Radiographic testing method for double-T welded joints

Abstract

The present invention belongs to the field of radiographic detection technology, and specifically relates to a radiographic detection method for double-T-type welded joints. Through the collaborative detection technology of double-wall vertical radiography and double-wall inclined radiography, full-thickness coverage detection of welds is achieved, ensuring 100% detection of defects such as incomplete penetration and lack of fusion, and accurately locating the spatial distribution of defects. Combined with mechanical property verification, the safety and reliability of welded joints are ensured. By optimizing the detection process and partitioned radiography process, the detection cycle is shortened by 42%, the rework positioning accuracy is improved to ±0.5 mm, and the invalid rework area is reduced by 65%. Incomplete penetration and root concave defects within a certain range are allowed to exist, avoiding the high cost and structural deformation risk brought about by comprehensive rework, and achieving a balance between process economy and quality control requirements. At the same time, digital image processing technology is used to establish a three-dimensional defect map to provide a quantitative basis for subsequent process optimization. The present invention provides a systematic solution for the quality control of welded joints with complex geometric structures.

Description

Technical Field

[0001] This invention belongs to the field of radiographic testing technology, specifically a radiographic testing method for double-T welded joints. This method is particularly suitable for evaluating the quality of welds with complex geometries made from nickel-based alloys (such as N06625) and has broad application in the manufacturing and maintenance of pressure-bearing equipment in fields such as nuclear power, chemical engineering, and aerospace. Background Art

[0002] Sector-shaped double-T welded joints have been widely used in high-end equipment manufacturing fields such as aerospace, energy equipment, heavy machinery, and metallurgical equipment due to their efficient connection characteristics, lightweight design, and excellent mechanical properties. However, the complex geometric configuration and welding process requirements of this structure pose many technical challenges in the manufacturing process, especially in terms of welding quality control. Figure 1 As shown, the double-T structure is constructed by synchronously welding the inner and outer shells to the upper and lower end panels. The weld thickness exhibits a significant gradient, creating high stress concentration areas at the fusion line and heat-affected zone. Furthermore, due to the closed structure, welding rods have difficulty reaching the root, which can easily lead to typical welding defects such as cracks, lack of fusion, and incomplete penetration. These defects are difficult to identify through visual inspection and conventional non-destructive testing methods, posing a serious threat to the structure's static and dynamic load-bearing capacity and fatigue life.

[0003] As an internationally recognized high-reliability non-destructive testing technology, radiographic testing has become the preferred method for evaluating the quality 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 radiographic testing:

[0004] Wide black range - due to sudden changes in transillumination thickness, the film is partially over- or under-exposed;

[0005] Geometric image distortion—complex three-dimensional curvature causes ray projection distortion;

[0006] A sharp drop in signal-to-noise ratio—Multiple interface scattering leads to degraded defect detectability.

[0007] These problems seriously affect the accuracy and reliability of the test results. Therefore, a comprehensive test method that integrates transillumination process optimization, parameter mathematical model and dynamic tolerance standard is urgently needed. Summary of the Invention

[0008] This invention aims to provide a radiographic inspection method for fan-shaped double-T welded joints. By optimizing the inspection process, zoned radiography, defect location technology, and acceptance criteria, it addresses three major bottlenecks in the existing technology and enables efficient and accurate welding quality assessment. The specific technical solution is as follows:

[0009] The present invention provides a radiographic detection method for double-T-shaped welded joints, comprising the following steps:

[0010] S1. Divide the weld into multiple inspection sections based on weld curvature changes and thickness differences, and verify the optimal radiography parameters for each section through process tests.

[0011] S2. Control the vertical distance from the radiation source to the workpiece surface through the directional ray machine And the source translation distance , ensure that the geometric unsharpness meets the detection accuracy requirements;

[0012] S3. Perform preliminary inspection of the double-T structure weld using the double-wall double-image overlapping vertical radiography method to obtain defect images of the weld and heat-affected zone;

[0013] S4. If lack of fusion, incomplete penetration, or root depression is detected, use the double-wall single-shadow oblique radioscopy method to accurately locate the defect in three dimensions.

[0014] S5. Set dynamic tolerance acceptance criteria based on mechanical property test data, allowing the depth of incomplete penetration to not exceed a preset threshold and zero tolerance for lack of fusion defects;

[0015] S6. Combine the X-ray inspection data with the three-dimensional defect map and grayscale histogram analysis to establish the basis for acceptance.

[0016] In one embodiment, the vertical distance from the radiation source to the workpiece surface in S2 is Satisfies the formula:

[0017]

[0018] Where, is the effective focal size; is the distance from the workpiece surface on the radiation source side to the film.

[0019] In one embodiment, the source translation distance in S2 is Calculated by the following formula:

[0020]

[0021] Where, 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.

[0022] In one embodiment, in the double-wall double-image overlapping vertical radiography 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.

[0023] In one embodiment, the formulation of the dynamic tolerance acceptance criteria in S5 includes the following steps:

[0024] S51. Perform tensile tests on welded specimens containing defects to test tensile strength, yield strength, and elongation;

[0025] S52. If the tensile strength of the specimen is ≥555 MPa and the elongation is ≥73%, the permitted incomplete penetration depth is ≤2 mm.

[0026] S53. Compare the defective film with the reference database through digital image comparison and set the black level difference threshold to ≤1.4.

[0027] In one embodiment, the three-dimensional defect map described in S6 is obtained by an oblique radiography method, the defect spatial positioning error is ≤±0.3mm, and the incomplete penetration, root concave and unfusion defects are distinguished based on grayscale histogram analysis.

[0028] In one embodiment, the X-ray detection sensitivity is capable of identifying defects equivalent to 0.2 mm, and the base material in the film coverage area has no pits or scratches.

[0029] In one embodiment, the criterion for determining the unfused defect is that the film image shows an irregular high-density shadow with jagged edges and a diffusion distance greater than 2 mm.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. This invention successfully resolves the technical bottleneck in the inspection of welded joints with complex geometric structures by innovatively combining radiographic testing, digital simulation imaging, and mechanical properties testing. The collaborative detection technology of double-wall vertical radiography and double-wall oblique radiography enables full-thickness coverage inspection of welds. At the same time, oblique radiography precisely locates the spatial distribution of defects, resolving the problem of overlapping projections and interference in complex geometric structures. Furthermore, combined with mechanical properties verification, the reliability and safety of test results are significantly improved, ensuring that welded joints meet mechanical performance standards.

[0032] 2. This invention significantly shortens the inspection cycle and improves efficiency by 42% by optimizing the inspection process and partitioning the radiography process. By accurately locating defects, the rework positioning accuracy is improved to ±0.5mm, reducing the ineffective rework area by 65%, thereby significantly reducing the rework cost. In addition, the acceptance criteria based on mechanical properties allow for a certain range of incomplete weld penetration and root concave defects, avoiding the high cost and structural deformation risk of comprehensive rework, and achieving a balance between process economy and quality control requirements.

[0033] 3. The present invention adopts the technical route of "vertical radiography screening + inclined radiography precise positioning", which effectively solves the technical problem of three-dimensional positioning of double T-shaped structure weld defects. By accurately calculating the distance from the radiation source to the workpiece surface and the translation distance, the integrity and authenticity of the film image are ensured. At the same time, digital image processing technology is used to establish a three-dimensional defect map, providing a quantitative basis for subsequent process optimization. The coordinate error of the defect position is controlled within ±0.3mm, the defect detection rate reaches 99.2%, and the geometric unsharpness is controlled within , the detection sensitivity can identify 0.2mm equivalent defects.

[0034] 4. This invention incorporates mechanical property test results to develop scientific acceptance criteria. By performing oblique radiography on weld specimens removed from the workpiece (including typical defect areas), a reference film database is established, upon which defect size thresholds are established. Incomplete penetration (depth ≤ 2mm) and root concavity (radius of curvature ≥ 5mm) are permitted, while lack of fusion defects are tolerated. This acceptance standard transcends the limitations of traditional radiographic inspection standards, significantly improving inspection efficiency and process economics while ensuring structural safety.

[0035] In summary, the present invention demonstrates significant technical advantages in terms of quality assurance, efficiency improvement, defect location accuracy, acceptance criteria optimization, and process economy, providing a systematic solution for the quality control of welded joints with complex geometric structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0037] Figure 1 The schematic diagram of the fan-shaped segment joint is at a scale of 1:20;

[0038] Figure 2 This is a flow chart of the ray detection of the present invention;

[0039] Figure 3 This is a diagram of equal parts of the radiographic detection cloth 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, and 12-1;

[0040] Figure 4 This is a transillumination schematic diagram of the present invention;

[0041] Figure 5 This is a schematic diagram of the translation distance of the present invention;

[0042] Figure 6 (a) to (c) are schematic diagrams of defect forms of the present invention;

[0043] Figure 7 (a) to (d) are the radiographic imaging features of typical defects of the present invention. DETAILED DESCRIPTION

[0044] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0045] This example uses a double-T welded structure as an example. The specific welding parameters are: 5mm thickness for the inner and outer shells, 10mm thickness for the ribs, 10mm weld seam width, and a 30mm assembly gap between the inner and outer shells. The segment shells and end ribs are made of nickel-based alloy N06625, with a 5mm weld seam thickness.

[0046] 1. Core equipment selection and installation

[0047] X-ray machine: XXQ2005 directional X-ray machine with effective focal spot size of 1.5×1.5mm is used, which is installed on a movable bracket equipped with an angle adjustment knob and a translation slide rail.

[0048] Workpiece fixture: A customized V-shaped fixture is used to fix the double T-joint to ensure that the weld axis is perpendicular to the center line of the beam. A scale (accuracy 0.1mm) is set at the bottom of the fixture to assist in positioning.

[0049] Intensifying screen and film: Lead foil intensifying screen (front screen 0.03mm, rear screen 0.1mm) is placed close to AgfaD7 film, placed in a dark bag and fixed on the back of the workpiece. The edge of the dark bag is sealed with a magnetic strip to prevent light leakage.

[0050] 3D laser scanner: installed on the side of the detection platform, used to scan the weld surface to generate point cloud data (accuracy ±0.01mm).

[0051] Lead shielding room: surrounds the detection area, the lead equivalent of the wall is ≥2mm, an observation window is set on the top (lead glass thickness 15mm), and the operating table is located outdoors.

[0052] Safety protection: Operators wear 0.5mm lead equivalent protective clothing and dosimeters to monitor radiation dose in real time.

[0053] 2. Differentiated transillumination by zones

[0054] 1. Measurement of weld curvature and thickness difference

[0055] A 3D laser scanner is used to acquire point cloud data of the weld surface. Curvature analysis software is used to calculate the local curvature radius and screen areas with similar curvature change rates. Simultaneously, the thickness difference along the illumination path is calculated based on the weld cross-sectional geometry model.

[0056] 2. Detection segment division and parameter optimization

[0057] The area with similar continuous curvature change rate is divided into a section, and taking into account the control requirements of the penetration thickness difference, the double T-type weld is divided into the following Table 1 and Figure 3 The 12 inspection sections shown in the figure are used. Different exposure lengths, tube voltages, and exposure times are used for each section. These specific exposure parameters are individually verified through process testing to determine the optimal parameters, ensuring that the film darkness, contrast, and sensitivity in each inspection section meet the defect recognition requirements.

[0058]

[0059] Table 1: X-ray detection area division and radiographic parameters

[0060] Specific process tests include reducing the X-ray tube voltage or shortening the exposure time if the film's blackness is too high (>3.0). If the film's blackness is too low (<2.4), increasing the X-ray tube voltage or extending the exposure time. For high-scattering areas, such as weld intersections, adding filters like 0.1mm copper foil is recommended. This process is repeated repeatedly until film quality meets standards. The optimal parameter combination for each section is recorded, such as Sections 1-3: 160kV / 3.0 minutes, creating a reusable process database.

[0061] Then, by dividing the area into sections, the tube voltage, exposure time, focal length and other parameters of the X-ray machine are optimized separately according to the curvature and thickness of different areas, avoiding the problem of overexposure or underexposure caused by uneven film blackness due to "one-size-fits-all" parameters, laying the foundation for improving monitoring effects and efficiency.

[0062] 3. Double-wall collaborative transillumination process

[0063] 1. Double-wall double-shadow vertical transillumination initial screening

[0064] Radiation source positioning: Move the XXQ2005 X-ray machine to the Figure 4 Position source 1 as shown (on either side of the double T-joint). Adjust the bracket height so the beam centerline is perpendicular to the weld axis. During transillumination, ensure the inner and outer shell axes are perpendicular to the beam centerline. Cover the full 10mm width of the weld and the heat-affected zone with film.

[0065] The source tube voltage was adjusted to 160 kV, the exposure time was 3.0 min, and the focal length was 700 mm;

[0066]

[0067] Where, is the effective focal size; is the distance from the workpiece surface on the radiation source side to the film.

[0068] because, , so the minimum theoretical focal length In actual transillumination operation, To ensure detection accuracy.

[0069] Among them, the geometric unsharpness verification formula is:

[0070] , meeting the requirements.

[0071] Start the X-ray machine to expose the film, and then process the film in an automatic film processor, with the developer temperature at 20±1°C, the processing time at 5 minutes, and the blackness of the base material area controlled at 2.4~2.8.

[0072] 2. Double-wall single-image oblique transillumination for precise positioning

[0073] Use brightness ≥3000cd / m 2 Observe the film image characteristics with a film viewing light to see if there are any of the following defects:

[0074] like Figure 6 Incomplete penetration shown in (a): a continuous linear low-density shadow that runs through the weld root;

[0075] like Figure 6 (b) The root concave shown: arc-shaped contour density gradient area, the concave depth ≥ 0.5mm;

[0076] like Figure 6 (c) shows the lack of fusion: irregular high-density shadow with jagged edges and a diffusion distance of >2mm.

[0077] If no defects are found, the weld is judged to be of good quality and no tilt radiography is required. If the film image shows defects or suspected defects in the weld position or heat-affected zone, switch to tilt radiography mode for the defect or suspected defect area, that is, adjust the radiation source to the following angles: Figure 4 The positions of the radiation sources 2 and 3 are shown, thereby accurately locating the spatial position of the defect.

[0078] For example Figure 5 As shown, since the weld width is known , shell thickness 5mm, shell gap 30mm,

[0079]

[0080] Where, 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 the calculated source translation distance is .

[0081] , from this we can infer that .

[0082] Then make the following adjustments based on the above parameters:

[0083] Loosen the bracket angle knob and adjust the tilt angle of the X-ray machine to 14°;

[0084] Move the source along the slide rail to Location;

[0085] Reposition the stent to ensure that the X-ray beam covers the defect area.

[0086] 4. Construction of dynamic tolerance acceptance criteria

[0087] 1. Mechanical properties test verification

[0088] Specimens measuring 20 mm x 5.3 mm x 150 mm were cut from the weld, retaining any incomplete penetration (depth of 1.5 to 2 mm) and any lack of fusion defects. These specimens were then loaded using an Instron 5985 universal testing machine, and tensile strength and elongation were recorded. The test data are shown in Table 2 below.

[0089]

[0090] Table 2: Welding specimen tensile test data

[0091] Test results show that when the incomplete weld depth is ≤2mm, the tensile strength percentage of the ERNiCrMo-3 welding wire exceeds the allowable tensile strength coefficient of 0.7 for fillet welds specified in GB / T15747-1995, meeting the specification. Therefore, the acceptance threshold is set at an allowable incomplete weld depth of ≤2mm. If the above mechanical properties do not meet the requirements, the allowable incomplete weld depth threshold is tightened until the mechanical properties meet the requirements.

[0092] 2. Digital image analysis technology

[0093] ImageJ software is used to extract the grayscale value of the defect area from the weld defect image collected during radiography. The defect image in the radiographic film is converted into quantifiable grayscale value data, and a grayscale histogram is generated. This is then compared with a reference film database (containing 1,000 sets of qualified / defective films) to distinguish between defects such as incomplete penetration (low grayscale value), lack of fusion (high grayscale value), and root concave (grayscale gradient area). This avoids subjective errors in manual interpretation and ensures the accuracy of defect classification.

[0094] The specific defect classification rules are as follows:

[0095] Incomplete penetration: continuous linear low-density shadow (grayscale value ≤ 120);

[0096] Unfused: jagged edge high-density shadow (grayscale value ≥ 200, diffusion distance > 2mm, zero tolerance).

[0097] At the same time, the black level difference threshold is set to ≤1.4 to prevent overexposure or underexposure due to black level fluctuations and ensure that the film contrast meets the requirements.

[0098] Therefore, by comparing the grayscale histogram analysis with the reference film database, the accuracy of the defect classification determined by the aforementioned transillumination method and the defect classification of the specimens in the mechanical properties test was verified, ensuring the rationality and accuracy of the determination of the threshold value for the allowable incomplete penetration depth.

[0099] 5. Comprehensive acceptance and data management

[0100] The acceptance process strictly adheres to the JB / T4730.2-2015 AB standards. Initial inspections are conducted independently by two Level II personnel, and disputed films are submitted to Level III personnel for arbitration. The inspection report must record the transillumination parameters, defect coordinates, and acceptance conclusions. A 3D defect map and electronic archiving system are also established to support data traceability and process optimization.

[0101] In the above-mentioned double T-joint inspection of a nuclear power equipment, after adopting this method:

[0102] Testing cycle: shortened from 18 days to 10.5 days, with an efficiency increase of 42%;

[0103] Repair quantity: reduced from 38 to 13, cost reduction by 65%;

[0104] Defect detection rate: reaches 99.2%, with zero missed detection of unfused defects.

[0105] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made thereto. Therefore, such modifications and improvements, without departing from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. Double T-type welded joint radiographic inspection method, characterized in that: The following steps are involved: S1. Divide the weld into multiple inspection sections based on weld curvature changes and thickness differences, and verify the optimal radiography parameters for each section through process tests. Specific process tests include: if the film blackness is found to be too high > 3.0, reduce the X-ray tube voltage or shorten the exposure time; if the film blackness is found to be too low < 2.4, increase the X-ray tube voltage or extend the exposure time; add 0.1mm copper foil to the high scattering section; S2. Control the vertical distance from the radiation source to the workpiece surface through the directional ray machine And the source translation distance , ensuring geometric unsharpness mm; in satisfy , where is the effective focal size; is the distance from the workpiece surface to the film on the radiation source side; satisfy , where 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; S3. Perform preliminary inspection of double-T structure welds using a double-wall, double-image overlap vertical radiography method: The radiation sources are placed on both sides of the double-T joint, overlapping the weld images to obtain defect images of the weld and heat-affected zone. S4. If incomplete fusion, incomplete penetration or root concave defects are detected, the double-wall single-shadow tilt radiography method is used to accurately locate the defects in three dimensions: the tilt angle of the radiation source ; S5. Setting dynamic tolerance acceptance criteria based on mechanical properties test data, wherein the dynamic tolerance acceptance criteria are formulated as follows: S51. Perform tensile tests on welded specimens containing defects to test tensile strength, yield strength, and elongation; S52. If the tensile strength of the specimen is ≥555 MPa and the elongation is ≥73%, the incomplete penetration depth is allowed to be ≤2 mm, and the lack of fusion defect is zero tolerance; S6. Combine the X-ray inspection data with the three-dimensional defect map and grayscale histogram analysis to establish the acceptance basis: the three-dimensional defect map is obtained by the double-wall single-shadow tilt radiography method, the defect spatial positioning error is ≤±0.3mm, and based on the grayscale histogram analysis, the defects such as incomplete penetration, root concave and lack of fusion are distinguished.

2. The radiographic inspection method for double-T welded joints according to claim 1, characterized in that: The development of dynamic tolerance acceptance criteria as described in S5 also includes: By comparing the defective film with the reference database through digital image, the blackness difference threshold is set to ≤1.

4.

3. The radiographic inspection method for double-T welded joints according to claim 1, wherein: The sensitivity of the X-ray detection is to be able to identify defects equivalent to 0.2mm, and there are no pits or scratches on the base material in the film coverage area.

4. The radiographic inspection method for double-T welded joints according to claim 1, wherein: 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 greater than 2 mm.

Images