GB/T 50538-2020_English: PDF (GB/T50538-2020)
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Technical standard for anti-corrosion and insulation coatings of buried steel pipeline
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Technical standard for anti-corrosion and insulation coating of buried steel pipeline
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| Standard ID | GB/T 50538-2020 (GB/T50538-2020) | | Description (Translated English) | Technical standard for anti-corrosion and insulation coatings of buried steel pipeline | | Sector / Industry | National Standard (Recommended) | | Classification of Chinese Standard | P94 | | Classification of International Standard | 23.040.01 | | Word Count Estimation | 83,868 | | Date of Issue | 2020-11-10 | | Date of Implementation | 2021-06-01 | | Older Standard (superseded by this standard) | GB/T 50538-2010 | | Quoted Standard | GB 50126; GB 50264; GB/T 51241; GB/T 1040.2; GB/T 1408.1; GB/T 1633; GB/T 1842; GB/T 3682.1; GB/T 4472; GB/T 5470; GB/T 6671; GB/T 8237; GB/T 8804.3; GB/T 8811; GB/T 8923.1; GB/T 10297; GB/T 10699; GB/T 11835; GB/T 13021; GB/T 13350; GB/T 17393; GB/T 1836 | | Summary | This standard applies to the external anti-corrosion insulation of buried steel pipelines whose temperature of the conveying medium is not higher than 350�� and the ambient temperature is not lower than -25��. The design, construction and inspection of the external anti-corrosion and thermal insulation layer of buried steel pipelines shall not only comply with this standard, but also comply with the provisions of the current relevant national standards. | | Standard ID | GB/T 50538-2010 (GB/T50538-2010) | | Description (Translated English) | Technical standard for anti-corrosion and insulation coating of buried steel pipeline | | Sector / Industry | National Standard (Recommended) | | Classification of Chinese Standard | P94 | | Word Count Estimation | 85,845 | | Date of Issue | 2010-11-03 | | Date of Implementation | 2011-12-01 | | Quoted Standard | GBJ 87; GB/T 1033.1; GB/T 1408.1; GB/T 1410; GB/T 1040.2; GB/T 1447; GB/T 1449; GB/T 1451; GB/T 1633; GB/T 1720; GB/T 1725; GB/T 1728; GB/T 1731; GB/T 1842; GB/T 2792; GB/T 3682; GB/T 3854; GB/T 4472; GB/T 4507; GB/T 5351; GB/T 5470; GB/T 6111; GB/T 6343; GB 6514; GB/T 6671; GB/T 7124; GB 7692; GB/T 8804.3; GB/T 8813; GB 8923; GB 9274; GB/T 10799; GB/T 12008.3; GB/T 12008.8; GB/T 12008.5; GB/T 12008.6; GB/T 22313; GB/T 12009.2; GB/T 12009.3; GB/T 12009.4; GB/T 12009.5; GB/T 13021; GB/T 14152; GB/T 17391; GB 50369; GB/T 23257; SY/T 0414; SY/T 0315; CJ/T 114; GBZ 1 | | Drafting Organization | Daqing Oilfield Engineering Co., Ltd. | | Regulation (derived from) | Ministry of Housing and Urban-Rural Development Bulletin No.817 | | Summary | This standard applies to the transmission medium temperature does not exceed 120��C design of buried steel pipeline wall corrosion layer and the insulation layer, prefabricated and construction inspection. |
GB/T 50538-2020 English name.Technical standard for anti-corrosion and insulation coatings of buried steel pipeline
1 General
1.0.1 This standard is formulated to standardize the design, construction and inspection of the external anti-corrosion insulation layer of buried steel pipelines.
1.0.2 This standard is applicable to the external anti-corrosion and thermal insulation of buried steel pipelines with the temperature of the conveying medium not higher than 350°C and the ambient temperature not lower than -25°C.
1.0.3 The design, construction and inspection of the external anti-corrosion and thermal insulation layer of buried steel pipelines shall not only comply with this standard, but also comply with the current relevant national standards.
2 terms
2.0.1 protective layer jacket layer
In order to prevent water or moisture from entering the insulation layer, a protective structure is set outside the insulation layer.
2.0.2 Water proof cap
It is made of radiation cross-linked polyethylene heat shrinkable material or other equivalent materials, and is used for waterproofing the end of the insulation pipe.
2.0.3 "one-step" process one-step process
The extrusion of polyethylene outer sheath and the foaming of polyurethane insulation layer are continuously and synchronously produced on one production line.
2.0.4 "pipe-in-pipe" process pipe-in-pipe process
The production process of pouring polyurethane insulation raw materials into the closed annular space formed by the outer protective pipe and the steel pipe, and foaming.
2.0.5 "spraying method" process spraying process
The manufacturing process of coating the polyurethane insulation material on the outer surface of the steel pipe by spraying to form the insulation layer.
2.0.6 reflecting layer reflecting layer
The material layer with heat reflection function set in the high temperature composite insulation structure.
2.0.7 Protective layer protective layer
In the high-temperature composite organic-inorganic insulation structure, there is an inorganic cushion layer that can reduce vibration and facilitate the relative movement between the pipeline and the inorganic insulation layer.
Figure 4.0.1-3 Structural diagram of "anticorrosion layer-insulation layer-protection layer-end waterproof layer" insulation pipeline with the temperature of the conveying medium higher than 80°C and not higher than 140°C
Figure 4.0.1-3 Structural diagram of "anticorrosion layer-insulation layer-protection layer-end waterproof layer" insulation pipeline with the temperature of the conveying medium higher than 80°C and not higher than 140°C
1-steel pipe; 2-anti-corrosion layer; 3-end waterproof layer; 4-insulation layer; 5-protective layer
4.0.2 When the temperature of the conveying medium is higher than 140°C and not higher than 350°C, a high-temperature anti-corrosion and thermal insulation structure shall be selected according to Table 4.0.2, and temporary waterproof measures shall be adopted at the end of the thermal insulation pipe, and the reserved length shall meet the following requirements.
1 When the insulation pipe has no anti-corrosion layer, the reserved length at the end of the insulation pipe should not be less than 100mm;
2 When the insulation pipe has an anti-corrosion layer, the reserved length at the end of the insulation pipe should not be less than 120mm.
Table 4.0.2 Form and structure of high temperature anticorrosion and heat preservation pipe
Table 4.0.2 Form and structure of high temperature anticorrosion and heat preservation pipe
4.0.3 The anti-corrosion and thermal insulation structure of special-shaped parts such as elbows and tees shall be determined according to the following regulations according to the temperature of the conveying medium.
1 When the temperature of the conveying medium is not higher than 80°C, it is advisable to adopt the structure of "anticorrosion layer-insulation layer protection layer-end waterproof cap" or the insulation structure made by spraying method;
2 When the temperature of the conveying medium is higher than 80°C and not higher than 140°C, the structure of "anticorrosion layer-insulation layer-protection layer-end waterproof layer" can be adopted;
3 When the temperature of the conveying medium is higher than 140°C and not higher than 350°C, a high-temperature anti-corrosion and heat-preservation structure shall be adopted according to 4.0.2 of this standard.
4.0.4 The waterproof measures at the end of the prefabricated thermal insulation pipes and elbows, tees and other special-shaped parts shall meet the following requirements.
1 When the temperature of the conveying medium is not higher than 80°C, the end waterproof measures should adopt radiation cross-linked polyethylene heat shrinkable waterproof cap;
2 When the temperature of the conveying medium is higher than 80°C, it is advisable to determine the material performance and structural form of the waterproof layer at the end according to the actual working conditions.
4.0.5 The anti-corrosion and heat-insulation structure of the insulation pipe made on site shall be consistent with the anti-corrosion and heat-preservation structure prefabricated in the factory, and the anti-corrosion and heat preservation structure at the joint shall match the anti-corrosion and heat preservation structure of the main pipeline.
5 materials
5.1 Anti-corrosion layer material
5.1.1 The outer anti-corrosion layer of steel pipelines should have good basic properties such as electrical insulation, mechanical properties, moisture and water resistance, adhesion, chemical resistance, thermal aging resistance, and microbial erosion resistance.
5.1.2 The materials for the anti-corrosion layer under the insulation layer of buried steel insulation pipelines should be selected according to Table 5.1.2.
Table 5.1.2 Commonly used anti-corrosion layer materials under the insulation layer of thermal insulation pipelines
Continued Table 5.1.2
Note. The lower limit of applicable temperature is the lowest ambient temperature for installation and storage of the anti-corrosion coating.
5.2 Insulation layer material
5.2.1 The insulation layer can be made of organic materials such as rigid polyurethane foam, rigid polyisocyanurate, and rigid phenolic foam, as well as inorganic materials such as rock wool and glass wool. The performance of commonly used insulation materials should meet the current national standards In addition to the basic performance requirements of thermal insulation materials in GB 50264 "Code for Design of Industrial Equipment and Pipeline Thermal Insulation Engineering", it should also meet the requirements in Table 5.2.1.
Table 5.2.1 Common insulation layer materials
5.2.2 The properties of "one-step method" rigid polyurethane foam shall meet the requirements in Table 5.2.2.
Table 5.2.2 "One-step" polyurethane foam properties
Note. 1 The heat resistance test condition is 100℃, 96h.
2 The production of foam plastic test pieces shall comply with the provisions of Appendix D of this standard.
5.2.3 "Pipe-in-pipe method" rigid polyurethane foam properties should meet the requirements of Table 5.2.3.
Table 5.2.3 "Pipe-in-pipe" polyurethane foam properties
Note. 1 The heat resistance test condition is 120℃, 96h.
2 The production of foam plastic test pieces shall comply with the provisions of Appendix D of this standard.
5.2.4 "Spray method" rigid polyurethane foam properties should meet the requirements of Table 5.2.4.
Table 5.2.4 "Spray method" polyurethane foam properties
Note. 1 The heat resistance test conditions are 120°C for normal temperature type polyurethane foam, 96h; 140°C for high temperature type polyurethane foam, 96h.
2 The production of foam plastic test pieces shall comply with the provisions of Appendix D of this standard.
5.2.5 The specifications of steel strips, steel wires and other binding materials shall comply with the relevant provisions of the current national standard "Code for Design of Industrial Equipment and Pipeline Thermal Insulation Engineering" GB 50264.
5.3 Material of protective layer
5.3.1 The material of the protective layer can be polyethylene material, glass fiber reinforced plastic, anti-corrosion steel pipe, etc. The performance of the material of the non-metallic protective layer should meet the requirements in Table 5.3.1.
Table 5.3.1 Non-metallic protective layer materials
5.3.2 The performance of the polyethylene raw material and protective layer of the "one-step" process shall meet the requirements in Table 5.3.2.
Table 5.3.2 Performance of polyethylene special materials and protective layer in "one-step" process
Table 5.3.2 Performance of polyethylene special materials and protective layer in "one-step" process
Note. 1 The chemical medium corrosion resistance and ultraviolet light aging resistance indicators are the tensile strength after the test and the retention rate of the nominal strain at break.
2 Tensile strength deviation is the ratio of the difference between axial and radial tensile strengths to the lower of the two.
5.3.3 The polyethylene raw material and protective layer properties of the "pipe-in-pipe method" shall meet the requirements in Table 5.3.3.
Table 5.3.3 Main properties of polyethylene special materials, compressed tablets and protective layers of "pipe-in-pipe method"
Continued Table 5.3.3
Note. 1 The heat aging index is the deviation of melt flow rate before and after the test.
2 The indicators of chemical medium corrosion resistance and ultraviolet light aging resistance are the tensile strength after the test and the retention rate of the nominal strain at break.
5.3.4 The properties of polyethylene special materials and compressed tablets for "spraying method" shall comply with the provisions in Table 5.3.3, and the performance of the protective layer shall comply with the provisions in Table 5.3.4.
Table 5.3.4 Main properties of polyethylene protective layer of "spraying method"
5.3.5 The performance of FRP raw materials and outer sheath shall meet the following requirements.
1 The outer sheath of FRP should be made of glass fiber untwisted yarn or roving and unsaturated polyester resin, and it should be constructed by wet winding;
2 The performance index of glass fiber roving shall comply with the relevant provisions of the current national standard "Glass Fiber Roving" GB/T 18369, and the performance index of the roving shall comply with the current national standard "Glass Fiber Roving" GB/T 18370 The relevant provisions;
3 The performance index of unsaturated polyester resin should meet the relevant provisions of the current national standard "Liquid Unsaturated Polyester Resin for Fiber Reinforced Plastics" GB/T 8237;
4 The performance index of the FRP outer sheath shall comply with the relevant provisions of the current national standard "Polyurethane Foam Plastic Prefabricated Direct Buried Insulation Pipe for Glass Fiber Reinforced Plastic Outer Sheath" CJ/T129.
5.3.6 The steel outer protection pipe shall comply with the relevant provisions of the current industry standard "Technical Specifications for Thermal Insulation of Directly Buried High Temperature Steel Pipelines" SY/T0324, and the steel outer protection pipe shall be treated with anti-corrosion treatment.
5.3.7 The performance indicators of the protective layer filling and repairing materials shall meet the following requirements.
1 The performance of the polyethylene electric heating sleeve should meet the relevant provisions of the current national standard "High-density polyethylene outer protection pipe rigid polyurethane foam prefabricated direct-buried insulation pipes and pipe fittings" GB/T 29047;
2 The performance of the radiation cross-linked polyethylene heat shrinkable tape should meet the relevant provisions of the current national standard "Polyethylene anti-corrosion coating for buried steel pipelines" GB/T 23257.
6 precast
6.1 General provisions
6.1.1 Thermal insulation prefabrication should be carried out indoors or in a rain-proof, sand-proof and sun-shading environment.
6.1.2 Before using the thermal insulation raw materials, a foam sample test should be carried out to verify the adaptability of the emulsification time, curing time and other parameters of the material to the production process, and the environmental conditions of the test should match the prefabrication process.
6.1.3 When polyurethane foam is foamed, the raw material temperature should be controlled at 20°C~35°C.
6.2 Preprocessing
6.2.1 Steel pipes shall meet the following requirements.
1 The technical data of steel pipes entering the factory should be complete.
2 The quality of steel pipes shall comply with relevant technical specifications.
6.2.2 The temperature of steel pipe pretreatment should be 3℃ higher than the dew point temperature.
6.2.3 Steel pipe pretreatment shall meet the following requirements.
1 The inspection of derusting quality shall comply with the current national standard "Visual assessment of surface cleanliness of steel surface treatment before coating Part 1.Rust on uncoated steel surface and steel surface after comprehensive removal of original coating Relevant provisions of GB/T 8923.1 for grades and treatment grades;
2 The inspection of the depth of the anchor pattern shall comply with the relevant provisions of the current industry standard "Code for Surface Treatment of Steel before Painting" SY/T0407;
3 The inspection of the dust degree shall comply with the current national standard "Assessment Test for Surface Cleanliness of Steel Surface Treatment Before Coating Part 3.Dust Evaluation on Steel Surface Before Coating (Pressure-sensitive Adhesive Tape Method)" GB/T 18570.3 the relevant regulations;
4 The inspection of salt content should comply with the relevant provisions of the current national standard "Evaluation Test for Surface Cleanliness of Steel Surface Treatment Before Coating Part 9.Field Conductivity Measurement of Water-Soluble Salt" GB/T 18570.9.
6.2.4 The surface dust, grease, dirt and other attachments should be removed before the insulation prefabrication of steel pipes with anti-corrosion layers.
6.3 Insulation
6.3.1 The prefabrication of the insulation layer shall be carried out after the quality inspection of the anticorrosion layer is qualified.
6.3.2 When the "one-step method" process is used to prefabricate the insulation pipe, the following regulations shall be met.
1 Before the official production, the proportion of the components transported by the proportional pump should be measured, and the mixing ratio should meet the technological requirements of the materials used.
2 The production line should be equipped with an automatic deviation correction device. The center of the steel pipe, the center of the extruder head and the center of the correction ring should be adjusted according to the diameter of the steel pipe and kept on the same horizontal operation line;
3 The distance between the foaming liquid surface and the sizing sleeve should be 0.5m~1.0m, and it should be kept stable. The correction ring should be at the position where the foam begins to solidify, and should be located 0.10m~0.15m behind the foam liquid surface; When cutting the polyethylene protective layer and foam layer at the joint of the steel pipe, it is advisable to wait until the foam layer is completely cured before cutting the end face;
4 After the foam is initially cured, it is advisable to wait until the foam layer is completely cured before cutting the end face of the polyethylene protective layer and the foam layer at the joint of the ring cut steel pipe;
5 When the polyethylene protective layer is formed, the temperature should be raised step by step from the feeding section to the extrusion section according to the characteristics of the processing material and the process design requirements;
6 After the polyethylene protective layer is formed, it should be cooled by water cooling, and the temperature of the protective layer after cooling should not be higher than 60°C.
6.3.3 When using the "pipe-in-pipe method" process to prefabricate insulation pipes, the following regulations shall be met.
1 Polyurethane foaming should be injected using a high-pressure foaming machine. The injection method can be end injection or intermediate injection, and should be injected according to the confirmed raw material ratio requirements;
2 The spacer should be placed equidistantly in the annular space between the working pipe and the outer protective pipe, and the distance between the spacers should comply with the thickness deviation of the insulation layer in Table 9.3.2, and the external sizing method can also be used;
3 When foaming, it is advisable to install sealing rings at both ends of the outer protective tube. Both ends should be reserved evenly, and the length deviation should not be greater than 40mm. The working tube should be longer than the outer protective tube. The length from the outer protective tube on one side to the end of the steel pipe Should not be less than 140mm;
4 The prefabrication process of the polyethylene outer protection pipe shall comply with the provisions of the current national standard "High-density polyethylene outer protection pipe rigid polyurethane foam prefabricated direct-buried insulation pipes and fittings" GB/T 29047;
5 The prefabrication process of the steel pipe protective layer insulation pipe shall comply with the relevant provisions of the current industry standard "Technical Specifications for Thermal Insulation of Direct Buried High Temperature Steel Pipelines" SY/TO324.
6.3.5 The "spraying method" process should meet the following requirements.
1 Before spraying the polyurethane insulation layer, the pipe body should be preheated to a dew point temperature above 3°C;
2 Spray according to the determined ratio of raw materials, and the pressure of the spray pump should meet the requirements of the production process;
3 When spraying polyurethane foam, a splash foam collection device shall be equipped;
4 The spraying operation should not be carried out under the condition that the wind speed is greater than 5m/s;
5 The requirements for the prefabrication of the heat-wound polyethylene protective layer shall comply with the relevant provisions of the current national standard "Hard Polyurethane Sprayed Polyethylene Wrapped Prefabricated Direct Buried Insulation Pipe" GB/T 34611.
6 The requirements for the prefabrication of the wet-winding FRP protective layer shall comply with the relevant provisions of the current industry standard "Technical Specifications for Thermal Insulation of Directly Buried High-temperature Steel Pipelines" SY/TO324.
6.3.6 The prefabrication requirements for high-temperature anti-corrosion and thermal insulation pipes shall comply with the relevant provisions of the current industry standard "Technical Specifications for Thermal Insulation of Directly Buried High-temperature Steel Pipelines" SY/T0324.
6.4 End Treatment
6.4.1 The structure of the end faces of insulation pipes, elbows, tees and other special-shaped parts shall comply with the provisions of Article 4.0.4 of this standard, and the end faces shall be cut and cleaned.
6.4.2 When the heat preservation pipe is a polyethylene protective layer, the end face of the heat preservation pipe whose temperature of the conveying medium is not higher than 80°C should be installed with a radiation cross-linked polyethylene heat-shrinkable waterproof cap, and the overlapping length of the waterproof cap, the anti-corrosion layer and the protective layer should not be less than 50mm; when the temperature of the conveying medium is higher than 80°C, other applicable end face waterproof structures should be adopted. The end treatment of radiation cross-linked polyethylene heat-shrinkable waterproof caps shall meet the following requirements.
1 When the wall thickness of the protective layer is greater than 5mm, the end face of the protective layer should be grooved and cleaned;
2 The polyethylene protective layer where the waterproof cap is installed should be roughened, and the surface of other material parts should be cleaned;
3 Heat the waterproof cap evenly, after the installation is complete, the hot melt adhesive should overflow evenly.
6.4.3 When the insulation pipe is made of fiberglass protective layer, the end surface treatment should be manually coated with resin or other waterproof materials.
6.4.4 When the insulation pipe is the protective layer of the steel pipe, the end surface treatment should adopt the waterproof measures of adding end waterproof caps or other materials.
7 live production
7.1 General provisions
7.1.1 The anti-corrosion and thermal insulation structure fabricated on site shall comply with the provisions of Article 4.0.5 of this standard, and the thermal insulation structure shall also comply with the following provisions according to the site embedding conditions.
1 The mechanical strength and rigidity of the thermal insulation structure shall be determined according to the site environmental conditions.
2 Hard and semi-rigid insulation materials with low water absorption should be selected, and strict waterproof measures should be taken;
3 In the case of environmental changes and vibrations, the integrity and tightness of its structure should be maintained;
4 When a high-temperature composite structure is adopted, the outer layer insulation material should be hard insulation material.
7.1.2 When the anti-corrosion layer needs to be coated, it should be applied according to the material and structure of the anti-corrosion layer, and the insulation layer should be made after passing the quality inspection.
7.1.3 The on-site construction environment should meet the construction requirements of the materials. When one of the following conditions exists and there are no effective measures, the anti-corrosion and thermal insulation layer construction should not be carried out in the open air.
1 Rainy and snowy days, windy and sandy days;
2 The wind speed reaches level 5 or above;
3 The ambient temperature is lower than the lower temperature limit required for material construction;
4 The relative humidity is greater than 85%.
7.2 Fabrication of insulation layer
7.2.1 The insulation layer can be made by on-site pouring and bundling, and should comply with the relevant provisions of the current national standard "Code for Construction of Industrial Equipment and Pipeline Thermal Insulation Engineering" GB 50126
7.2.2 When polyurethane foam is cast on site, it shall comply with the following regulations.
1.Foaming machine should be used for on-site pouring;
2 Before formal pouring, test pouring should be carried out to determine the technical parameters of on-site pouring;
3 When pouring, the surface temperature of the pipe should be higher than the dew point temperature by more than 3°C;
4 The mold should have tight joints, accurate dimensions, firm fulcrums, and reliable demoulding measures;
5 When pouring large areas, symmetrical multi-point pouring gates should be set up and carried out in sections.
7.2.3 When using the bundling method for construction, the following regulations shall be complied with.
1 The thermal insulation layer of the variable diameter pipe section should adopt fan-shaped thermal insulation products, and the thermal insulation layer of other special-shaped parts can determine the shape and production method of the thermal insulation product according to the shape of the special-shaped parts;
2 The construction of the insulation layer of the pipe elbow should use formed insulation products. If there is no formed insulation product, the pipe shell should be cut into shrimp waists and installed in sections. When the nominal diameter of the pipeline is less than 25mm, soft materials with similar thermal conductivity can be used for installation;
3 Expansion joints shall be provided for rigid thermal insulation products, and soft thermal insulation materials shall be filled. When the thermal insulation layer is double or multi-layered, expansion joints shall be provided for each layer, and the expansion joints of two adjacent layers shall be staggered. greater than 100mm;
4.The bundling spacing should not be greater than 400mm, and each product should not be bundled less than two times. For pipes with a nominal diameter greater than 600mm, the spacing should be 500mm, and spiral bundling should not be used;
5.The insulation layer of different diameter pipes should be bundled in a hoop or net shape, and the bundled iron wires should be longitudinally connected with the bundled iron wires of the large diameter pipe section.
7.2.4 The on-site construction of the insulation layer should be completed before the ditch. After the construction of the insulation layer is completed, the outer surface should be flat, dry and clean.
7.3 Fabrication of protective layer
7.3.1 When the protective layer of adhesive tape is used for construction, the following regulations shall be met.
1 When winding the protective layer of the adhesive tape, it is advisable to use a special winding machine or a manual winding machine for construction;
2 The overlapping length of the beginning and end of the adhesive tape should not be less than 1/4 of the circumference of the pipe, and should not be less than 100mm. The overlapping seams should be parallel and must not be warped, twisted or wrinkled.
7.3.2 When the glass fiber reinforced plastic protective layer is used, the following regulations shall be met.
1 The FRP protective layer can be made by prefabrication or on-site production, and the production of FRP should meet the relevant technical requirements;
2 The prefabricated FRP can be connected by pasting, riveting and assembling, and the seams should be waterproofed;
3 When the FRP protective layer is made on site, the lining base cloth should be closely attached, and the air bubbles should be removed in sequence. The rubber should be fully applied and should reach the specified number of layers and thickness.
8 Supplementary deductions and supplementary injuries
8.1 General provisions
8.1.1 The joint structure of the anti-corrosion and thermal insulation layer should adopt the joint structure of the anti-corrosion and thermal insulation layer with a waterproof cap, the joint structure of the anti-corrosion and thermal insulation layer without a waterproof cap at the end, and the joint structure of the anti-corrosion and thermal insulation layer sealed at the end of the protective layer (Figure 8.1.1-1~Figure 8.1.1-3). The joint structure of high-temperature composite thermal insulation pipes shall comply with the relevant provisions of the current industry standard "Technical Specifications for Thermal Insulation of Directly Buried High-temperature Steel Pipelines" SY/T0324.
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