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Welding Technology and Applications of Furnace Tubes in Atmospheric Pressure Heating Furnaces. Li Wending. In a project to replace the furnace tubes of an atmospheric pressure heating furnace at Nanyang Fine Paraffinization Plant, Henan Oilfield, the furnace tubes were made of F127×820 boiler steel pipes, and the connections between these tubes were achieved using F127×10 1Cr5M elbow fittings. 100% X-ray inspection is required for the furnace tube welds, with a qualification grade of Level II. 1? Analysis of welding process properties: 1Cr5M is a chromium-molybdenum alloyed heat-resistant steel; it has a pearlitic structure at room temperature, and the material supplied should be in an annealed state. This material has poor weldability and a strong tendency to harden upon air cooling, resulting in the formation of martensite structure. It is necessary to ensure that the material is in an annealed state before welding, and care should be taken to prevent the occurrence of cold cracks during welding. At 250°C, the average linear expansion coefficient of 1Cr5M is 11.66×106 mm/mm°C, while that of steel grade 20 is 12.56×106 mm/mm°C; therefore, it is sufficient to ensure the normal mechanical properties of the joint. 2? Key points and methods of welding process: The welding materials to be used are J507 electrodes and wire, as well as H08Mn2Si. The respective welding coefficients are detailed in Table 1 below. Preheating temperature: 250°C–350°C; measured using an infrared thermometer within a range of 100 mm on either side of the weld. Welding requirements: ① Once preheating has reached the required level, weld immediately and complete the welding in one continuous process ； ② The interlayer welding temperature shall be no less than 350℃ ； ③ The weld joints at each layer are offset from one another ； ④Arc initiation is not allowed within the weld bead. Post-weld treatment: ① After welding, wrap the weld seam with an insulating layer to facilitate slow cooling ； ②Heat treatment is carried out by heating with an electric heating tape. 3? Conclusion Through the process evaluation of welding joints made of alloy steel and medium-carbon steel, reasonable welding parameters were determined and applied in actual welding, thereby solving the welding problems associated with 1Cr5M/20# steel joints. In a project to replace the heating furnace tubes at a refined wax plant in the Henan Oilfield, TIG welding with H08Mn2Si wire was used for the root pass, and J507 electrodes were employed for welding a total of 43 weld joints, achieving a first-pass qualification rate of 90%. Since its commissioning at the end of August 1999, no problems have occurred; practice has proven the feasibility of the aforementioned process, which has yielded good economic benefits and received positive feedback from users. □