Key Points to Ensure the Service Life of Nitrogen Electric Heaters
1 Electric heating tube
(1)Select high-quality materials. The electric heating tube uses SS321 stainless steel seamless pipe with a thickness of 1.5mm. The heating wire should be high-quality high-temperature nickel-chromium alloy resistance wire (Ni80Cr20). Compared with ordinary heating wires, high-temperature nickel alloy resistance wire has properties such as high temperature resistance, oxidation resistance, high resistivity, higher yield strength, stronger sulfur resistance, and higher elongation, thus resulting in a longer working life.
(2)Selection of filling material. High-purity crystalline magnesium oxide powder is used as the filling material, with reasonable particle size and proportion to ensure high flow rate and density during the production of the heating tube, improving heat conduction efficiency. The insulation density should be ensured at 2.45g/cm³.
(3)Adopt advanced manufacturing processes. Use fully automatic wire winding machines and advanced welding processes, and carry out fully automatic powder filling, automatic tube shrinking, and high-temperature annealing treatment to eliminate stress in the electric heating tube and remove moisture. The welding of the electric heating element and the sleeve must be strictly carried out according to process requirements, and hydraulic tests, dielectric strength, and insulation resistance tests must be conducted according to the test pressure.
2 Ensure structural optimization of the nitrogen electric heater
(1)The container material of the explosion-proof nitrogen electric heater adopts 15CrMoR. The electric heater should be designed with reasonable types and quantities of baffles after scientific calculation to avoid heating dead corners and to make the medium flow in a 360° baffle pattern within the cylinder, increasing the flow rate of the medium on the surface of the heating elements. The welding of the electric heater uses computer-controlled fully automatic tube-sheet argon arc welding to ensure firm and reliable welding between the tube shell of the heating element and the flange. The welding joints between the electric heating tube and the sleeve should be inspected by ammonia penetration. The electric heater should be equipped with a temperature sensor for over-temperature alarm inside.
(2)High-quality electric heating tube products should be selected, and they must pass pressure tests before adding filling material. It is required that after the welding of the protective sleeves of the electric heating tubes on the heating core flange and the wiring chamber flange, a hydraulic test should be conducted in the heat dissipation area, with the test pressure reaching the container test pressure. The welding joints between the electric heating tube and the protective sleeve should be 100% inspected to ensure welding quality and pass the pressure test.
(3)The explosion-proof wiring chamber is a detachable structure using low-pressure nitrogen positive pressure ventilation. The explosion-proof junction box is equipped with grounding protection internally. The wiring chamber shell is treated with baking paint, making it safe and reliable. The explosion-proof level is Exd II CT3, and the protection level is IP54. It is strictly designed according to the requirements of GB3836-2000 to meet fire and explosion-proof requirements. The flameproof surfaces must be strictly designed according to the electric heater standard to ensure fit tolerances.
