What are the methods of pipeline welding construction?

Winter construction scheme for pipeline welding \ x0d \ x0d \ The construction period of this project has entered the winter, and it is the guarantee to complete the project construction on time with good quality and quantity to formulate effective snow-proof, wind-proof and cold-proof measures. In winter construction, special measures should be taken according to the requirements of construction specifications to ensure the construction quality. \x0d\ 2. 1 Determination of winter construction \x0d\ Installation project: when the ambient temperature is lower than 0℃, it will be transferred to winter construction; \x0d\ Concrete, reinforced concrete engineering and masonry engineering: when the average outdoor temperature is steadily lower than 5℃ for five consecutive days, it will be transferred to winter construction; \x0d\x0d\ 2.2 management measures \ x0d \ winter construction to overcome the influence of cold weather on engineering quality and safety in production, the key is to do a good job of preparation before construction and inspection during construction. Before the construction of each project, technicians should make detailed technical disclosure to the constructors in combination with specific meteorological conditions and the characteristics of engineering tasks, ensure that each constructor understands the construction requirements of each step, and supervise the constructors to carry out the construction according to the construction plan. \x0d\ During the whole winter construction period, the construction site is designated for temperature measurement, meteorological records and coverage, and technicians and QA/QC engineers check the insulation and coverage of each construction project before leaving work every afternoon. \x0d\ Winter climate conditions and characteristics must be considered in the construction plan. If the overall progress permits, the construction of projects that are not suitable for winter construction should be postponed until next spring to avoid winter construction as much as possible. Relevant personnel listen to the weather forecast every day and arrange construction and production according to the weather conditions. \x0d\ Before winter, organize a comprehensive safety and quality inspection of production and living facilities, and solve the problems found in the inspection in time. \x0d\ In the winter construction process, in addition to the requirements of this measure, technical documents such as relevant design requirements, specifications and specific construction schemes should also be implemented. \x0d\ 2.3 technical measures \x0d\2.3. 1 civil engineering \x0d\★ earthwork \x0d\ earthwork excavated in winter should be excavated by preventing freezing. During excavation, before freezing, straw bags can be used to cover or plow topsoil, and the depth is generally not less than 0.3; For the excavation of frozen earthwork, the soil melting method is adopted, that is, a greenhouse is built before excavation, and the earthwork in the greenhouse is heated and melted. \x0d\ earthwork backfill should use good soil or crushed stone without frozen soil, and the virtual paving thickness of each layer of backfill should be selected according to the construction machinery used, and it is required to be reduced by 20% ~ 25% compared with normal temperature construction. Backfilling shall be carried out continuously to prevent foundation soil or fill from freezing; \x0d\ During excavation in winter, the frozen soil shall be piled together and covered with antifreeze for backfilling; \x0d\ lime soil construction should pay special attention to inspection. Permafrost and lime soil are not allowed to mix. Compacted lime soil surface and mixed lime soil cannot be used up on the same day, so heat preservation measures should be taken. \x0d\★ Reinforcement Engineering \x0d\ Reinforcement shall be processed and welded indoors, processed into finished products or semi-finished products, and transported to the site for binding. Steel welding must be carried out outdoors, the minimum temperature shall not be lower than -20℃, and snow and wind prevention measures shall be taken. When the ambient temperature is lower than-10℃, the reinforcement shall be preheated. After welding, it is forbidden to touch the ice and snow immediately. \x0d\★ Concrete Engineering \x0d\ When preparing concrete, portland cement or ordinary portland cement shall be preferred, and the minimum cement dosage shall not be less than 300kg/m3. \x0d\ In order to ensure that the compressive strength of the poured concrete before freezing is not less than 30% of the design mark, measures such as hot mixing concrete, heating and curing or adding additives to the concrete mixture can be taken during construction, and thermal calculation is carried out for heating, mixing, transportation and curing of raw materials, so as to guide construction. \x0d\ When mixing concrete with hot water, the heating temperature of water and aggregate shall be determined according to thermal calculation. Cement can't be directly heated, so it should be stored in a greenhouse before use. \x0d\ When the aggregate is not heated, the water can be heated to 100℃, but the cement above 80℃ is not in direct contact with water. Add aggregate and hot water first, and then add cement. \x0d\ When mixing concrete, adding a certain amount of admixture can accelerate the hardening of concrete, thus reaching the critical strength in advance or lowering the freezing point of water, so that concrete will not freeze at negative temperature. The composite early strength agent with the functions of reducing water, early strength and freezing point of water is preferred, and the specific construction is determined according to the design requirements or through consultation with designers. Concrete and reinforced concrete equipment foundation, tower foundation frame, outdoor frame foundation and other concrete shall not be mixed with chloride antifreeze. \x0d\ During pouring and maintenance construction, use scaffolding erected during construction to build greenhouses, and introduce heating into the greenhouses for pouring and maintenance. Central heating should be adopted to prevent insufficient heating from affecting the construction quality. \x0d\2.3.2 Installation works \x0d\★ Equipment platform ladder, pipeline and steel structure welding \x0d\ Equipment platform, ladder and its accessories are prefabricated in sections in the prefabrication yard according to the construction drawings. After effective reinforcement measures are taken, all assembly welds are welded to reduce outdoor high-altitude welding. \x0d\ The steel structure is assembled into pieces in the prefabrication yard. After the pieces are in place, the contact beams are temporarily spot-welded, then the steel structure is enclosed with canvas to prevent wind, rain and snow, and then the welded joints of the steel structure are welded. \x0d\ When the ambient temperature is lower than 5℃, oxygen-acetylene flame shall be used to heat and dry both sides of the weld groove 100mm before welding to drive away dew and moisture in the groove, and neutral flame shall be used. \x0d\ When the ambient temperature is lower than 0℃, except austenitic stainless steel, steel grades without preheating requirements shall be preheated to above 15℃ within the range of 100mm during initial welding. \x0d\ welding shall be carried out continuously. When welding is interrupted, heat preservation measures should be taken. Immediately wrap the weld with asbestos cloth or rock wool, and preheat the weld when welding again. The interlayer temperature during welding shall not be lower than the preheating temperature. After welding, the weld should be insulated and cooled slowly. \x0d\ When the welding ambient temperature is lower than the following requirements, measures must be taken to improve the welding ambient temperature: \x0d\① Ordinary carbon steel welding, not lower than-200 C; \x0d\② Low alloy steel welding, not less than-100c; \x0d\③ Austenitic stainless steel welding, not less than-50c; \ x0d \ ④ Welding of low alloy steel with yield point greater than 390MPa and not less than 00C. \x0d\ The measures to improve the temperature of welding environment adopt the scheme of liquefied petroleum gas flame heating, and the preheating temperature of carbon steel and alloy steel welded in low temperature environment is implemented according to the upper limit of preheating temperature in the following table. \x0d\ Thickness or wall thickness of steel grade steel plate (mm) Welding ambient air temperature (0C) Preheating temperature 0C \x0d\ Ordinary carbon steel 20≤δ≤30 \ x0d \ 30