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 sulfidation resistance, and higher elongation, thus providing a longer working life.
(2)Selection of filler material. Use high-purity crystalline magnesium oxide powder as the filler, with reasonable particle size and proportion to ensure high flow rate and density during tube manufacturing, improving heat conduction efficiency. The insulation density should be guaranteed at 2.45g/cm³.
(3)Adopt advanced manufacturing processes. Use fully automatic wire winding machines and advanced welding processes, along with 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 heating element and the sleeve must be strictly carried out according to process requirements, and hydrostatic tests, dielectric strength tests, and insulation resistance tests must be performed at 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 use a reasonable form and number of baffles after scientific calculation to avoid heating dead zones and to make the medium flow in a 360° baffle within the cylinder, increasing the flow rate of the medium on the surface of the heating element. The welding of the electric heater uses computer-controlled fully automatic tube-sheet argon arc welding to ensure firm and reliable welding between the heating element shell and the flange. The welding area 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 the pressure test before adding filler. The heat dissipation area requires a hydrostatic test after welding the heating core flange and the junction box flange to the electric heating tube protective sleeve, with the test pressure reaching the container test pressure. The welding area 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 junction box adopts a detachable structure and uses low-pressure nitrogen positive pressure ventilation. The explosion-proof junction box is internally equipped with grounding protection. The junction box shell is treated with baking paint for safety and reliability. The explosion-proof level is Exd II CT3, and the protection level is IP54. It is designed strictly according to the requirements of GB3836-2000 to meet fire and explosion-proof requirements. The flameproof surface must be strictly designed according to the electric heater standard to ensure fit tolerance.
