation and propagation in the base material 210 side region below the fusion surface. The two newly added flat-bottomed holes can complete the simulated defect coverage of the base material region near the fusion surface, allowing the test block to completely cover all high-incidence areas of reheat cracks, meeting the full-depth range testing and calibration requirements. The first preset value is preferably 2 mm, and the second preset value is preferably 4 mm. After machining the fifth and sixth flat-bottomed holes, the structure of this standard test block is similar to... Figure 1 The structure of the special test block 100 is exactly the same.

[0055] All flat-bottomed holes are arranged at equal intervals along the length of the dedicated test block. This equal-interval arrangement avoids the superposition and interference of ultrasonic reflection signals from adjacent flat-bottomed holes, ensuring that the signal from each flat-bottomed hole can be independently identified and acquired during the scanning process. It also facilitates the quick location of simulated defect holes at corresponding depths by the testing personnel during the scanning process, improving the consistency and convenience of the calibration operation.

[0056] S24. Perform full-range ultrasonic testing on the processed test block. Full-range ultrasonic testing verifies that no internal defects affecting the use of the test block were introduced during the processing, confirms that the processing position and dimensional accuracy of all flat-bottomed holes meet the design requirements, and verifies that the annular ridges of each flat-bottomed hole can generate stable and repeatable diffraction wave signals. This ensures that the performance of the modified test block meets the requirements for reheat crack detection under the weld overlay and complies with the acceptance specifications for nuclear-grade test blocks.

[0057] The special test block for detecting reheat cracks under weld overlay provided by this invention has the following advantages compared with the prior art: 1. The special test block adopts a unique structure with all flat bottom holes. All reflectors can stably generate tip diffraction echoes that are completely consistent with real reheat cracks through the annular ridge. This solves the fatal defects of existing ASME test blocks that cannot simulate the acoustic characteristics of reheat cracks and fail in detection calibration from the design source, greatly improving the detection rate of reheat cracks and fully meeting the stringent testing requirements of nuclear-grade equipment.

[0058] 2. The six flat-bottomed holes are arranged in layers to perfectly match the initiation and propagation patterns of reheat cracks under the weld overlay, covering the calibration requirements for reheat cracks initiating within the weld overlay; the three flat-bottomed holes at the fusion surface and at depths of 2mm and 4mm below the fusion surface lock the core initiation area of ​​reheat cracks, achieving blind-zone-free calibration of the entire depth range of reheat cracks, and completely filling the gap in the detection coverage of existing test blocks.

[0059] 3. The acoustic response characteristics of all flat-bottomed holes are completely consistent, which solves the problem of inconsistent calibration benchmarks and large systematic errors in existing hybrid reflector test blocks. It provides a unified, stable and repeatable calibration benchmark for the detection of reheat cracks under the weld overlay, greatly improves the quantitative accuracy of cracks, and eliminates systematic errors in detection at different depths.

[0060] 4. The flat-bottom hole design is compatible with the transverse scanning method. During on-site testing, the probe only needs to be aligned with the bottom of the flat-bottom hole to obtain stable crack diffraction echoes. Compared with the complex scanning method of existing test blocks, it greatly reduces the difficulty of on-site operation, reduces human error, and is fully compatible with the harsh testing environment of nuclear power plant sites.

[0061] 5. The two manufacturing methods for specialized test blocks can achieve standardized batch preparation of specialized test blocks, ensuring the consistency and accuracy of newly manufactured test blocks; or they can upgrade existing ASME standard test blocks on site at low cost by changing the original long horizontal holes to flat bottom holes, which can achieve accurate calibration for reheat crack detection, greatly reducing application costs and having strong engineering promotion value.

[0062] It will be apparent to those skilled in the art that various modifications and variations can be made to the exemplary embodiments described above without departing from the spirit and scope of the invention. Therefore, it is intended that this invention cover modifications and variations falling within the scope of the appended claims and their equivalents.

Claims

1. A special test block for detecting reheat cracking under a weld overlay, having the same structure as the weld overlay, the special test block comprising a base material and a weld overlay covering the surface of the base material, wherein the thickness of the base material is greater than twice the thickness of the weld overlay; On one side of the weld overlay, three flat-bottomed holes are formed along the width direction of the special test block, including a first flat-bottomed hole, a second flat-bottomed hole, and a third flat-bottomed hole; on the same side of the base material and the opening of the weld overlay, three flat-bottomed holes are formed along the width direction of the special test block, including a fourth flat-bottomed hole, a fifth flat-bottomed hole, and a sixth flat-bottomed hole. The distance between the first flat-bottomed hole and the surface of the weld overlay is 1 / 4 of the weld overlay thickness; the distance between the second flat-bottomed hole and the surface of the weld overlay is 1 / 2 of the weld overlay thickness; the distance between the third flat-bottomed hole and the surface of the weld overlay is 3 / 4 of the weld overlay thickness; the fourth flat-bottomed hole is abutted against the bonding surface of the base material and the weld overlay; the distance between the fifth flat-bottomed hole and the bonding surface is a first preset value; and the distance between the sixth flat-bottomed hole and the bonding surface is a second preset value. The first to sixth flat-bottomed holes are arranged in parallel at equal intervals along the length of the special test block and are arranged sequentially along the thickness of the special test block.

2. The special test block as described in claim 1, characterized in that, The first to sixth flat-bottomed holes are all cylindrical blind holes, and the bottom surface of each flat-bottomed hole is perpendicular to the central axis of the corresponding hole. The hole wall intersects with the bottom surface to form an annular ridge.

3. The special test block as described in claim 1, characterized in that, The distance between two adjacent flat-bottomed holes in the length direction of the special test block is 23mm to 27mm. The central axis of each hole is parallel to the detection surface of the special test block, and the central axes of each hole are parallel to each other.

4. The special test block as described in claim 3, characterized in that, The diameter of each of the flat-bottomed holes ranges from 1 mm to 3 mm, and the minimum drilling depth is 38 mm.

5. The special test block as described in claim 3, characterized in that, The inner wall roughness Ra of each flat-bottomed hole is ≤1.6μm, the hole diameter tolerance is ±0.025mm, the hole depth tolerance is ±0.1mm, and the parallelism between the hole axis and the test surface of the special test block is ≤0.05mm / m.

6. The special test block as described in claim 1, characterized in that, The surface roughness Ra of the special test block is ≤3.2μm, the parallelism between the test surface and the bottom surface is ≤0.03mm, and the perpendicularity between adjacent sides is ≤0.05mm.

7. The special test block as described in claim 1, characterized in that, The special test block is a homogeneous composite structure that has undergone overall stress-relieving heat treatment.

8. A method for manufacturing a special test block, the special test block being suitable for detecting reheat cracking under a weld overlay, the manufacturing method comprising the following steps: S11. Select a metal material with the same material and heat treatment state as the base material of the nuclear grade equipment to be tested as the base material of the test block. The thickness of the base material after cutting is greater than twice the design thickness of the weld overlay layer to be simulated. S12, on one side of the base material, a weld overlay layer is formed by welding with welding materials, welding process and post-weld heat treatment process that are completely consistent with the nuclear grade equipment to be inspected. The forming thickness of the weld overlay layer is consistent with the design thickness of the weld overlay layer of the nuclear grade equipment to be inspected. S13, the test block blank after the welding is completed is subjected to overall stress relief heat treatment. After the heat treatment is completed, the test surface, corresponding bottom surface and each side surface of the test block are machined so that the external dimensions and geometric tolerances of the special test block meet the basic accuracy requirements of ASME standard test blocks. S14, on the side of the weld overlay layer of the special test block, a first flat-bottomed hole, a second flat-bottomed hole, and a third flat-bottomed hole are sequentially machined along the width direction of the special test block. On the same side of the base material and the weld overlay layer opening, a fourth flat-bottomed hole, a fifth flat-bottomed hole, and a sixth flat-bottomed hole are sequentially machined along the width direction of the special test block. The distance between the first flat-bottomed hole and the surface of the weld overlay layer is 1 / 4 of the weld overlay layer thickness; the distance between the second flat-bottomed hole and the surface of the weld overlay layer is 1 / 2 of the weld overlay layer thickness; the distance between the third flat-bottomed hole and the surface of the weld overlay layer is 3 / 4 of the weld overlay layer thickness; the fourth flat-bottomed hole is abutted against the fusion surface of the weld overlay layer and the base material; the distance between the fifth flat-bottomed hole and the fusion surface is a first preset value; and the distance between the sixth flat-bottomed hole and the fusion surface is a second preset value. The six flat-bottomed holes are evenly spaced along the length direction of the special test block. S15, Perform full-range ultrasonic testing on the processed special test block.

9. The manufacturing method as described in claim 8, characterized in that, Each of the flat-bottomed holes is machined into a cylindrical blind hole using deep hole drilling technology. The bottom surface of the hole is perpendicular to the central axis of the corresponding hole, and the hole wall intersects with the bottom surface to form an annular ridge line used to simulate the crack tip. The diameter tolerance of each flat-bottomed hole is controlled within ±0.025mm, the hole depth tolerance is controlled within ±0.1mm, the parallelism between the hole axis and the test surface of the test block is ≤0.05mm / m, and the roughness Ra of the inner wall of the hole is ≤1.6μm.

10. A method for manufacturing a special test block, the special test block being suitable for detecting reheat cracking under a weld overlay, the manufacturing method comprising the following steps: S21, Select an ASME standard test block with first to fourth transverse holes suitable for reheat crack detection under weld overlay. The standard test block includes a base material and a weld overlay covering the surface of the base material, and a fusion surface is formed between the base material and the weld overlay. S22, the ends of the first to fourth transverse holes on the standard test block are processed into the first to fourth flat-bottomed holes, so that the hole walls of the first to fourth flat-bottomed holes intersect with the bottom surface to form an annular ridge line for simulating the crack tip. S23, on the same side of the base material and the weld overlay opening, a fifth flat-bottomed hole and a sixth flat-bottomed hole are machined. The distance between the fifth flat-bottomed hole and the fusion surface is a first preset value, and the distance between the sixth flat-bottomed hole and the fusion surface is a second preset value. All flat-bottomed holes are arranged at equal intervals along the length of the special test block. S24, Perform full-range ultrasonic testing on the processed test block.

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