Waterproof connector connecting method for outer pipe of heat preservation layer of straight heat preservation pipe

Abstract

The invention relates to the technical field of heat preservation pipes, in particular to a straight heat preservation pipe heat preservation layer outer pipe waterproof connector connecting method which comprises the steps that surface treatment is conducted on a composite layer outside a welded metal core pipe, the composite layer is sleeved with an outer protection sleeve, the thickness of the composite layer and the total pipe diameter of a heat preservation pipe are obtained, and size characteristic values are obtained; determining an interface connection mode according to the size characteristic value, and moving the outer protective sleeve to an interface area for coating; under the condition that hot melting connection is adopted as an interface connection mode, a heating plate is started for heating, the outer protective sleeve and the composite layer are fused and combined, and an interface fusion characteristic value is obtained; when judging that the hot-melt connection does not meet the standard according to the interface fusion characteristic value, performing secondary judgment according to the circumferential coverage integrity rate, or determining the reason that the hot-melt connection does not meet the preset standard according to the circumferential deformation characterization value of the outer protective sleeve; and the interface meeting the preset standard is cooled, so that the interface connection quality is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of heat-insulating pipes, and particularly to a method for connecting a waterproof interface of an outer pipe of a heat-insulating layer of a direct heat-insulating pipe. Background Art

[0002] In many fields such as petroleum, chemical industry, urban heating, and cooling, heat-insulating pipes, as an important conveying pipeline, their performance directly affects the operation efficiency and safety of the system. As a common type of heat-insulating pipe, a direct heat-insulating pipe usually includes a metal core pipe in the inner layer, a heat-insulating layer wrapped on the metal core pipe, and an anti-corrosion layer in the outermost layer. This multi-layer structure effectively improves the heat-insulating performance and corrosion resistance of the pipeline.

[0003] During the installation and use of a direct heat-insulating pipe, the connection of the waterproof interface of the outer pipe of the heat-insulating layer is a key link.

[0004] Chinese Patent Publication No.: CN105757357A discloses a prefabricated directly buried heat-insulating plastic pipe with a glass fiber-reinforced PERT pipe as the working pipe, including a working inner pipe and an outer protective sleeve. The working inner pipe and the outer protective sleeve are connected through a heat-insulating layer. The working inner pipe is a glass fiber-reinforced PERT pipe, and the outer protective sleeve is an HDPE pipe. The prefabricated directly buried heat-insulating plastic pipe with a glass fiber-reinforced PERT pipe as the working pipe proposed by the present invention can not only retain the advantages of long service life, non-corrosion, and easy installation of traditional prefabricated directly buried heat-insulating plastic pipes, but also greatly improve the design stress of the working pipe and the rigidity of the plastic pipe.

[0005] It can be seen that the above technical solutions do not consider the influence of pipe diameter on the interface connection method, nor do they consider the influence of heating temperature, heating time, or the thickness of the molten layer on the connection quality during the interface connection process, resulting in poor interface connection quality. Summary of the Invention

[0006] Therefore, the present invention provides a method for connecting a waterproof interface of an outer pipe of a heat-insulating layer of a direct heat-insulating pipe to overcome the problems in the prior art that the influence of pipe diameter on the interface connection method is not considered, and the influence of heating temperature, heating time, or the thickness of the molten layer on the connection quality during the interface connection process is not considered, resulting in poor interface connection quality.

[0007] To achieve the above object, the present invention provides a method for connecting a waterproof interface of an outer pipe of a heat-insulating layer of a direct heat-insulating pipe, including:

[0008] Performing surface treatment on the composite layer outside the metal core pipe that has been welded, sleeving an outer protective sleeve on the composite layer, and obtaining the thickness of the composite layer and the total pipe diameter of the heat-insulating pipe to obtain a dimensional characteristic value;

[0009] Determine the interface connection method according to the dimensional characteristic value, and move the outer protective sleeve to the interface area for wrapping, wherein both ends of the outer protective sleeve are respectively lapped on both ends of the composite layer;

[0010] Under the condition of using hot melt connection as the interface connection method, start the heating plate inside the outer sheath for heating, melt-bond the outer protective sleeve and the composite layer, obtain the thickness of the molten layer, and obtain the interface fusion characteristic value;

[0011] When it is determined that the hot melt connection does not meet the preset standard according to the interface fusion characteristic value, perform a secondary determination according to the circumferential coverage integrity rate of the molten layer, or determine the reason why the hot melt connection does not meet the preset standard according to the circumferential deformation characterization value of the outer protective sleeve;

[0012] Cool the interface that meets the preset standard.

[0013] Furthermore, the insulated pipe is composed of a metal core pipe and a composite layer, wherein the composite layer includes a thermal insulation layer wrapped on the metal core pipe and an anti-corrosion layer wrapped on the thermal insulation layer.

[0014] Furthermore, a heating plate is embedded in the area where the inner wall of the outer protective sleeve contacts the composite layer.

[0015] Furthermore, determine the connection method of the interface according to the dimensional characteristic value of the insulated pipe, wherein,

[0016] If the dimensional characteristic value is less than the preset surface dimensional characteristic value, use adhesive bonding as the interface connection method;

[0017] If the dimensional characteristic value is greater than or equal to the preset surface dimensional characteristic value, use hot melt connection as the interface connection method;

[0018] The dimensional characteristic value is jointly determined by the thickness of the composite layer and the total diameter of the insulated pipe.

[0019] Furthermore, in response to the interface fusion characteristic value being greater than or equal to the first preset interface fusion characteristic threshold, determine that the hot melt connection does not meet the preset standard.

[0020] Furthermore, the process of obtaining the interface fusion characteristic value includes:

[0021] Starting from the edge of the outer protective sleeve, cut the preset surface dimension at equal intervals in the circumferential direction perpendicular to the axis of the outer protective sleeve to obtain a longitudinal section sample;

[0022] Use a metallographic microscope to measure the thickness of the molten layer of each longitudinal section sample;

[0023] Calculate the arithmetic mean of the thicknesses of the molten layers of all longitudinal section samples;

[0024] The ratio of the arithmetic mean to the preset thickness is recorded as the interface fusion characteristic value.

[0025] Further, if the interface fusion eigenvalue is greater than or equal to the first preset interface fusion feature threshold and less than the second preset interface fusion feature threshold, it is determined that the hot melt connection does not meet the preset standard, and whether the hot melt connection meets the preset standard is re-determined according to the circumferential coverage integrity rate of the molten layer;

[0026] If the interface fusion eigenvalue is greater than or equal to the second preset interface fusion feature threshold, it is determined that the hot melt connection does not meet the preset standard, and the reason for the non-compliance of the hot melt connection with the preset standard is determined according to the circumferential deformation characterization value of the outer protective sleeve.

[0027] Further, whether the hot melt connection meets the preset standard is re-determined according to the circumferential coverage integrity rate of the molten layer, where,

[0028] If the circumferential coverage rate is less than the preset circumferential coverage rate, it is determined that the hot melt connection does not meet the preset standard, and the heating duration of the heating plate is increased according to the difference between the preset circumferential coverage rate and the circumferential coverage rate;

[0029] If the circumferential coverage rate is greater than or equal to the preset circumferential coverage rate, it is determined that the hot melt connection meets the preset standard;

[0030] The circumferential coverage rate is the ratio between the covered arc length of the molten material in the circumferential direction of the composite layer and the outer circumferential arc length of the composite layer during the hot melt connection process.

[0031] Further, the increase amplitude of the heating duration of the heating plate is positively correlated with the circumferential coverage difference, where the molten layer difference is the difference between the preset circumferential coverage rate and the circumferential coverage rate.

[0032] Further, determining the reason for the non-compliance of the hot melt connection with the preset standard according to the circumferential deformation characterization value of the outer protective sleeve includes: the fitting gap between the outer protective sleeve and the composite layer is too large, or the heating temperature is too high, where the circumferential deformation characterization value is the ratio between the ovality of the outer protective sleeve after melting and the ovality of the outer protective sleeve before melting.

[0033] Compared with the prior art, the beneficial effects of the present invention are that through the directional temperature control design of the heating plate embedded in the outer protective sleeve, the present invention ensures the melting uniformity; the size characteristic values of the insulating pipe dynamically select the bonding or hot melt connection method; based on the dual determination mechanism of the interface fusion eigenvalue and the circumferential coverage integrity rate, the hot melt connection effect can be accurately identified and corresponding adjustments can be made, improving the reliability and adaptability of the interface connection; at the same time, the circumferential deformation characterization value is combined to distinguish the defects of excessive gap or overheating deformation, thereby improving the interface connection quality.

[0034] Furthermore, the present invention ensures that heat is concentrated in the melting layer by setting an outer protective sleeve internally embedded with a heating plate, achieving precise positioning of the heat source. The heating plate can uniformly and efficiently transfer heat to the insulation pipe interface, thereby ensuring rapid and reliable connection of the interface.

[0035] Furthermore, the present invention determines the connection method of the interface according to the dimensional characteristic values of the insulation pipe, including bonding or hot melt connection. By comprehensively considering dimensional characteristic values such as the total diameter of the insulation pipe and the thickness of the composite layer, the present invention can accurately select the most suitable connection method; for smaller-sized insulation pipes, the bonding method is adopted to ensure the sealing performance of the interface; while for larger-sized insulation pipes, the hot melt connection method is selected to achieve a more stable connection, thus avoiding connection quality problems caused by improper connection methods.

[0036] Furthermore, the present invention determines whether the hot melt connection meets the preset standard according to the interface fusion characteristic value and conducts a secondary determination or determines the reason for non-compliance when it does not meet the standard. By real-time monitoring and calculating the interface fusion characteristic value, the quality of the hot melt connection can be accurately evaluated. This index takes into account the influence of the thickness of the melting layer on the connection quality of the interface; when it is determined that the hot melt connection does not meet the standard, corresponding measures can be quickly identified and taken, thereby improving the accuracy of the connection quality evaluation.

[0037] Furthermore, under the condition that the present invention determines that the hot melt connection does not meet the preset standard according to the interface fusion characteristic value, it secondly determines whether the hot melt connection meets the preset standard according to the circumferential coverage integrity rate of the melting layer, and increases the heating duration of the heating plate when the hot melt connection does not meet the standard; the coverage of the melting layer in the circumferential direction of the pipeline is evaluated, and the dual determination criteria together constitute a comprehensive evaluation of the quality of the hot melt connection, thereby effectively reducing the possibility of misjudgment.

[0038] Furthermore, the present invention makes the increase amplitude of the heating duration of the heating plate positively correlated with the circumferential coverage difference value, where the melting layer difference value is the difference between the preset circumferential coverage rate and the circumferential coverage rate, thereby realizing precise control of the increase amplitude of the heating duration.

[0039] Furthermore, the present invention sets the circumferential deformation characterization value of the outer protective sleeve and determines the reason why the hot melt connection does not meet the preset standard according to the circumferential deformation characterization value. The reasons include that the fitting gap between the outer protective sleeve and the composite layer is too large, or the heating temperature is too high; precise positioning of the problem, thereby improving the accuracy of the connection quality evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a flowchart of the waterproof interface connection method for the insulation layer outer pipe of the direct protection insulation pipe in the embodiment of the present invention;

[0041] Figure 2Flow chart for determining the connection mode of the interface in the embodiments of the present invention;

[0042] Figure 3 Flow chart for determining whether the hot melt connection meets the preset standard according to the interface fusion characteristic value in the embodiments of the present invention;

[0043] Figure 4 Flow chart for determining the reason why the hot melt connection does not meet the preset standard according to the circumferential deformation characterization value of the outer protective sleeve in the embodiments of the present invention. Detailed implementation manners

[0044] In order to make the objectives and advantages of the present invention clearer and more understandable, the present invention will be further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0045] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principle of the present invention and do not limit the protection scope of the present invention.

[0046] It should be noted that the data in this embodiment are obtained through comprehensive analysis and evaluation of the historical detection data and corresponding historical detection results of the present invention in the three months before this detection. Those skilled in the art can understand that the determination method of the present invention for a single above-mentioned parameter can be to select the value with the highest proportion according to the data distribution as the preset standard parameter, use weighted summation to take the obtained value as the preset standard parameter, substitute each historical data into a specific formula and take the value obtained by using this formula as the preset standard parameter or other selection methods, as long as it satisfies that the method of the present invention can clearly define different specific situations in the single determination process through the obtained value.

[0047] Please refer to Figure 1 、 Figure 2 、 Figure 3 and Figure 4 as shown, which are respectively the flow charts of the waterproof interface connection method for the outer pipe of the thermal insulation layer of the direct protection thermal insulation pipe in the embodiments of the present invention; the flow chart for determining the connection mode of the interface in the embodiments of the present invention; the flow chart for determining whether the hot melt connection meets the preset standard according to the interface fusion characteristic value in the embodiments of the present invention; the flow chart for determining the reason why the hot melt connection does not meet the preset standard according to the circumferential deformation characterization value of the outer protective sleeve in the embodiments of the present invention.

[0048] Please refer to Figure 1 as shown, the embodiments of the present invention provide a waterproof interface connection method for the outer pipe of the thermal insulation layer of a direct protection thermal insulation pipe, including:

[0049] Step S1: Perform surface treatment on the composite layer outside the metal core pipe that has been welded. The surface treatment is to roughen the outer surface of the composite layer using a grinding wheel grinder, sleeve the outer protective sleeve on the composite layer, obtain the thickness of the composite layer through a thickness gauge, and obtain the total pipe diameter of the insulation pipe through a diameter gauge to obtain size characteristic values. Among them, the surface treatment ensures a reliable connection between the outer protective sleeve and the composite layer, that is, it increases the molten contact area between the outer protective sleeve and the composite layer.

[0050] Step S2: Determine the interface connection method according to the size characteristic values, and move the outer protective sleeve to the interface area for wrapping. Among them, both ends of the outer protective sleeve are respectively lapped on both ends of the composite layer.

[0051] Step S3: Under the condition of using hot melt connection as the interface connection method, start the heating plate inside the outer protective sleeve for heating, melt and bond the outer protective sleeve and the composite layer, obtain the thickness of the molten layer, and obtain the interface fusion characteristic value.

[0052] Step S4: When it is determined that the hot melt connection does not meet the preset standard according to the interface fusion characteristic value, make a secondary determination according to the circumferential coverage integrity rate of the molten layer, or determine the reason why the hot melt connection does not meet the preset standard according to the circumferential deformation characterization value of the outer protective sleeve.

[0053] Step S5: Cool the interface that meets the preset standard.

[0054] Specifically, the insulation pipe is composed of a metal core pipe and a composite layer. Among them, the composite layer includes a thermal insulation layer wrapped on the metal core pipe and an anti-corrosion layer wrapped on the thermal insulation layer.

[0055] In this embodiment, the metal core pipe is a carbon steel pipe, and a 30-mm-thick polyurethane thermal insulation layer and a 3-mm-thick polyethylene anti-corrosion layer are sequentially wrapped outside to form a composite layer.

[0056] Specifically, a heating plate is embedded in the area where the inner wall of the outer protective sleeve contacts the composite layer.

[0057] In this embodiment, the heating plate is embedded inside the outer protective sleeve. After the heating plate is turned on, the heating plate makes the inner wall of the outer protective sleeve in contact with the composite layer and the composite layer melt and bond through heat conduction.

[0058] Please refer to Figure 2 As shown, specifically, determine the connection method of the interface according to the size characteristic values of the insulation pipe, where

[0059] If the size characteristic value is less than the preset surface size characteristic value of 7000 mm2, use adhesive bonding as the interface connection method;

[0060] If the size characteristic value is greater than or equal to the preset surface size characteristic value, use hot melt connection as the interface connection method;

[0061] The value range of the preset surface dimension characteristic value is (5000 mm 2 , 9000 mm 2 ), preferably, the preset surface dimension characteristic value is selected as 7000 mm 2 .

[0062] The dimension characteristic value is jointly determined by the thickness of the composite layer and the total diameter of the insulation pipe.

[0063] The dimension characteristic value is calculated by the following formula:

[0064] P = D × T

[0065] In the formula, P represents the dimension characteristic value; D represents the thickness of the composite layer; T represents the total diameter of the insulation pipe;

[0066] The thickness of the composite layer directly affects the filling amount of the interface connection: the greater the thickness, the more material needs to be filled during melting or bonding, and the higher the requirements for the heating time and the amount of adhesive used;

[0067] The pipe diameter determines the circumference of the interface. The longer the circumference, the larger the contact area between the outer protective sleeve and the composite layer, and the stricter the requirements for the uniformity and reliability of the connection;

[0068] Unifying the thickness and the pipe diameter into a comprehensive parameter can not only reflect the filling amount but also reflect the contact area, which better meets the requirements in actual engineering.

[0069] In this embodiment, the bonding method is to evenly apply the adhesive at the interface of the composite layer. At the same time, the interface of the outer protective sleeve is also coated with the adhesive. The outer protective sleeve is fitted to the interface of the composite layer, and an appropriate pressure is applied to make the adhesive infiltrate and fill the gap between the composite layer and the outer protective sleeve. Among them, the adhesive can be epoxy resin adhesive or polyurethane adhesive, and no specific limitation is made, as long as the bonding requirements are met.

[0070] Please refer to Figure 3 shown. Specifically, it is determined whether the hot melt connection meets the preset standard according to the interface fusion characteristic value. Among them,

[0071] If the interface fusion characteristic value is less than the first preset interface fusion characteristic threshold of 0.83, it is determined that the hot melt connection meets the preset standard;

[0072] If the interface fusion characteristic value is greater than or equal to the first preset interface fusion characteristic threshold and less than the second preset interface fusion characteristic threshold of 1.12, it is determined that the hot melt connection part meets the preset standard, and it is further determined whether the hot melt connection meets the preset standard according to the circumferential coverage integrity rate of the molten layer;

[0073] If the interface fusion characteristic value is greater than or equal to the second preset interface fusion characteristic threshold, it is determined that the hot melt connection does not meet the preset standard, and the reason for the non - compliance of the hot melt connection with the preset standard is determined according to the circumferential deformation characterization value of the outer protective sleeve.

[0074] Specifically, the process of obtaining the interface fusion characteristic value includes:

[0075] Starting from the edge of the outer protective sleeve, longitudinally sample with a preset surface size of 10 mm×10 mm at equal circumferential intervals in the direction perpendicular to the axis of the outer protective sleeve to obtain a longitudinal cross - section sample; the preset surface size is the length and width of the sample.

[0076] Use a metallurgical microscope to measure the thickness of the molten layer of each longitudinal cross - section sample;

[0077] Calculate the arithmetic mean of the thicknesses of the molten layers of all longitudinal cross - section samples;

[0078] The ratio of the arithmetic mean to the preset thickness of 1.5 mm is recorded as the interface fusion characteristic value.

[0079] In this embodiment, the thickness of the polyethylene anti - corrosion layer is selected as 3 mm, and the preset thickness is taken as 50% of it, that is, 1.5 mm, which not only ensures the molten bonding strength but also avoids the decline of material properties caused by over - heating.

[0080] Specifically, the value range of the first preset interface fusion characteristic threshold is (0.65, 0.90), and the value range of the second preset interface fusion characteristic threshold is (0.95, 1.25). Preferably, the first preset interface fusion characteristic threshold is selected as 0.83, and the second preset interface fusion characteristic threshold is selected as 1.12.

[0081] Specifically, according to the circumferential coverage integrity rate of the molten layer, it is determined again whether the hot melt connection meets the preset standard, where

[0082] If the circumferential coverage rate is less than the preset circumferential coverage rate of 75%, it is determined that the hot melt connection does not meet the preset standard, and the heating duration of the heating plate is increased according to the difference between the preset circumferential coverage rate and the circumferential coverage rate;

[0083] If the circumferential coverage rate is greater than or equal to the preset circumferential coverage rate, it is determined that the hot melt connection meets the preset standard;

[0084] Specifically, the value range of the preset circumferential coverage rate is (70%, 90%), and in this embodiment, it is selected as 75% to ensure uniform bonding in the circumferential direction.

[0085] The circumferential coverage rate is the ratio between the covered arc length of the molten material in the circumferential direction of the composite layer during the hot melt connection process and the outer circumferential arc length of the composite layer. Among them, the circumferential arc length is obtained by an industrial endoscope, and the type of the industrial endoscope can be Olympus IPLEX NX, and there is no specific limitation, as long as the circumferential arc length measurement requirement is met.

[0086] Specifically, the increase amplitude of the heating duration of the heating plate is positively correlated with the circumferential coverage difference. Among them, the positive correlation is, for example, a linear positive correlation or a non-linear positive correlation, and the linear slope of the linear positive correlation is not specifically limited. It can be understood that the greater the circumferential coverage difference, the greater the increase amplitude of the heating duration of the heating plate; the molten layer difference is the difference between the preset circumferential coverage rate and the circumferential coverage rate.

[0087] Please refer to Figure 4 as shown. Specifically, the reason for the hot melt connection not meeting the preset standard is determined according to the circumferential deformation characterization value of the outer protective sleeve, where

[0088] if the circumferential deformation characterization value is less than the preset circumferential deformation threshold of 1.07, it is determined that the reason for the hot melt connection not meeting the preset standard is that the fitting gap between the outer protective sleeve and the composite layer is too large;

[0089] if the circumferential deformation characterization value is greater than or equal to the preset circumferential deformation threshold, it is determined that the reason for the hot melt connection not meeting the preset standard is that the heating temperature is too high;

[0090] The circumferential deformation characterization value is the ratio between the ellipticity of the outer protective sleeve after melting and the ellipticity of the outer protective sleeve before melting, and the ellipticity is obtained by a laser measuring instrument.

[0091] So far, the technical solution of the present invention has been described in combination with the preferred embodiments shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present invention.

[0092] The above are only the preferred embodiments of the present invention and are not used to limit the present invention; for those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for connecting the waterproof interface of the outer pipe of the insulation layer of a straight insulation pipe, characterized in that: include: The composite layer outside the welded metal core tube is surface treated, the outer protective sleeve is sleeved on the composite layer, and the thickness of the composite layer and the total diameter of the insulation tube are obtained to obtain the dimensional characteristic value; Determine the interface connection mode according to the size characteristic value, and move the outer sleeve to the interface area for covering, wherein the two ends of the outer sleeve are overlapped at the two ends of the composite layer respectively; Under the condition that hot-melt connection is adopted as the interface connection mode, the heating plate inside the outer sheath is started to heat, the outer sheath tube and the composite layer are melted and combined, the thickness of the melt layer is obtained, and the interface fusion characteristic value is obtained; When the hot melt connection is judged not to meet the preset standard according to the interface fusion characteristic value, a secondary judgment is made according to the circumferential coverage completeness rate of the molten layer, or the reason why the hot melt connection does not meet the preset standard is determined according to the circumferential deformation characteristic value of the outer sleeve; The interfaces that meet the preset standards are cooled.

2. The method for connecting the outer pipe of the insulation layer of the straight insulation pipe with a waterproof interface according to claim 1 is characterized in that: The thermal insulation pipe is composed of a metal core pipe and a composite layer, wherein the composite layer comprises a thermal insulation layer coated on the metal core pipe and an anti-corrosion layer coated on the thermal insulation layer.

3. The method for connecting the outer pipe of the insulation layer of the straight insulation pipe with a waterproof interface according to claim 2 is characterized in that: A heating plate is embedded in the area where the inner wall of the outer protective sleeve contacts the composite layer.

4. The waterproof interface connection method of the outer pipe of the insulation layer of the straight insulation pipe according to claim 3 is characterized in that: The connection method of the interface is determined according to the size characteristic value of the insulation pipe, where: If the size characteristic value is smaller than the preset surface size characteristic value, gluing is used as the interface connection method; If the size characteristic value is greater than or equal to the preset surface size characteristic value, hot melt connection is used as the interface connection method; The dimension characteristic value is determined by the thickness of the composite layer and the total diameter of the insulation pipe.

5. The method for connecting the outer pipe of the insulation layer of the straight insulation pipe with a waterproof interface according to claim 4 is characterized in that: In response to the interface fusion characteristic value being greater than or equal to a first preset interface fusion characteristic threshold, it is determined that the hot melt connection does not meet the preset standard.

6. The method for connecting the outer pipe of the insulation layer of the straight insulation pipe with a waterproof interface according to claim 5 is characterized in that: The process of obtaining the interface fusion characteristic value includes: Starting from the edge of the outer sleeve, the preset surface size is cut at equal intervals in the circumferential direction perpendicular to the axis of the outer sleeve to obtain a longitudinal cross-sectional sample; The thickness of the molten layer of each longitudinal cross-section sample was measured using a metallographic microscope; Calculate the arithmetic mean of the thickness of the molten layer of all longitudinal cross-section samples; The ratio of the arithmetic mean value to the preset thickness is recorded as the interface fusion characteristic value.

7. The method for connecting the outer pipe of the insulation layer of the straight insulation pipe with a waterproof interface according to claim 6 is characterized in that: If the interface fusion characteristic value is greater than or equal to the first preset interface fusion characteristic threshold value and less than the second preset interface fusion characteristic threshold value, it is determined that the hot melt connection does not meet the preset standard, and a second determination is made as to whether the hot melt connection meets the preset standard based on the circumferential coverage completeness rate of the molten layer; If the interface fusion characteristic value is greater than or equal to the second preset interface fusion characteristic threshold, it is determined that the hot melt connection does not meet the preset standard, and the reason why the hot melt connection does not meet the preset standard is determined according to the circumferential deformation characterization value of the outer protective sleeve.

8. The method for connecting the outer pipe of the insulation layer of the straight insulation pipe with a waterproof interface according to claim 7 is characterized in that: The circumferential coverage completeness rate of the molten layer is used to determine whether the hot melt connection meets the preset standard. If the circumferential coverage is less than the preset circumferential coverage, it is determined that the hot melt connection does not meet the preset standard, and the heating time of the heating plate is increased according to the difference between the preset circumferential coverage and the circumferential coverage; If the circumferential coverage is greater than or equal to the preset circumferential coverage, the hot melt connection is determined to meet the preset standard; The circumferential coverage is the ratio between the arc length of the molten material in the circumferential direction of the composite layer and the arc length of the outer circumferential direction of the composite layer during the heat welding process.

9. The method for connecting the outer pipe of the insulation layer of the straight insulation pipe with a waterproof interface according to claim 8 is characterized in that: The increase in the heating time of the heating plate is positively correlated with the circumferential coverage difference, wherein the molten layer difference is the difference between the preset circumferential coverage rate and the circumferential coverage rate.

10. The method for connecting the outer pipe of the insulation layer of the straight insulation pipe according to claim 9 is characterized in that: The reasons why the hot melt connection does not meet the preset standards are determined based on the circumferential deformation characterization value of the outer protective sleeve, including: the fitting clearance between the outer protective sleeve and the composite layer is too large, or the heating temperature is too high, wherein the circumferential deformation characterization value is the ratio between the ovality of the outer protective sleeve after melting and the ovality of the outer protective sleeve before melting.

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