What are the common faults and solutions of tubular electric heating elements?

What are common faults and solutions for tubular electric heating elements?

Common faults with sheathed electric heaters (such as the SRY and HRY series) are often related to the heating core, insulation system, temperature control, sheath structure, and explosion-proof seals. Targeted troubleshooting is required based on the material properties (magnesium oxide/ceramic insulation, stainless steel/carbon steel sheath) and application scenario (high/medium/low temperature, explosion-proof/non-explosion-proof). The following is a cause analysis and step-by-step solutions for six common faults:

1. Core Fault: Heater Not Heating

Possible Causes

Abnormal power input: Phase loss (common with 380V equipment, such as loose three-phase wiring), voltage mismatch (such as mistakenly connecting a 220V model to 380V), or circuit breaker tripping (overload or short circuit).

Heating core damage:

SRY (integral type): Aging and breakdown of the magnesium oxide insulation layer causes the heating element to melt (this condition is prone to aging due to prolonged high temperatures in medium and low temperature environments);

HRY (pull-out type): Thermal shock cracking of the ceramic insulation core, or the heating element burning out due to power overload (common in high-power density models).

Terminal failure: Loose or oxidized terminals in the junction box (especially explosion-proof junction boxes, where poor sealing allows moisture intrusion), or insufficient wire cross-sectional area (long-term heating can cause wire core burnout).

Solution for tubular electric heating elements

Power supply troubleshooting:

Use a multimeter to measure the input voltage (for 380V devices, check the three-phase voltage balance, with a deviation of ≤5%).

Check the circuit breaker capacity (it must match the heater power; for example, for a 10kW/380V device, select a 20A or higher circuit breaker). If the circuit breaker trips, check for a short circuit and reset it.

Heating Core Inspection:

After powering off, remove the junction box and use a multimeter set to the "resistance" setting to measure both ends of the heating core. Normal resistance = (voltage²) / power (e.g., 380V/5kW, resistance ≈ 28.9Ω). If the resistance is infinite, the heating element is blown.

SRY (integral type): The entire heater needs to be replaced (the magnesium oxide insulation cannot be repaired separately).

HRY (pull-out type): Only the heating element needs to be replaced (no need to remove the sheath, reducing maintenance costs).

Wiring Repair:

Clean the oxide layer from the terminals (use fine sandpaper) and re-tighten the screws (torque according to the manual, e.g., 5-8 N·m for M6 terminals).

Replace the adapter cable (copper core cross-sectional area ≥ power / (1.732 × voltage × 0.8). For 5kW/380V, the cross-sectional area should be ≥ 1.5 mm²). Explosion-proof models require flame-retardant cable and proper sealing.

2. Safety Failure: Frequent Overheat Protection Triggers

Possible Causes

Temperature Control System Failure:

Damage to the temperature sensor (e.g., PT100) (SRY typically uses medium- and low-temperature sensors, while HRY requires sensors capable of temperatures above 500°C);

Incorrect thermostat settings (e.g., HRY mistakenly set to 200°C in a 300°C scenario, or failure to enable the high-temperature protection threshold).

Poor Heat Dissipation/Heat Transfer:

Oil circulation failure (e.g., a hydraulic station pump stall, causing "localized overheating" of the oil around the heater);

Sheath Fouling (HRY ceramic insulation sheaths are prone to carbon deposition in high-temperature scenarios, or SRY sheaths are susceptible to reduced thermal conductivity due to oil impurities adhering to them).

Power Overload: The actual heating medium has a low thermal conductivity (e.g., high-viscosity heavy oil), but a high-power density model is selected (e.g., a 2.8W/cm² HRY model is used with low-flow oil, resulting in localized overheating).

Solution

Temperature Control Repair:

Use a multimeter to measure the sensor resistance (PT100 resistance is 100Ω at 0°C, approximately 175.8Ω at 200°C). If the resistance is abnormal, replace the sensor with a sensor of the same specification (HRY should be a high-temperature resistant model over 500°C).

Reset the temperature control parameters: set the protection threshold to 20-30°C above the normal operating temperature (e.g., if heated to 250°C, set the protection threshold to 280°C). Also, enable the "Oil Cutoff" function (if equipped with a liquid level sensor).

Improve Heat Transfer:

Check the oil circulation system: Start the oil pump and observe the pressure gauge (ensure the differential pressure is ≥ 0.1 MPa). If there is no pressure, repair the oil pump or clear the oil line.

Clean the sheath for scale: After powering off, soak the sheath in a dedicated descaling agent (such as citric acid solution to avoid corrosion on stainless steel sheaths), or blow it with high-pressure air (0.3 MPa). (HRY ceramic sheaths require gentle blowing to prevent cracking).

Power Matching Adjustment:

If the medium has poor thermal conductivity (such as asphalt or heavy oil), it's necessary to switch to a lower watt density model (e.g., changing the HRY from 2.8W/cm² to 0.7W/cm²) or increase the sheath's heat dissipation area (using a larger diameter sheath).

III. Hidden Fault: Degraded Insulation Performance (Leakage Risk)

Possible Causes

Aging/Moisture of Insulation Material:

SRY (Magnesium Oxide Insulation): Magnesium oxide absorbs moisture (due to poor sealing of the junction box or oil seeping into the sheath), resulting in a decrease in insulation resistance (standard requirement: ≥100MΩ/500V);

HRY (Ceramic Insulation): The ceramic layer cracks due to thermal shock (e.g., sudden cooling from high temperature), allowing oil to penetrate and break down the insulation.

Sheath Damage: Stainless steel/carbon steel sheaths can develop holes due to corrosion (e.g., acidic oil, high-temperature oxidation) or mechanical impact, allowing the heater core to come into direct contact with the oil.

Water ingress into the junction box: Deterioration of the sealing ring of the explosion-proof junction box (such as the ExdeⅡCT4 model of the SRY) or loosening of the fastening screws can lead to rainwater/moisture intrusion, causing ground leakage from the terminals.

Solution

Insulation Inspection and Repair:

Use an insulation resistance meter (500V setting) to measure the resistance of the heater core to ground. If <10MΩ, disassemble the unit.

SRY: Place the entire unit in an oven (120°C ± 5°C) for 4-6 hours (magnesium oxide absorbs moisture reversibly). After drying, retest the insulation resistance and ensure it is ≥100MΩ before use.

HRY: Check for cracks in the ceramic core. If so, replace the core (ceramic insulation damage is irreversible).

Sheath Repair/Replacement:

Minor damage (<5mm): Use stainless steel welding rods (304 material) for repair welding. Polish the weld surface after welding to avoid scratching the oil pipeline.

Extensive corrosion/deformation: SRY requires complete replacement. HRY allows individual sheath replacement (due to the core-pulling design).

Junction Box Seal Enhancement:

Replace aging sealing rings (use oil-resistant nitrile rubber with a temperature rating suitable for the equipment, e.g., -40°C to 200°C).

Tighten the junction box screws (tighten evenly diagonally to avoid deformation of the flameproof surface). For explosion-proof models, apply anti-rust grease to the flameproof surface (do not use regular butter).

IV. Structural Failure: Sheath Corrosion/Deformation

Possible Causes

Media Corrosion: Oil containing acidic substances (such as aged hydraulic oil) or high-temperature oxidation (for HRY at temperatures above 300°C) can cause corrosion and perforation of the stainless steel sheath (commonly made of 304).

Deformation Due to Dry Burning: When the oil level is too low or the circulation is interrupted, the sheath temperature rises sharply locally (SRY magnesium oxide insulation has slow thermal conductivity and can easily reach over 600°C), causing bulging and deformation of the stainless steel sheath.

Mechanical Impact: Collision during installation/maintenance, or high-speed impact from impurities in the oil (such as metal particles), can cause dents in the sheath.

Solutions

Corrosion Countermeasures:

Replace the corrosion-resistant sheath: If the medium is acidic or high-temperature oil, use 316L stainless steel (which has better corrosion resistance than 304) or Hastelloy alloy sheaths (for HRY at high temperatures).

Regularly test the oil quality: Take samples for analysis every three months. Replace the oil when the acidity value exceeds 0.1mgKOH/g to prevent further corrosion.

Dry-burn Prevention and Repair:

Install a liquid level protection switch (such as a float-type switch that cuts off power when the oil level falls below a set value). High-power HRY models require both temperature and liquid level protection.

Minor deformation: Use specialized tools to correct (avoid excessive force that may damage the insulation). Severe deformation (bulging, cracking): Replace the entire SRY unit; replace the HRY unit's sheath.

Mechanical Protection:

During installation, install a protective net (pore diameter <10mm) around the sheath to prevent impact.

Install a filter (precision ≤10μm) in the oil circulation system to reduce impurity impact.

5. Explosion-Proof Failure: Failure of the Explosion-Proof Structure (Explosion-Proof Models Only)

Possible Causes

Damaged Flameproof Surface: The Exd II BT4 flameproof surface of the HRY (or the Exd II CT4 composite flameproof surface of the SRY) is scratched, rusted, or has excessive clearance (standard requirement ≤ 0.15mm).

Aging Explosion-Proof Seal: The seal (oil-resistant rubber) connecting the junction box or housing to the flange has hardened or cracked, allowing explosive gas to penetrate.

Unauthorized Disassembly of Explosion-Proof Components: Failure to open the explosion-proof junction box according to regulations, or replacing non-original parts (e.g., replacing explosion-proof screws with standard screws).