Abstract: Electric heat tracing is of great significance for the antifreeze of pipelines and equipment operating safely in winter. When other heat tracing methods are not available, electric heat tracing plays an irreplaceable role. However, the safety issues of electric heat tracing cannot be ignored, especially in flammable and explosive places. Once problems occur, they may cause fire accidents. This article discusses the safety issues in the use and installation of electric heat tracing. Keywords: electric heat tracing; explosion-proof area; safety. 1. Problems in installation and use of electric heat tracing 1.1 Preparation before installation (1) Understand the product's specifications, structure, and installation methods in detail. (2) Before installation, all process pipelines (containers) must be completed and pass hydraulic (air tightness) tests. The surface of pipelines (containers) should be derusted, anti-corrosion treated, dry, and smooth, free of burrs and dirt. (3) Before installation, visually inspect the product for any damage, deformation, cracks, or other abnormalities. (4) Understand the system installation diagram in detail, and confirm the specifications, types, quantities, and installation locations of the products. (5) Ensure that the insulation material is dry. (6) Prepare the installation manual to record installation contents at any time. 1.2 Key points during installation (1) Do not drag or fold the electric heat tracing cable on the ground over long distances to avoid wearing the insulation and affecting its performance. (2) Avoid contact with high-temperature objects. Do not allow high-temperature welding slag to splash onto the surface of the electric heat tracing cable, causing burns. (3) Avoid external impact or sharp objects damaging the electric heat tracing cable. (4) The bending radius of the electric heat tracing cable must not be less than the specified value (generally five times its thickness). (5) When connecting the electric heat tracing cable to accessories, leave some slack (usually about 30 cm) for easy maintenance. (6) During installation, the electric heat tracing cable should be tightly attached to the pipeline (container) surface and fixed (special cases handled separately). (7) When installing on plastic pipes, lay the electric heat tracing cable on the surface and then stick aluminum foil tape to facilitate uniform heat dissipation and improve efficiency. (8) Lay the electric heat tracing cable at 45 degrees below the pipeline as much as possible to facilitate heat conduction and uniform temperature distribution. (9) At locations frequently disassembled, such as valves, flanges, and pumps, consider the winding method to facilitate maintenance without damaging the electric heat tracing cable. (10) When matching the electric heat tracing cable with accessories, follow the wiring requirements, and firmly attach the nameplate with adhesive at a distance of mm from the power connection. The electric heat tracing cable must be equipped with explosion-proof accessories suitable for the environment. During wiring, do not short-circuit the two bus wires or connect the metal shielding layers to avoid leakage and short circuits. (11) The size of the sealing rings of each accessory must match the model of the electric heat tracing cable. All fasteners should be tightened securely to ensure proper protection and explosion-proof performance. (12) If a mechanical thermostat is used in the system, adjust the temperature set point before powering on. Do not adjust while powered on. The temperature probe should be kept away from the electric heat tracing cable to avoid inaccurate measurement and system malfunction. (13) Ensure the system is well grounded, with a grounding resistance not exceeding 4 Ω. (14) After all wiring is completed, perform insulation and performance tests on the system (insulation resistance should be greater than 20 MΩ). Measure the power resistance of each circuit; the theoretical value should be close to the actual value (generally within ±10% deviation). (15) After passing the above installation tests, proceed with trial operation. Check the heating condition and electrical parameters section by section. If no abnormalities are found after four hours of power-on, the pipeline can be insulated. 2. Issues and key points during the use of electric heat tracing (1) Electric heat tracing methods include self-limiting, constant power, high-temperature armored, and skin effect tracing. (2) Explosion-proof, reinforced, and corrosion-resistant types. (3) The conductor consists of stranded tinned or nickel-plated copper wires. (4) Self-limiting electric heat tracing cables are composed of conductive plastic and two parallel bus wires with an insulating layer. The power decay phenomenon of polymer conductive composites seriously affects service life, and the high starting surge current (3-8 times) also affects the service life and length of the electric heat tracing cable. (5) Self-limiting heat tracing cables have different temperature grades (65°C, 105°C, 135°C). Use heat tracing cables that meet the on-site requirements to prevent 1. Electric heat tracing cable used (1) Model: DXW Output power: 30w/m Without thermostat (assuming thermostat failure) (2) Model: ZBR Output power: 60w/m Without thermostat (assuming thermostat failure) 2. Temperature test: Test: Assuming thermostat failure, the heat tracing cable is placed in insulation material. (1) Time 00:00 Model ① Current 1.0A, room temperature; Model ② Current 4.5A, room temperature. (3) Time 00:10 Model ① Current 0.09A, temperature 64°C; Model ② Current 0.16A, temperature 80°C. 3. Destructive tests (1) Short circuit test: Damage the insulation of the heat tracing cable at cm intervals, lay it on the ground, and connect to power. The current and switch are normal. Then apply large water droplets at 20cm, 40cm, and 100cm; the leakage circuit breaker trips instantly. The insulation resistance between the two phases of the heat tracing cable is zero, and between the two wires and the outer shielding wire is above MΩ. (2) Combustion test: Apply gasoline at 20cm, 40cm, and 100cm; the current and switch are normal (since the two wires are cm apart). Apply gasoline at cm and short-circuit the two wires at that point; combustion may occur (no combustion due to open space), and the leakage circuit breaker trips instantly. At the core of the heat tracing cable, everything is normal. Then artificially short-circuit the core at that point; the leakage circuit breaker trips instantly, and the gasoline-soaked cotton yarn ignites. (3) Place the bare end of the heat tracing cable directly into gasoline; the current and leakage circuit breaker are normal, and the gasoline does not ignite. 4. Insulation test At room temperature: Insulation resistance between the two phases of the heat tracing cable is zero (the core is a complex polymer composite composed of multiple materials and conductive media); between the two wires and the outer shielding wire is MΩ. At °C: Insulation resistance between the two phases of the heat tracing cable is zero; between the two wires and the outer shielding wire is above MΩ.
