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1. Are the specifications, materials, and welding requirements for the oil transfer lines that carry radiation flow identical to those of the convection tubes? The specifications, materials, and welding requirements for the oil transfer lines that carry radiation flow are exactly the same as those of the convection tubes. VI. Nailed Tubes and Finned Tubes 2. What is a nailed tube? To increase the heat transfer coefficient on the flue gas side of the convective tubes, a certain number of nails of specified dimensions are welded to the outer wall of these tubes; such tubes with welded nails are called nailed tubes. 3. What is a finned tube? To increase the heat transfer coefficient on the flue gas side of the convective tube, a certain number of fins of specified dimensions are welded to the outer wall of the convective tube; such a tube with fins is called a finned tube. 4. In what parts of a heating furnace are nail-head tubes and finned tubes used? Both nail-head tubes and finned tubes are used as convection furnace tubes in heating furnaces. The radiant furnace tubes of the heating furnace do not use nail-head tubes or finned tubes. 5. What are the functions of nail-head tubes and finned tubes? Convection tubes in heating furnaces use either nail-head tubes or finned tubes, and their main purpose is to increase the heating surface area and thereby improve the thermal efficiency of the heating furnace. 6. What are the conditions for using nail-head pipes? The conditions for using nail-head pipes are that the flue gas temperature must not be lower than 380°C. Nipple tubes can be used in oil or gas-fired heating furnaces, but soot blowers must be installed; for each row of soot blowers, 3 to 4 rows of nipple tubes can be considered above and below. Nail-head tubes cannot be used in heaters for burning contaminated oil or high-viscosity residue oil. 7. What are the conditions for using finned tubes? The conditions for using finned tubes are that the flue gas temperature must not be lower than 380℃ ； Heating usually only works with gas. When burning heavy oil, the fin spacing must not be less than 2 fins per 25 mm. Finned tubes cannot be used in heaters for burning contaminated oil or high-viscosity residue oil. 8. What are the materials and welding methods for nail-head tubes and fin tubes? The materials and welding methods for nail-head tubes and fin tubes are shown in Table 6-1. Table 6-1 Materials and Welding Methods for Nail-headed Tubes and Finned Tubes. Furnace tube materials: carbon steel (10#, 20#), Cr5Mo1, Cr18Ni9Ti. Fin material. Welding methods: For 1 mm thick 1Cr13 steel strips, resistance spot welding; the same as above. CO2 shielded welding. Nail-headed material. Welding methods: For thicknesses ≤12 mm, Q235-A.F round steel – resistance welding or submerged arc welding; the same as above. Submerged arc welding. 9. What are the technical requirements for manufacturing nail-headed tubes? Nail-headed tubes must be manufactured under the following conditions: (1) More than 80% of the area at the bottom of the nail head should be fused with the metal of the furnace tube. (2) The nail head should be perpendicular to the furnace tube, with a deviation of no more than 2 mm; the distance error of the nail head along the circumference and length of the furnace tube shall not exceed +2 mm. (3) The allowable error for the total number of nail heads is 2%. (4) The longitudinal bending of the nail head tube shall not exceed 8 mm over its entire length. (5) The nail heads are manufactured by pickling and cold-drawing round steel with a diameter of φ 10 mm or more. (6) After welding the nail-head pipe, the pipe shall undergo a hydrostatic test, with the test pressure determined in accordance with the requirements specified in the \"Nail-Head Pipe Manufacturing Diagram\". 10. What is the maximum operating temperature for the materials used in pins and fins? The materials for pins and fins should be selected according to the highest calculated temperature at their ends, as specified in Table 6-2. Table 6-2 Maximum service temperatures for nail head and fin materials. Maximum service temperature for nail head material / °C; Maximum service temperature for fin material / °C: Carbon steel: 5Cr-1/2Mo, 11-13Cr18Cr-8Ni – 510, 600, 600; 815. Carbon steel: 11-13Cr18Cr-8Ni – 450, 600, 815