Evaluation model for nondestructive testing of polyethylene hot melting joint and design method

Abstract

The invention relates to the technical field of urban gas pipeline detection, in particular to an evaluation model for nondestructive testing of a polyethylene hot melting joint and a design method. The design method comprises the following steps: evaluating the influence of different factors of a polyethylene gas pipe fitting on welding forming, and performing mechanical property evaluation on polyethylene pipeline incomplete fusion defect samples formed in different combination modes by utilizing an advancing and retreating method in a combined optimal algorithm to obtain a combination mode of an optimal mechanical property test scheme; and taking the optimal combination mode and the hot melting process parameters as standards to obtain the nondestructive testing evaluation model for the polyethylene hot melting joint. According to the design method, the application effect of a nondestructive testing method in quality control of the fuel gas polyethylene hot melting joint is greatly improved, and a brand new thought is provided for solving the problem of incomplete fusion defect manufacturing of the current fuel gas polyethylene pipe hot melting joint.

Description

Technical Field

[0001] The invention relates to the technical field of urban gas pipeline detection, and in particular to an evaluation model and a design method for nondestructive detection of polyethylene hot-melt joints. Background Art

[0002] Polyethylene (PE) pipes have been widely used in gas transmission systems due to their excellent corrosion resistance, high toughness and long service life. However, the quality control of polyethylene pipe hot-melt joints has always been a technical problem in the industry. Although existing construction specifications, such as CJJ 63-2018 "Technical Standards for Polyethylene Gas Pipeline Engineering", have put forward clear requirements for the acceptance of hot-melt joints and the testing of pipeline projects, including crimping symmetry inspection, joint alignment inspection, partial joint crimping removal inspection, and pipeline purging, strength testing and tightness testing, these methods mainly focus on the appearance of the joints and the overall performance of the pipeline, and cannot effectively explore the welding quality inside the hot-melt joints.

[0003] The welding quality of polyethylene pipe hot-melt joints is directly related to the safety of the gas pipeline system. In actual applications, due to improper control of the welding process, such as the end face of the pipe is not milled flat, the joint is not evenly cooled after welding, and oil stains are mixed into the fusion surface during welding, etc., it may cause unfused defects inside the joint. These defects may be difficult to detect under the existing acceptance standards, but once they expand during use, they will seriously threaten the safe operation of the gas pipeline and cause serious accidents such as gas leakage.

[0004] As a non-destructive testing method, non-destructive testing technology can effectively identify welding defects inside joints and avoid safety risks caused by defect expansion. However, due to the significant differences in materials and welding methods between polyethylene pipes and metal pipes, traditional non-destructive testing methods for metal pipes are difficult to directly apply to polyethylene hot-melt joints. Therefore, it is necessary to develop applicable non-destructive testing methods and testing processes based on the structural characteristics, main defect types and failure modes of polyethylene hot-melt joints.

[0005] At present, the preparation method of polyethylene pipe unfusion defect specimens mainly relies on artificial defect production techniques such as drilling and notching. These methods are not only difficult to accurately simulate the unfusion defects generated in the actual welding process, but also lack standardization and systematization, and cannot provide effective reference maps for non-destructive testing personnel. This greatly limits the application of non-destructive testing technology in the quality control of polyethylene hot-melt joints, making the detection and evaluation of unfusion defects difficult.

[0006] In view of the above problems, the present invention proposes a multi-factor unfused defect sample design method for non-destructive testing of polyethylene heat-melt joints. The method aims to evaluate the influence of different factors on unfused welds by simulating unfused defects under different welding conditions, and realize a standardized production method for unfused defects that considers the combined influence of multiple factors. This innovation not only solves the problem of producing unfused defect samples for heat-melt joints of gas polyethylene pipes, but also provides a reliable foundation for the effective application of non-destructive testing technology, and meets the urgent needs of comprehensive testing and evaluation of heat-melt joints of gas polyethylene pipelines. Summary of the invention

[0007] The purpose of the present invention is to provide a design method for a non-destructive testing and evaluation model of polyethylene hot-melt joints. This design method not only greatly improves the application effect of non-destructive testing methods in the quality control of gas polyethylene hot-melt joints, but also provides a new idea for solving the current problem of unfused defects in the production of gas polyethylene pipe hot-melt joints.

[0008] In a first aspect, the present invention provides a method for designing a nondestructive testing and evaluation model for polyethylene hot melt joints, comprising the following steps:

[0009] By evaluating the influence of different factors of polyethylene gas pipe fittings on welding formation, the advance and retreat method in the combined optimal algorithm is used, that is, the optimal solution is approached by gradually adjusting the search interval. The mechanical properties of polyethylene pipe unfused defect specimens formed by different combinations are evaluated, and the combination of the optimal mechanical properties test scheme is obtained. Based on the optimal combination and hot-melt process parameters, the non-destructive testing and evaluation model of polyethylene hot-melt joints is obtained.

[0010] As a preferred embodiment of this technical solution, the following steps are included:

[0011] S1. Design a combination of different factors based on the factors that cause the unfused defects of polyethylene hot-melt joints;

[0012] S2, according to the combination scheme of step S1, preparing polyethylene hot-melt joint unfused defect samples with different combination factors;

[0013] S3, performing mechanical property test on the polyethylene hot-melt joint unfused defect sample prepared in step S2 to obtain the main factors affecting the polyethylene hot-melt joint unfused defect;

[0014] S4, combining the multiple main factors obtained in step S3 to prepare a multi-factor polyethylene hot-melt joint unfusion defect sample, and obtaining an optimal combination of mechanical property test schemes by comparing the mechanical properties of different multi-factor polyethylene hot-melt joint unfusion defect samples;

[0015] S5. Based on the combination of the optimal mechanical properties test scheme and the hot-melt process parameters, a non-destructive testing and evaluation model for polyethylene hot-melt joints is obtained.

[0016] As a preferred embodiment of the present technical solution, in step S1, the formation factors include end face not being milled flat, uneven cooling, end face inclusions and end face shape, feed rate, welding temperature and time, welding pressure and raw material quality.

[0017] As a preferred embodiment of the present technical solution, in step S2, when preparing polyethylene hot-melt joint unfused defect samples with different combination factors, the parameters of the hot-melt welding machine remain unchanged.

[0018] As a preferred embodiment of the present technical solution, in step S3, the mechanical property test includes a tensile strength test and a failure form test.

[0019] As a preferred embodiment of the present technical solution, in step 4, the parameters of the hot melt process are: heating plate temperature 200-240°C, and preferably 220°C, endothermic pressure 0.1-0.3MPa, and preferably 0.2MPa, and endothermic time is the wall thickness of the welded pipe × 10s.

[0020] As a preferred embodiment of the present technical solution, the uneven cooling includes different cooling rates.

[0021] As a preferred embodiment of the present technical solution, the method for non-destructive testing of polyethylene hot-melt joints includes ultrasonic testing method and microwave scanning method.

[0022] As a preferred embodiment of the present technical solution, the nominal outer diameter of the polyethylene gas pipe fitting is ≥63 mm, and the nominal wall thickness is 6 mm-30 mm.

[0023] In the second aspect, the present invention also discloses a non-destructive testing and evaluation model for polyethylene hot-melt joints obtained by the above-mentioned design method, which should also fall within the protection scope of the present invention.

[0024] The design method of the polyethylene hot melt joint nondestructive testing and evaluation model of the present invention at least has the following

[0025] Beneficial effects:

[0026] In the design method of the polyethylene hot-melt joint non-destructive testing and evaluation model of the present invention, first, starting from the main causes of the unfused defects of the polyethylene hot-melt joint, such as the end face not being milled flat, uneven cooling, oiling of the fusion surface and the shape of the prefabricated pipe end, etc. By identifying these factors, a list of different factors and their possible combinations is designed to systematically explore and identify which factors have a significant impact on the formation of unfused defects; then, a polyethylene hot-melt butt welding machine is used to make polyethylene hot-melt joint unfused defect specimens containing different combination factors. Further, the tensile strength and failure form of these specimens are measured by tensile tests to quantify the influence of different factors on the mechanical properties of the unfused defects, so as to determine which are the main influencing factors. Finally, after determining the main influencing factors, different factors are combined to make multi-factor polyethylene unfused defect specimens, and by comparing the mechanical property curves of different schemes, the optimal tensile test scheme combination method is found, and the polyethylene hot-melt joint non-destructive testing and evaluation model can be obtained.

[0027] The polyethylene hot-melt joint unfusion defect factor assessment model and sample design method proposed in the present invention provide a scientific and reliable means to determine the defect tolerance of hot-melt joints, and form a set of strict non-destructive testing acceptance standards accordingly. It not only greatly improves the application effect of non-destructive testing methods in the quality control of gas polyethylene hot-melt joints, but also provides a new idea for solving the current problem of unfusion defect production of gas polyethylene pipe hot-melt joints.

[0028] It is worth mentioning that the design method of the polyethylene hot-melt joint nondestructive testing and evaluation model of the present invention is simple to operate, easy to implement, and has low economic cost and high reliability. This makes it not only able to meet the comprehensive testing and evaluation needs of gas polyethylene pipeline hot-melt joints, but also plays a vital role in ensuring the safe operation of gas pipelines and preventing leakage failure accidents. It effectively avoids potential casualties and property losses caused by the lack of nondestructive testing quality control means, and brings significant economic and social benefits to society.

[0029] In addition, this design method is also highly universal. It can not only be widely used in the welding process of polyethylene hot-melt joints in urban gas, oil field gathering and transportation pipelines, but is also expected to be expanded to more fields in the future, providing strong technical support for the quality control of hot-melt joints of various types of plastic pipes.

[0030] In summary, the polyethylene hot-melt joint unfusion defect factor assessment model and sample design method proposed in the present invention not only solve the current technical problems, but also point out the direction for future pipeline welding quality control work, and have important theoretical and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 It is a schematic diagram of the end section of the original polyethylene gas pipe fitting of the present invention;

[0033] Figure 2 This is a schematic diagram of the end section of the improved polyethylene gas pipe fitting of the present invention;

[0034] Figure 3 It is a flow chart of the design method of the polyethylene hot-melt joint non-destructive testing and evaluation model of the present invention;

[0035] Figure 4 The tensile strength and failure form of the unfused defect sample of DN160×14.6mm polyethylene hot-melt joint made by the present invention without milling the end surface are determined, and it is identified as ductile failure;

[0036] Figure 5 The tensile strength and failure form of the DN160×14.6mm polyethylene hot-melt joint unfused defect sample made according to the present invention according to the uneven cooling are determined, and it is identified as ductile failure;

[0037] Figure 6 The tensile strength and failure form of the unfused defect sample of DN160×14.6mm polyethylene hot-melt joint made by adding oil to the fusion surface according to the present invention are measured, and it is identified as brittle failure. DETAILED DESCRIPTION

[0038] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0040] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] Example 1

[0042] like Figure 3 As shown, this embodiment provides a design method for a polyethylene hot melt joint nondestructive testing and evaluation model, comprising the following steps:

[0043] By evaluating the influence of different factors of polyethylene gas pipe fittings on welding formation, the advance and retreat method in the combined optimal algorithm is used, that is, the optimal solution is approached by gradually adjusting the search interval. The mechanical properties of polyethylene pipe unfused defect specimens formed by different combinations are evaluated, and the combination of the optimal mechanical properties test scheme is obtained. Based on the optimal combination and hot-melt process parameters, the non-destructive testing and evaluation model of polyethylene hot-melt joints is obtained.

[0044] In the design method of the polyethylene hot-melt joint non-destructive testing and evaluation model of the present invention, first, starting from the main causes of the unfused defects of the polyethylene hot-melt joint, such as the end face not being milled flat, uneven cooling, oiling of the fusion surface and the shape of the prefabricated pipe end, etc. By identifying these factors, a list of different factors and their possible combinations is designed to systematically explore and identify which factors have a significant impact on the formation of unfused defects; then, a polyethylene hot-melt butt welding machine is used to make polyethylene hot-melt joint unfused defect specimens containing different combination factors. Further, the tensile strength and failure form of these specimens are measured by tensile tests to quantify the influence of different factors on the mechanical properties of the unfused defects, so as to determine which are the main influencing factors. Finally, after determining the main influencing factors, different factors are combined to make multi-factor polyethylene unfused defect specimens, and by comparing the mechanical property curves of different schemes, the optimal tensile test scheme combination method is found, and the polyethylene hot-melt joint non-destructive testing and evaluation model can be obtained. This evaluation method not only greatly improves the application effect of non-destructive testing methods in the quality control of gas polyethylene hot-melt joints, but also provides a new idea for solving the current problem of unfused defects in gas polyethylene pipe hot-melt joints.

[0045] On the basis of the above technical solution, it is further preferred that the following steps are included:

[0046] S1. Design a combination of different factors based on the factors that cause the unfused defects of polyethylene hot-melt joints;

[0047] Among them, the formation factors include end face not milled flat, uneven cooling, end face inclusions and end face shape (such as Figure 1-2 As shown in Figure 1), feed rate, welding temperature and time, welding pressure and raw material quality. The uneven cooling here includes different cooling rates. Table 1 is a list of different combinations of factors.

[0048] Table 1 Combinations of different factors

[0049]

[0050]

[0051] S2. According to the combination scheme of step S1, under the premise that the parameters of the hot melt welding machine remain unchanged, polyethylene hot melt joint unfused defect samples with different combination factors are prepared, wherein the process parameters of the hot melt welding machine are: the heating plate temperature is 220° C., the heat absorption pressure is 0.2 MPa, and the heat absorption time is the wall thickness of the welded pipe × 10 s;

[0052] S3, performing a tensile strength test and a failure form test on the polyethylene hot-melt joint unfused defect sample prepared in step S2, to obtain the main factors affecting the polyethylene hot-melt joint unfused defect;

[0053] S4, combining the multiple main factors obtained in step S3 to prepare a multi-factor polyethylene hot-melt joint unfusion defect sample, and obtaining an optimal combination of mechanical property test schemes by comparing the mechanical properties of different multi-factor polyethylene hot-melt joint unfusion defect samples;

[0054] S5. Based on the combination of the optimal mechanical properties test scheme and the hot-melt process parameters, a non-destructive testing and evaluation model for polyethylene hot-melt joints is obtained.

[0055] The method of the invention is applicable to polyethylene gas pipe fittings with a nominal outer diameter of ≥63 mm and a nominal wall thickness of 6 mm-30 mm.

[0056] Finally, the methods for nondestructive testing of polyethylene hot-melt joints include ultrasonic testing and microwave scanning, which are not strictly limited in the present invention.

[0057] Example 2

[0058] A gas company needs to make DN160×14.6mm polyethylene hot-melt joint unfused defect specimens to verify the effectiveness and defect detection rate of the non-destructive testing method. The design method of the present invention is used to make unfused defect specimens for non-destructive testing of polyethylene hot-melt joints.

[0059] The specific steps include:

[0060] Step 1: According to the factors causing the unfused defects of polyethylene hot melt joints, a combination scheme of different factors is designed according to Table 1;

[0061] Step 2: Select DN160×14.6mm PE100 high-density polyethylene pipes, and cut several pipe sections from the pipes of this specification. According to the generation mechanism of the unfused defects of the hot-melt joints, imitate the formation conditions under the influence of various factors, and use a semi-automatic PE hot-melt butt welding machine to make polyethylene hot-melt joint unfused defect samples with different combinations of factors. The process parameters of the hot-melt welding machine are: the heating plate temperature is 220℃, the endothermic pressure is 0.2MPa, and the endothermic time is 146s;

[0062] Step 3: The tensile strength and failure form of the various unfused defect samples were measured by tensile tests, such as Figure 4-6 As shown;

[0063] Step 4: Combine the multiple main factors obtained in step 3 to produce a multi-factor polyethylene hot-melt joint unfused defect sample. By comparing the mechanical properties of different multi-factor polyethylene hot-melt joint unfused defect samples, the combination of the optimal mechanical property test scheme is obtained as end face inclusion + end face unmilled;

[0064] Step 5: Based on the combination of end face inclusion + end face not milled flat and hot melt process parameters, a non-destructive testing and evaluation model of polyethylene hot melt joints is obtained.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A design method for a nondestructive testing and evaluation model for polyethylene hot-melt joints, characterized in that: The following steps are involved: By evaluating the influence of different factors on the welding formation of polyethylene gas pipe fittings, the mechanical properties of polyethylene pipe unfused defect specimens formed by different combinations were evaluated using the advance and retreat method in the combined optimal algorithm, and the optimal combination of mechanical properties test schemes was obtained. Based on the optimal combination and hot-melt process parameters, a non-destructive testing and evaluation model for polyethylene hot-melt joints was obtained.

2. The design method according to claim 1, characterized in that: The following steps are involved: S1. Design a combination of different factors based on the factors that cause the unfused defects of polyethylene hot-melt joints; S2, according to the combination scheme of step S1, preparing polyethylene hot-melt joint unfused defect samples with different combination factors; S3, performing mechanical property test on the polyethylene hot-melt joint unfused defect sample prepared in step S2 to obtain the main factors affecting the polyethylene hot-melt joint unfused defect; S4, combining the multiple main factors obtained in step S3 to prepare a multi-factor polyethylene hot-melt joint unfusion defect sample, and obtaining an optimal combination of mechanical property test schemes by comparing the mechanical properties of different multi-factor polyethylene hot-melt joint unfusion defect samples; S5. Based on the combination of the optimal mechanical properties test scheme and the hot-melt process parameters, a non-destructive testing and evaluation model for polyethylene hot-melt joints is obtained.

3. The design method according to claim 2, characterized in that: In step S1, the formation factors include end surface not being milled flat, uneven cooling, end surface inclusions and end surface shape, feed rate, welding temperature and time, welding pressure and raw material quality.

4. The design method according to claim 2, characterized in that: In step S2, when preparing polyethylene hot-melt joint unfused defect samples with different combination factors, the parameters of the hot-melt welding machine remain unchanged.

5. The design method according to claim 2, characterized in that: In step S3, the mechanical property test includes a tensile strength test and a failure form test.

6. The design method according to claim 2, characterized in that: In step 4, the parameters of the hot melt process are: the heating plate temperature is 200-240°C, the endothermic pressure is 0.1-0.3MPa, and the endothermic time is the wall thickness of the welded pipe × 10s.

7. The design method according to claim 3, characterized in that: The non-uniform cooling includes different cooling rates.

8. The design method according to claim 2, characterized in that: The nondestructive testing method for polyethylene hot melt joints includes an ultrasonic testing method and a microwave scanning method.

9. The design method according to claim 1, characterized in that: The nominal outer diameter of the polyethylene gas pipe fitting is ≥63mm, and the nominal wall thickness is 6mm-30mm.

10. A nondestructive testing and evaluation model for polyethylene hot melt joints, characterized in that: Obtained according to the design method according to any one of claims 1-9.

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