Radiographic inspection method for double-T-shaped welded joint

Abstract

The invention belongs to the technical field of radiographic inspection, and particularly relates to a radiographic inspection method for a double-T-shaped welded joint. Through a double-wall vertical transillumination and double-wall inclined transillumination cooperative detection technology, full-thickness coverage detection of a welding seam is realized, 100% detection of defects such as incomplete penetration and incomplete fusion is ensured, and spatial distribution of the defects is accurately positioned. And mechanical property verification is combined, so that the safety and reliability of a welding joint are ensured. By optimizing the detection process and the partition transillumination process, the detection period is shortened by 42%, the repair positioning precision is improved to + / -0.5 mm, and the invalid repair area is reduced by 65%. The defects of incomplete penetration and root indentation within a certain range are allowed to exist, high cost and structural deformation risks caused by comprehensive repair are avoided, and the balance of process economy and quality control requirements is achieved. Meanwhile, a three-dimensional defect map is established by utilizing a digital image processing technology, so that a quantitative basis is provided for subsequent process optimization. The invention provides a systematic solution for the quality control of the welding joint with the complex geometric structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of ray detection, and particularly relates to a ray detection method for double-T welded joints. This method is particularly suitable for the quality assessment of welds with complex geometric structures made of nickel-based alloy materials (such as N06625), and can be widely applied to the manufacturing and maintenance of pressure-bearing equipment in the fields of nuclear power, chemical industry, aerospace, etc. Background Art

[0002] Due to its high-efficiency connection characteristics, lightweight design, and excellent mechanical properties, the double-T welded joint of the segment has been widely used in the manufacturing of high-end equipment such as aerospace, energy equipment, heavy machinery, and metallurgical equipment. However, such complex geometric configurations and welding process requirements pose many technical challenges during the manufacturing process, especially in welding quality control. For example Figure 1 As shown, the double-T structure is formed by synchronously welding the inner and outer shells and the upper and lower end gusset plates. There are significant gradient changes in the weld thickness, and high stress concentration areas are formed at the fusion line and the heat-affected zone. In addition, due to the closed structure, it is difficult for the welding rod to reach the root, which is extremely likely to cause typical welding defects such as cracks, lack of fusion, and lack of penetration. These defects are difficult to identify through visual inspection and conventional non-destructive testing methods, posing a serious threat to the static / dynamic load-bearing capacity and fatigue life of the structure.

[0003] As an internationally recognized non-destructive testing technology with high reliability, ray detection has become the preferred method for the quality evaluation of double-T joints due to its intuitive imaging of defect morphology, high spatial resolution, and quantitative analysis capabilities. However, this joint faces three major technical bottlenecks during the ray detection process: Wide blackness range - local overexposure or underexposure of the film due to sudden changes in the penetration thickness; Geometric image distortion - ray projection distortion caused by complex three-dimensional curvature; Sharp drop in signal-to-noise ratio - deterioration of defect detectability due to multiple interface scattering.

[0004] These problems seriously affect the accuracy and reliability of the detection results. Therefore, there is an urgent need for a comprehensive detection method integrating optimized exposure process, parameter mathematical model, and dynamic tolerance standard. Summary of the Invention

[0005] The present invention aims to provide a ray detection method for the double-T welded joint of the segment, which solves the three major bottleneck problems in the prior art and realizes efficient and accurate welding quality assessment by optimizing the detection process, zonal exposure process, defect location technology, and acceptance criteria. The specific technical solutions are as follows: The present invention provides a ray detection method for double-T welded joints, including the following steps: S1. Divide the weld into multiple inspection sections according to the change in weld curvature and the difference in penetration thickness, and verify the optimal radiographic parameters for each section through process tests; S2. Control the vertical distance from the radiation source to the workpiece surface by a directional ray machine and the translation distance of the radiation source to ensure that the geometric unsharpness meets the detection accuracy requirements; S3. Adopt the double-wall double-image overlapping vertical radiographic method to conduct a preliminary inspection on the double-T structure weld, and obtain the defect images of the weld and the heat-affected zone; S4. If defects such as lack of fusion, lack of penetration, or root depression are detected, use the double-wall single-image inclined radiographic method to accurately locate the defects in three dimensions; S5. Set the dynamic tolerance acceptance criteria based on the mechanical property test data, allowing the depth of lack of penetration not to exceed the preset threshold, and zero tolerance for lack of fusion defects; S6. Combine the radiographic inspection data with the three-dimensional defect atlas and grayscale histogram analysis to establish the acceptance basis.

[0006] In one embodiment, the vertical distance from the radiation source to the workpiece surface in S2 satisfies the formula:

[0007] In the formula, is the effective focal spot size; is the distance from the workpiece surface on the radiation source side to the film.

[0008] In one embodiment, the translation distance of the radiation source in S2 is calculated by the following formula:

[0009] In the formula, is the vertical distance from the radiation source to the film; is the vertical distance from the radiation source to the workpiece surface; is the weld width.

[0010] In one embodiment, in the double-wall double-image overlapping vertical radiographic method in S3, the radiation sources are arranged on both sides of the double-T joint, so that the weld images are overlapped and imaged, and the film blackness is controlled within the range of 2.4 - 3.0.

[0011] In one embodiment, the formulation of the dynamic tolerance acceptance criteria in S5 includes the following steps: S51. Conduct a tensile test on the welded specimen containing defects, and test the tensile strength, yield strength, and elongation; S52. If the tensile strength of the specimen ≥ 555 MPa and the elongation ≥ 73%, then allow the depth of lack of penetration ≤ 2 mm; S53. Set the blackness difference threshold ≤ 1.4 by comparing the defective negative film with the reference database through digital image comparison.

[0012] In one of the embodiments, the three-dimensional defect map described in S6 is obtained by the inclined transmission radiography method, the defect spatial positioning error ≤ ±0.3 mm, and the lack of penetration, root concavity and lack of fusion defects are distinguished based on the analysis of the gray histogram.

[0013] In one of the embodiments, the radiographic detection sensitivity is to identify a 0.2 mm equivalent defect, and there are no pit or scratch artifacts in the base metal area covered by the negative film.

[0014] In one of the embodiments, the criterion for judging lack of fusion defects is that the negative film image shows a serrated edge with irregular high-density shadows and the diffusion distance > 2 mm.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By innovatively combining three technologies of radiographic testing, digital simulation image and mechanical property testing, the present invention successfully solves the technical bottleneck in the detection of welded joints with complex geometric structures. The cooperative detection technology of double-wall vertical transmission radiography and double-wall inclined transmission radiography is adopted to achieve full-thickness coverage detection of the weld. At the same time, the spatial distribution of defects is accurately positioned by inclined transmission radiography, and the problem of projection overlap interference of complex geometric structures is solved. In addition, combined with mechanical property verification, the reliability and safety of the detection results are significantly improved on the premise that the welded joints meet the mechanical property standards.

[0016] 2. By optimizing the detection process and the partitioned transmission radiography process, the present invention significantly shortens the detection cycle, and the efficiency is increased by 42%. By accurately positioning the defects, the repair positioning accuracy is improved to ±0.5 mm, and the ineffective repair area is reduced by 65%, thus significantly reducing the repair cost. In addition, the acceptance criteria based on mechanical properties allow the existence of lack of penetration and root concavity defects within a certain range, avoiding the high cost and structural deformation risk caused by comprehensive repair, and achieving the balance between process economy and quality control requirements.

[0017] 3. The present invention adopts the technical route of "vertical transmission radiography for preliminary screening + inclined transmission radiography for precise positioning", effectively solving the technical problem of three-dimensional positioning of defects in double-T structure welds. By accurately calculating the distance from the radiation source to the workpiece surface and the translation distance, the integrity and authenticity of the negative film image are ensured. At the same time, using digital image processing technology, a three-dimensional defect map is established to provide a quantitative basis for subsequent process optimization. The defect position coordinate error is controlled within ±0.3 mm, the defect detection rate reaches 99.2%, and the geometric unsharpness is controlled at , and the detection sensitivity can identify a 0.2 mm equivalent defect.

[0018] 4. Combining the results of mechanical property tests, the present invention has formulated a scientific acceptance standard. By performing inclined penetration radiography on welded specimens (including typical defect areas) cut from the workpiece, a reference radiograph database is established, and based on this, the allowable threshold for defect size is formulated. Incomplete penetration (depth ≤ 2 mm) and root concavity (radius of curvature ≥ 5 mm) are allowed, while lack of fusion defects are not tolerated. This acceptance standard breaks through the limitations of traditional radiographic inspection acceptance standards, significantly improving the inspection efficiency and process economy while ensuring the structural safety.

[0019] In summary, the present invention demonstrates significant technical advantages in terms of quality assurance, efficiency improvement, defect location accuracy, acceptance standard optimization, and process economy, providing a systematic solution for the quality control of welded joints with complex geometric structures. Brief Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art.

[0021] Figure 1 It is a schematic diagram of the segment joint with a scale of 1:20; Figure 2 It is a flowchart of the radiographic inspection of the present invention; Figure 3 It is an equal-part diagram of radiographic film placement of the present invention, specifically divided into 12 equal parts: 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-1; Figure 4 It is a schematic diagram of penetration radiography of the present invention; Figure 5 It is a schematic diagram of the translation distance of the present invention; Figure 6 (a) - (c) are schematic diagrams of the defect forms of the present invention; Figure 7 (a) - (d) are radiographic imaging characteristics of typical defects of the present invention. Detailed Embodiment

[0022] The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0023] This embodiment takes the inspection of a certain double-T welded structure as an example. The specific welding parameters are as follows: the thickness of the inner and outer shells is 5 mm, the thickness of the rib plate is 10 mm, the weld width is 10 mm, and an assembly gap of 30 mm is maintained between the inner and outer shells. The segment shell and the end rib plate are both made of nickel-based alloy N06625 material, and the weld thickness is 5 mm.

[0024] I. Selection and Installation of Core Equipment Radiographic machine: The XXQ2005 directional radiographic machine is adopted, with an effective focal spot size of 1.5×1.5 mm, installed on a movable bracket, and the bracket is equipped with an angle adjustment knob and a translation slide rail.

[0025] Workpiece fixture: A customized V-shaped fixture is used to fix the double T-joint, ensuring that the axis of the weld is perpendicular to the center line of the radiation beam. A scale (accuracy 0.1 mm) is set at the bottom of the fixture to assist in positioning.

[0026] Intensifying screen and film: Lead foil intensifying screens (front screen 0.03 mm, rear screen 0.1 mm) are closely attached to the Agfa D7 film, and after being loaded into a light-tight bag, they are fixed to the back of the workpiece, and the edge of the light-tight bag is sealed with magnetic strips to prevent light leakage.

[0027] 3D laser scanner: Installed on the side of the inspection platform, used to scan the weld surface to generate point cloud data (accuracy ±0.01 mm).

[0028] Lead shielding room: Surround the inspection area, the lead equivalent of the wall is ≥2 mm, an observation window (lead glass thickness 15 mm) is set on the top, and the operating console is located outdoors.

[0029] Safety protection: The operator wears a 0.5 mm lead equivalent protective suit and a dosimeter to monitor the radiation dose in real time.

[0030] II. Differentiated radiography by zone 1. Measurement of weld curvature and thickness difference Use a 3D laser scanner to obtain the point cloud data of the weld surface, calculate the local radius of curvature through curvature analysis software, and screen out the areas with similar curvature change rates. At the same time, according to the geometric model of the weld cross-section, calculate the thickness difference on the radiographic path.

[0031] 2. Detection section division and parameter optimization Regions with similar continuous curvature change rates are divided into one section, and considering the control requirements of radiographic thickness difference, the double T-joint weld is divided into 12 detection sections as shown in Table 1 below and Figure 3 shown. Different radiographic lengths, tube voltages, and radiographic times are adopted for each different section. These specific radiographic parameters are all verified one by one through process tests to determine the optimal parameters, ensuring that the film blackening, contrast, and sensitivity of each detection section meet the defect identification requirements.

[0032]

[0033] Table 1: Table of radiographic detection section division and parameters Specific process tests include: during the tests, when it is found that the film blackness is too high > 3.0, the tube voltage of the ray machine can be reduced or the exposure time can be shortened; when it is found that the film blackness is too low < 2.4, the tube voltage of the ray machine can be increased or the exposure time can be extended; for high-scattering sections such as weld intersections, filters such as 0.1 mm copper foil can be added. Thus, parameter adjustments and retests are continuously carried out until the film quality meets the standards, and the optimal parameter combinations for each section at this time are recorded, such as for sections 1 - 3: 160 kV / 3.0 minutes, to form a reusable process database.

[0034] Subsequently, by dividing the sections and optimizing parameters such as the tube voltage, exposure time, and focal length of the ray machine separately according to the curvature and thickness of different regions, the problem of uneven film blackness, overexposure, or underexposure caused by "one-size-fits-all" parameters is avoided, laying a foundation for improving the monitoring effect and efficiency.

[0035] III. Double-wall collaborative radiography process 1. Double-wall double-image vertical radiography for preliminary screening Radiation source positioning: Move the XXQ2005 ray machine to the position of radiation source 1 as shown (on both sides of the double-T joint), and adjust the height of the support to make the center line of the radiation beam perpendicular to the axis of the weld. During radiography, it is necessary to ensure that the axes of the inner and outer shells are perpendicular to the center line of the radiation beam, and the film covers the entire width of the weld by 10 mm and the heat-affected zone. Figure 4 The tube voltage of the radiation source is adjusted to 160 kV, the exposure time is 3.0 min, and the focal length is 700 mm;

[0036] In the formula,

[0037] is the effective focal spot size; is the distance from the surface of the workpiece on the radiation source side to the film. Because,

[0038] so the minimum theoretical focal length In actual radiography operations, take to ensure the detection accuracy.

[0039] Among them, the geometric unsharpness verification formula: meets the requirements.

[0040] Start the ray machine to expose the film, and then process the film through an automatic film processor, where the developer temperature is 20 ± 1 °C, the time is 5 min, and the blackness of the base metal area is controlled at 2.4 - 2.8.

[0041] 2. Double-wall single-image inclined radiography for precise positioning Use a brightness ≥ 3000 cd / m 2Observe the film image characteristics with a view box to see if there are the following defects: Such as Figure 6 The incomplete penetration shown in (a): a continuous linear low-density shadow running through the root of the weld; Such as Figure 6 The root concavity shown in (b): an arc-shaped contour density gradient area with a depression depth ≥ 0.5 mm; Such as Figure 6 The lack of fusion shown in (c): a serrated-edge irregular high-density shadow with a diffusion distance > 2 mm.

[0042] If no defect indication is found, it is determined that the weld quality is qualified and no inclined radiography is required. If defects or suspected defect indications are found in the weld position or the heat-affected zone in the film image, switch to the inclined radiography mode for the defect or suspected defect area, that is, adjust the radiation source to the positions of the radiation sources 2 and 3 as shown in Figure 4 to accurately locate the spatial position of the defect.

[0043] For example Figure 5 As shown, since the weld width is known, the shell thickness is 5 mm, and the shell gap is 30 mm,

[0044] In the formula, is the vertical distance from the radiation source to the film; is the vertical distance from the radiation source to the workpiece surface; is the weld width. So it is calculated that the radiation source translation distance .

[0045] , and thus it is deduced that it is .

[0046] Then make the following specific adjustments according to the above parameters: Loosen the bracket angle knob and adjust the tilt angle of the ray machine to 14°; Translate the radiation source along the slide rail to the position; Fix the bracket again to ensure that the radiation beam covers the defect area.

[0047] IV. Construction of the dynamic tolerance acceptance standard 1. Verification by mechanical property tests Cut 20 mm × 5.3 mm × 150 mm specimens from the weld, retaining incomplete penetration (depth 1.5 - 2 mm) and lack of fusion defects. Then it can be loaded by an Instron 5985 universal testing machine to record the tensile strength and elongation. The test data are shown in Table 2 below.

[0048]

[0049] Table 2: Tensile Test Data Sheet of Welded Specimens The test results show that when the lack of penetration depth ≤ 2 mm, the percentage of the tensile strength of ERNiCrMo-3 welding wire reaches is higher than the allowable tensile strength coefficient of 0.7 for fillet welds specified in GB / T 15747-1995, meeting the specification requirements. Accordingly, the acceptance threshold is set to allow a lack of penetration depth ≤ 2 mm. If the above mechanical properties do not meet the standards, the threshold of the allowable lack of penetration depth is tightened until the mechanical properties meet the standards.

[0050] 2. Digital Image Analysis Technology Use ImageJ software to extract the gray values of the defect areas from the weld defect images collected during fluoroscopy, convert the defect images on the radiographic film into quantifiable gray value data, generate a gray histogram, and compare it with the reference film database (including 1000 qualified / defective films) to distinguish several types of defects such as lack of penetration (low gray values), lack of fusion (high gray values), and root concavity (gray gradient area), avoiding the subjective errors of manual interpretation and ensuring the accuracy of defect classification.

[0051] The specific defect classification rules are as follows: Lack of penetration: Continuous linear low-density shadow (gray value ≤ 120); Lack of fusion: Serrated-edge high-density shadow (gray value ≥ 200, diffusion distance > 2 mm, zero tolerance).

[0052] At the same time, set the blackness difference threshold ≤ 1.4 to prevent overexposure or underexposure caused by blackness fluctuations and ensure that the film contrast meets the requirements.

[0053] Thus, through the analysis of the gray histogram and comparison with the reference film database, verify the accuracy of the defect classification determined by the aforementioned fluoroscopy method and the defect classification of the specimens in the mechanical property test, and ensure the rationality and accuracy of the determination of the allowable lack of penetration depth threshold.

[0054] V. Comprehensive Acceptance and Data Management The acceptance process strictly follows the AB-level standard of 《JB / T4730.2-2015》. The initial inspection is independently evaluated by two Level II personnel, and the controversial films are submitted to Level III personnel for arbitration. The inspection report needs to record the fluoroscopy parameters, defect coordinates, and acceptance conclusions, and establish a three-dimensional defect atlas and an electronic file system to support data traceability and process optimization.

[0055] In the detection of the double T-joint of a certain nuclear power equipment above, after adopting this method: Detection cycle: shortened from 18 days to 10.5 days, with an efficiency improvement of 42%; Rework quantity: reduced from 38 to 13, with a cost reduction of 65%; Defect detection rate: reaching 99.2%, no missed detection of lack of fusion defects.

[0056] Although the present invention has been described in detail with general descriptions and specific embodiments above, modifications or improvements can be made to it on the basis of the present invention, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A double T-type welded joint radiographic detection method, characterized in that: The following steps are involved: S1. Divide the weld into multiple inspection sections according to the change of weld curvature and the difference in penetration thickness, and verify the optimal penetration parameters of each section through process tests; S2. Control the vertical distance from the radiation source to the workpiece surface through a directional ray machine And the source translation distance , ensure that the geometric unsharpness meets the detection accuracy requirements; S3. Use double-wall double-image overlapping vertical transillumination method to conduct preliminary inspection on double T-shaped structure welds to obtain defect images of welds and heat-affected zones; S4. If lack of fusion, lack of penetration or root depression defects are detected, the double-wall single-image tilted transillumination method is used to accurately locate the defects in three dimensions; S5. Set dynamic tolerance acceptance criteria based on mechanical properties test data, allowing the depth of incomplete penetration to not exceed the preset threshold and zero tolerance for incomplete fusion defects; S6. Combine the X-ray inspection data with the three-dimensional defect map and grayscale histogram analysis to establish the basis for acceptance.

2. The double T-shaped weld joint radiographic detection method according to claim 1, characterized in that: The vertical distance from the radiation source to the workpiece surface in S2 Satisfy the formula: ； In the formula, is the effective focal size; It is the distance from the workpiece surface on the radiation source side to the film.

3. The double T-shaped weld joint radiographic detection method according to claim 1, characterized in that: S2 is the source translation distance Calculated by the following formula: ； In the formula, is the vertical distance from the radiation source to the film; is the vertical distance from the radiation source to the workpiece surface; is the weld width.

4. The double-T-shaped weld joint radiographic detection method according to claim 1, characterized in that: In the double-wall double-image overlapping vertical transillumination method described in S3, the radiation sources are arranged on both sides of the double T-joint so that the weld images overlap and the film blackness is controlled within the range of 2.4 to 3.

0.

5. The double T-shaped weld joint radiographic detection method according to claim 1, characterized in that: The development of the dynamic tolerance acceptance criteria described in S5 includes the following steps: S51. Conduct tensile tests on defective welded specimens to test tensile strength, yield strength and elongation; S52. If the tensile strength of the specimen is ≥555MPa and the elongation is ≥73%, the incomplete penetration depth is allowed to be ≤2mm; S53. Compare the defective film with the reference database through digital image and set the black level difference threshold ≤ 1.

4.

6. The double T-shaped weld joint radiographic detection method according to claim 1, characterized in that: The three-dimensional defect map described in S6 is obtained by the oblique transillumination method, and the defect spatial positioning error is ≤±0.3mm. The defects such as incomplete penetration, root concave and lack of fusion are distinguished based on the grayscale histogram analysis.

7. The double-T-shaped weld joint radiographic detection method according to claim 1, characterized in that: The X-ray detection sensitivity is capable of identifying 0.2mm equivalent defects, and there are no pits or scratches on the base material in the film coverage area.

8. The double-T-shaped weld joint radiographic detection method according to claim 1, characterized in that: The criterion for determining the unfused defect is that the negative image shows an irregular high-density shadow with jagged edges and a diffusion distance of >2 mm.

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