Working condition: The air outlet is 250 ℃, and the shell is subjected to high temperature hot air. It is also necessary to consider thermal expansion, oxidation, insulation, structural strength, fan pressure, and corrosion prevention, and distinguish between the inner shell that comes into contact with high temperature wind and the outer insulation shell.
Firstly, selection of inner liner (inner cavity shell, directly in contact with hot air)
Option 1: Q235-B carbon steel (cost-effectiveness priority, non corrosive dry air)
1. Usage conditions: Clean and dry air, free of corrosive media such as water vapor, sulfur and chlorine.
2. Long term use temperature ≤ 350 ℃, meeting this working condition.
3. Processing requirements: The inner cavity must undergo high-temperature anti rust and anti-corrosion treatment, and be sprayed with organic silicon high-temperature paint (resistant to 350-400 ℃); Polish the weld seam flat and apply high-temperature resistant paint to all parts.
4. Disadvantages: Rust may occur when exposed to humid air or condensed water vapor; Long term high temperature will oxidize and peel, and the falling debris will be blown to the rear pipeline by the wind.
5. Wall thickness recommendation: For air ducts with low air pressure, the inner steel plate should be 4-5mm; for high air pressure and large air volume, 5-6mm should be selected, with reserved thermal deformation allowance, and expansion joints should be installed on the shell.
Plan 2:304 Stainless Steel (General mainstream, recommended for most working conditions)
1. Operating temperature: Long term ≤ 450 ℃, fully compatible with 250 ℃ air outlet conditions, and safe with an internal wall temperature of around 300 ℃.
2. Advantages: Anti high temperature oxidation, not afraid of condensation and moisture, not easy to peel off oxide skin, good air cleanliness, not easy to rust.
3. Applicable: Ordinary industrial hot air, drying, circulating air, with a small amount of water vapor in the air.
4. Wall thickness: 3-4mm; choose 4-5mm for high wind pressure and large section air ducts.
5. Attention: 304 will corrode in environments containing chloride ions, so do not choose media containing chloride salts.
Plan 3: 310S stainless steel (local overheating, high temperature cycling, with a small amount of smoke)
1. Applicable: The local temperature inside the heater is too high, occasionally exceeding 350 ℃ for a short period of time; Hot air carries trace amounts of smoke.
2. High cost, generally does not require the entire shell to be 310S, only the cylinder section around the heating tube uses 310S, and the rest of the shell uses 304, reducing costs.
Secondly, external insulation shell (outer protective shell, not in contact with hot air)
External protection refers to the outer shell wrapped with insulation cotton, typically at a temperature of 50-80 ℃, and does not require high-temperature resistant materials
1. Economic type: Q235B steel plate 2-3mm, painted/sprayed.
2. Outdoor humid environment: 304 stainless steel 2-2.5mm.
Thirdly, key structural points for supporting (250 ℃ air duct heater is very important)
1. Thermal expansion compensation
The shell will elongate when the temperature rises, and an expansion joint must be installed; If hard connected, the shell welds and flanges are prone to tearing and deformation. The expansion of carbon steel shell is greater than that of stainless steel, so carbon steel equipment should be given special attention.
2. Material selection for insulation layer
The insulation between the inner liner and the outer casing is made of aluminum silicate refractory fiber cotton (temperature resistance ≥ 400 ℃) with a thickness of 100-150mm. Ordinary rock wool is prohibited as it will pulverize and fail at 250 ℃. Insulation should be sealed to prevent hot air from entering the outer casing.
3. Flanges and sealing gaskets
Flexible graphite gaskets/high-temperature ceramic gaskets are selected for flange gaskets, while ordinary rubber gaskets fail directly due to carbonization at 250 ℃.
4. Shell welding
Stainless steel liner must be welded with argon arc welding; Polish the weld seam of the carbon steel inner liner, and cover the weld seam completely with high-temperature paint.
5. Temperature margin reminder
When the air outlet measures 250 ℃, the actual wall temperature inside the heater chamber will be higher. It is recommended to reserve a temperature margin of 100 ℃ for the selected material, and not just exceed the upper limit of 250 ℃ material.
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Post time: Aug-10-2026
