Fig. 1: Localized breach in sheath of titanium sheathed process heater
Fig. 2: Multiple physical and wire breaks in a titanium sheathed process heater
Heater coils are mostly resistive element which consumes whole active power and dissipates the same as heat. It is the Jule effect ( H= I2 x R x t) which produces the heat. Overheating is the main root cause of such heater failure because every heater does have a certain power dissipation capability beyond that it can fail.
2. Common causes of heater coil burning:
- a. High voltage imbalance in the lines where heater is connected
- b. High current imbalance in the lines where heater is connected.
Effect of high voltage imbalance in heater input line:
By OHM’ law:
Current (I) = Voltage (V) / Resistor (R)
By JULE’s law:
Heat (H) = I2 x R x t………………….(i)
= V2 / R x t ……………………(ii)
As per equation (ii), it is clear that a mere 2% voltage imbalance (∆V ↑) can produce 4% additional heating in the heater element. This overheating can damage the coil. So all you need to have a close monitoring of the voltage imbalance in your system.Effect of high current imbalance in heater input line:
As per equation (i), it is clear that a mere 5% current imbalance (∆I ↑) can produce 25% additional heating in the heater element. This overheating can damage the coil. So all you need to have a close monitoring of the current imbalance in your system.
- Voltage and current need to be checked 24x7. To mitigate voltage imbalance problem, use voltage stabilizer.
- Current demand is set by the load. Current imbalance can appear due to voltage imbalance, due to loose connection in a particular heater banks and also due to change in resistance because of constant heating. If it is not taken cared, loose wire can either create short circuit or current imbalance. So it is mandatory to monitor current imbalance 24x7 to know the status of heater bank running whether anything wrong happens in heater banks.