Tungsten crucible internal flaw detection method and tungsten standard test block thereof

Abstract

The invention relates to the technical field of nondestructive testing, and particularly discloses a tungsten crucible internal flaw detection method and a tungsten standard test block thereof.The method comprises the following steps that S1, calibration is conducted, specifically, the tungsten standard test block made of the same material as the detected tungsten crucible is used for conducting sound velocity calibration; s2, scanning: adopting a double-crystal normal probe and a plurality of single-crystal angle probes with different K values to ultrasonically scan the bottom surface and the side surface of the tungsten crucible respectively; and S3, judging: judging the internal defect of the tungsten crucible based on the echo signal obtained by scanning. The special tungsten standard test block made of the same material as the detected workpiece is adopted for sound velocity calibration, a combined strategy of primary scanning of the double-crystal normal probe and fine scanning of the single-crystal angle probe with the K value optimized according to the thickness is adopted, a cross validation judgment rule based on multi-probe data fusion is established, the reliability and scientificity of a detection result are remarkably improved, and the accuracy of the detection result is improved. And finally, a set of special ultrasonic flaw detection system for the tungsten crucible, which is controllable in cost, high in operability and capable of stably detecting tiny defects, is formed.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, and specifically discloses a method for internal flaw detection of a tungsten crucible and a tungsten standard test block thereof. Background Technology

[0002] Tungsten crucibles are widely used in key fields such as crystal growth, metallurgy, and high-temperature processing due to their high melting point, high density, and excellent high-temperature stability. However, tungsten material itself has high sound velocity (approximately 5000-5200 m / s), coarse grain structure, and significant ultrasonic attenuation characteristics, which pose serious challenges to traditional ultrasonic non-destructive testing techniques. The high sound velocity leads to a mismatch in the preset sound velocity parameters of conventional ultrasonic flaw detectors, easily causing serious deviations in defect location; coarse grains cause strong structural noise and sound wave scattering, and the echo signals of small defects are easily obliterated; in addition, the curved geometry of tungsten crucibles easily leads to poor beam coupling, energy loss, and beam deformation, further increasing the difficulty of defect identification, location, and quantitative evaluation.

[0003] Currently, for internal flaw detection of complex workpieces such as tungsten crucibles, the industry mainly relies on the following technologies: Phased array ultrasonic testing, as an advanced ultrasonic imaging technology, can provide relatively intuitive images of defects. However, this technology requires extremely high equipment and maintenance costs, has complex operation and data analysis processes, and demands a high level of technical expertise from the testing personnel. Furthermore, its testing effectiveness is also affected by the workpiece surface condition and material grain size, and it still faces the challenge of low signal-to-noise ratio in coarse-grained tungsten materials.

[0004] Radiographic testing (RT) carries inherent radiation safety risks, requiring strict protective measures for operators and the environment. More importantly, its sensitivity for detecting area-type defects (such as cracks) is relatively low, especially when the crack direction is parallel to the X-ray beam, making it prone to missed detection. Furthermore, radiographic testing cannot accurately determine the depth direction of defects, and both equipment investment and testing costs are high.

[0005] In recent years, although some studies have attempted to apply intelligent ultrasonic flaw detectors to the testing of special materials, there are still no publicly reported, in China, mature and reliable testing methods for tungsten crucibles that systematically solve the problems of sound velocity matching, coarse grain noise suppression, and surface testing adaptation by fabricating dedicated tungsten standard test blocks. Existing general methods, when applied to tungsten crucibles, generally suffer from problems such as inaccurate positioning, low signal-to-noise ratio, cumbersome and inefficient testing procedures, and insufficient detection capability for small-sized defects and dangerous orientation cracks.

[0006] Therefore, it is necessary to develop a dedicated ultrasonic testing method and supporting tools that are low-cost and provide accurate and reliable test results, specifically tailored to the material properties and structural characteristics of tungsten crucibles. Summary of the Invention

[0007] To address the aforementioned issues, this invention provides a method for internal flaw detection of tungsten crucibles and a tungsten standard test block. By employing a dedicated tungsten standard test block made of the same material as the workpiece under inspection for sound velocity calibration, the core challenges of inaccurate defect localization and low signal-to-noise ratio caused by the high sound velocity, high attenuation, and coarse-grained structure of tungsten material are fundamentally solved. A combined strategy of initial scanning with a dual-crystal straight probe and fine scanning with a single-crystal angled probe (K value optimized based on thickness) is adopted, along with a simplified detection scheme using straight probes to replace curves for sides with large curvature. This achieves full coverage, high efficiency, and high precision detection of tungsten crucibles with complex shapes. Furthermore, by establishing cross-validation rules based on multi-probe data fusion, the reliability and scientific validity of the detection results are significantly improved. Ultimately, a cost-effective, highly operable, and stable ultrasonic flaw detection system for tungsten crucibles capable of detecting defects as small as 0.5 mm is formed.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A method for internal flaw detection of a tungsten crucible, comprising the following steps: S1. Calibration: Use a tungsten standard test block of the same material as the tungsten crucible being tested to calibrate the sound velocity of the ultrasonic flaw detector and probe; S2. Scanning: Using a dual-crystal straight probe and several single-crystal angle probes with different K values, ultrasonic scanning is performed on the bottom and sides of the tungsten crucible. S3. Judgment: Based on the echo signal obtained in the scanning step, the internal defects of the tungsten crucible are determined.

[0009] The basic principle of this invention is based on the precise matching of the physical characteristics of ultrasonic wave propagation in a solid medium with the acoustic properties of the material. Through systematic optimization of the detection strategy, it achieves effective detection of internal defects in tungsten products, a special material. Its core lies in solving three major problems posed by the high sound velocity, coarse grains, and workpiece geometry of tungsten to traditional ultrasonic testing: inaccurate positioning, low signal-to-noise ratio, and poor coupling.

[0010] The calibration procedure works by establishing an accurate measurement benchmark through matching the acoustic properties of the materials. The propagation speed of ultrasound in a medium (sound velocity) is a key parameter for defect location calculations. The sound velocity of tungsten is significantly higher than that of ordinary steel. If a conventional steel test block is used for calibration, the sound velocity value set by the instrument will not match the actual sound velocity of the workpiece, resulting in a systematic error in depth positioning. This solution ensures the accuracy of depth display from the source, overcoming the fundamental positioning error caused by sound velocity mismatch.

[0011] The scanning procedure is based on a comprehensive detection strategy that combines the complementary characteristics of multiple probes with the adaptation of the detection area. Dual-crystal straight probes offer advantages such as small blind zones, high resolution for near-surface defects, and insensitivity to surface conditions, making them suitable for rapid initial scanning and near-surface assessment. Single-crystal angled probes generate transverse waves through refraction, effectively detecting defects at an angle to the detection surface, such as vertical cracks or tilted defects. For different thicknesses of the bottom surface, angled probes with different K values ​​(refractive angles) are dynamically selected. This essentially optimizes the propagation path and coverage of the sound beam in workpieces of specific thicknesses, balancing detection depth, resolution, and beam coverage. For large-diameter sidewalls, an approximation principle of using straight lines to represent curves is adopted. While ensuring engineering accuracy, a K1 probe with good directivity is selected for detection, avoiding complex surface path calculations and improving detection efficiency. This combination is not a simple superposition but a targeted deployment based on the possible morphology of defects and regional characteristics.

[0012] The principle behind the judgment process is to introduce a decision-making mechanism involving multi-angle data fusion and cross-validation to improve the reliability and objectivity of the judgment. Detection with a single probe or from a single angle may result in missed detections or false alarms. This solution requires that any initially suspected defects be re-examined using a probe with a different acoustic beam path or type. Only when detection signals from different acoustic paths can confirm the presence of a defect echo at the same location, and after quantitative evaluation based on a distance-amplitude curve (DAC curve) prepared in advance using a tungsten test block, is a final judgment made. This mechanism greatly reduces the risk of misjudgment caused by material noise, surface condition, or limitations of single probe characteristics, making the detection conclusions more scientific and reliable, based on the mutual verification of multi-source information.

[0013] Furthermore, the S1 calibration step specifically includes: S11. Initial calibration: Perform zero-bias initial calibration on the probe using a standard steel test block; S12. Fine calibration: Place the probe in the defect-free area of ​​the tungsten standard test block, and adjust the sound velocity value to make the bottom echo depth displayed by the instrument consistent with the actual thickness of the test block, thus completing the sound velocity fine calibration.

[0014] Furthermore, during the sound speed fine-tuning process, the sound speed adjustment range is from 5050 m / s to 5200 m / s.

[0015] Furthermore, in the S2 scanning step, the scanning of the bottom surface of the tungsten crucible specifically involves: first, a preliminary scan is performed using a dual-crystal straight probe, and then a fine scan is performed using a single-crystal angled probe with a K value selected according to the nominal thickness t of the bottom surface, wherein: When t < 20 mm, select the K2.5 angle probe; when 20 mm ≤ t ≤ 40 mm, select the K2 angle probe; when t > 40 mm, select the K1 angle probe.

[0016] Furthermore, after a thorough scan of the bottom surface, a K2.5 angled probe was used to perform a focused scan of the near-surface area.

[0017] Furthermore, in the S2 scanning step, when scanning the side of a tungsten crucible with a diameter ≥250mm, its side curvature is approximated as a plane, and a K1 single-crystal angle probe is mainly used for detection.

[0018] Furthermore, the S3 determination step specifically includes: S31. Initial screening: When the echo amplitude of a defect detected by any probe exceeds the quantitative line of the distance-amplitude curve based on the tungsten standard test block, it is marked as a suspected defect. S32. Re-inspection: For suspected defects, use another type of probe to perform a verification scan at the same location; S33. Final judgment: The tungsten crucible is deemed unqualified only if at least two different types of probes receive repeatable defect echoes at the said location and the echo amplitude reaches or exceeds the rejection line.

[0019] A tungsten standard test block for an internal flaw detection method of a tungsten crucible, the test block being made of tungsten material and having artificial defects machined inside for the calibration of an ultrasonic flaw detector and the verification of detection sensitivity.

[0020] Furthermore, the artificial defect includes a set of transverse through holes at different depths for calibrating the angle probe and creating distance-amplitude curves.

[0021] Furthermore, the artificial defect also includes at least one of the following: Flat-bottomed holes at different depths are used to evaluate the ability to detect point defects; A stepped area with continuously varying thickness was used to verify the accuracy of acoustic path localization. Narrow wire-cut grooves at different angles to the surface are used to simulate cracks and verify the detection sensitivity for defects with different orientations.

[0022] The beneficial effects of this invention are: (1) By using a dedicated tungsten standard test block of the same material for sound velocity calibration, the problems caused by the high sound velocity, high attenuation and coarse grain structure of tungsten are overcome in one fell swoop, ensuring the accuracy of defect depth positioning, significantly suppressing material noise, improving the signal-to-noise ratio, and providing a unified evaluation standard that is highly matched with the characteristics of the workpiece for all subsequent testing steps. This is the cornerstone of the entire technical solution, and the accurate acoustic parameters it provides enable the effective implementation of all subsequent optimization strategies.

[0023] (2) The combined strategy of initial scanning with dual-crystal straight probes and fine scanning with angled probes of optimal K-value based on thickness, along with the simplified detection method for large-curvature sidewalls, forms a three-dimensional detection network. The combination of rapid coverage with straight probes and directional in-depth inspection with angled probes enables thorough screening of defects in different locations and orientations, from near the surface to the interior, and from parallel to the detection surface to inclined to the detection surface. Dynamically selecting the K-value based on the bottom thickness is essentially an adaptive optimization of the sound beam propagation path and focusing area based on the accurate sound velocity obtained through calibration, ensuring optimal detection sensitivity and signal-to-noise ratio in different thickness regions. Simplifying the large-diameter sidewalls into a plane for detection greatly improves efficiency while ensuring engineering accuracy. The effectiveness of this strategy depends on the accuracy of the initial calibration and the rationality of probe selection, and is a key design feature that balances high precision and high efficiency in the entire scheme.

[0024] (3) The multi-probe repeated verification and the quantitative judgment rule based on the DAC curve of the tungsten test block form a strong closed loop with the aforementioned steps. The judgment step performs reverse verification and data fusion on the suspected defects found in the scanning step, and uses the differences in the sound beam paths of different probes (straight / oblique, different K values) for cross-verification, which effectively eliminates false alarms caused by single probe characteristics, accidental interference or material inherent noise, while reducing the risk of missed detection through multi-angle detection. The final rejection criterion is strictly based on the DAC curve made by the special tungsten test block, which upgrades the judgment from qualitative experience judgment to quantitative and standardized scientific decision-making, ensuring the consistency and repeatability of the test results.

[0025] (4) This solution, through the integrated design of tungsten test block, probe combination, scanning method, and rigorous judgment process, successfully transforms advanced detection concepts into a standardized operating procedure with clear steps, well-defined parameters, and ease of on-site implementation. It not only significantly improves the accuracy and reliability of detection (detecting defects as small as 0.5 mm), but also effectively controls implementation complexity and time costs through strategic simplification (such as simplified side processing) and process optimization, ultimately achieving the best balance between detection performance, operational efficiency, and economy, filling the gap in this sub-field where there is a lack of efficient dedicated methods. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the method for detecting internal flaws in a tungsten crucible in Embodiment 1 of the present invention.

[0027] Figure 2 This is a schematic diagram of the calibration steps of the method for detecting internal flaws in a tungsten crucible in Embodiment 1 of the present invention.

[0028] Figure 3 This is a schematic diagram of the scanning steps in the method for detecting internal flaws in a tungsten crucible in Embodiment 1 of the present invention.

[0029] Figure 4This is a schematic diagram of the determination steps in the method for detecting internal flaws in a tungsten crucible in Embodiment 1 of the present invention.

[0030] Figure 5 This is an isometric view of the tungsten standard test block in Example 1 of the present invention.

[0031] Figure 6 This is a bottom view of the tungsten standard test block in Embodiment 1 of the present invention.

[0032] Figure 7 This is a side view of the tungsten standard test block in Embodiment 1 of the present invention.

[0033] Reference numerals in the attached figures: 1. Tungsten standard test block; 2. Horizontal through hole; 3. Wire-cut narrow groove; 4. Stepped area; 5. Flat bottom hole. Detailed Implementation

[0034] The specific implementation method is described below with reference to the accompanying drawings.

[0035] Example 1 Basic as Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown: This embodiment focuses on internal flaw detection of a tungsten crucible with an outer diameter of 300mm, a nominal bottom thickness of 50mm, and a sidewall height of 80mm. First, the core preparatory work before testing is to calibrate the intelligent ultrasonic flaw detector using a dedicated standard test block made from the same batch of tungsten material as the crucible under test. Specifically, the operator selected a dual-crystal straight probe (5PD20F20) and a K1 single-crystal angled probe (5P8X12K1) as the main tools. The calibration process strictly follows a two-step method: First, the dual-crystal straight probe is placed on the CSK-IA steel test block, and the instrument's zero bias is adjusted so that the echo depth display of the 25mm thick bottom surface is accurately 25mm. This step aims to establish a stable initial time reference. Second, the same probe is moved to a defect-free area of ​​the tungsten standard test block 11 (30mm thick), combined with... Figure 5 , Figure 6 and Figure 7 As shown, the instrument's sound velocity value was finely adjusted until the bottom echo depth displayed on the screen was precisely 30.0 mm, at which point the sound velocity value stabilized at approximately 5180 m / s. This step is crucial, as it forces the instrument to use sound velocity parameters that are perfectly matched to the workpiece material, fundamentally correcting the systematic deviation in depth positioning that might be caused by the high sound velocity characteristics of tungsten material, and laying a precise dimensional foundation for all subsequent measurements.

[0036] After completing the sound velocity calibration, a distance-amplitude curve (DAC curve) is generated using a tungsten standard test block 1 to provide a benchmark for the quantitative determination of defects. The operator uses a calibrated single-crystal angle probe to locate artificial transverse holes 2 at different depths (e.g., 20mm, 30mm, 40mm) on the test block and records the highest echo amplitude of each hole. The instrument will automatically generate a reference curve based on these data points, showing the amplitude attenuation as the sound path (depth) increases. When generating the curve, surface compensation (e.g., increasing by 3-5 dB) is required based on the workpiece surface condition (usually rougher than the standard test block). The function of the DAC curve is to convert the physical quantity of the defect echo height into its equivalent magnitude relative to an artificial defect of known size.

[0037] Before or during the formal inspection of tungsten crucible workpieces, the standard test block also plays a role in verifying the overall performance of the detection system. Using flat-bottomed holes 5 of different depths and stepped areas 4 on the tungsten standard test block 1, it is possible to verify whether the system's ability to detect minute point defects meets the design requirements; using wire-cut narrow grooves 3 of different angles on the tungsten standard test block 1, it is possible to evaluate the sensitivity of the probe to dangerous planar defects such as simulated cracks, especially to verify the detection effect of the selected probe on vertical or tilted defects.

[0038] The tungsten crucible was then scanned. For the bottom surface of the crucible with a thickness of 50 mm (t>40 mm), machine oil was first evenly applied as a coupling agent, and a calibrated dual-crystal straight probe was used for a 100% coverage initial scan. The characteristics of the dual-crystal probe provide high resolution for near-surface areas. This step is used to quickly screen for near-bottom or large volumetric defects and to make a preliminary assessment of the overall quality of the bottom area. Subsequently, according to the principle of selecting the optimal K value based on thickness in the plan, a fine scan was performed using a K1 single-crystal angled probe. Due to the smaller K value, its refraction angle is smaller, and the propagation path of the sound beam in the material is closer to perpendicular incidence, resulting in better directivity and stronger penetration. This step is specifically used to detect defects that may exist deep in the thicker bottom, especially planar defects that may be at an angle to the detection surface. For the side surface of the crucible with a diameter of 300 mm, due to its large radius of curvature, it can be approximated as a plane using a simplified strategy of substituting straight lines for curves. After applying chemical paste to the sides, a rapid initial scan is performed using a dual-crystal straight probe to assess the overall condition of the sidewalls. Then, a systematic scan is primarily conducted using a K1 angled probe. The K1 probe's relatively vertical sound beam effectively detects radially distributed defects (i.e., perpendicular to the tangent direction of the curved surface) within the sidewalls. This combination of scanning strategies achieves directional optimization of detection methods for different geometric feature areas, ensuring that the sound beam covers all potential defect locations along the most efficient path.

[0039] After scanning, the judgment phase begins. Throughout the scanning process, no abnormal echoes exceeding the quantitative line of the DAC curve based on the transverse through-hole 2 of the tungsten sample appeared on the instrument screen. According to the judgment rules, there is no need to initiate a re-inspection process; it can be directly determined that no recordable internal defects were found on the bottom and sides of the tungsten crucible within the sensitivity range of this detection method. The final technical effect achieved is that material matching calibration ensures the fundamental accuracy of the measurement, probe combination and area adaptation strategy enables efficient and thorough screening of complex-shaped workpieces, and rigorous judgment rules ensure the reliability of the conclusions, thus efficiently and reliably completing the quality assessment of this thick-walled tungsten crucible.

[0040] Example 2 Unlike the previous embodiments, this embodiment provides a test for a tungsten crucible with an outer diameter of 260 mm and a nominal bottom thickness of 15 mm. A tiny wire-cut narrow groove 3 with a depth of 2 mm and an angle of 90° to the surface is artificially pre-set on the near surface of the crucible's side wall to simulate a highly dangerous near-surface vertical crack. The calibration process also adopts a two-step method, using a dual-crystal straight probe to perform sound velocity fine calibration on the tungsten standard test block 1 to ensure the accuracy of the benchmark.

[0041] During the scanning phase, considering the characteristics of the thin-walled (t<20mm) bottom surface, a combination of a dual-crystal straight probe and a K2.5 single-crystal angled probe (5P8X12K2.5) was selected. The dual-crystal straight probe was used for initial scanning, leveraging its small near-surface blind zone to preliminarily explore the bottom area. Subsequently, according to the optimized strategy, the K2.5 probe was used for fine scanning. The K2.5 probe has a larger refraction angle, allowing the sound beam to propagate at a more inclined angle in thin-walled workpieces, generating a longer sound path. This not only facilitates coverage of a larger inspection area but also provides a stronger detection capability for tilted defects and near-surface defects (such as micro-cracks that do not extend to the surface). This is a precise design for the defect characteristics of thin-walled areas. When scanning the side, when the K1 angled probe swept across the preset wire-cut groove position, a clear echo signal appeared on the instrument screen. Its amplitude exceeded the quantitative line of the DAC curve but was slightly below the rejection line. This signal was marked as a suspicious defect.

[0042] Subsequently, a rigorous judgment procedure was initiated. First, a re-verification was conducted, with the operator using a dual-crystal straight probe to carefully verify the scan at the same location indicated by the signal. Because the defect was a vertical, near-surface narrow groove, the sound beam from the dual-crystal straight probe was incident perpendicularly, and a clear and fixed-position echo signal was received. Both types of probes (angle probe and straight probe) obtained repeatable defect indications at the same geometric location, completing the first cross-verification. Next, for final quantification, the operator, according to the judgment rules, read and compared the wave height of the defect echo measured by the two probes after surface compensation, confirming that it had reached the rejection threshold (DAC-10dB). At this point, the final judgment condition of confirmation by at least two different types of probes and the echo reaching the rejection threshold was met.

[0043] The technical effect achieved by this embodiment, based on the thickness-dynamically selected K2.5 probe, successfully enhanced the ability to capture dangerous defects in thin-walled areas and near-surface regions, realizing a leap from area coverage to precise targeting. Secondly, the multi-probe data fusion judgment mechanism played a crucial role. Cross-verification by angled and straight probes not only confirmed the authenticity of the defect and eliminated the possibility of accidental interference, but also enhanced confidence in the qualitative judgment of defects (such as orientation) through verification by different sound beam paths. Finally, the entire process, with standardized operation and quantified criteria, scientifically and reliably detected and determined a representative hazardous defect, fully demonstrating the comprehensive effectiveness of the method of this invention in improving detection sensitivity, reliability, and addressing specific engineering challenges.

Claims

1. A method for internal flaw detection of a tungsten crucible, characterized in that, Includes the following steps: S1. Calibration: Use a tungsten standard test block (1) of the same material as the tungsten crucible being tested to calibrate the sound velocity of the ultrasonic flaw detector and probe; S2. Scanning: Using a dual-crystal straight probe and several single-crystal angle probes with different K values, ultrasonic scanning is performed on the bottom and sides of the tungsten crucible. S3. Judgment: Based on the echo signal obtained in the scanning step, the internal defects of the tungsten crucible are determined.

2. The method for internal flaw detection of a tungsten crucible according to claim 1, characterized in that, The S1 calibration step specifically includes: S11. Initial calibration: Perform zero-bias initial calibration on the probe using a standard steel test block; S12. Fine calibration: Place the probe in the defect-free area of ​​the tungsten standard test block (1), and adjust the sound velocity value so that the bottom echo depth displayed by the instrument is consistent with the actual thickness of the test block, thus completing the sound velocity fine calibration.

3. The method for internal flaw detection of a tungsten crucible according to claim 2, characterized in that, During the sound velocity fine-tuning process, the sound velocity adjustment range is from 5050 m / s to 5200 m / s.

4. The method for internal flaw detection of a tungsten crucible according to claim 1, characterized in that, In the S2 scanning step, the scanning of the bottom surface of the tungsten crucible specifically involves: first, a preliminary scan is performed using a dual-crystal straight probe; then, a fine scan is performed using a single-crystal angled probe with a K value selected based on the nominal thickness t of the bottom surface. Specifically: When t < 20 mm, select a K2.5 angle probe; When 20 mm ≤ t ≤ 40 mm, select the K2 angle probe; When t > 40 mm, select the K1 angle probe.

5. The method for internal flaw detection of a tungsten crucible according to claim 4, characterized in that, After a thorough scan of the bottom surface, a K2.5 angle probe was used to perform a focused scan of the near-surface area.

6. The method for internal flaw detection of a tungsten crucible according to claim 1, characterized in that, In the S2 scanning step, when scanning the side of a tungsten crucible with a diameter ≥250mm, its side curvature is approximated as a plane, and the K1 single crystal angle probe is mainly used for detection.

7. The method for internal flaw detection of a tungsten crucible according to claim 1, characterized in that, The S3 determination step specifically includes: S31. Initial screening: When the amplitude of the defect echo detected by any probe exceeds the quantitative line of the distance-amplitude curve based on the tungsten standard test block (1), it is marked as a suspected defect; S32. Re-inspection: For suspected defects, use another type of probe to perform a verification scan at the same location; S33. Final judgment: The tungsten crucible is deemed unqualified only if at least two different types of probes receive repeatable defect echoes at the said location and the echo amplitude reaches or exceeds the rejection line.

8. A tungsten standard test block for use in the internal flaw detection method of the tungsten crucible according to any one of claims 1-7, characterized in that, The test block is made of tungsten material and has artificial defects machined inside for the calibration of ultrasonic flaw detectors and the verification of detection sensitivity.

9. The tungsten standard test block according to claim 8, characterized in that, The artificial defects include a set of transverse through-holes (2) at different depths for calibration of the angle probe and fabrication of distance-amplitude curves.

10. The tungsten standard test block according to claim 9, characterized in that, The artificial defects also include at least one of the following: Flat-bottomed holes (5) at different depths were used to evaluate the ability to detect point defects; A stepped area with continuously varying thickness (4) was used to verify the accuracy of acoustic path positioning. Narrow wire-cut grooves (3) at different angles to the surface were used to simulate cracks and verify the detection sensitivity for defects with different orientations.

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