A nondestructive testing method for eliminating blind areas in weld detection in pipes

Abstract

The application discloses a kind of nondestructive testing methods for eliminating the blind area of pipeline weld detection, belong to the technical field of pipeline nondestructive testing.The method sets up multiple contrast test blocks with same material and different thickness of pipeline, adopts traditional RT detection technology to collect the film of pipeline weld area and contrast test block, obtains high-precision digital image after digital processing, generates gray-scale-high-precision calibration curve based on the digital image of contrast test block, compares the gray distribution curve of weld with the calibration curve, calculates the excess height and inner wall smoothness of weld, to judge the quality of weld inner wall.The application uses existing RT detection device to cooperate contrast test block to carry out pipeline weld inner wall nondestructive testing, reduces detection cost while ensuring the measurement accuracy of excess height and smoothness, improves detection efficiency.

Description

Technical Field

[0001] This invention relates to pipeline non-destructive testing technology, and more particularly to a non-destructive testing method for eliminating blind spots in pipeline weld inspection. Background Technology

[0002] Commonly used non-destructive testing methods for pipe welds in the prior art include radiographic testing, conventional ultrasonic testing, and phased array ultrasonic testing. These methods can detect volumetric and area defects in welds, such as porosity, slag inclusions, lack of fusion, and cracks, without damaging the object being tested, as described in patent applications, etc.

[0003] For welds on the inner walls of pipelines, especially those in high-pressure oxygen pipes where internal smoothness is extremely important, existing inspection technologies have significant limitations. Current methods primarily focus on the qualitative or localization of defects, lacking effective means for quantitatively assessing the weld reinforcement (the height of the weld protrusion above the base material) and the smoothness of the pipeline's inner wall. Excessive reinforcement or poor smoothness can cause violent collisions and friction between the high-speed flowing oxygen and the inner wall, generating localized high temperatures. This high temperature can provide sufficient ignition energy for residual iron powder, weld slag, and other impurities within the pipeline to ignite, potentially "exploding" the entire pipeline system. Therefore, effectively eliminating blind spots in the inspection of pipeline welds under non-destructive conditions and achieving accurate measurement of weld reinforcement and inner wall smoothness has become a pressing problem in this field. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a non-destructive testing method for eliminating blind spots in the inspection of weld seams inside pipelines. This method aims to eliminate blind spots in the inspection of weld seams inside pipelines and to achieve a quantitative assessment of the weld seam height and smoothness inside the pipeline.

[0005] The objective of this invention can be achieved through the following technical means: A non-destructive testing method for eliminating blind spots in pipeline weld inspection includes the following steps: Step 1: Prepare multiple comparative test blocks of the same material but different thicknesses as the pipe to be tested; Step 2: Use radiography to examine the weld seam of the pipe to be tested and the comparison test block, and collect pipe and test block films. Use a film digitizer to convert the pipe and test block films into digital images of the pipe and test blocks, respectively. Step 3: Draw a sampling line in the digital image of the pipeline along the direction perpendicular to the weld length. The length of the sampling line covers the weld and the base material on both sides of the pipeline under test, and generate the grayscale distribution curve of the weld along the sampling line. Step 4: Extract the grayscale curve of the sampling line in the digital image of each test block to obtain the average grayscale value of each comparison test block. Generate the corresponding residual height based on the thickness of the comparison test block, and generate the grayscale-residual height calibration curve according to the mapping relationship between the residual height and the average grayscale value. Step 5: Compare the grayscale distribution curve with the grayscale-remaining height calibration curve to calculate the maximum remaining height and inner wall smoothness of the weld seam of the pipe to be tested.

[0006] In this invention, in step 1, the outer surface of the weld of the pipe to be tested and the comparison test block are ground, requiring the surface roughness of the outer surface of the weld to be less than 3.2 μm, and the difference between the surface roughness of the comparison test block and the surface roughness of the outer surface of the weld to be less than 1 μm.

[0007] In this invention, in step 1, a set of comparative test blocks are prepared at intervals of 0.5 mm between thicknesses of 14 mm and 22 mm, and the side length of the comparative test blocks is not less than 10 mm.

[0008] In this invention, in step 2, the radiation is X-ray or gamma ray, the pipe film and the test block film are X-ray films, and the pipe digital image and the test block digital image are in DICOM format.

[0009] In this invention, the grayscale distribution curve of the sampling line is generated by DICOM analysis software, the digital resolution of the film digitizer is 16 bits, and the grayscale distribution curve has 65,536 gray levels.

[0010] In this invention, in step 5, the sampling line is divided into N equally spaced sampling points. The gray values ​​of each sampling point are extracted based on the gray-scale distribution curve of the weld, generating a gray-scale value sequence. The maximum gray-scale value g is then extracted from the gray-scale value sequence. max Based on the grayscale-residual height calibration curve, the maximum grayscale value g is determined. max Mapped to the corresponding maximum redundant height h max .

[0011] In this invention, in step 5, the gray level difference between adjacent sampling points in the gray level value sequence is calculated, the gray level smoothness of the corresponding sampling point is calculated based on the gray level difference, and then the inner wall smoothness is calculated based on the gray level smoothness.

[0012] In this invention, step 6 is also included, repeating steps 3 to 5 to obtain multiple sets of maximum excess height and inner wall smoothness of the weld seam of the pipeline to be tested, then calculating the total out-of-tolerance length and smoothness grade of the pipeline to be tested, and combining the maximum excess height, out-of-tolerance length, and smoothness grade to generate a comprehensive evaluation result of the weld inner wall quality.

[0013] In this invention, in step 6, K equally spaced sampling lines are drawn in the digital image of the pipeline along the length of the weld seam of the pipeline to be tested, and the maximum excess height and inner wall smoothness corresponding to each sampling line are extracted to obtain multiple sets of maximum excess height and inner wall smoothness.

[0014] In this invention, the maximum value of the excess height is extracted from multiple sets of maximum excess heights, and the corresponding excess index is generated based on the maximum excess height of each sampling line. The excess indexes of all sampling lines are combined to generate an excess sequence. The total excess length is calculated based on the excess sequence. Then, the overall smoothness is calculated based on multiple sets of inner wall smoothness, and a smoothness level is generated based on the overall smoothness.

[0015] The non-destructive testing method for eliminating blind spots in pipeline weld inspection, as described in this invention, offers the following advantages: This invention eliminates blind spots in pipeline weld inspection through film digitization and achieves precise quantification of weld reinforcement and smoothness through comparative test blocks. This prevents combustion and explosion accidents caused by weld reinforcement friction in hyperbaric oxygen pipes, ensuring the safety of personnel and property. This invention can be completed using existing RT testing equipment, resulting in low testing costs and high efficiency. It provides quantitative evidence for pipeline inner wall quality acceptance, demonstrating significant safety, economic, and social benefits. Attached Figure Description

[0016] Figure 1 This is a flowchart of the non-destructive testing method for eliminating blind spots in pipeline weld inspection according to the present invention; Figure 2 This is a schematic diagram of the weld grayscale distribution curve generated by the present invention; Figure 3 This is a grayscale curve of the comparative test blocks of different thicknesses in this invention; Figure 4 This is a graph showing the relationship between grayscale value and thickness in this invention. Figure 5 This is a graph showing the blackness and grayness of the film of this invention. Figure 6 Digital images of comparative test blocks of different thicknesses according to the present invention; Figure 7 This is a grayscale curve of the 0.5mm excess height comparison test block of the present invention; Figure 8 This is a grayscale distribution curve of the weld seam of the present invention.

[0017] The reference numerals in the attached figures are: pipe 11, weld 12, and comparison test block 13. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0019] Radiographic testing (RT) is a common non-destructive testing technique for pipeline defects. Its principle utilizes the strong penetrating power of X-rays or gamma rays. As they pass through a workpiece, the attenuation varies depending on the material's density or thickness. Internal defects (porosity, inclusions, cracks, etc.) have lower density and less attenuation, resulting in higher transmission intensity. This ultimately forms a grayscale difference image on film or a digital detector, allowing for the determination of the defect's location, size, and shape. This invention addresses the problem of inaccurate measurement of weld reinforcement height in high-pressure oxygen pipelines by proposing a non-destructive testing method based on RT film digitization, comparative test blocks of the same material, and comprehensive evaluation. This method uses DICOM software to quantify and compare grayscale curves, enabling numerical determination and smooth, objective evaluation of weld reinforcement height in high-pressure oxygen pipelines. Example 1

[0020] like Figures 1 to 4 As shown, the present invention provides a non-destructive testing method for eliminating blind spots in the inspection of welds inside pipelines, comprising the following steps.

[0021] Step 1: Prepare multiple comparative test blocks of the same material but different thicknesses as the pipe to be tested. Specifically, take a material of the same material as the pipe to be tested and process it to prepare multiple comparative test blocks with a thickness between 14mm and 22mm and an adjacent thickness gradient of 0.5mm. The side length of each comparative test block is not less than 10mm to ensure that a sufficiently large uniform grayscale area can be obtained during radiographic imaging. The smaller the adjacent thickness gradient, the higher the accuracy of subsequent weld reinforcement and smoothness measurements. In this invention, in order to ensure that the grayscale changes reflected by the pipe film originate only from the weld inner wall reinforcement, and to make the surface condition of the comparative test blocks consistent with the actual weld outer surface, the weld outer surface of the pipe to be tested and the comparative test blocks are ground. The surface roughness of the ground weld outer surface should be less than 3.2μm, and the difference between the surface roughness of each comparative test block and the surface roughness of the weld outer surface should be less than 1μm.

[0022] Step 2: Irradiate the weld seam of the pipeline under test and the control block using radiography, acquiring pipeline and control block films. Use a film digitizer to convert the pipeline and control block films into digital images of the pipeline and control block, respectively. The radiation source is either X-ray or gamma-ray, selected based on pipeline thickness and required detection sensitivity. In this embodiment, the radiation source parameters are first set, and then single-wall radiography is used to irradiate the weld seam area of ​​the pipeline under test and the control block using radiation generated by the radiation source. The radiation parameters include tube voltage, tube current, exposure time, and focal length. The radiation parameters for the control block are consistent with those for the pipeline under test. For example, the radiation source in this invention is an XXG2505L X-ray machine, and the tube voltage, tube current, exposure time, and focal length are set to 100kV, 5mA, 3min, and 700mm, respectively. The obtained pipeline and control block films are X-ray films, and the film quality must meet the requirements of NB / T-47013.2. Furthermore, the pipe film and test block film are scanned using a film digitizer to convert them into DICOM format digital images of the pipe and test block. The film digitizer has a digital resolution of at least 12 bits, and different scanning parameters (digital resolution) of the film digitizer can be selected according to the density of different films. In this invention, a film digitizer with a digital resolution of 16 bits is used.

[0023] Step 3: Draw a sampling line in the digital image of the pipeline along a direction perpendicular to the weld length. The length of the sampling line covers the weld and the base material on both sides of the pipeline under test, generating a grayscale distribution curve of the weld along the sampling line. In this invention, the grayscale value change of the weld in the digital image of the pipeline is used to determine the weld reinforcement height and smoothness. Specifically, the digital image of the pipeline is imported into DICOM analysis software (such as ISEE), and references... Figure 2 In the weld area of ​​the pipeline under test, sampling lines are drawn along the direction perpendicular to the weld length (i.e., the axial direction of the circumferential weld), and a grayscale distribution curve of the sampling lines is generated. In this invention, since the digital image of the pipeline is obtained by a 16-bit film digitizer, its original grayscale level is 65536 levels (corresponding to grayscale values ​​from 0 to 65535). Therefore, the grayscale level of the grayscale distribution curve can be set to any value not exceeding this original grayscale level. In this embodiment, to preserve the complete grayscale information of the pipeline digital image, the grayscale distribution curve is directly generated using 65536 grayscale levels.

[0024] Step 4: Extract the grayscale curve of the sampling lines from the digital image of each test block to obtain the average grayscale value of each comparison test block. Generate the corresponding residual height based on the thickness of the comparison test blocks, and generate a grayscale-residual height calibration curve based on the mapping relationship between the residual height and the average grayscale value. Use the same method as in Step 3 to draw sampling lines in the digital image of each test block, and generate the corresponding grayscale curve using DICOM analysis software. For example... Figure 3 As shown, Figure 3 The left side consists of digital images of comparative test blocks with thicknesses ranging from 14mm to 22mm. A sampling line is plotted on this digital image to obtain... Figure 3 The grayscale curve on the right corresponds to the thickness curve. The grayscale curve in the figure shows a stepped distribution, with each horizontal fluctuation step corresponding to a thickness value. The grayscale value monotonically increases with increasing thickness, from low to high grayscale, corresponding to 14mm, 16mm, 18mm, 20mm, and 22mm respectively. The average grayscale value of the grayscale curve corresponding to each comparison test block is calculated. Let the thickness of the pipe under test be H0, then the thickness is h. b The relative height h of the test block to the test pipe x =h b -H0. Extract the average gray value and residual height corresponding to each comparison test block, and plot the gray-gray value-residual height calibration curve based on multiple sets of average gray values ​​and residual heights.

[0025] Step 5: Compare the grayscale distribution curve with the grayscale-residual height calibration curve to calculate the maximum residual height and inner wall smoothness of the weld seam in the pipeline under test. Specifically, the sampling line is divided into N equally spaced sampling points. Based on the grayscale distribution curve of the weld seam, the grayscale values ​​of each sampling point are extracted to generate a grayscale value sequence. The maximum grayscale value g is extracted from the grayscale value sequence. max Based on the grayscale-residual height calibration curve, the maximum grayscale value g is determined. max Mapped to the corresponding maximum redundant height h max Furthermore, the gray-level difference Δg between adjacent sampling points in the gray-level value sequence is calculated. i i = 1, 2, ..., N-1. The grayscale smoothness of each sampling point is calculated based on the grayscale difference, and then the inner wall smoothness is calculated based on the grayscale smoothness. In a more preferred embodiment, the maximum residual height can also be obtained by curve fitting the grayscale-residual height calibration curve. The specific calculation steps for the maximum residual height and inner wall smoothness are as described in Embodiment 2.

[0026] Step 6: Repeat steps 3 to 5 to obtain multiple sets of maximum excess height and inner wall smoothness of the weld seam of the pipeline under test. Then calculate the out-of-tolerance length and smoothness level of the pipeline under test. Combine the maximum excess height, out-of-tolerance length, and smoothness level to generate a comprehensive evaluation result of the weld inner wall quality. Specifically, draw K equally spaced sampling lines along the length of the weld seam of the pipeline under test in the digital image of the pipeline. Extract the maximum excess height and inner wall smoothness corresponding to each sampling line. Referring to Example 3, generate the corresponding out-of-tolerance index based on the maximum excess height of each sampling line. Combine the out-of-tolerance indices of all sampling lines to generate an out-of-tolerance sequence. Extract all out-of-tolerance segments based on the out-of-tolerance sequence, calculate the out-of-tolerance length of each out-of-tolerance segment, and sum them to obtain the total out-of-tolerance length L. x Then, based on multiple sets of inner wall smoothness, the overall smoothness S is calculated. avg And extract the maximum residual height H from multiple groups of maximum residual heights.th Combined with the maximum residual height H th Total out-of-tolerance length L x and smoothness level S L A comprehensive evaluation of the quality of the weld inner wall is conducted. For example, in this embodiment, if H is satisfied simultaneously... th ≤H std L x ≤L std And S L If the value is ≥2, the quality of the inner wall of the weld in the pipe under test is deemed acceptable; otherwise, it is deemed unacceptable. Wherein, H... std L is the maximum acceptable clearance height specified for the pipeline under test. std This is the preset allowable value for total out-of-tolerance length. Example 2

[0027] This embodiment further discloses a preferred method for calculating the maximum residual height and inner wall smoothness. The sampling line is divided into N equally spaced sampling points. The grayscale values ​​of each sampling point are extracted based on the grayscale distribution curve of the weld, generating a grayscale value sequence G=[g1,g2,…,g…]. N ].

[0028] Calculate the maximum height. Extract the maximum gray value g from the gray value sequence. max Based on the grayscale-residual height calibration curve, the maximum grayscale value g is determined. max Mapped to the corresponding maximum redundant height h max In a more preferred embodiment, curve fitting is performed on the grayscale-residual height calibration curve to establish the residual height h. x The functional relationship h of grayscale value g x =f(g), based on this functional relationship, calculate the residual height corresponding to each gray value in the gray value sequence to obtain the residual height sequence. Extract the maximum value of the residual height sequence, which is the maximum residual height.

[0029] Calculate the smoothness of the inner wall. Extract the gray value g of sampling point i and its neighboring sampling point i+1 from the gray value sequence. x,i g x,i+1 Calculate the grayscale difference Δg between the two sampling points. i , Δg i =|g x,i+1 -g x,i |. i=1,2,…,N-1. Based on grayscale difference Δg i Calculate the grayscale smoothness S of sampling point i G,i S G,i =1-Δg i / Δg max Δg max The maximum grayscale difference is calculated. The grayscale value G0 corresponding to the thickness H0 of the pipe under test is extracted, along with the maximum acceptable residual height H of the pipe under test.std The corresponding grayscale value G std , Δg max =G std -G0. S G,i The value range of is [0,1], when Δg i >Δg max At that time, S G,i =0. Theoretically, the grayscale change is most drastic at the junction of the weld and the base material on both sides, and its grayscale smoothness is lower than other locations. Therefore, the two smallest grayscale smoothness values ​​S are extracted. min1 and S min2 The smoothness S of the inner wall of the weld is calculated accordingly. in S in =(S min1 +S min2 ) / 2. Example 3

[0030] This embodiment further discloses a preferred method for calculating the total deviation length and smoothness grade. In this invention, K equally spaced sampling lines are drawn along the weld length direction of the pipe under test in the digital image of the pipe, and the maximum excess height and inner wall smoothness corresponding to each sampling line are extracted.

[0031] Calculate the total deviation length. Define a deviation index C. k If the maximum redundant height h of sampling line k max,k Exceeding the maximum acceptable clearance H of the pipeline under test std Then C k =1; otherwise, C k =0. k=1,2,…,K. Combine the out-of-tolerance indices of all sampling lines to generate an out-of-tolerance sequence C. Extract all out-of-tolerance segments based on the out-of-tolerance sequence. Calculate the corresponding out-of-tolerance length L based on the number of sampling lines M and the sampling line spacing ΔL for each out-of-tolerance segment. c L c =(M-1)ΔL. Then sum the excess lengths of all excess segments to obtain the total excess length L. x The out-of-tolerance segment is a subsequence in the out-of-tolerance sequence consisting of consecutive out-of-tolerance indices of 1. For example, in the out-of-tolerance sequence C=[1,1,0,0,0,1,1,1,0,0], there are two out-of-tolerance segments P1=[1,1] and P2=[1,1,1]. Assuming the sampling line spacing ΔL=1mm, then the out-of-tolerance length L of P1 is... c,1 =(2-1)×1mm=1mm, the out-of-tolerance length L of P2 c,2 =(3-1)×1mm=2mm, at this time the total out-of-tolerance length L x =L c,1 +L c,2 =3mm.

[0032] Calculate the smoothness level. Extract the inner wall smoothness corresponding to K sampling lines to obtain the smoothness sequence S=[S in,1 ,S in,2 ,…,S in,K The overall smoothness S of the weld seam of the pipeline under test is calculated based on the smoothness sequence S. avg , According to the overall smoothness S avg Smoothness grade S of generated weld L Overall smoothness S avg The closer the value is to 1, the smoother the transition between the weld and the base material on both sides of the tested pipe. The smoothness level S is determined accordingly. L The higher the value, the better. For example, in this embodiment, S avg When <0.5, the corresponding smoothness level S L =Level 1; 0.5≤S avg When <0.8, the corresponding smoothness level S L =Level 2; S avg When the value is ≥0.8, the corresponding smoothness level is S. L =Level 3. Example 4

[0033] This embodiment experimentally verifies that there is a linear relationship between grayscale value and thickness.

[0034] (1) Test equipment and materials Equipment model: XXG2505L, serial number 218396; Test blocks: 14mm-22mm thick stepped test blocks; Test parameters: focal length 700 mm, voltage 180 kV, current 5 mA, time 3 minutes.

[0035] (2) Test results Figure 3 These are digital images of the 14mm-22mm thick comparison test blocks obtained by scanning, and the grayscale value change curves of the 14mm-22mm thick comparison test blocks; Figure 4 It is a curve showing the relationship between grayscale value and thickness, which generally exhibits a linear growth relationship. If only the 16mm-20mm segment is selected, the linear growth is even more obvious.

[0036] (3) Manufacturer's test data Zhongjing, the manufacturer, has also conducted data statistics on blackness and grayness, for reference. Figure 5 According to the manufacturer's data, there is a clear linear relationship between blackness and grayness, especially in the range of qualified film (2.0-4.0).

[0037] (4) Summary ① Under the same exposure parameters, there is a linear relationship between the gray values ​​corresponding to different thicknesses; ② According to the blackness and grayness curves provided by the manufacturer, especially qualified negatives with a blackness of 2.0-4.0, the linear relationship is stronger (closer to a straight line). ③ Based on the above theories and objective experimental data, there is a direct logical relationship between the grayscale value and thickness of a qualified negative after digitization. Example 5

[0038] This embodiment discloses an application scenario of a non-destructive testing method for eliminating blind spots in the inspection of weld seams inside pipelines.

[0039] High-pressure oxygen pipelines are classified as GC1 level pressure pipelines. The hazards of high-pressure oxygen pipelines with a design pressure of 9.3 MPa include: they do not require an open flame; friction, impact, static electricity, and thermal compression can all ignite them; the combustion speed is extremely fast, capable of creating a detonation wave that can directly shatter everything in its vicinity; and they are strong oxidizers with extremely high flame temperatures, causing metal fittings to melt and splatter, triggering numerous secondary fires. Therefore, unevenness in the inner wall of the pipeline poses a significant safety hazard to the safe, stable, and long-term operation of the equipment.

[0040] During on-site construction, due to the length of each pipe, some pipe welds lack the conditions for visual (endoscopic) inspection, making it difficult to scientifically inspect the internal height and smooth transition of the welds. To address this issue, existing technologies primarily offer two solutions: RT film density assessment and digital radiography (DR+CR) inspection. RT film density assessment does not increase costs, but the judgment relies on the experience of the evaluator and cannot be quantified. While DR+CR technology provides precise measurements, it suffers from high inspection costs and long inspection times, and faces significant challenges in handling pipes of varying sizes and working at heights, making its implementation on-site difficult.

[0041] To address this issue, this invention proposes a non-destructive testing method to eliminate blind spots in pipeline weld inspection. This method utilizes the RT testing method specified in 47013.2 (with the addition of a test block under the same conditions), and after digitizing the film, accurately judges the results based on changes in grayscale values. The procedures and technical specifications for implementing this method are described below.

[0042] (a) RT testing. According to the requirements of 47013.2, during RT testing, additional test blocks of 0.5mm, 1mm, 1.5mm, and 2mm diameter are added for each pipe specification, placed parallel to the weld (avoiding the heat-affected zone). Figure 6 As shown. The quality of the tested film meets the requirements specified in 47013.2.

[0043] (b) Film Digitization. In accordance with GB / T26141 standards, different scanning parameters should be selected based on the density of different films, and should not be lower than DB level, with DS level being optimal. The table below shows the parameter requirements for different levels in GB / T26141 standards: <![CDATA[Density Range D R > 0.5D~4.5D 0.5D~4.5D 0.5D~4.0D 0.5D~3.5D Digital resolution (bits) 16bit ≥12bit ≥10 bits ≥10 bits <![CDATA[density contrast sensitivity ΔD cs > ≤0.02 ≤0.02 ≤0.02 ≤0.02

[0044] The radiographic film digitization system (film digitizer) is divided into three levels: DS, DB, and DA. DS: Enhancement technology, a digitization conversion that does not significantly reduce signal-to-noise ratio and spatial resolution, applied to the digital archiving (digital storage) of film. DB: Enhancement technology, allowing for some reduction in image quality, applied to the digital analysis of film; the original radiographic film must be archived. DA: Basic technology, allowing for some reduction in image quality and further reduction in spatial resolution, applied to the digital analysis of film; the original radiographic film must be archived. This invention actually implements the DS level, but the color gradation (mathematical resolution) is performed in 16-bit mode.

[0045] (c) Judgment and Analysis. In this embodiment, the quality of the internal weld is judged based on the internal weld height standard and the smooth transition standard. Regarding the internal weld height standard, the forming requirements for the internal welds in high-pressure oxygen pipelines are extremely high; a smooth transition (without burrs, etc.) is mandatory. The weld reinforcement height control within the pipeline must meet the following table: Internal reinforcement ≤1.5mm ≤2mm ≤3mm For smooth transition standards, in principle, the thickness is 0.5mm for thicknesses below 13mm, and can be appropriately relaxed by 1.5-2 times for thicknesses exceeding 13mm (the specific amount depends on the weld location; for welds at inlets / outlets or elbows, the lower limit should be applied).

[0046] The following judgment steps are performed based on the aforementioned internal weld height standard and smooth transition standard: 1) Use specialized software to open the digitized negative; DICOM format is generally required. 2) Determine the grayscale value corresponding to a 0.5mm margin of error based on measurements taken on the film. For example, Figure 7 The grayscale curve of the test block under the same conditions with a residual height of 0.5mm shows that the grayscale value corresponding to a residual height of 0.5mm is 6000. 3) such as Figure 8 Measure the weld seam, ensuring the heat-affected zone is included, and observe the grayscale distribution curve to compare whether the weld seam meets the inner weld seam height standard. Since this pipe's dimensions are 219*12.5mm, check... Figure 8 It can be seen that if there are no curves exceeding 12000 in the weld, it means that the weld height inside the pipe is compliant; otherwise, it is unqualified. 4) such as Figure 8 Observe whether there are any curves in the grayscale distribution curve that exceed the level of non-smooth transition; 5) Repeatedly measure to draw a final conclusion on whether it is qualified.

[0047] This invention's method is primarily applied to the inspection of weld seams inside high-pressure oxygen-nitrogen pipelines. In terms of accuracy, this method is more precise than the traditional RT film density determination method, achieving 819 times higher accuracy with 12 gray levels and 13107 times higher with 16 gray levels, and is no less accurate than DR+CR technology. In terms of efficiency, this method is the same as the traditional approach, but approximately 50% more efficient than DR+CR. In terms of cost, this method costs 1-2 yuan more per film than the traditional method, equivalent to about 20% of the cost of DR+CR.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A non-destructive testing method for eliminating blind spots in the inspection of welds inside pipelines, characterized in that, Includes the following steps: Step 1: Prepare multiple comparative test blocks of the same material but different thicknesses as the pipe to be tested; Step 2: Use radiography to examine the weld seam of the pipe to be tested and the comparison test block, and collect pipe and test block films. Use a film digitizer to convert the pipe and test block films into digital images of the pipe and test blocks, respectively. Step 3: Draw a sampling line in the digital image of the pipeline along the direction perpendicular to the weld length. The length of the sampling line covers the weld and the base material on both sides of the pipeline under test, and generate the grayscale distribution curve of the weld along the sampling line. Step 4: Extract the grayscale curve of the sampling line in the digital image of each test block to obtain the average grayscale value of each comparison test block. Generate the corresponding residual height based on the thickness of the comparison test block, and generate the grayscale-residual height calibration curve according to the mapping relationship between the residual height and the average grayscale value. Step 5: Compare the grayscale distribution curve with the grayscale-remaining height calibration curve to calculate the maximum remaining height and inner wall smoothness of the weld seam of the pipe to be tested.

2. The non-destructive testing method for eliminating blind spots in pipeline weld inspection according to claim 1, characterized in that, In step 1, the outer surface of the weld of the pipe to be tested and the comparison test block are ground. The surface roughness of the outer surface of the weld is required to be less than 3.2 μm, and the difference between the surface roughness of the comparison test block and the surface roughness of the outer surface of the weld is less than 1 μm.

3. The non-destructive testing method for eliminating blind spots in pipeline weld inspection according to claim 1, characterized in that, In step 1, a set of comparative test blocks are prepared at intervals of 0.5 mm between 14 mm and 22 mm in thickness, and the side length of the comparative test blocks is not less than 10 mm.

4. The non-destructive testing method for eliminating blind spots in pipeline weld inspection according to claim 1, characterized in that, In step 2, the radiation is X-ray or gamma ray, the pipe film and the test block film are X-ray films, and the pipe digital image and the test block digital image are in DICOM format.

5. The non-destructive testing method for eliminating blind spots in pipeline weld inspection according to claim 1, characterized in that, The grayscale distribution curve of the sampling line is generated by DICOM analysis software. The digital resolution of the film digitizer is 16 bits, and the grayscale distribution curve has 65,536 gray levels.

6. The non-destructive testing method for eliminating blind spots in pipeline weld inspection according to claim 1, characterized in that, In step 5, the sampling line is divided into N equally spaced sampling points. The gray values ​​of each sampling point are extracted based on the gray-scale distribution curve of the weld, generating a gray-scale value sequence. The maximum gray-scale value g is then extracted from the gray-scale value sequence. max Based on the grayscale-residual height calibration curve, the maximum grayscale value g is determined. max Mapped to the corresponding maximum redundant height h max .

7. The non-destructive testing method for eliminating blind spots in pipeline weld inspection according to claim 6, characterized in that, In step 5, the grayscale difference between adjacent sampling points in the grayscale value sequence is calculated, the grayscale smoothness of the corresponding sampling point is calculated based on the grayscale difference, and then the inner wall smoothness is calculated based on the grayscale smoothness.

8. The non-destructive testing method for eliminating blind spots in pipeline weld inspection according to claim 1, characterized in that, It also includes step 6, repeating steps 3 to 5 to obtain multiple sets of maximum excess height and inner wall smoothness of the weld seam of the pipeline to be tested, then calculating the total out-of-tolerance length and smoothness grade of the pipeline to be tested, and combining the maximum excess height, out-of-tolerance length, and smoothness grade to generate a comprehensive evaluation result of the weld inner wall quality.

9. The non-destructive testing method for eliminating blind spots in pipeline weld inspection according to claim 8, characterized in that, In step 6, K equally spaced sampling lines are drawn along the length of the weld of the pipe to be tested in the digital image of the pipe. The maximum excess height and inner wall smoothness corresponding to each sampling line are extracted to obtain multiple sets of maximum excess height and inner wall smoothness.

10. The non-destructive testing method for eliminating blind spots in pipeline weld inspection according to claim 9, characterized in that, Extract the maximum value of the excess height from multiple sets of maximum excess height, generate the corresponding excess index based on the maximum excess height of each sampling line, combine the excess indexes of all sampling lines to generate an excess sequence, calculate the total excess length based on the excess sequence, calculate the overall smoothness based on multiple sets of inner wall smoothness, and generate a smoothness level based on the overall smoothness.

Images