Anti-aging directly buried heat preservation pipe and preparation method thereof

Abstract

The application relates to the technical field of heat preservation pipes, and discloses an anti-aging direct-buried heat preservation pipe and a preparation method thereof, the anti-aging direct-buried heat preservation pipe comprises, from inside to outside, a steel pipe, a polyurethane heat preservation layer and a polyethylene outer protection pipe layer, the polyethylene outer protection pipe layer comprises a polyethylene outer protection pipe inner layer and a polyethylene outer protection pipe outer layer, the raw material of the polyethylene outer protection pipe inner layer comprises the following components in parts by weight: 60 parts of first polyethylene and 6-16 parts of first carbon black, the raw material of the polyethylene outer protection pipe outer layer comprises the following components in parts by weight: 60 parts of second polyethylene and 8-20 parts of second carbon black, the weight of the second carbon black is greater than that of the first carbon black, and the first polyethylene and the second polyethylene each independently comprises high-pressure polyethylene and low-pressure polyethylene in a weight ratio of 1:9-9:1. Through the technical scheme, the problem that the mechanical strength of the polyethylene outer protection pipe layer outside the direct-buried heat preservation pipe is low and the impact resistance is poor in the related art is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat preservation pipe, in particular, relates to an anti-aging directly buried heat preservation pipe and a preparation method thereof. BACKGROUND

[0002] The directly buried heat preservation pipe is widely used in urban central heating, cooling, petroleum and chemical industry, municipal water supply and drainage and other fields as an efficient heat preservation pipeline. The structure of the directly buried heat preservation pipe is usually composed of a working steel pipe, a heat preservation layer and a polyethylene outer pipe layer. The outer pipe layer as a key structure directly contacting with underground soil, moisture, microorganisms and external environment, plays an important role in protecting the heat preservation layer, resisting external corrosion and aging, and resisting mechanical impact. Especially, the anti-aging performance of the polyethylene outer pipe layer is of great significance to ensure the service life and operation safety of the directly buried heat preservation pipe in harsh environments.

[0003] As the main material of the outer pipe layer of the directly buried heat preservation pipe, the polyethylene material has the function of better matching the internal heat preservation layer. However, the anti-aging performance of the polyethylene material itself is poor, and long-term exposure to light or oxygen environment will cause the molecular chain of the polyethylene material to break, reducing the anti-aging performance of the polyethylene outer pipe layer. In order to solve the problem of poor aging resistance of the polyethylene outer pipe layer, carbon black is usually added to the polyethylene outer pipe layer. The carbon black can absorb ultraviolet rays and resist the penetration of oxygen, thereby improving the stability of the polyethylene material and to some extent improving the anti-aging performance of the polyethylene outer pipe layer. However, the addition of carbon black can improve the light and oxygen aging resistance of polyethylene, but it can reduce the mechanical strength and impact resistance of the polyethylene outer pipe layer. This is because the interfacial adhesion between carbon black and polyethylene matrix is relatively poor, and in the whole mixed system, carbon black is locally aggregated, which cannot effectively disperse external stress, resulting in relatively poor mechanical strength and impact resistance of the polyethylene outer pipe layer.

[0004] Therefore, it is of great significance to develop a directly buried heat preservation pipe with good anti-aging performance and improved mechanical strength and impact resistance of the polyethylene outer pipe layer, which can prolong the service life of the directly buried heat preservation pipe in harsh environments. SUMMARY

[0005] The present application provides an anti-aging directly buried heat preservation pipe and a preparation method thereof, which solves the problems of low mechanical strength and poor impact resistance of the polyethylene outer pipe layer of the directly buried heat preservation pipe in the related art.

[0006] The technical scheme of the present application is as follows:

[0007] The application provides an anti-aging directly-buried heat preservation pipe, which comprises a steel pipe, a polyurethane heat preservation layer and a polyethylene outer pipe layer from inside to outside.

[0008] The raw material of the polyethylene outer pipe inner layer comprises the following components in parts by weight:

[0009] 60 parts of the first polyethylene and 6-16 parts of the first carbon black;

[0010] The raw material of the polyethylene outer pipe outer layer comprises the following components in parts by weight:

[0011] 60 parts of the second polyethylene and 8-20 parts of the second carbon black;

[0012] The weight of the second carbon black is greater than that of the first carbon black.

[0013] The first polyethylene and the second polyethylene each independently comprises high-pressure polyethylene and low-pressure polyethylene in a weight ratio of 1:9-9:1.

[0014] As a further technical solution, the weight ratio of the high-pressure polyethylene and the low-pressure polyethylene in the first polyethylene is 0.5-1:1.5.

[0015] As a further technical solution, the weight ratio of the high-pressure polyethylene and the low-pressure polyethylene in the second polyethylene is 3-5:1.

[0016] In the polyethylene outer pipe layer of the anti-aging directly-buried heat preservation pipe, the content ratio of the high-pressure polyethylene and the low-pressure polyethylene in the polyethylene outer pipe inner layer and the polyethylene outer pipe outer layer is adjusted, when the weight ratio of the high-pressure polyethylene and the low-pressure polyethylene in the first polyethylene is 0.5-1:1.5 and the weight ratio of the high-pressure polyethylene and the low-pressure polyethylene in the second polyethylene is 3-5:1, the mechanical strength of the polyethylene outer pipe layer can be further improved, and the tensile strength can be increased to more than 25.2 MPa. It is speculated that the reason may be that the content of carbon black in the polyethylene outer pipe outer layer is relatively high, when the weight ratio of the high-pressure polyethylene and the low-pressure polyethylene is 3-5:1, the polyethylene matrix material can better wrap the carbon black with relatively high content, better adjust the structural stability of the polyethylene outer pipe outer layer, the content of carbon black in the polyethylene outer pipe inner layer is relatively low, when the weight ratio of the high-pressure polyethylene and the low-pressure polyethylene is 0.5-1:1.5, it is more conducive to reducing the migration of carbon black in the polyethylene outer pipe inner layer, thereby better dispersing external stress, and finally the mechanical strength of the polyethylene outer pipe layer as a whole is further improved.

[0017] As a further technical solution, the raw materials of the polyethylene outer pipe inner layer and the polyethylene outer pipe outer layer each comprise an antioxidant, an ultraviolet absorber and a compatibilizer.

[0018] The antioxidant includes one or both of antioxidant 1010 and antioxidant 1076;

[0019] The ultraviolet absorber includes one or both of benzotriazole and 2,4-dihydroxybenzophenone;

[0020] The compatibilizer includes maleic anhydride grafted polyethylene.

[0021] As a further technical solution, the addition amount of the antioxidant in the inner layer of the polyethylene outer protective pipe and the outer layer of the polyethylene outer protective pipe is independently 2-4 parts;

[0022] The addition amount of the ultraviolet absorber in the inner layer of the polyethylene outer protective pipe and the outer layer of the polyethylene outer protective pipe is independently 0.5-1 part;

[0023] The addition amount of the compatibilizer in the inner layer of the polyethylene outer protective pipe and the outer layer of the polyethylene outer protective pipe is independently 2-4 parts.

[0024] As a further technical solution, the raw material of the outer layer of the polyethylene outer protective pipe further includes chitosan and aromatic aminocarboxylic compounds in a weight ratio of 3-9:1.

[0025] When the raw material of the outer layer of the polyethylene outer protective pipe of the anti-aging direct-buried heat preservation pipe of the application further includes chitosan and aromatic aminocarboxylic compounds, the addition of aromatic aminocarboxylic compounds and chitosan can make carbon black more uniformly dispersed in the polyethylene matrix, thereby improving the bonding with the polyethylene matrix, better shielding ultraviolet rays and resisting the penetration of oxygen. At the same time, the amino groups in the aromatic aminocarboxylic compounds can also consume peroxides generated in the aging process of polyethylene to some extent, thereby inhibiting the aging of polyethylene and effectively improving the anti-aging performance of the outer layer of the polyethylene outer protective pipe, thereby effectively improving the anti-aging performance of the direct-buried heat preservation pipe.

[0026] As a further technical solution, the aromatic aminocarboxylic compound includes one or more of 3-aminobenzenedicarboxylic acid, 3,5-diaminobenzoic acid, and m-aminobenzoic acid, preferably 3,5-diaminobenzoic acid.

[0027] In the application, the aromatic aminocarboxylic compound can be 3-aminobenzenedicarboxylic acid, 3,5-diaminobenzoic acid, or m-aminobenzoic acid. When the aromatic aminocarboxylic compound is 3,5-diaminobenzoic acid, the anti-aging performance of the outer layer of the polyethylene outer protective pipe is best improved. It is speculated that the reason is that compared with 3-aminobenzenedicarboxylic acid and m-aminobenzoic acid, 3,5-diaminobenzoic acid contains more amino active groups, which can better disperse carbon black and better inhibit the aging of polyethylene.

[0028] As a further technical solution, the weight ratio of the chitosan and the aromatic aminocarboxylic compound to the weight of the second carbon black is 4-8:20.

[0029] As a further technical solution, the steel pipe includes one of a seamless steel pipe and a straight seam steel pipe, and is preferably a seamless steel pipe.

[0030] The application provides a preparation method of the anti-aging directly-buried heat preservation pipe.

[0031] A1, blending raw materials of the inner layer of the polyethylene outer protective pipe, and extruding to obtain the inner layer of the polyethylene outer protective pipe;

[0032] A2, blending raw materials of the outer layer of the polyethylene outer protective pipe, and extruding to the outer surface of the inner layer of the polyethylene outer protective pipe to obtain the polyethylene outer protective pipe layer including the inner layer of the polyethylene outer protective pipe and the outer layer of the polyethylene outer protective pipe;

[0033] A3, after the polyethylene outer protective pipe layer is fixed, the steel pipe is sent into the polyethylene outer protective pipe layer and fixed, and polyurethane heat preservation layer material is poured between the polyethylene outer protective pipe layer and the steel pipe to obtain the anti-aging directly-buried heat preservation pipe.

[0034] The application also provides a preparation method of the anti-aging directly-buried heat preservation pipe.

[0035] S0, dispersing the aromatic aminocarboxylic compound in ethanol, adding the second carbon black, carrying out first mixing, concentrating, and drying to obtain the second carbon black treatment I, dispersing the chitosan in an ethanol aqueous solution, adding the second carbon black treatment I, carrying out second mixing, concentrating, and drying to obtain the second carbon black treatment II;

[0036] S1, blending raw materials of the inner layer of the polyethylene outer protective pipe, and extruding to obtain the inner layer of the polyethylene outer protective pipe;

[0037] S2, blending the second polyethylene, the second carbon black treatment II and the remaining components except the second polyethylene, the second carbon black, the aromatic aminocarboxylic compound and the chitosan in the outer layer of the polyethylene outer protective pipe, and extruding to the outer surface of the inner layer of the polyethylene outer protective pipe to obtain the polyethylene outer protective pipe layer including the inner layer of the polyethylene outer protective pipe and the outer layer of the polyethylene outer protective pipe;

[0038] S3, after the polyethylene outer protective pipe layer is fixed, the steel pipe is sent into the polyethylene outer protective pipe layer and fixed, and polyurethane heat preservation layer material is poured between the polyethylene outer protective pipe layer and the steel pipe to obtain the anti-aging directly-buried heat preservation pipe.

[0039] In the present application, the aromatic aminocarboxylic acid compound and chitosan are first surface compounded with carbon black, and then the formed carbon black treatment product is blended with other components in the outer layer of the polyethylene outer sheath pipe to prepare the outer layer of the polyethylene outer sheath pipe, which is better for improving the anti-aging performance of the outer layer of the polyethylene outer sheath pipe.

[0040] As a further technical solution, in step S0, the stirring speed of the first mixing is 400-600 rpm, and the time is 30-60 min.

[0041] The temperature of the second mixing is 30-40 DEG C, the stirring speed is 500-800 rpm, and the time is 1.5-2.5 h.

[0042] The working principle and beneficial effects of the present application are as follows:

[0043] In the anti-aging directly buried heat preservation pipe of the present application, the polyethylene outer sheath pipe layer comprises a two-layer structure of a polyethylene outer sheath pipe inner layer and a polyethylene outer sheath pipe outer layer, high-pressure polyethylene and low-pressure polyethylene are used in the two-layer structure at the same time, and the carbon black content in the two layers is adjusted, so that the carbon black content in the polyethylene outer sheath pipe inner layer is less than that in the polyethylene outer sheath pipe outer layer, which can effectively improve the mechanical strength and impact resistance of the polyethylene outer sheath pipe layer of the directly buried heat preservation pipe.

[0044] The carbon black content in the polyethylene outer sheath pipe outer layer is relatively high, and when external stress acts on the outer sheath pipe, relatively more carbon black particles can effectively disperse the external stress in the surrounding polyethylene matrix and the polyethylene outer sheath pipe inner layer. The carbon black content in the polyethylene outer sheath pipe inner layer is relatively small, which disperses the stress transmitted by the polyethylene outer sheath pipe outer layer, and at the same time, does not affect the combination of the polyethylene outer sheath pipe inner layer and the polyurethane insulation layer due to excessive carbon black, thereby facilitating the enhancement of the stability of the overall structure of the directly buried heat preservation pipe. In addition, high-pressure polyethylene and low-pressure polyethylene are used in the polyethylene outer sheath pipe inner layer and the polyethylene outer sheath pipe outer layer, and the flexibility of high-pressure polyethylene and the rigidity of low-pressure polyethylene are adjusted with each other, which can improve the interfacial cohesion of carbon black with polyethylene to some extent, thereby facilitating the improvement of the stability of the overall polyethylene outer sheath pipe layer. Therefore, the polyethylene outer sheath pipe layer comprises a two-layer structure of a polyethylene outer sheath pipe inner layer and a polyethylene outer sheath pipe outer layer, and high-pressure polyethylene and low-pressure polyethylene are contained in the two-layer structure, which improves the interfacial combination of polyethylene and carbon black, and adjusts the carbon black content in the polyethylene outer sheath pipe inner layer to be less than that in the polyethylene outer sheath pipe outer layer, thereby forming a carbon black gradient distribution from inside to outside, effectively dispersing external stress, and finally facilitating the improvement of the mechanical strength and impact resistance of the polyethylene outer sheath pipe layer, and finally improving the mechanical stability of the directly buried heat preservation pipe. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0046] In the following examples and comparative examples, the high-pressure polyethylene is LDPE FB5005, the low-pressure polyethylene is HDPE PX2413, the carbon black is N330, the chitosan has a degree of deacetylation of 90% and a weight average molecular weight of 150,000, and the maleic anhydride grafted polyethylene is E100.

[0047] Example 1

[0048] A preparation method of an anti-aging direct-buried thermal insulation pipe, comprising the following steps:

[0049] A1, blending 6 parts of high-pressure polyethylene, 54 parts of low-pressure polyethylene, 6 parts of carbon black, 2 parts of antioxidant 1010, 0.5 parts of 2,4-dihydroxybenzophenone, and 2 parts of maleic anhydride grafted polyethylene, and then extruding to obtain a polyethylene outer protective pipe inner layer;

[0050] A2, blending 6 parts of high-pressure polyethylene, 54 parts of low-pressure polyethylene, 8 parts of carbon black, 2 parts of antioxidant 1010, 0.5 parts of 2,4-dihydroxybenzophenone, and 2 parts of maleic anhydride grafted polyethylene, and then extruding to the outer surface of the polyethylene outer protective pipe inner layer to obtain a polyethylene outer protective pipe layer containing the polyethylene outer protective pipe inner layer and the polyethylene outer protective pipe outer layer;

[0051] A3, fixing the polyethylene outer protective pipe layer by using a pipe clamp, binding a support to a seamless steel pipe, and then feeding the support into the polyethylene outer protective pipe layer and fixing the support, pouring polyurethane thermal insulation layer material between the polyethylene outer protective pipe layer and the seamless steel pipe, and obtaining an anti-aging direct-buried thermal insulation pipe.

[0052] Example 2

[0053] A preparation method of an anti-aging direct-buried thermal insulation pipe, comprising the following steps:

[0054] A1, blending 6 parts of high-pressure polyethylene, 54 parts of low-pressure polyethylene, 6 parts of carbon black, 2 parts of antioxidant 1010, 0.5 parts of 2,4-dihydroxybenzophenone, and 2 parts of maleic anhydride grafted polyethylene, and then extruding to obtain a polyethylene outer protective pipe inner layer;

[0055] A2, 30 parts of high pressure polyethylene, 30 parts of low pressure polyethylene, 20 parts of carbon black, 3 parts of antioxidant 1010, 1 part of 2,4-dihydroxybenzophenone and 3 parts of maleic anhydride grafted polyethylene are blended, and then extruded to the outer surface of the inner layer of the polyethylene outer protective pipe to obtain a polyethylene outer protective pipe layer containing the inner layer and the outer layer of the polyethylene outer protective pipe;

[0056] A3, after the polyethylene outer protective pipe layer is fixed by using a pipe clamp, the seamless steel pipe is sent into the polyethylene outer protective pipe layer after being bound by a support and fixed, and a polyurethane thermal insulation layer material is poured between the polyethylene outer protective pipe layer and the seamless steel pipe to obtain an anti-aging direct-buried thermal insulation pipe.

[0057] Example 3

[0058] A preparation method of an anti-aging direct-buried thermal insulation pipe, comprising the following steps:

[0059] A1, 54 parts of high pressure polyethylene, 6 parts of low pressure polyethylene, 16 parts of carbon black, 4 parts of antioxidant 1010, 1 part of 2,4-dihydroxybenzophenone and 4 parts of maleic anhydride grafted polyethylene are blended, and then extruded to obtain the inner layer of the polyethylene outer protective pipe;

[0060] A2, 54 parts of high pressure polyethylene, 6 parts of low pressure polyethylene, 20 parts of carbon black, 4 parts of antioxidant 1010, 1 part of 2,4-dihydroxybenzophenone and 4 parts of maleic anhydride grafted polyethylene are blended, and then extruded to the outer surface of the inner layer of the polyethylene outer protective pipe to obtain a polyethylene outer protective pipe layer containing the inner layer and the outer layer of the polyethylene outer protective pipe;

[0061] A3, after the polyethylene outer protective pipe layer is fixed by using a pipe clamp, the seamless steel pipe is sent into the polyethylene outer protective pipe layer after being bound by a support and fixed, and a polyurethane thermal insulation layer material is poured between the polyethylene outer protective pipe layer and the seamless steel pipe to obtain an anti-aging direct-buried thermal insulation pipe.

[0062] Example 4

[0063] The difference between the present embodiment and example 2 is that, in the preparation of the inner layer of the polyethylene outer protective pipe, 15 parts of high pressure polyethylene and 45 parts of low pressure polyethylene are added; and in the preparation of the outer layer of the polyethylene outer protective pipe, 45 parts of high pressure polyethylene and 15 parts of low pressure polyethylene are added.

[0064] Example 5

[0065] The difference between the present embodiment and example 2 is that, in the preparation of the inner layer of the polyethylene outer protective pipe, 24 parts of high pressure polyethylene and 36 parts of low pressure polyethylene are added; and in the preparation of the outer layer of the polyethylene outer protective pipe, 50 parts of high pressure polyethylene and 10 parts of low pressure polyethylene are added.

[0066] Example 6

[0067] The difference between this embodiment and embodiment 5 is only that the preparation method of the anti-aging direct-buried heat-insulating pipe in this embodiment is different, specifically:

[0068] S0, 8 parts of 3,5-diaminobenzoic acid were dispersed in 50 parts of ethanol, 20 parts of carbon black were added, and after stirring at 400 rpm for 60 min, concentration and drying were carried out to obtain a second carbon black treated product;

[0069] S1, 24 parts of high-pressure polyethylene, 36 parts of low-pressure polyethylene, 10 parts of carbon black, 3 parts of antioxidant 1010, 1 part of 2,4-dihydroxybenzophenone and 3 parts of maleic anhydride grafted polyethylene were blended, and then extruded to obtain a polyethylene outer protective pipe inner layer;

[0070] S2, 50 parts of high-pressure polyethylene, 10 parts of low-pressure polyethylene, 3 parts of antioxidant 1010, 1 part of 2,4-dihydroxybenzophenone, 3 parts of maleic anhydride grafted polyethylene and the above-mentioned second carbon black treated product were blended, and then extruded to the outer surface of the polyethylene outer protective pipe inner layer to obtain a polyethylene outer protective pipe layer containing a polyethylene outer protective pipe inner layer and a polyethylene outer protective pipe outer layer;

[0071] S3, after the polyethylene outer protective pipe layer was fixed by using a pipe clamp, the seamless steel pipe was sent into the polyethylene outer protective pipe layer after being bound by a support and fixed, and a polyurethane heat-insulating layer material was poured between the polyethylene outer protective pipe layer and the seamless steel pipe to obtain an anti-aging direct-buried heat-insulating pipe.

[0072] Embodiment 7

[0073] The difference between this embodiment and embodiment 6 is only that the step S0 in the preparation method of the anti-aging direct-buried heat-insulating pipe in this embodiment is different, specifically:

[0074] S0, 8 parts of 3,5-diaminobenzoic acid were dispersed in 50 parts of ethanol, 20 parts of carbon black were added, and after stirring at 400 rpm for 60 min, concentration and drying were carried out to obtain a second carbon black treated product;

[0075] Embodiment 8

[0076] The difference between this embodiment and embodiment 6 is only that the step S0 in the preparation method of the anti-aging direct-buried heat-insulating pipe in this embodiment is different, specifically:

[0077] S0, 8 parts of 3,5-diaminobenzoic acid were dispersed in 50 parts of ethanol, 20 parts of carbon black were added, and after stirring at 400 rpm for 60 min, concentration and drying were carried out to obtain a second carbon black treated product; 6 parts of chitosan were dispersed in 50 parts of an ethanol aqueous solution (the weight fraction of ethanol was 20%), and the above-mentioned second carbon black treated product I was added, and after stirring at 30°C and 500 rpm for 2.5 h, concentration and drying were carried out to obtain a second carbon black treated product II.

[0078] Example 9

[0079] The difference between this example and Example 6 is only that, in the preparation method of the anti-aging directly-buried thermal-insulation pipe of this example, the step S0 is different, specifically as follows:

[0080] S0, 1 part of 3,5-diaminobenzoic acid is dispersed in 50 parts of ethanol, 20 parts of carbon black is added, after stirring at 400 rpm for 60 min, concentration, drying, to obtain the second carbon black treated material I; 7 parts of chitosan is dispersed in 50 parts of ethanol aqueous solution (the weight fraction of ethanol is 20%), the above-mentioned second carbon black treated material I is added, after stirring at 30℃, 500 rpm for 2.5 h, concentration, drying, to obtain the second carbon black treated material II.

[0081] Example 10

[0082] The difference between this example and Example 6 is only that, in the preparation method of the anti-aging directly-buried thermal-insulation pipe of this example, the step S0 is different, specifically as follows:

[0083] S0, 0.8 parts of 3,5-diaminobenzoic acid is dispersed in 50 parts of ethanol, 20 parts of carbon black is added, after stirring at 400 rpm for 60 min, concentration, drying, to obtain the second carbon black treated material I; 7.2 parts of chitosan is dispersed in 50 parts of ethanol aqueous solution (the weight fraction of ethanol is 20%), the above-mentioned second carbon black treated material I is added, after stirring at 30℃, 500 rpm for 2.5 h, concentration, drying, to obtain the second carbon black treated material II.

[0084] Example 11

[0085] The difference between this example and Example 6 is only that, in the preparation method of the anti-aging directly-buried thermal-insulation pipe of this example, the step S0 is different, specifically as follows:

[0086] S0, 0.4 parts of 3,5-diaminobenzoic acid is dispersed in 50 parts of ethanol, 20 parts of carbon black is added, after stirring at 600 rpm for 30 min, concentration, drying, to obtain the second carbon black treated material I; 3.6 parts of chitosan is dispersed in 50 parts of ethanol aqueous solution (the weight fraction of ethanol is 20%), the above-mentioned second carbon black treated material I is added, after stirring at 40℃, 800 rpm for 1.5 h, concentration, drying, to obtain the second carbon black treated material II.

[0087] Example 12

[0088] A preparation method of an anti-aging directly-buried thermal-insulation pipe, comprising the following steps:

[0089] S1, 24 parts of high-pressure polyethylene, 36 parts of low-pressure polyethylene, 10 parts of carbon black, 3 parts of antioxidant 1010, 1 part of 2, 4-dihydroxybenzophenone and 3 parts of maleic anhydride grafted polyethylene were blended and then extruded to obtain a polyethylene inner layer of a polyethylene outer protective pipe;

[0090] S2, 50 parts of high-pressure polyethylene, 10 parts of low-pressure polyethylene, 3 parts of antioxidant 1010, 1 part of 2, 4-dihydroxybenzophenone, 3 parts of maleic anhydride grafted polyethylene, 20 parts of carbon black, 2 parts of 3, 5-diaminobenzoic acid and 6 parts of chitosan were blended and then extruded to the outer surface of the polyethylene inner layer of the polyethylene outer protective pipe to obtain a polyethylene outer protective pipe layer containing the polyethylene inner layer and the polyethylene outer layer of the polyethylene outer protective pipe;

[0091] S3, after the polyethylene outer protective pipe layer was fixed by using a pipe clamp, the seamless steel pipe was sent into the polyethylene outer protective pipe layer after being bound by a support and fixed, and a polyurethane thermal insulation layer material was poured between the polyethylene outer protective pipe layer and the seamless steel pipe to obtain an anti-aging directly buried thermal insulation pipe.

[0092] Comparative Example 1

[0093] The difference between the present comparative example and Example 2 is that in the present comparative example, the low-pressure polyethylene in the polyethylene inner layer and the polyethylene outer layer of the polyethylene outer protective pipe is replaced by an equal amount of high-pressure polyethylene.

[0094] Comparative Example 2

[0095] The difference between the present comparative example and Example 2 is that in the present comparative example, the high-pressure polyethylene in the polyethylene inner layer and the polyethylene outer layer of the polyethylene outer protective pipe is replaced by an equal amount of low-pressure polyethylene.

[0096] Comparative Example 3

[0097] The difference between the present comparative example and Example 2 is that in the present comparative example, 10 parts of carbon black in the polyethylene inner layer of the polyethylene outer protective pipe is replaced by 15 parts of carbon black, and 20 parts of carbon black in the polyethylene outer layer of the polyethylene outer protective pipe is replaced by 15 parts of carbon black.

[0098] Comparative Example 4

[0099] The difference between the present comparative example and Example 2 is that in the present comparative example, 10 parts of carbon black in the polyethylene inner layer of the polyethylene outer protective pipe is replaced by 20 parts of carbon black, and 20 parts of carbon black in the polyethylene outer layer of the polyethylene outer protective pipe is replaced by 10 parts of carbon black.

[0100] Experimental Example 1

[0101] The directly buried thermal insulation pipes prepared in Examples 1-5 and Comparative Examples 1-4 were subjected to the following performance tests:

[0102] (1) Tensile strength: The polyethylene outer sheath layer of the directly buried thermal insulation pipe prepared from Examples 1-5 and Comparative Examples 1-4 was tested for tensile strength according to the method in GB / T 1040.1-2018 "Determination of tensile properties of plastics - Part 1: General principles", wherein the test sample was a 1A sample, the sample size was 170 mm x 10 mm x 4 mm, the test speed was 100 mm / min, and the test results are shown in Table 1.

[0103] (2) The impact resistance was tested according to the method in GB / T 29047-2021 "High-density polyethylene outer sheath rigid polyurethane foam plastic prefabricated directly buried thermal insulation pipe and pipe fittings", wherein the polyethylene outer sheath layer was impacted by a 3.0 kg drop hammer from a height of 2 m under the condition of -20 ℃, and the presence or absence of visible cracks on the polyethylene outer sheath layer was observed, and the test results are shown in Table 1.

[0104] Table 1 Performance test results of Examples 1-5 and Comparative Examples 1-4

[0105]

[0106] As can be seen from Table 1, compared with Comparative Examples 1-4, the tensile strength of the polyethylene outer sheath layer of the directly buried thermal insulation pipe prepared from Examples 1-5 is improved, which can reach more than 22.8 MPa, and after impact test, the polyethylene outer sheath layer has no cracks, indicating that the polyethylene outer sheath layer includes a two-layer structure of the polyethylene outer sheath inner layer and the polyethylene outer sheath outer layer, and the use of high-pressure polyethylene and low-pressure polyethylene in the two-layer structure, and the carbon black content in the polyethylene outer sheath inner layer is less than that in the polyethylene outer sheath outer layer, can effectively solve the problems of low mechanical strength and poor impact resistance of the polyethylene outer sheath layer of the directly buried thermal insulation pipe.

[0107] Experimental Example 2

[0108] The directly buried thermal insulation pipes prepared from Examples 4-12 were tested for axial shear strength before aging and axial shear strength after aging according to the method in GB / T 29047-2021 "High-density polyethylene outer sheath rigid polyurethane foam plastic prefabricated directly buried thermal insulation pipe and pipe fittings", wherein the aging test conditions were: steel pipe temperature of 170 ℃ and aging time of 1450 h, and the test results are shown in Table 2.

[0109] Table 2 Performance test results of Examples 4-12

[0110]

[0111] According to axial shear strength retention rate = axial shear strength after aging / axial shear strength before aging*100%, compared with examples 4~7 and 12, the axial shear strength retention rate of the direct-buried thermal insulation pipe prepared in examples 8~11 after the aging test is improved and can reach 94.8% or more, indicating that when the raw material of the outer layer of the polyethylene outer protective pipe further includes chitosan and aromatic amino carboxylic acid compounds, the surface of the carbon black in the outer layer of the polyethylene outer protective pipe is first compounded by chitosan and aromatic amino carboxylic acid compounds, and then the formed carbon black treatment is blended with other components in the outer layer of the polyethylene outer protective pipe to prepare the outer layer of the polyethylene outer protective pipe, which can effectively improve the anti-aging performance of the outer layer of the polyethylene outer protective pipe, thereby effectively improving the anti-aging performance of the direct-buried thermal insulation pipe.

[0112] The above only is the preferred embodiment of the present application, and does not limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An anti-aging directly buried heat preservation pipe, comprising a steel pipe, a polyurethane heat preservation layer and a polyethylene outer protective pipe layer from inside to outside, characterized in that, The polyethylene outer sheath pipe layer comprises a polyethylene outer sheath pipe inner layer and a polyethylene outer sheath pipe outer layer; The raw material of the polyethylene outer sheath pipe inner layer comprises the following components by weight: 60 parts of first polyethylene, 6-16 parts of first carbon black; The raw material of the polyethylene outer sheath pipe outer layer comprises the following components by weight: 60 parts of second polyethylene, 8-20 parts of second carbon black; The weight of the second carbon black is greater than that of the first carbon black; The first polyethylene and the second polyethylene each independently comprises high-pressure polyethylene and low-pressure polyethylene in a weight ratio of 1:9-9:1; The raw materials of the polyethylene outer sheath pipe inner layer and the polyethylene outer sheath pipe outer layer each comprise an antioxidant, an ultraviolet absorber, and a compatibilizer; The compatibilizer comprises maleic anhydride grafted polyethylene; The raw material of the polyethylene outer sheath pipe outer layer further comprises chitosan and aromatic aminocarboxylic compounds in a weight ratio of 3-9:

1.

2. The anti-aging directly buried heat preservation pipe according to claim 1, characterized in that, The weight ratio of high-pressure polyethylene to low-pressure polyethylene in the first polyethylene is 0.5-1:1.

5.

3. The anti-aging directly buried heat preservation pipe according to claim 1, characterized in that, The weight ratio of high-pressure polyethylene to low-pressure polyethylene in the second polyethylene is 3-5:

1.

4. The anti-aging directly buried heat preservation pipe according to claim 1, characterized in that, The antioxidant comprises one or both of antioxidant 1010 and antioxidant 1076; The ultraviolet absorber comprises one or both of benzotriazole and 2,4-dihydroxybenzophenone.

5. The anti-aging directly buried heat preservation pipe according to claim 1, characterized in that, The aromatic aminocarboxylic compound comprises one or more of 3-aminobenzenedicarboxylic acid, 3,5-diaminobenzoic acid, and m-aminobenzoic acid.

6. The anti-aging directly buried heat preservation pipe according to claim 1, characterized in that, The weight ratio of the chitosan and the aromatic aminocarboxylic compound to the second carbon black is 4-8:

20.

7. The anti-aging directly buried heat preservation pipe according to claim 1, characterized in that, The steel pipe comprises one of a seamless steel pipe and a straight seam steel pipe.

8. A preparation method of an anti-aging directly buried thermal insulation pipe, used for preparing the anti-aging directly buried thermal insulation pipe according to any one of claims 5-6, characterized in that, The method comprises the following steps: S0, dispersing the aromatic aminocarboxylic compound in ethanol, adding the second carbon black, performing first mixing, concentrating, drying to obtain a second carbon black treatment I, dispersing the chitosan in an aqueous ethanol solution, adding the second carbon black treatment I, performing second mixing, concentrating, and drying to obtain the second carbon black treatment II; S1, blending the raw material of the polyethylene outer sheath pipe inner layer, and extruding to obtain a polyethylene outer sheath pipe inner layer; S2, blending the second polyethylene, the second carbon black treatment II, and the remaining components of the polyethylene outer sheath pipe outer layer except for the second polyethylene, the second carbon black, the aromatic aminocarboxylic compound, and the chitosan, and extruding to the outer surface of the polyethylene outer sheath pipe inner layer to obtain a polyethylene outer sheath pipe layer comprising a polyethylene outer sheath pipe inner layer and a polyethylene outer sheath pipe outer layer; S3, after fixing the polyethylene outer sheath pipe layer, feeding the steel pipe into the polyethylene outer sheath pipe layer and fixing, and pouring polyurethane insulation layer material between the polyethylene outer sheath pipe layer and the steel pipe to obtain the anti-aging direct-buried insulation pipe.

9. The method for preparing an anti-aging directly-buried heat preservation pipe according to claim 8, characterized in that, In step S0, the stirring speed of the first mixing is 400-600 rpm, and the time is 30-60 min; The temperature of the second mixing is 30-40℃, the stirring speed is 500-800 rpm, and the time is 1.5-2.5 h.

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