Knowledge of winter construction for chemical plants

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I. Definition of winter construction 1. Building construction: China’s current standard JGJ104-2011 \"Code for Winter Construction of Building Engineering\" stipulates that winter construction begins when the average daily outdoor temperature remains below 5°C for 5 consecutive days, and it ends when the average daily outdoor temperature remains above 5°C for 5 consecutive days. This definition is primarily aimed at concrete construction, and it is based on the following: (1) When the temperature remains consistently below 5°C for 5 consecutive days, there are few chances for it to rise again. (2) The freezing temperature of free water in freshly mixed concrete is -2 to 2°C. When the daily average temperature is 5°C, the minimum temperature is mostly between -1 and 0°C (accounting for about 85%). This temperature represents the threshold at which concrete can be damaged by freezing. Therefore, the principle criterion for defining winter construction conditions is that when the temperature drops to 0°C or below, anti-freezing measures must be taken during construction. (3) When the average temperature on that day is 5°C or below, the strength development of concrete during curing is very slow; after 28 days of curing at such temperatures, the strength achieved is only about 60% of that obtained after 28 days of standard curing. Under such conditions, special measures must be taken to ensure a relatively rapid increase in concrete strength. 2. For pipeline construction, Clause 8.1.5 of SHT 3501-2021 \"Code for Construction and Acceptance of Steel Pipeline Projects for Toxic and Flammable Media in the Petrochemical Industry\" stipulates that protective measures shall be taken if any of the following conditions occur during pipeline welding; otherwise, welding work must be stopped: (1) When using shielded metal arc welding, if the wind speed is equal to or greater than 8 m/s ； (2) During gas shielded welding, the wind speed should be 2 m/s or higher ； (3) Relative humidity greater than 90% ； (4) Working outdoors in rain or snow ； (5) Ambient temperature is below -20°C. This regulation applies to all pipe welding. Alloy steels and some special materials require preheating before welding. 3. For steel structure construction, Article 6.3.7 of the GB 50755-2012 \"Code for Construction of Steel Structures\" stipulates that when the welding environment temperature is below 0°C but not lower than -10°C, the welding joints and welding surfaces must be heated to a temperature of at least 20°C, or to the specified minimum preheating temperature, within a range of at least 2 times the thickness of the steel plate in all directions and not less than 100 mm; this temperature must be maintained throughout the welding process. 4. Equipment 4.1 Welding operations: Article 7 of Part 4 of GBT 150.4 \"Fixed Pressure Vessels\" stipulates that: (1) When using shielded metal arc welding, the wind speed shall be equal to or greater than 8 m/s ； (2) During gas shielded welding, the wind speed should be 2 m/s or higher ； (3) Relative humidity greater than 90% ； (4) Working outdoors in rain or snow ； (5) Ambient temperature is below -20°C. Section 7.1.3 stipulates that when the temperature of the welded piece is below -20°C, it must be preheated to above 15°C within a range of 100 mm around the welding area. 4.2 Pressure testing: Clause 11.4.9.3 of Part 4 of GBT 150.4 \"Fixed pressure vessels\" stipulates that when conducting hydraulic tests on pressure vessels made of Q345B, Q370R, or 07MnMoVR, the temperature of the liquid must be no lower than 5℃ ； When conducting hydraulic tests on other carbon steel and low-alloy steel containers, the test temperature must not be lower than 15℃ ； The liquid temperature for the hydraulic test of low-temperature vessels should be not lower than the impact test temperature of the vessel material and welded joints (taking the higher value) plus 20°C. If factors such as plate thickness cause the material’s temperature at plastic transformation to rise, the test temperature must be increased accordingly. When supported by experimental data, tests can be conducted using a liquid at a lower temperature; however, it must be ensured that the test temperature (the temperature of the metal walls of the container) is at least 30°C higher than the temperature at which plastic deformation of the container walls occurs. II. Preparation and Requirements for Winter Construction 1. Winter construction management process 1.1 The construction unit prepares and submits the relevant plans, which must be approved by the client and the supervisor before implementation (this applies to the costs associated with winter construction measures). 1.2 The winter construction plan prepared by the construction unit should be targeted and feasible, taking into account the characteristics of the project. When changes occur in the construction situation, the original plan must be promptly revised and supplemented, and submitted to the original reviewing authority for approval before implementation. 1.3 The management department of Party A shall monitor and manage the entire winter construction process. 1.4 The costs for winter construction measures and the procurement methods must be determined. 2. Technical preparations for winter construction 2.1 Before starting winter construction, it is necessary to carry out advance preparations for winter construction in terms of materials, equipment, personnel, etc., in accordance with the requirements outlined in the winter construction plan. 2.2 Conduct winter construction training for temperature measurers and testers; provide technical briefings on winter construction to foremen, team leaders, and construction workers. 2.3 When using ready-mixed concrete, it is necessary to evaluate aspects such as the transportation distance of the batching plant, its production capacity, and quality assurance measures. Additionally, written instructions must be provided regarding the quality (specifications) requirements for concrete (mortar) used in winter construction. 3. Winter Construction Plan 3.1 The principles for formulating a winter construction plan are: (1) Comply with the regulations for winter construction as well as the corresponding acceptance standards ； (2) Ensure project quality ； (3) Economically reasonable, with minimal additional costs for winter application ； (4) The required heat sources and materials have reliable sources ； (5) Facilitate on-site safety and fire management. 3.2 The winter construction plan shall include the following contents: 3.2.1 Basis for preparation: (1) Winter construction projects: It is necessary to detail the winter construction projects, the specific areas involved, the main volume of work, and the estimated construction time. (2) Winter construction plan: winter construction leadership team, labor and schedule arrangements, etc. (3) Main methods and measures for winter construction: including various heating and insulation measures, the heating methods used in finishing work, the selection of admixtures and the procedures for their testing, thermal calculations, temperature measurement methods and layout diagrams of temperature measurement points, as well as requirements for preparing test blocks. (4) Site layout: includes the source and location of heat sources, temporary structures used during winter construction, power arrangements, etc. (5) Main plans: include plans for the materials, equipment, testing and measurement instruments required for winter construction, as well as personnel training plans. (6) Measures for quality, safety, fire prevention and security during winter construction. (7) Attachments (layout diagram of temperature measurement points, schematic diagram of enclosure, schematic diagram of heat source location). III. Winter construction in building projects 1. Earthwork, foundation, and substructure works 1.1 For foundation and substructure work, the excavated foundation pits should be covered promptly with insulating materials; such materials must meet environmental protection requirements as well as flame-retardancy standards. 1.2 When the subsequent processes for the cushion layer cannot be carried out continuously, the insulation duration of the cushion layer must not merely meet the requirements for the critical strength of concrete. The adverse effects of sub-zero temperatures on the foundation must also be taken into account. Before the next process begins, the insulation measures for the cushion layer should not be removed, so as to prevent the foundation from freezing and deforming. 1.3 During winter excavation, the slope should be shaped in accordance with the specifications based on the soil conditions, and the slope surface should be kept straight. Monitoring of the soil in the slope area should be intensified, especially in cases of repeated freezing and thawing, to ensure the safety of the slope. 1.4 During earth backfilling in winter, the thickness of each layer of soil laid should be reduced by 20% compared to normal temperatures. When using frozen soil for backfilling, the diameter of the frozen soil clumps must not exceed 15 cm, their proportion must not exceed 15%, and they should be evenly distributed. Backfilling work should not be carried out when the temperature is below -10°C. 2. Concrete works 2.1 The critical strength of concrete under freezing conditions is specified as follows: For concrete made using portland cement or ordinary portland cement (slag portland cement), the value shall be 30% (40%) of the design strength standard, with a minimum value of 5 Mpa. When antifreeze is used, the critical strength of concrete against freezing is 5 Mpa when the lowest outdoor temperature is not lower than minus 30 degrees Celsius. 2.2 When preparing concrete for winter construction, Portland cement or ordinary Portland cement should be preferred. Its strength grade must not be lower than 32.5 MPa. The amount of cement used per cubic meter of concrete must not be less than 300 kg, and the water-cement ratio must not exceed 0.6. 2.3 Chloride-free salts are preferred as antifreeze agents. For concrete with high frost resistance requirements, air-entraining agents (with an air content of 2% to 4%) or air-entraining water reducers should be used. All types of antifreeze agents must be tested before use, and must comply with the provisions of the \"Technical Specifications for the Use of Concrete Admixtures\" (GB50119). 2.4 For the winter construction of concrete, hot water should be used for mixing, with the water temperature not exceeding 80℃ ； If the requirements of thermal calculations are still not met, the method of heating the aggregates can be employed; generally, they are heated to around 50°C. The sequence for mixing the materials is: aggregates first, followed by hot water, and then cement and admixtures. Ensure that the temperature of the concrete upon discharge is not lower than 15°C, and the temperature when placed in the formwork is not lower than 5°C. 2.5 The aggregate must be clean and free of frozen substances such as ice or snow; the mixing time should be 1.5 times that required at normal temperature ； During transportation, heat loss from concrete should be minimized, and the containers used for transporting and pouring concrete should have insulation measures. 2.6 When pouring concrete in layers, the temperature of the previously poured layer must not be lower than the temperature determined by thermal calculations before it is covered by the upper layer of concrete, and it must not be less than 2°C. 2.7 For winter concrete construction, the combined heat storage method is recommended. 2.8 Insulation materials used to cover the outside of the formwork and the concrete surface should not be in a wet state, nor should the insulation materials be placed directly on a wet concrete surface; a layer of plastic film should be laid on the surface of freshly poured concrete. 2.9 The wall formwork and insulation layer shall not be removed until the concrete has reached its critical strength and cooled to 5 degrees Celsius. When removing the formwork, if the temperature difference between the concrete surface and the ambient temperature is greater than 20 degrees Celsius, the concrete surface shall be covered with insulation promptly after removal. Reliable thermal insulation measures must be taken at the horizontal construction joints of walls to prevent freezing damage. 2.10 Concrete quality inspection: 2.10.1 Temperature inspection: Check the temperature of the concrete upon leaving the mixer and before it is placed in the formwork, at least 4 times per working shift. 2.10.2 Measurement of concrete curing temperature: When using the combined heat retention method for curing, measurements should be taken every 2 hours until the concrete reaches its critical strength, and thereafter every 6 hours ； A layout diagram of the temperature measurement holes should be drawn, and the holes should be numbered. These holes are to be placed at representative structural locations and at locations where temperature changes are significant and cooling occurs easily. The depth of each hole should be 15 cm or half of the thickness of the slab or wall. During non-temperature measurement periods, the temperature measurement holes should be plugged with insulating material. 2.10.3 Inspection of the concrete surface: Check whether the concrete surface has been frozen or become sticky, whether there are shrinkage cracks, whether the edges and corners have chipped off, and whether there are signs of freezing at the construction joints. 2.10.4 Inspection of the retention of specimens cured under the same conditions and their compressive strength: The specimens cured under the same conditions that must be retained on site include: (1) Specimens for critical strength testing ； (2) Test blocks for concrete strength testing during the removal of formwork for roofs and walls ； (3) Test blocks for detecting wall strength when using external wall scaffolding ； (4) Test blocks cured under the same conditions at room temperature for 28 days. 3. Masonry Work
3.1 For all types of bricks and blocks, surface dirt, ice, and snow must be removed. Bricks and blocks that have been water-damaged or frozen must not be used. 3.2 When mixing mortar, the water temperature must not exceed 80°C, and the sand temperature must not exceed 40°C. The consistency of the mortar should be appropriately increased compared to that at normal temperatures. 3.3 In winter, brick masonry should be constructed using the “three-one” method, with joint widths not exceeding 1 cm ； After construction each day, protective covering should be applied promptly; no mortar should remain on the surface of the masonry. Before continuing with construction, the surface of the masonry must be cleaned thoroughly. 3.4 In addition to the requirements specified normally for the retention of mortar test blocks, an additional set of test blocks should be prepared and cured under the same conditions as the masonry, in order to determine the mortar strength after 28 days. 3.5 The temperature of the mortar on the wall shall not be lower than 5°C. 3.6 When constructing with ordinary bricks, perforated bricks, and hollow bricks at temperatures above 0°C, they should be moistened by watering. It is strictly prohibited to construct load-bearing structures at temperatures below 0°C. 4. Waterproofing works 4.1 Membrane waterproofing should generally not be carried out during winter; if construction must take place in winter, it is advisable to choose days with clear weather and temperatures of at least 5°C, with the work to be carried out between 10 a.m. and 4 p.m. 4.2 Waterproofing layer construction shall not be carried out under weather conditions of snow, wind, extreme cold, or cold snaps. 4.3 For construction using the hot-melting method, the temperature should be no lower than -10°C; for construction using the cold-adhesion method, the temperature should not be lower than -5°C℃ ； When using a coating waterproof layer, the construction temperature should not be lower than -5°C, and the storage and transportation temperature of the coating should not be lower than 0°C. 5. Decoration Works 5.1 Before carrying out interior plastering, it is advisable to first complete the roof waterproofing and implement indoor insulation measures. The \"heating method\" should be used for interior plastering, with the room temperature maintained above 8°C, and the insulation curing period should be no less than 10 days ； Plastering of exterior walls and installation of tiles must not be carried out in winter. 5.2 The ambient temperature for the execution of outdoor plastering, finishing, and decorative work, as well as high-quality plastering and colored painting tasks, should not be lower than 5℃ ； The construction temperature for intermediate and standard plastering work, tinted painting projects, and glass work should be above 8°C ； The ambient temperature for applying outdoor coatings should generally be no lower than 5°C, and it must meet the requirements specified in the coating instructions. 5.3 For plastering work carried out during winter, the mortar used shall have insulation and anti-freezing measures; for example, admixtures may be added, and their dosage shall be determined through laboratory tests. 6. Roofing Works 6.1 The roof insulation materials used during winter construction must meet the design requirements and must not contain ice, snow, frozen masses, or impurities. 6.2 The dry-laid insulation layer can be installed at negative temperatures, while the slab-type insulation layer should be installed when the temperature is not lower than -10°C. However, the sheets should be laid flat and securely on the surface of the base layer, in layers. The joints between the upper and lower layers of the slab should be offset from each other, and the gaps between these joints should be filled tightly with debris made from the same material. 6.3 Insulation layer construction shall not be carried out in snowy weather or when the wind force is at level 5 or above. 6.4 When constructing the roof finishing layer in winter, antifreeze should be added in accordance with the requirements regarding temperature and curing temperatures. Joint gaps should be created during construction, with a width of 20 mm. 7. Plumbing works: In any completed building where heating cannot be provided, no water should remain in the heating system; after testing the sanitary fixtures, the water inside them as well as in the trap chambers must be completely drained. 8. Reinforcement work 8.1 Reinforcement used under negative temperature conditions shall be subject to enhanced inspection during construction. Reinforcing bars should be protected from impact and scratches during transportation and processing. 8.2 The cold drawing temperature of steel bars should not be lower than -20°C. The tensioning temperature for prestressed steel bars should not be lower than -15°C. The straightening and cold drawing rate for grade 1 steel bars should be kept within 4%. 8.3 Welding of steel bars in winter should preferably be carried out indoors; when welding must take place outdoors, the temperature should not be lower than -20°C, and measures to protect against snow and wind must be in place. The welded joints must not be exposed to ice or snow immediately after welding. 8.4 Steel bars drawn at low temperatures shall be inspected one by one for their visual quality; their surfaces must not have any cracks or localized necking ； The cold drawing equipment, instruments, and hydraulic system fluids should be selected based on the ambient temperature, and they must be calibrated accordingly under the operating temperature conditions. IV. Pipeline Engineering 1. The following measures should be taken for pipeline joints: (1) For arc-welded steel pipe joints: When welding at low temperatures (not lower than -20°C), the ice and snow at the joint area must be removed, and wind protection measures should be in place. Preheating is required before welding (with a preheating width of 20–25 cm). Welded steel pipes must not be struck, and the joining of the joints should be carried out at normal temperatures. 2. The following anti-freezing measures should be taken when conducting hydrostatic tests in winter: (1) Exposed pipe joints and pipe sections should be covered. (2) During the pressure testing process, temporary pipelines must be wrapped with flame-retardant straw mats. (3) Release water promptly after the pressure test is successful to prevent the pipes from freezing and cracking. 3. During pipeline pressure testing, the ambient temperature should not be lower than 5°C; when it is below 5°C, anti-freezing measures must be taken during the testing. After the hydraulic test, the water supply should be cut off, the water accumulated inside the pipes drained, and the pipes dried out. 4. Requirements for construction during the winter rainy season in underground works 4.1 The excavated soil should be sloped in accordance with regulations, and regular inspections should be carried out to prevent landslides. Special attention must be paid to preventing freeze-thaw collapse during excavation; the backfill soil should be compacted before freezing occurs, and proper drainage on the surface should be ensured promptly. When backfilling, the content of small frozen soil clumps shall not exceed 15% of the fill material. 4.2 The construction of valve chambers should be carried out at temperatures above zero degrees; if necessary, the grade of the mortar can be increased to ensure the strength of the chamber. Frozen mortar must not be used, and the chamber should be covered with straw after it has been built. 5. For the welding of pressure pipelines, the provisions of GBT 20801.1–20801.6–2020, Pressure Piping Codes – Industrial Piping, section 8.2.1, shall be followed: when the ambient temperature is below 0°C, the preheating temperature must meet the requirements specified in the design documents. When the design documents do not specify, the minimum preheating temperature for various materials shall comply with the provisions in Table 6. Image 6: Pressure testing of pressure pipelines. 6.1 Liquid testing: According to GBT 20801.1-20801.6-2020, Code for Pressure Pipelines – Industrial Pipelines, clause 9.1.3 stipulates that the temperature of the fluid during testing should be no lower than 5°C. 6.2 Gas testing: According to GBT 20801.1-20801.6-2020, Code for Pressure Piping – Industrial Piping, clause 9.1.4 states that during gas pressure testing, the possibility of brittle failure must be reduced to a minimum, and the effect of the testing temperature must be taken into account. The pressure test temperature must be at least 17°C higher than the lowest allowable metal temperature of the pipeline system material. When the minimum allowable metal temperature of the material is unknown, the test temperature shall not be lower than 17°C. Brittle materials such as cast iron shall not be included in the test system. V. Steel Structure Projects 1. Steel components are manufactured under normal temperature conditions, and when installed in low-temperature conditions, technical measures to adjust for deviations must be in place during construction. When steel components are manufactured at normal temperatures but installed at low temperatures, the amount of shrinkage of the components must be taken into account based on the differences in environmental temperature, and technical measures to adjust for such deviations should be employed during construction. 2. Welders who participate in the welding of steel structures at negative temperatures must receive training in welding techniques for such conditions, pass the relevant examinations, and obtain the appropriate certification before they can carry out welding work on steel structures at negative temperatures. Position spot welding work should be carried out by welders who hold a certificate for position spot welding. 3. Use electrodes and wires suitable for welding steel structures at negative temperatures; while meeting the strength requirements, select low-hydrogen electrodes with low yield strength and good impact toughness, and for critical structures, high-toughness ultra-low-hydrogen electrodes can be used. 4. High-strength bolts and ordinary bolts used in steel structures at negative temperatures must come with product certificates. High-strength bolts require retesting of their torque coefficient and axial force at negative temperatures, and they can only be used if they meet the specified requirements. 5. The coatings used for steel structures must meet the performance requirements for application at low temperatures; water-based coatings shall not be used. 6. The assembly of components must be carried out in the sequence specified by the process, starting from the inside and working outward. When welding structures are assembled at negative temperatures, the amount of shrinkage of the reserved welds should be determined through experiments, while the number and length of spot welds should be determined by calculation. 6. When assembling the parts, rust, brush marks, dirt, oil, ice, and snow within 50 mm on each side of the joint must be removed, and the joint must be kept dry with no residual moisture. 7. When welding steel structures outdoors at negative temperatures, it is advisable to set up temporary protective shelters. Rainwater and snowflakes must not fall on the hot welds. 8. When inspecting and accepting the dimensional accuracy of steel components manufactured at negative temperatures, the influence of the temperature at the time of inspection should be taken into account. The visual inspection of welds must be fully satisfactory; joints that are to have equal strength to the base material and welds that require full penetration must undergo 100% ultrasonic testing, while the remaining welds can be inspected by ultrasonic testing at a rate of 30%–50%. If required by the design, inspections shall be carried out in the quantity specified by the design. At negative temperatures, a non-freezing oil-based coupling agent should be used between the probe of the ultrasonic flaw detector and the steel surface. 9. Before applying an anti-corrosion coating to steel components at temperatures below 0°C, a coating application test should be conducted. During painting, rust, oil stains on the component surface, as well as burrs and spurs from holes along the edges must be thoroughly removed, and the component surface must be kept dry. It can be dried using hot air or infrared radiation; the drying temperature and time should be determined through testing. Painting work must not be carried out in rainy, snowy weather or when there is thin ice on the components. 10. When installing components at negative temperatures, a sequence table for the installation of steel components should be prepared based on the temperature conditions, and the installation must be carried out strictly in accordance with this specified sequence. On the plan view, installation should proceed gradually from the center of the building outward; on the elevation view, it is advisable to install the components one by one from the bottom up. 11. When installing large components such as columns, main beams, and supports at negative temperatures, correction should be carried out immediately; once the correct position has been achieved, permanent fixation should be done right away. The components installed on that day should form a spatially stable system. 12. Steel materials and related connection materials to be used at low temperatures must be accompanied by quality certificates, ensuring that their properties meet the requirements of design and product standards. 13. The exposed length of electrodes used at low temperatures shall not exceed 2 hours; if it exceeds 2 hours, they must be re-baked, with the number of baking cycles for the electrodes not exceeding 3 times. 14. The flux must be baked as specified before use to ensure that its moisture content does not exceed 0.1 %. 15. When cutting the components, a shrinkage allowance should be reserved, and the welding shrinkage and compression deformation should be in line with the shrinkage deformation of the steel at negative temperatures. 16. When assembling the components, assemble them from the inside out in accordance with the sequence specified by the manufacturing process; when assembling at low temperatures, conduct tests to determine the weld contraction amount that needs to be accounted for. 17. When welding steel plates over 9 mm thick at low temperatures, multi-layer welding should be employed, with the welds being built up layer by layer from bottom to top; each weld should be completed in one pass. If welding is interrupted, any welding defects must be removed before resuming welding. Arc starting on the welded base metal is strictly prohibited. 18. During the on-site installation of steel structures, if it is snowy or the wind speed exceeds 6 m/s, a protective shelter should be set up. 19. Unqualified welds shall be removed and rewelded in accordance with the specifications for welding steel structures at negative temperatures. 20. When the ambient temperature is below 0°C, a coating process test should be conducted before applying the anti-corrosion coating. Before applying the coating, it is necessary to remove rust, oil, burrs, and other contaminants from the surface of the components, and to keep the surface dry. Painting work must not be carried out in snowy conditions or when there is a thin layer of ice on the surfaces. 21. During winter transportation and stacking of steel structures, anti-slip measures should be taken; the stacking area must be level and solid, free of puddles, with no ice on the ground. When components of the same type are stacked, they should be kept horizontal, with shims placed on the same vertical line to prevent the components from sliding. 22. Before the installation of the steel structure, its quality is rechecked in accordance with the requirements under low-temperature conditions; components that were missed during fabrication or became deformed during transportation and storage are repaired and corrected on the ground. 23. When using steel cables to lift steel components, anti-slip spacers must be placed. Node plates lifted together with the components, as well as clamps and other tools required by installers, must be securely tied down with ropes. 24. Prepare a chart showing the sequence of installation for steel components based on temperature conditions, and strictly follow this specified sequence during construction. 25. Develop a welding procedure for the installation of steel structures; welding shall not be carried out on both ends of a single component at the same time. 26. Remove ice, snow, and dew from the surface of the components before installation, but do not damage the coating. 27. Columns and main beams installed at negative temperatures must be promptly corrected; once their positions are correctly adjusted, they should be permanently fixed. Components installed on the same day must form a stable spatial structure. 28. When installing high-strength bolt joints, the friction surfaces of the components must be free of snow and ice, and must not come into contact with dirt, oil, or other contaminants. 29. For the installation quality of steel structures at low temperatures, in addition to complying with the requirements of the \"Code for Construction and Acceptance of Steel Structure Engineering\" (GB50250), inspections and acceptances shall also be carried out in accordance with the design specifications. VI. Equipment 1. Before installing the equipment, check its connections and seals to ensure they are in good condition; also drain any accumulated water. After installation, all open inlets and outlets should be sealed to prevent rain and snow from entering the equipment. 2. During the installation of the storage tank, proper protective measures must be taken around it to prevent safety accidents involving welders during welding operations. When working on the tank roof, safety harnesses must be properly fastened as required to ensure personnel safety during construction. 3. Precautions for welding during the winter rainy season 3.1 The secondary storage area for welding rods must maintain a certain temperature and humidity level, as well as good ventilation; the welding rods should be stored at a certain distance from the ground and walls to prevent them from becoming damp and deteriorating. 3.2 Welding shall not be carried out in rainy weather; welding operations must be conducted in areas equipped with protection against rain, snow, and wind ； When welding workpieces with large dimensions during the winter rainy season, the areas about 100 mm on both sides of the weld should first be preheated to 40–50°C to remove moisture and water. 3.3 When spot-welding workpieces with high rigidity in winter, the weld metal should be 1.5 times thicker than at normal temperatures to prevent cracking due to low temperatures. 3.4 During the winter rainy season, special attention must be paid to keeping the welding rod insulation containers sealed to prevent them from getting damp. 3.5 Welding shall not be performed when the surface of the weldment is moist or covered with ice and snow, or when it is raining, snowing, or windy, and when welders and the weldment are not provided with any protective measures. 3.6 During construction, it is strictly prohibited to strike an arc on the equipment during welding; the neutral wire of the welder must not be connected to the equipment. 4. The hydraulic pressure testing of equipment must comply with the provisions of TSG 21 “Technical Safety Regulations for Pressure Vessels”: When conducting hydraulic tests on pressure vessels made of Q345B, Q370R, and 07MnMoVR, the liquid temperature shall not be lower than 5°C℃ ； When conducting hydraulic tests on other carbon steel and low-alloy steel containers, the test temperature must not be lower than 15℃ ； The liquid temperature for the hydraulic test of low-temperature vessels should be not lower than the impact test temperature of the vessel material and welded joints (taking the higher value) plus 20°C. If factors such as plate thickness cause the material’s temperature at plastic transformation to rise, the test temperature must be increased accordingly. When supported by experimental data, tests can be conducted using a liquid at a lower temperature; however, it must be ensured that the test temperature (the temperature of the metal walls of the container) is at least 30°C higher than the temperature at which plastic deformation of the container walls occurs. VII. Other: Cable laying is not easy to carry out when the ambient temperature is below 5°C. VIII. Fire protection and safety requirements for construction in winter 1. The insulation and protective materials used in winter construction must meet flame-retardant standards. 2. Cross-operation is strictly prohibited; for work involving open flames, a fire permit must be obtained, a dedicated person must be assigned to monitor the fire, and fire extinguishing and firefighting measures must be in place. 3. Flammable, toxic, and chemical substances should be stored in dedicated warehouses, with designated personnel in charge of their receipt and dispatch. 4. Wear a safety helmet properly; climbing operations should be carried out with bare hands, and the working platform must have anti-slip measures. 5. Strengthen daily safety inspections and edge protection. 6. Strengthen the daily management of temporary electricity; cables and facilities should be regularly maintained and inspected. 7. The materials brought in must meet the insulation requirements specified in the plan, as well as the fire safety and environmental protection requirements. 8. A certain surplus of materials should be kept on site to meet the insulation requirements of the project during cold snaps.