A method and application for comparing defects in dielectric layer of polyurethane insulation pipe based on lift-off effect

Abstract

The present invention discloses a method and application for comparing defects in the dielectric layer of a polyurethane insulation pipe based on the lift-off effect, comprising receiving input capacitance imaging detection signals at different lift-off heights; calculating the distortion rate and determining whether it is greater than or equal to a preset threshold value, and if so, determining that a defect exists; extracting the distortion rate at the center of the defect and drawing a curve cluster diagram at the same lift-off height; determining whether the curve cluster is monotonic; if so, the monotonically increasing curve cluster is a protective layer defect; determining whether there are intersecting curves in the monotonically decreasing curve cluster; if so, determining that the curve with a larger value on the left side of the intersection point of the curve cluster is a working pipe defect, and the curve with a smaller value is an insulation layer defect; if not, classifying the curve cluster according to whether the curves corresponding to the protective layer defect intersect, wherein the intersecting curve is a working pipe defect; and the non-intersecting curve is an insulation layer defect. The present invention can accurately distinguish three types of dielectric layer defects using a single capacitance sensor, saving detection costs.

Description

Technical Field

[0001] The present invention relates to the technical field of non-destructive testing signal processing, in particular to a method and application for comparing defects in a dielectric layer of a polyurethane thermal insulation pipe based on a lift-off effect. Background Art

[0002] Polyurethane insulated pipe is a new type of insulation material with excellent thermal insulation performance and durability. It is widely used in insulation projects for various pipelines and equipment. In industries such as petroleum, chemical, electric power, and metallurgy, pipelines are important transportation and processing equipment and require insulation to ensure the temperature and quality of the fluid. Polyurethane insulated pipe can effectively reduce heat loss in pipelines, improve transportation efficiency, and save energy. In refrigeration and freezing equipment, polyurethane insulated pipe can be used as an insulation material to effectively maintain a low temperature inside the equipment and avoid the impact of temperature fluctuations on the quality of refrigerated products. In geothermal energy utilization systems, polyurethane insulated pipe can be used as insulation material for buried pipes in ground-source heat pump systems, effectively improving the utilization efficiency of geothermal energy.

[0003] For polyurethane insulated pipes, the working pipe is the core part of the polyurethane insulated pipe. If the working pipe has defects, the thermal insulation performance of the pipe will be reduced or even unable to insulate. The insulation layer is an important component of the polyurethane insulated pipe. If the insulation layer has defects, the thermal insulation performance of the pipe will be reduced. The protective layer is the outer layer of the polyurethane insulated pipe, which mainly plays the role of protecting the pipe and the insulation layer. If the protective layer has defects, the insulation layer of the pipe will be damaged, thereby affecting the thermal insulation performance and service life of the pipe. Comparing and distinguishing defects in the working pipe, insulation layer, and protective layer of polyurethane insulated pipes will help to adopt reasonable maintenance plans and eliminate safety hazards as early as possible. This is of great significance to ensuring the safety of polyurethane insulated pipes in the application field and extending the service life of polyurethane insulated pipes.

[0004] Capacitive imaging detection technology is a new type of non-destructive testing technology that can effectively detect defects in insulating materials and metal materials. The lift-off effect of capacitance imaging detection technology refers to the fact that when the capacitance sensor based on capacitance imaging detection technology uses different lift-off heights to detect the test piece, the capacitance sensor will obtain more physical features in the test piece. At present, although the spacing effect of capacitance imaging detection technology can be used to compare and distinguish the three dielectric layer defects of polyurethane insulation pipes, this distinction method has the following problems: (1) It is necessary to manufacture and process capacitance sensors with multiple working electrode spacings, which greatly increases the detection cost; (2) When using capacitance sensors with multiple working electrode spacings to detect the test piece, it is difficult to maintain the same detection conditions, which can easily cause inaccurate detection results, thereby misjudging the distinction between the three dielectric layer defects of polyurethane insulation pipes.

[0005] Therefore, it is necessary to propose a method to accurately distinguish the three types of dielectric layer defects in polyurethane insulation pipes, namely protective layer defects, insulation layer defects and working pipe defects, using a single capacitive sensor. Summary of the Invention

[0006] In order to overcome the above-mentioned problems existing in the prior art, the present invention proposes a method and application for comparing defects of a dielectric layer of a polyurethane thermal insulation pipe based on a lift-off effect.

[0007] The technical solution adopted by the present invention to solve the technical problem is: a method for comparing defects in the dielectric layer of a polyurethane insulation pipe based on a lift-off effect, comprising the following steps:

[0008] Step 1: receiving input capacitance imaging detection signals at different lift-off heights;

[0009] Step 2: Calculate the distortion rate AY of the capacitance imaging detection signal obtained in step 1 n , and judge |AY n Is it greater than or equal to the preset threshold P? n If not, it is determined that the three medium defects do not exist. If so, it is determined that the defects exist;

[0010] Step 3: After determining the existence of the defect, the distortion rate at the defect center is extracted as BY n , and draw BY at the same lift-off height n Curve cluster graph;

[0011] Step 4, judge BY n Whether the curve cluster is monotonic; if not, it is determined that it does not belong to a single dielectric layer defect; if so, proceed to the next step of judgment;

[0012] Step 5, monotonically increasing BY n The curve cluster is the protective layer defect; judge the monotonically decreasing BY n Does the curve cluster intersect BY n curve; if yes, determine in BY n BY with a larger value on the left side of the intersection of the curve cluster n The curve is the defect of the working tube, and the BY value with a smaller value n The curve indicates insulation layer defects. If not, proceed to the next step;

[0013] Step 6, according to BY n Curve clusters corresponding to protective layer defects BY n The curves are classified according to whether they intersect, and the BY corresponding to the protective layer defect n The curve is the BY of the protective layer defects identified previously. n Curve; Intersecting BY nThe curve is the working pipe defect; the non-intersecting BY n The curve represents insulation layer defects.

[0014] The above-mentioned method for comparing defects in the dielectric layer of polyurethane insulation pipes based on the lift-off effect, wherein the capacitance imaging detection signal at different lift-off heights in step 1 includes the detection signal Y of the polyurethane insulation pipe containing three dielectric layer defects detected by the capacitance sensor at a finite number of continuously increasing lift-off heights. n The detection signal YS of the non-defective polyurethane insulation pipe detected by the capacitance sensor at different lifting heights n .

[0015] The above-mentioned method for comparing defects in the dielectric layer of a polyurethane insulation pipe based on the lift-off effect, wherein the distortion rate AY in step 2 is n =(Y n -YS n ) / YS n , BY at the defect center n The maximum or minimum value of the distortion rate, the BY n The curve cluster is composed of discrete distortion rates BY n Fitted.

[0016] The above-mentioned method for comparing defects in the dielectric layer of a polyurethane insulation pipe based on the lift-off effect, wherein the threshold value P is preset in step 2. n The preset threshold value P is set based on the absolute value of the distortion rate of the minimum body defect detection result according to the capacitance imaging detection technology. n .

[0017] The above-mentioned method for comparing defects in the dielectric layer of a polyurethane insulation pipe based on the lift-off effect, the distortion rate RY in step 2 n , the distortion rate at the defect center in step 3 BY n , judge BY in step 4 n Whether the curve cluster is monotonic is determined simultaneously with the help of Excel software, LabVIEW software, MathType software, Matlab software, and Python software to ensure the accuracy of the determination.

[0018] The above-mentioned method for comparing dielectric layer defects of polyurethane thermal insulation pipes based on the lift-off effect is applied to defect judgment of polyurethane thermal insulation pipes containing three types of dielectric layer defects at multiple lift-off heights.

[0019] The beneficial effect of the present invention is that the method provided by the present invention can accurately distinguish three types of dielectric layer defects using a single capacitive sensor, by judging whether the distortion rate curve cluster is monotonic, classifying the distortion rate curve cluster according to the monotonically increasing trend and the monotonically decreasing trend, judging whether there are intersecting distortion rate curves in the monotonically decreasing distortion rate curve cluster, and classifying according to whether the distortion rate curve cluster intersects with the distortion rate curve corresponding to the protective layer defect, thereby realizing comparative distinction of the three types of dielectric layer defects of the polyurethane insulation pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below with reference to the accompanying drawings and examples.

[0021] Figure 1 This is a flow chart of the defect comparison method of the present invention;

[0022] Figure 2 A flow chart for setting a preset threshold value of the present invention;

[0023] Figure 3 This is a structural diagram of the polyurethane thermal insulation pipe under test in Example 1 of the present invention;

[0024] Figures 4 to 12 This is a cluster diagram of distortion rate curves for detecting defects in three dielectric layers of a polyurethane insulation pipe under nine unknown working electrode spacings in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1 As shown, the present invention discloses a method for comparing dielectric layer defects of polyurethane thermal insulation pipes based on the lift-off effect, which can be applied to defect judgment of polyurethane thermal insulation pipes containing three types of dielectric layer defects at multiple lift-off heights, and specifically includes the following steps:

[0027] S101, receiving input capacitance imaging detection signals at different lift-off heights, wherein the capacitance imaging detection signals at different lift-off heights include a finite number of continuously increasing lift-off heights (l1 <l2<……<l n-1 <l n ) under the capacitive sensor to detect the detection signal of polyurethane insulation pipe with three dielectric layer defects (Y1, Y2, ..., Y n-1 、Y n ) and different lift-off heights (l1 <l2<……<l n-1 <l n ) under the capacitive sensor to detect the detection signal of the defect-free polyurethane insulation pipe (YS1, YS2, ..., YS n-1 、YS n ).

[0028] Specifically, the signal and mathematical processing software receives input capacitance imaging detection signals at different lift-off heights, wherein the capacitance imaging detection signal is a finite number of continuously increasing lift-off heights (l1 <l2<……<l n-1 <l n ) under the capacitive sensor to detect the detection signal of polyurethane insulation pipe with three dielectric layer defects (Y1, Y2, ..., Y n-1 、Y n ) and different lift-off heights (l1 <l2<……<l n-1 <l n ) under the capacitive sensor to detect the detection signal of the defect-free polyurethane insulation pipe (YS1, YS2, ..., YS n-1 、YS n ).

[0029] S102, calculating the distortion rate AY of the capacitance imaging detection signal n =(Y n -YS n ) / YS n ;

[0030] S103, determine the absolute value of the distortion rate |AY n Is it greater than or equal to the preset threshold P? n ;

[0031] S104, if no, it is determined that the three dielectric layer defects do not exist;

[0032] S105, if yes, it is determined that a defect exists.

[0033] Specifically, after receiving the detection signal, the signal or mathematical processing software calls a pre-programmed computer processing program to calculate the distortion rate AY n =(Y n -YS n ) / YS n . Introducing the preset threshold P n , the absolute value of the distortion rate |AY n |With the preset threshold P n Compare, it is greater than the threshold P n The defect exists, which is less than the threshold P n The defect does not exist. Among them, the preset threshold P n The determination is based on the absolute value of the distortion rate of the minimum body defect detection result of the capacitance imaging detection technology, which is used to avoid the interference of capacitance stray signals and improve the accuracy of the three dielectric layer defect discrimination. For example, P n It is 0.4 to 0.8 times the absolute value of the distortion rate of the minimum defect detection result, such as Figure 2As shown, it includes: a01, receiving the detection result of the smallest body defect detected by the capacitance imaging detection technology; a02, presetting the threshold value P according to the absolute value of the distortion rate of the detection result n .

[0034] Preferably, the distortion rate AY of the capacitance imaging detection signal is calculated n =(Y n -YS n ) / YS n Including using Excel software to calculate the distortion rate AY n 、Labview software calculates the distortion rate AY n 、Calculate the distortion rate AY using MathType software n 、Calculate the distortion rate AY using matlab software n Calculate the distortion rate AY with Python software n .

[0035] S106, extract the distortion rate AY at the defect center n is the distortion rate BY n , and draw BY at the same lift-off height n Curve cluster graph;

[0036] S107, judge by n Whether the curve family is monotonic;

[0037] S108, if no, it is determined that it is not a single dielectric layer defect; if yes, proceed to the next step;

[0038] Specifically, the distortion rate AY at the center of the defect is extracted through signal or mathematical processing software n is the distortion rate BY n , at the same lift-off height, the discrete distortion rate BY n Fitting into BY n Curve cluster diagram. Judge by signal or mathematical processing software n Is the curve family monotonic? If BY n If the curve cluster is not monotonic, then the BY n The curve cluster does not belong to a single dielectric layer defect; if BY n If the curve cluster is monotonic, proceed to the next step.

[0039] Preferably, the distortion rate AY at the center of the extracted defect is n is the distortion rate BY n Including using Excel software to extract the distortion rate AY n , LabVIEW software extracts the distortion rate AY n , MathType software extracts distortion rate AY n, matlab software extracts distortion rate AY n , Python software extracts distortion rate AY n .

[0040] Preferably, the BY n The curve cluster diagram includes drawing BY with the help of Excel software n Curve cluster diagram, LabVIEW software drawing BY n Curve cluster diagram, drawn by MathType software n Curve cluster diagram, matlab software drawing BY n Curve cluster diagram, Python software drawing BY n Curve cluster diagram, drawn by Origin software n Curve cluster chart.

[0041] Preferably, judge by n Whether the curve cluster is monotonic can be determined by using Excel software, LabVIEW software, MathType software, Matlab software, and Python software.

[0042] S109, according to the monotonically increasing trend and the monotonically decreasing trend, BY n Classify the curve clusters;

[0043] S110, monotonically increasing BY n The cluster of curves represents the defects of the protective layer;

[0044] S111, determine the monotonically decreasing BY n Does the curve cluster intersect BY n curve;

[0045] S112, if yes, determine in BY n BY with a larger value on the left side of the intersection of the curve cluster n The curve is the defect of the working tube, and the BY value with a smaller value n If the curve indicates insulation layer defects, go to the next step;

[0046] S113, according to BY n Curve clusters corresponding to protective layer defects BY n The curves are classified according to whether they intersect, and the BY corresponding to the protective layer defect n The curve is the BY of the protective layer defects identified previously. n curve;

[0047] S114, intersecting BY n The curve represents the defects of the working tube;

[0048] S115, disjoint BY n The curve represents insulation layer defects.

[0049] The present invention provides a method for comparing and distinguishing defects of three dielectric layers of polyurethane insulation pipes based on the lift-off effect of capacitance imaging detection technology. After receiving the input capacitance imaging detection signals at different lift-off heights, the capacitance imaging detection signals at different lift-off heights are obtained, including a finite number of continuously increasing lift-off heights (l1 <l2<……<l n-1 <l n ) under the capacitive sensor to detect the detection signal of polyurethane insulation pipe with three dielectric layer defects (Y1, Y2, ..., Y n-1 、Y n ) and different lift-off heights (l1 <l2<……<l n-1 <l n ) under the capacitive sensor to detect the detection signal of the defect-free polyurethane insulation pipe (YS1, YS2, ..., YS n-1 、YS n ) ; calculate the distortion rate AY through signal and mathematical processing software n =(Y n -YS n ) / YS n , and determine the absolute value of the distortion rate |AY n Is it greater than or equal to the preset threshold P? n If not, it is determined that the three dielectric layer defects do not exist; if yes, it is determined that the defects exist, realizing the distinction between stray capacitance signals and defect signals. In order to display the three dielectric layer defects in the same condition in the same figure, the distortion rate AY at the defect center is extracted through signal and mathematical processing software. n is the distortion rate BY n , and draw BY at the same starting point n Curve cluster diagram, where the distortion rate BY n is the distortion rate AY corresponding to the defect center position n , the same starting point is the same lifting height, BY n The curve cluster is composed of discrete distortion rates BY n In order to distinguish the defects of a single dielectric layer, the signal and mathematical processing software are used to judge BY n Is the curve cluster monotonic? If not, it is determined that it does not belong to a single dielectric layer defect; if yes, proceed to the next step. The capacitance imaging test experiment found that the monotonically increasing and monotonically decreasing trends of the distortion rate curve can distinguish the protective layer defect from the other two defects. In order to first distinguish the protective layer defect from the other two defects, the BY n Classify curve clusters; monotonically increasing BY nThe curve cluster is the protective layer defect; judge the monotonically decreasing BY n Does the curve cluster intersect BY n curve; if yes, determine in BY n BY with a larger value on the left side of the intersection of the curve cluster n The curve is the defect of the working tube, and the BY value with a smaller value n If the curve is an insulation layer defect, go to the next step. In order to distinguish between working pipe defects and insulation layer defects, according to BY n Curve clusters corresponding to protective layer defects BY n The curves are classified according to whether they intersect, and the BY corresponding to the protective layer defect n The curve is the BY of the protective layer defects identified previously. n Curve; Intersecting BY n The curve is the working pipe defect; the non-intersecting BY n The curve represents an insulation layer defect. The method provided by the present invention can accurately distinguish three types of dielectric layer defects using a single capacitive sensor. This method determines whether the distortion rate curve cluster is monotonic, classifies the distortion rate curve clusters according to monotonically increasing and monotonically decreasing trends, determines whether monotonically decreasing distortion rate curve clusters contain intersecting distortion rate curves, and classifies the distortion rate curve clusters based on whether they intersect with the distortion rate curves corresponding to the protective layer defects. This allows for comparative differentiation of the three dielectric layer defects in polyurethane insulation pipes.

[0050] [Example 1]

[0051] Based on the above-mentioned method for distinguishing defects of three dielectric layers of polyurethane insulation pipe based on the lift-off effect of capacitance imaging detection technology, this embodiment gives the lift-off height l n The experimental implementation method of the specific numerical value is used to verify the effectiveness of the method. Figure 3 As shown in the figure, the polyurethane insulation pipe consists of a protective layer, an insulation layer and a working pipe. These three dielectric layers are made of high-density polyethylene, rigid polyurethane foam plastic and steel respectively. There is a defect in each dielectric layer. n The defects of the protective layer, insulation layer and working tube in the polyurethane insulation pipe were detected under the experimental conditions of 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm and 5mm. In addition, in order to avoid the influence of the working electrode spacing factor on the method of the present invention during the capacitance imaging detection process, 9 capacitance sensors with unknown working electrode spacing were used to detect the polyurethane insulation pipe during the experiment. The distortion rate AY of the obtained detection signal was calculated respectively. n =(Y n -YS n) / YS n , determine the absolute value of the distortion rate |AY n Is it greater than or equal to the preset threshold P? n , extract the distortion rate AY at the defect center n is the distortion rate BY n And draw BY at the same starting point n Curve cluster diagram, 9 curve cluster diagrams such as Figures 4 to 12 shown.

[0052] by Figure 4 For example, Figure 4 The three fitting curves are all monotonic. According to the present invention, it is determined that there are three types of dielectric layer defects. The distortion rate curve clusters are classified according to the monotonically increasing trend and the monotonically decreasing trend. The monotonically increasing distortion rate curve is a protective layer defect. Figure 4 It can be seen that the distortion rate curve No. 1 presents a monotonically increasing trend, and thus the distortion rate curve No. 1 is determined to be a defect in the protective layer; it is determined whether there are intersecting distortion rate curves in the monotonically decreasing distortion rate curve cluster, and the distortion rate curve with a larger value on the left side of the intersection point of the distortion rate curve cluster is determined to be a defect in the working tube, and the distortion rate curve with a smaller value is a defect in the insulation layer. Figure 4 It can be seen that the curve II intersects with the curve III, and the value of the curve III is greater than that of the curve II on the left side of the intersection. According to the present invention, the curve II is judged to be an insulation layer defect, and the curve III is a working tube defect. The above three methods of comparing and distinguishing dielectric layer defects are completely consistent with the icon. Figure 12 For example, Figure 12 The three fitting curves are all monotonic. According to the present invention, it is determined that there are three types of dielectric layer defects. The distortion rate curve clusters are classified according to the monotonically increasing trend and the monotonically decreasing trend. The monotonically increasing distortion rate curve is a protective layer defect. Figure 12 It can be seen that the distortion rate curve No. 1 shows a monotonically increasing trend, and thus the distortion rate curve No. 1 is determined to be a protective layer defect; it is determined whether there are intersecting distortion rate curves in the monotonically decreasing distortion rate curve cluster. Figure 12 It can be seen that there is no intersecting distortion rate curve in the monotonically decreasing distortion rate curve cluster. According to the present invention, the next step is to classify the distortion rate curve cluster according to whether it intersects with the distortion rate curve corresponding to the protective layer defect. Figure 12 It can be seen that curve III intersects with the distortion rate curve of the protective layer defect, that is, curve III is a working tube defect; curve II does not intersect with the distortion rate curve of the protective layer defect, that is, curve II is an insulation layer defect. The above three methods of comparing and distinguishing dielectric layer defects are completely consistent with the icon.

[0053] for Figures 5 to 11 The comparison and differentiation results of the defects of the three dielectric layers are completely consistent with the actual situation of the defects, and will not be repeated here.

[0054] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the scope of the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the spirit and scope of protection of the present invention, and such modifications or equivalent substitutions shall also be deemed to fall within the scope of protection of the present invention.

Claims

1. A method for comparing defects in the dielectric layer of a polyurethane insulation pipe based on the lift-off effect, characterized in that: The steps include: Step 1: receiving input capacitance imaging detection signals at different lift-off heights; Step 2: Calculate the distortion rate AY of the capacitance imaging detection signal obtained in step 1 n , and judge |AY n Is it greater than or equal to the preset threshold P? n If not, it is determined that the three medium defects do not exist. If so, it is determined that the defects exist; Step 3: After determining the existence of the defect, the distortion rate at the defect center is extracted as BY n , and draw BY at the same lift-off height n Curve cluster graph; Step 4, judge BY n Whether the curve cluster is monotonic; if not, it is determined that it does not belong to a single dielectric layer defect; if so, proceed to the next step of judgment; Step 5, monotonically increasing BY n The curve cluster is the protective layer defect; judge the monotonically decreasing BY n Does the curve cluster intersect BY n curve; if so, determine in BY n BY with a larger value on the left side of the intersection of the curve cluster n The curve is the defect of the working tube, and the BY value with a smaller value n The curve indicates insulation layer defects. If not, proceed to the next step; Step 6, according to BY n Curve clusters corresponding to protective layer defects BY n The curves are classified according to whether they intersect, and the BY corresponding to the protective layer defect n The curve is the BY of the protective layer defects identified previously. n Curve; Intersecting BY n The curve is the working pipe defect; the non-intersecting BY n The curve represents insulation layer defects.

2. The method for comparing defects in the dielectric layer of a polyurethane thermal insulation pipe based on the lift-off effect according to claim 1, characterized in that: The capacitance imaging detection signals at different lifting heights in step 1 include detection signals Y of the polyurethane insulation pipe containing three dielectric layer defects detected by the capacitance sensor at a finite number of continuously increasing lifting heights. n The detection signal YS of the non-defective polyurethane insulation pipe detected by the capacitance sensor at different lifting heights n .

3. The method for comparing defects in the dielectric layer of a polyurethane thermal insulation pipe based on the lift-off effect according to claim 2, characterized in that: The distortion rate AY in step 2 n =(Y n -YS n ) / YS n , BY at the defect center n The maximum or minimum value of the distortion rate, the BY n The curve cluster is composed of discrete distortion rates BY n Fitted.

4. The method for comparing defects in the dielectric layer of a polyurethane thermal insulation pipe based on the lift-off effect according to claim 1, characterized in that: The threshold value P is preset in step 2 n The preset threshold value P is set based on the absolute value of the distortion rate of the minimum body defect detection result according to the capacitance imaging detection technology. n .

5. The method for comparing defects in the dielectric layer of a polyurethane thermal insulation pipe based on the lift-off effect according to claim 1, characterized in that: The distortion rate AY in step 2 n , the distortion rate at the defect center in step 3 BY n , judge BY in step 4 n Whether the curve cluster is monotonic is determined simultaneously with the help of Excel software, LabVIEW software, MathType software, Matlab software and Python software to ensure the accuracy of the determination.

6. Application of the method for comparing defects in the dielectric layer of a polyurethane thermal insulation pipe based on the lift-off effect according to any one of claims 1 to 5, characterized in that: It is used to judge defects of polyurethane insulation pipes containing three types of dielectric layer defects at multiple lift-off heights.

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