Analysis of the Causes of Explosion of Electric Heating Tubes for Heating Liquids

1. If the heating tube is damp and its insulation resistance falls below 10 megohms when powered on, it can easily cause insulation breakdown and tube bursting.

2. If the connection between the heating tube's terminal rod and the heating wire is a tapped-wire connection with a cylindrical bottom, shrinking the tube during powder filling may cause it to become hollow or loose. After prolonged heating, due to poor thermal conductivity at this location, heat dissipation is slow, causing the heating wire to fuse or melt, break, and burst.

3. When heating oil or water, scale or grease will form on the surface of the heating tube. These deposits directly affect the heat transfer of the heating tube, causing the internal temperature of the heating tube to overheat and burn out. In severe cases, tube bursting may occur.

4. The magnesium oxide powder used in heating tubes is generally high-quality medium- and high-temperature powder. Medium- and high-temperature powder requires an operating temperature below 800°C. However, some heating tubes are designed with a high surface load (simply put, the power per meter of heating area is very high). Once dehydrated and dry-burned, the temperature continues to rise, quickly reaching over 1000°C, which can cause the magnesium oxide powder to burn out. Over time, this deteriorates the insulation properties of the magnesium powder, leading to leakage and tube explosion.

5. Heating tubes used to heat liquids primarily use iron-chromium-aluminum heating wire (0Cr25Al5). This type of heating wire theoretically has a temperature resistance of up to 1200°C. However, this alloy contains aluminum, which has a very low temperature resistance (660.4°C). During heating, if the temperature is too high, the aluminum ions in the heating wire become very active and precipitate, combining with the magnesium oxide powder. Since aluminum is a conductor, this deteriorates the insulation properties of the magnesium powder over time, shortening the life of the heating tube.

From points 3, 4, and 5, it can be seen that the most taboo thing about heating tubes for heating liquids is that the surface temperature of the heating tubes is too high. Therefore, the control of the excessively high surface temperature of the heating tubes mainly focuses on two aspects:

(1) The surface load setting of the heating tube for heating liquids must be determined according to the heating liquid medium.

(2) When designing, it is important to remember to confirm the heating area and the non-heating area in advance;

(3) When using the heating tube, it is important to pay attention to the fact that the heating area cannot be separated from the liquid and dry-burned.

6. The lead rod of the heating tube is generally an iron rod because the iron rod has a fast heat and electricity conduction. However, due to the poor oxidation resistance of the iron rod, if it is not used in time after cleaning, it will oxidize and rust. It is not ruled out that some factories use rusty lead rods. When filling powder, the oxide iron particles may be mixed with magnesium oxide powder, resulting in a decrease in the insulation performance of the electric heating tube.