Gas steel pipeline three-layer structure polyethylene corrosion prevention technology suitable for open-air use

Abstract

The invention discloses a gas steel pipeline three-layer structure polyethylene anti-corrosion technology (weather-proof 3PE anti-corrosion) suitable for outdoor use, which adopts a weather-proof polyethylene material to realize that the three-layer structure polyethylene anti-corrosion (3PE anti-corrosion) of a steel pipeline is improved from buried use to outdoor use. Comprising the following steps: S1, technical research and development of a weather-resistant polyethylene raw material; s2, corrosion prevention outside the steel pipe; and S3, technical research and development (joint coating) of the weather-resistant anticorrosive material at the joint part of the anticorrosive pipe. Wherein in the step S1, a polyethylene material serving as a raw material in polyethylene corrosion prevention of the three-layer structure of the buried steel pipeline is improved; in the step S3, the joint coating material used in cooperation with the three-layer structure polyethylene corrosion prevention is improved, open-air use of the three-layer structure polyethylene corrosion prevention of the steel pipeline is achieved, and the average service life is 30 years or longer.

Description

Technical Field

[0001] The present invention relates to the technical field of outdoor use of gas steel pipes, and specifically to the technical application and promotion of weather-resistant 3PE anti-corrosion pipes (anti-corrosion steel pipes) and matching weather-resistant patching materials (heat shrink tapes) in the field of gas pipeline construction. Background Art

[0002] Gas pipeline operation usually uses anti-corrosion technology to extend the service life of steel pipes. For buried steel pipes, they are usually prefabricated in the factory according to the "Three-layer Polyethylene Anti-corrosion Layer for Buried Steel Pipes" standard (GB / T23257-2017). 3PE anti-corrosion is a commonly used anti-corrosion technology for buried steel pipelines at home and abroad. It has good insulation performance, low water absorption, high mechanical strength, impact resistance, bending resistance, resistance to soil stress and cathodic disbonding, and can effectively maintain constant insulation resistance over time. However, this standard does not cover outdoor use. Steel pipes used outdoors are mostly anti-corrosion with zinc-rich primer and fluorocarbon paint. Generally, they need to be repainted every two to three years. The rust removal effect at the construction site is poor and incomplete, and the paint falls off quickly after application, causing pipeline corrosion. It is especially difficult to operate at height. Repair and replacement require a lot of manpower and material resources, increasing operating costs. Summary of the Invention

[0003] Based on the problems existing in the background technology, the present invention provides a 3PE anti-corrosion technology for gas steel pipelines suitable for outdoor use. The steel pipes prefabricated with weather-resistant 3PE anti-corrosion technology and the weather-resistant heat shrinkable tape (for patching the connection parts of the steel pipes) used in conjunction with them have an outdoor service life of more than 30 years.

[0004] The present invention is implemented through the following technical solutions:

[0005] A weather-resistant 3PE anti-corrosion technology and patching kit for steel pipelines, comprising the following steps:

[0006] S1. Research and development of weather-resistant polyethylene materials;

[0007] S2. Prefabrication of weather-resistant 3PE anti-corrosion steel pipes;

[0008] S3. Research and development of weather-resistant radiation-cross-linked polyethylene (patching material);

[0009] S4. Matching construction of weather-resistant 3PE anti-corrosion steel pipes and weather-resistant radiation cross-linked polyethylene (patching material).

[0010] Furthermore, the preparation of the weather-resistant polyethylene material in step S1 is specifically carried out as follows: utilizing the good UV aging resistance of materials such as antioxidants, nano zinc oxide, and carbon black masterbatch, adding them to the modified polyethylene material in proportion, and through mixing, drying, and stirring high-density polyethylene, low-density polyethylene, and auxiliary materials, the production of weather-resistant polyethylene raw materials is achieved by a twin-screw extruder.

[0011] Furthermore, in step S2, 3PE anti-corrosion of prefabricated steel pipes is performed; medium and small specifications (specifications below Φ325) steel pipes usually adopt a coating vacuum adsorption film-forming process to complete 3PE anti-corrosion; medium and large specifications (specifications above Φ159) steel pipes usually adopt a side-wrapped extrusion film-forming process to complete 3PE anti-corrosion; the steel pipe is subjected to shot blasting, internal blowing, rust removal process inspection and other processes to achieve steel pipe surface treatment; the steel pipe anti-corrosion layer is applied through medium frequency induction heating, epoxy powder spraying, adhesive extrusion, polyethylene extrusion, flowing water cooling and other processes; and qualified products are put into storage through coating quality inspection.

[0012] Furthermore, in step S2, the product quality inspection, in addition to meeting the requirements of GB / T23257-2017, is required to undergo a salt spray test, a 1200-hour artificial accelerated aging test, a chemical corrosion resistance test, and an anti-corrosion coating sampling (PE) oxidation induction period test. When the 1000-hour salt spray test shows no bubbles, no hollowing, no cracking, and no peeling; the 1200-hour artificial accelerated aging test shows level 1 discoloration, level 1 loss of gloss, no powdering, no blistering, no cracking, and no peeling; the 90-day chemical corrosion resistance (20°C ± 3°C, 90d, 1 / 2 immersion) shows no bulging, softening, blistering, cracking, or peeling, and the peel strength index is greater than 120N / cm; the anti-corrosion coating sampling (PE) oxidation induction period (220°C) is ≥40min, and the product quality is qualified. The test is a sampling test and is conducted once a year. Through the use of 3PE anti-corrosion production and processing technology with weather-resistant polyethylene, the polyethylene anti-corrosion coating of steel pipes has both good anti-corrosion performance and good resistance to ultraviolet light aging, thus realizing the outdoor use of 3PE anti-corrosion steel pipes.

[0013] Furthermore, in step S3, the research and development of weather-resistant radiation cross-linked polyethylene (patching material) is carried out by adding auxiliary materials to improve the polyethylene and adhesive used in the preparation of the material so that it has good heat resistance, aging resistance and UV aging resistance, which specifically includes the following steps:

[0014] The preparation of weather-resistant polyethylene materials in S3-1 is specifically carried out as follows: utilizing the good UV-resistant aging effects of antioxidants, nano zinc oxide, additives and other materials, adding them to low-density polyethylene materials in proportion, and through mixing, drying, and stirring low-density polyethylene and auxiliary materials, the production of weather-resistant polyethylene raw materials is achieved by a twin-screw extruder.

[0015] The preparation of the weather-resistant adhesive material in S3-2 is specifically carried out as follows: utilizing the good resistance to ultraviolet aging and heat aging of materials such as antioxidants, nano zinc oxide, and additives, adding them in proportion to low-density polyethylene and 30% grafted maleic anhydride polyethylene materials, and through mixing, drying, stirring and other measures, the production of weather-resistant polyethylene raw materials is achieved by a twin-screw extruder.

[0016] S3-3. Compression bonding of weather-resistant polyethylene sheet and hot melt adhesive layer.

[0017] S3-4. The pressed sheet is irradiated with ultraviolet light to produce a weather-resistant radiation cross-linked polyethylene heat shrinkable tape.

[0018] S3-5. Weather-resistant radiation cross-linked polyethylene heat shrinkable tape is used in conjunction with weather-resistant 3PE anti-corrosion steel pipe (on-site patching construction).

[0019] Furthermore, in step S301, the specific operation of the UV-resistant polyethylene sheet is as follows: the weather-resistant polyethylene raw material is extruded into a sheet-shaped polyethylene film through a screw extruder, and the thickness of the polyethylene film is 1.2-1.5 mm; in S302, the weather-resistant adhesive is extruded into a sheet-shaped adhesive film through a screw extruder, and the thickness of the adhesive film is greater than 1 mm. The key to this process is to ensure that the coating thickness of the two materials is uniform, and the thickness of the PE layer and the adhesive layer meet the requirements.

[0020] Furthermore, in step S303 , the sheet-like polyethylene film and the sheet-like adhesive film are bonded and pressed together to test whether the polyethylene and the adhesive layer have good adhesion.

[0021] Furthermore, in step S304, ultraviolet light is used to irradiate the polyethylene and adhesive composite layer so that its heat shrinkage ratio exceeds 25%. The key to this process is to ensure the irradiation time and light irradiation intensity.

[0022] Furthermore, in step S304-1, in addition to meeting the requirements of GB / T23257-2017 standard, the technical indicators of the weather-resistant radiation cross-linked polyethylene heat shrinkable tape need to be tested by salt spray test, 1200 hours artificial accelerated aging test, chemical corrosion resistance test, and anti-corrosion coating sampling (PE) oxidation induction period test.

[0023] Furthermore, the specific operation of the weather-resistant radiation cross-linked polyethylene patching in step S305 is: according to the requirements of GB / T23257-2017 standard, the patching construction is carried out on the outside of the connection part using the same process as the mother body external anti-corrosion.

[0024] Beneficial effects of the present invention:

[0025] 1. The present invention adopts a 3PE anti-corrosion technology for gas steel pipelines suitable for outdoor use. On the basis of the original 3PE anti-corrosion of steel pipes, weather-resistant polyethylene materials are selected to replace the original modified polyethylene raw materials to make weather-resistant anti-corrosion pipes. Through the matching use of weather-resistant patching materials, the outdoor service life of the 3PE anti-corrosion steel pipe can reach more than 30 years.

[0026] 2. The present invention conducts technical research and development on the improvement of auxiliary raw materials for weather-resistant polyethylene raw materials, the addition of materials such as antioxidants, nano-zinc oxide, and carbon black masterbatch, and the selection and addition of antioxidants, nano-zinc oxide, and additives in polyethylene and adhesives in the patching heat shrink tape materials, so as to achieve good outdoor use effects of steel pipelines for gas. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described in detail below with reference to specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0028] Example 1

[0029] Preparation of weather-resistant polyethylene raw materials:

[0030] The invention comprises the following components in parts by weight: 58 parts of high-density polyethylene, 29 parts of low-density polyethylene, 1 part of polyester viscoelastic, 2 parts of nano zinc oxide, 8 parts of carbon black masterbatch, 1 part of antioxidant and 1 part of peroxide.

[0031] Among them, the antioxidant is a polyphenol antioxidant with the molecular formula C 73 H 108 O 12 , Chinese name: Tetrakis (pentaerythritol 3,5-di-tert-butyl-4-hydroxyphenylpropionate); the peroxide is diisopropylbenzene peroxide.

[0032] The raw materials high-density polyethylene, low-density polyethylene and auxiliary materials are mixed, dried, stirred and other measures, and then compounded into granular weather-resistant polyethylene raw materials through a twin-screw extruder.

[0033] Example 2

[0034] Preparation of weather-resistant 3PE anti-corrosion steel pipe:

[0035] According to the requirements of GB / T23257-2017 standard, epoxy powder, adhesive and modified weather-resistant polyethylene that meet the standard requirements are selected. Through the pretreatment of steel pipes and the coating of anti-corrosion layer, the weather-resistant 3PE anti-corrosion production of steel pipes is achieved.

[0036] Among them, the steel pipes are surface treated through processes such as shot blasting, internal purging, and rust removal process inspection; the steel pipes are coated with an anti-corrosion layer through processes such as medium-frequency induction heating, epoxy powder spraying, adhesive extrusion, polyethylene extrusion, and flowing water cooling; and qualified products are put into storage through coating quality inspection.

[0037] Among them, according to the test method in GB / T23257-2017, the coating appearance inspection: the surface of the polyethylene layer is smooth, without dark bubbles, wrinkles, pitting, cracks, uniform color, and no warping at the tube end; coating peel strength test: 20±5℃ peel strength ≥100N / cm, 60±5℃ peel strength ≥70N / cm; coating thickness test: meet the thickness (ordinary grade) requirements specified in GB / T23257-2017 standard; powder bottom layer glass transition temperature test: |△tg|≤5℃; impact strength ≥8J / mm; coating bending resistance (-30℃, 2.5°) test shows that the polyethylene has no cracks; hot water immersion (80°, 48h) the average warping depth is ≤2mm, the maximum is ≤3mm; cathodic peeling (65℃, 48h) ≤15mm, cathodic peeling (65℃, 30d) ≤25mm.

[0038] Among them, based on the characteristics of outdoor use, salt spray testing, 1200-hour artificial accelerated aging test, chemical corrosion resistance test, and anti-corrosion coating sampling (PE) oxidation induction period test are required. If the 1000-hour salt spray test shows no bubbles, no hollows, no cracking, and no peeling; the 1200-hour artificial accelerated aging test shows level 1 discoloration, level 1 gloss loss, no powdering, no blistering, no cracking, and no peeling; the 90-day chemical corrosion resistance (20℃±3℃, 90d, 1 / 2 immersion) shows no bulging, softening, blistering, cracking, or peeling, and the peel strength index is greater than 120N / cm; the anti-corrosion coating sampling (PE) oxidation induction period (220℃) is ≥35min, the product quality is qualified. The test is a sampling test and is conducted once a year.

[0039] Example 3

[0040] Preparation of weather-resistant patching materials:

[0041] 3-1 Preparation of polyethylene in weather-resistant patching materials

[0042] The composition includes the following components in parts by weight: 82 parts of low-density polyethylene, 1 part of polyester viscoelastic, 2 parts of nano zinc oxide, 8 parts of carbon black masterbatch, 1 part of antioxidant, 1 part of peroxide, and 5 parts of additives.

[0043] Among them, the antioxidant is a polyphenol antioxidant with the molecular formula C 73 H 108 O 12, Chinese name: Tetrakis (pentaerythritol 3,5-di-tert-butyl-4-hydroxyphenylpropionate); the peroxide is diisopropylbenzene peroxide.

[0044] The low-density polyethylene and auxiliary materials in the raw materials are mixed, dried, stirred, etc., and then compounded into granular weather-resistant polyethylene raw materials through a twin-screw extruder.

[0045] 3-2 Preparation of adhesive for weather-resistant patching material

[0046] The composition includes the following components in parts by weight: 56 parts of low-density polyethylene, 30 parts of grafted maleic anhydride polyethylene, 5 parts of polyester viscoelastic, 2 parts of nano zinc oxide, 1 part of antioxidant, 1 part of peroxide and 5 parts of auxiliary agent.

[0047] Among them, the antioxidant is a polyphenol antioxidant with the molecular formula C 73 H 108 O 12 , Chinese name: Tetrakis (pentaerythritol 3,5-di-tert-butyl-4-hydroxyphenylpropionate); the peroxide is diisopropylbenzene peroxide.

[0048] The low-density polyethylene, grafted maleic anhydride polyethylene and auxiliary materials in the raw materials are mixed, dried, stirred and the like, and then compounded by a twin-screw extruder to form a granular weather-resistant adhesive raw material.

[0049] 3-3 Preparation of weather-resistant radiation cross-linked polyethylene heat shrinkable tape:

[0050] An extruder is used to extrude polyethylene and adhesive into sheet films that meet the thickness requirements of GB / T23257-2017 standards. The rubber layer and PE layer are squeezed into one, and the pressed sheet is irradiated with ultraviolet light and cut to the size specified by the standard to make a weather-resistant radiation cross-linked polyethylene heat shrinkable tape. In addition to meeting the requirements of GB / T23257-2017 standards, the heat shrinkable tape is required to undergo a 1000-hour salt spray test, a 1200-hour artificial accelerated aging test, a chemical corrosion resistance test, and an anti-corrosion coating sampling (PE) oxidation induction period test. The index requirements are the same as those for weather-resistant 3PE anti-corrosion steel pipes.

[0051] 3-4. Preparation of epoxy primer

[0052] Choose an epoxy primer that meets the requirements of GB / T23257-2017.

[0053] 3-5. Anti-corrosion construction of 3PE anti-corrosion steel pipes used in the open air

[0054] After welding the steel pipe, electric tools are used to remove rust, and the rust removal level reaches the technical requirements of St3.0;

[0055] The PE layer on the surface of the anti-corrosion pipe is roughened 15 cm away from both ends of the weld at the steel pipe connection, with a roughening depth of 0.2 to 0.3 cm.

[0056] Apply solvent-free epoxy primer (liquid epoxy and curing agent in a 4:1 ratio) to the exposed parts of the steel pipe connection, apply it evenly, and the wet film thickness should be ≥150μm.

[0057] Install radiation cross-linked polyethylene heat shrink tape to ensure that the material shrinks evenly and the hot melt adhesive overflows evenly from both sides of the heat shrink tape.

[0058] The quality inspection of the patching is carried out according to the GB / T23257 standard, including appearance inspection: smooth appearance, no wrinkles, no hollows, no bubbles, no burning and carbonization, no slippage of the fixing plate, and even overflow of hot melt adhesive around the circumference of the heat shrink tape; leakage point detection is carried out using a spark leak detector with a leakage detection voltage of 15KV, and no leakage points are found; peel strength test (conducted 24 hours after the completion of construction): 1 peel strength test is randomly inspected for every 100 joints. Under the environment of 15-25℃, the peel strength is ≮50N / cm, and cohesive failure occurs.

[0059] Test example

[0060] Performance test of gas pipelines used outdoors (219*7, 89*4.5 specifications)

[0061] Open-air corrosion resistance test: 8 89*4.5 specification and 8 219*7 specification weather-resistant 3PE pipe sections (produced in November 2008) were cut, with a length of 50 cm each; 2 89*4.5 specification steel pipes and 2 219*7 specification weather-resistant 3PE pipe sections were welded into 4 groups to prepare test pipe sections.

[0062] The welded areas of the test pipe segments were patched with 89-gauge and 219-gauge weather-resistant heat shrink tape, respectively. The procedures were followed as described in S304. The ends of the patched pipe segments in four groups (one 89-gauge welded pipe segment and one 219-gauge welded pipe segment per group) were sealed with weather-resistant heat shrink tape. The test pipe segments were stored in a designated open-air storage yard.

[0063] According to GB / T23257, the quality of weather-resistant anti-corrosion steel pipes and patching for outdoor use is tested: the peel strength of weather-resistant anti-corrosion steel pipe 219 specification at 23℃ (20±5℃) is 260N / cm (cohesive failure), and the peel strength at 61℃ (60±5℃) is 230N / cm (cohesive failure). The PE sheet on the anti-corrosion pipe is tested for 220℃ oxidation induction period and the test value is 42.6min. The peel strength of 89 specification at 21℃ (20±5℃) is 190N / cm (cohesive failure), and the peel strength at 58℃ (60±5℃) is 160N / cm. m (cohesive failure), the 220℃ oxidation induction period test value of the PE sheet on the anti-corrosion pipe is 43.1min; the peel strength of the 89 specification at the patch at 21℃ (20±5℃) is 150N / cm, with obvious cohesive failure, the 220℃ oxidation induction period test value of the PE sheet on the heat shrink tape is 42.9min, the 219 specification at 23℃ (20±5℃) is 190N / cm, and the 220℃ oxidation induction period test value of the PE sheet on the heat shrink tape is 41.6min, which meets the requirements specified in GB / T23257.

[0064] Quality loss inspection of test pipe sections during open air storage: inspections are conducted after 3 years (November 2011), 5 years (October 2013), 10 years (October 2018), and 15 years (November 2023) of storage. One group of samples is taken each time for inspection at each time period. The inspection items include surface quality inspection of the anti-corrosion layer of the anti-corrosion pipe sections and patching parts, peel strength inspection at 20±5℃, and oxidation induction period inspection (220℃) of PE layer sampling.

[0065] Appearance quality inspection of anti-corrosion layer and patching parts: The surface of the outer coating of the anti-corrosion layer and patching parts at each time period showed no bubbles, no hollows, no cracks, no peeling, and no powdering.

[0066] The peel strength of the samples of the pipe body anti-corrosion layer at room temperature at different time periods are: 219 specifications 250N / cm (cohesive failure), 235N / cm (cohesive failure), 215N / cm (cohesive failure), 180N / cm (cohesive failure), and the mass loss results are 3.8%, 9.6%, 17.3%, and 30.8%, respectively; 89 specifications 185N / cm (cohesive failure), 170N / cm (cohesive failure), 155N / cm (cohesive failure), 135N / cm (cohesive failure), and the mass loss results are 2.6%, 10.5%, 18.4%, and 28.9%, respectively.

[0067] PE sheets sampled from the pipe body's anti-corrosion layer at various intervals were tested during the 220°C oxidation induction period. The results for the 219 specification were: 2.6%, 6.3%, 15.5%, and 27.0% at 41.5 minutes, 39.9 minutes, 36.0 minutes, and 31.1 minutes, respectively. For the 89 specification, the mass losses were 2.3%, 7.2%, 16.7%, and 30.0% at 42.1 minutes, 40.0 minutes, 35.9 minutes, and 30.2 minutes, respectively.

[0068] The peel strengths of the samples at different time periods at room temperature at the patching part were: 185N / cm, 175N / cm, 155N / cm, and 130N / cm for 219 specifications, and the mass loss results were 2.6%, 7.9%, 18.4%, and 31.6%, respectively; and 145N / cm, 135N / cm, 120N / cm, and 105N / cm for 89 specifications, and the mass loss results were 3.3%, 10.0%, 20.0%, and 30.0%, respectively.

[0069] PE sheets sampled at the patching site at different time intervals were tested for oxidation induction period at 220°C. The results were: 219 specification, 40.1min, 38.8min, 34.2min, and 29.0min, with mass losses of 3.6%, 6.7%, 17.8%, and 30.3%, respectively. 89 specification, 40.2min, 39.0min, 34.1min, and 29.2min, with mass losses of 6.3%, 9.1%, 20.5%, and 31.9%, respectively.

[0070] Under the simulation state, the quality loss of the anti-corrosion pipe and the patch is about 30% after 15 years of outdoor storage. It can be inferred that the maximum quality loss of the anti-corrosion pipe and the anti-corrosion patch will not exceed 85% after 30 years of outdoor storage. This shows that the weather-resistant 3PE anti-corrosion and the weather-resistant radiation cross-linked polyethylene patching tape of the present invention can be used in the open air for more than 30 years.

[0071] Finally, it should be noted that the above-described embodiments merely represent several implementation methods of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made by a person skilled in the art without departing from the spirit of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention should be based on the appended claims.

Claims

1. A three-layer polyethylene anti-corrosion technology (weather-resistant 3PE anti-corrosion) for gas steel pipelines suitable for outdoor use, characterized by: The following steps are involved: Technical research and development of S1 weather-resistant polyethylene raw materials; S2. External corrosion protection of steel pipes; S3. Technical research and development of weather-resistant radiation cross-linked polyethylene heat shrinkable tape; S4. Anti-corrosion of the interface of the anti-corrosion pipe (patching).

2. The method according to claim 1, characterized in that Step S1 specifically includes the following steps: S101. Main raw materials: ratio of high-density polyethylene and low-density polyethylene; S102. Auxiliary materials: Control of antioxidant, nano zinc oxide, and carbon black masterbatch content; S103. The main raw materials and auxiliary materials are mixed and stirred evenly, mixed and extruded through a twin-screw extruder, dried, and classified.

3. The method according to claim 1, characterized in that Step S3 specifically includes the following steps: S301. Polyethylene required for polyethylene heat shrink tape S301-1. Main raw material: low-density polyethylene S301-2. Auxiliary materials: control of the content of antioxidants, additives, nano zinc oxide and carbon black masterbatch. S301-3. The main raw materials and auxiliary materials are mixed and stirred evenly, mixed and extruded through a twin-screw extruder, dried and granulated. S302. Adhesive for heat shrink tape S302-1. Main raw materials: low-density polyethylene, 30% maleic anhydride grafted polyethylene; S302-2. Auxiliary materials: antioxidants, additives, and control of nano zinc oxide content; S302-3. The main raw materials and auxiliary materials are mixed and stirred evenly, mixed and extruded through a twin-screw extruder, dried and granulated.

4. The material according to claim 1, characterized in that In step S101, the ratio of high-density polyethylene to low-density polyethylene is 2:1, and the density is controlled at 0.94-0.96 g / cm 3 ; Antioxidant in S102 (polyphenol antioxidant, molecular formula C 73 H 108 O 12 , Chinese name: Tetrakis (3,5-di-tert-butyl-4-hydroxyphenylpropionate)) content ≥8‰; Nano zinc oxide content is controlled at 1.8% to 2.0%; Carbon black content ≥2.6% (masterbatch addition ≥6%); In S103, the main raw materials and auxiliary materials are mixed, dried, and stirred evenly, and extruded through a twin-screw extruder with an extrusion temperature of <220°C, and then dried, granulated, packaged and put into storage.

5. The material according to claim 4, characterized in that Weather-resistant polyethylene products, raw material performance test: density 0.956g / cm 3 ; Melt flow rate (190℃, 2.16Kg) 0.45 / g / 10min; Carbon black content 2.62%; Water content 0.09%; Oxidation induction period (220℃) 45.31min; Yield strength 15.61Mpa; Tensile strength 22.09Mpa; Nominal strain at break 712%; Vicat softening point 115℃; Nano zinc oxide content 1.92%.

6. The material according to claim 5 is made into a pressed tablet, characterized in that The circumferential tensile strength of the pressed tablet is ≥20.5MPa, and the axial tensile strength is ≥20.8MPa (deviation <1.5%); the nominal strain at break is ≥700%; the indentation hardness (23℃) is 0.02mm, and 0.03mm at 80℃.

7. The method according to claim 2, wherein the steel pipe anti-corrosion processing is carried out according to GB / T23257-2017 standard, characterized in that: The three-layer polyethylene anticorrosion method in claim 2 specifically comprises the following steps: S201. Shot blasting of steel pipes to a rust removal grade of Sa2.5; anchor mark depth 50-90 μm; dust level ≤ Level 2; salt content ≤ 20 mg / m 2. . S202. For steel pipe coating, standard steel pipes (DN≤300mm) use a wrapping mold; large-size steel pipes (DN>150mm) use a side-wrapping mold. The S202-1 steel pipe is heated using a non-contact continuous heating device (medium frequency induction heating device) with the temperature controlled at 180-220°C (the powder is in a gelled state). S202-2. Powder spraying: use an electrostatic generator to achieve continuous powder spraying. The powder uses modified thermosetting epoxy powder. The coating thickness is determined according to the pipe diameter: DN ≥ 500mm, powder coating thickness ≥ 150μm; DN < 500mm, powder coating thickness ≥ 120μm. S202-3. Adhesive extrusion: a single-screw extruder is used to achieve adhesive extrusion. The main component of the adhesive is modified grafted maleic anhydride polyethylene. The extrusion temperature is 190-210°C, and the coating thickness is ≥170μm. S202-4. Polyethylene extrusion: a single-screw extruder is used to achieve the polyethylene extrusion described in claim 2, the extrusion temperature is 200-220°C, the coating is extruded densely, and the coating thickness is implemented in accordance with the ordinary grade thickness requirements of GB / T23257-2017 standard. S202-5. Cooling with running water, the outlet temperature shall not exceed 60℃. S202-6. Leakage point detection: use 25KV online spark leak detector to conduct 100% area leakage point detection. S202-7. Anti-corrosion coating identification spraying, including steel pipe information and anti-corrosion information. S202-8. Grind the end of the finished pipe, leaving 100 to 150 mm of the reserved end, chamfer less than 30°, and expose the epoxy layer less than 2 mm. S202-9. Anti-corrosion coating quality inspection.

8. The method according to claim S202-9 is inspected according to GB / T23257-2017 standard (suitable for buried use), characterized in that: In step S202-9-1, the coating appearance is inspected: the surface of the polyethylene layer is smooth, without dark bubbles, wrinkles, pitting, cracks, uniform color, and no warping at the tube end; in step S202-9-2, the coating peel strength is tested: the peel strength at 20±5℃ is ≥100N / cm, and the peel strength at 60±5℃ is ≥70N / cm; in step S202-9-3, the coating thickness is tested: it meets the thickness (ordinary grade) requirements specified in GB / T23257-2017 standard; in step S202-9-4, the glass transition temperature of the powder bottom layer is tested: |△tg|≤5℃; in step S202-9-5, the impact strength is ≥8J / mm; in step S202-9-6, the coating bending resistance (-30℃, 2.5°) is tested to see that the polyethylene has no cracks; in step S202-9-7, the hot water immersion (80°, 48h) warping depth is ≤2mm on average, and ≤3mm at maximum. In S202-9-8, cathodic peeling (65°C, 48h) ≤ 15mm, cathodic peeling (65°C, 30d) ≤ 25mm.

9. The method according to claim S202-9, wherein the three-layer polyethylene anticorrosion (weather-resistant 3PE) suitable for outdoor use is characterized in that: Additional inspection items for anti-corrosion coating: Step S202-9-(1), 1000-hour salt spray test, no bubbles, no hollows, no cracks, no peeling; Step S202-9-(2), 1200-hour artificial accelerated aging test, discoloration level 1, gloss loss level 1, no powdering, no blistering, no cracking, no peeling; Step S202-9-(3), 90-day chemical corrosion resistance (20℃±3℃, 90d, 1 / 2 immersion), no bulging, softening, blistering, cracking, peeling, etc., peel strength index greater than 120N / cm; Step S202-9-(4), anti-corrosion coating sampling (PE) oxidation induction period (220℃) ≥40min.

10. The method according to claim 3, wherein the raw material of the heat shrinkable tape used for patching is low-density polyethylene, characterized in that: In step S301-1, the density of low-density polyethylene is controlled at 0.91-0.93 g / cm 3 ; Antioxidant in S301-2 (polyphenol antioxidant, molecular formula C 73 H 108 O 12 , Chinese name: Tetrakis (3,5-di-tert-butyl-4-hydroxyphenylpropionate)) content ≥8‰; Nano zinc oxide content is controlled at 1.8% to 2.0%; Carbon black content ≥2.6% (masterbatch addition ≥6%); The main raw materials and auxiliary materials in S301-3 are mixed, dried, and stirred evenly, and extruded through a twin-screw extruder with an extrusion temperature of <210°C. After drying, granulation, packaging and storage.

11. The method according to claim 3, wherein the raw material of the heat shrinkable tape used for patching is prepared: adhesive, characterized in that: In step S302-1, the density is controlled at 0.92-0.94 g / cm 3 , S302-2 antioxidant (polyphenol antioxidant, molecular formula C 73 H 108 O 12 , Chinese name: Tetrakis (3,5-di-tert-butyl-4-hydroxyphenylpropionic acid pentaerythritol ester)) content ≥8‰; auxiliary agent 4.5~5%, nano zinc oxide content controlled at 1.8%~2.0%; the main raw materials and auxiliary materials in S302-3 are mixed, dried and stirred evenly, and extruded through a twin-screw extruder with an extrusion temperature of <205℃, and then dried, granulated, packaged and put into storage.

12. The weather-resistant polyethylene raw material according to claim 10 is used to make a PE sheet, and the weather-resistant adhesive raw material according to claim 11 is used to make a film, and the specific operations are: in step S301, the polyethylene sheet and the adhesive pressed sheet are extruded by an extruder; in step S302, the polyethylene sheet and the adhesive pressed sheet are integrally formed by extrusion; in step S303, a radiation cross-linked polyethylene heat shrinkable tape is made by ultraviolet irradiation technology, which is suitable for outdoor use of weather-resistant 3PE anti-corrosion pipes; in step S304, the heat shrinkable tape is cut to make heat shrinkable tapes of different specifications.

13. The material according to claim S3, a weather-resistant radiation cross-linked polyethylene heat shrinkable tape suitable for outdoor use, characterized in that: Quality inspection is carried out in accordance with the requirements of GB / T23257-2017 standard, and step S303-1 is added, 1000 hours of salt spray test, no bubbles, no hollows, no cracks, and no peeling; step S303-2, 1200 hours of artificial accelerated aging test, discoloration level 1, gloss loss level 1, no powdering, no blistering, no cracking, and no peeling; step S303-3, 90 days of chemical corrosion resistance (20℃±3℃, 90d, 1 / 2 immersion) with no bulging, softening, blistering, cracking, peeling, etc., and the peel strength index is greater than 120N / cm; step S303-4, heat shrink tape sampling (PE) oxidation induction period (220℃) ≥40min.

14. According to the materials described in claims S2 and S3, the patching construction is carried out in accordance with the requirements of GB / T23257-2017. According to claim S4, the anti-corrosion construction is carried out by specifically adopting the following steps: S401. After welding, use electric tools to remove rust from steel pipes, and the rust removal level must meet the technical requirements of St3.

0. S402. The PE layer on the surface of the anti-corrosion pipe is roughened 15 cm away from both ends of the weld at the steel pipe connection, with a roughening depth of 0.2 to 0.3 cm. S403. Apply solvent-free epoxy primer (liquid epoxy and curing agent in a ratio of 4:1) to the exposed parts of the steel pipe connection, apply evenly, and the wet film thickness should be ≥150μm. S404. Install the radiation cross-linked polyethylene heat shrink tape to ensure that the material shrinks evenly and the hot melt adhesive overflows evenly from both sides of the heat shrink tape. S405. Carry out joint patching quality inspection according to GB / T23257 standard, including appearance inspection: smooth appearance, no wrinkles, no hollows, no bubbles, no charring and carbonization, no slippage of the fixing plate, and uniform overflow of hot melt adhesive around the heat shrink tape; use a spark leak detector with a leakage detection voltage of 15KV to detect leaks, and there should be no leaks; peel strength test (conducted 24 hours after the completion of construction): one peel strength test is conducted for every 100 joints. Under the environment of 15-25℃, the peel strength is ≮50N / cm, and cohesive failure occurs.