Common Failure Modes of Cartridge Heaters and How to Avoid Them

A production line suddenly stops. The maintenance staff finds that the problem is a broken cartridge heater. The heater is taken out and replaced, and then production starts again. Three weeks later, the heater breaks down again. This cycle happens all too often in industries that use single head electric heating tubes. If you know why these failures occurred, you may save a lot of time and money on repairs and replacements.


The most common reason cartridge heaters break is that they are not the right size for the job. Industry statistics shows that 90% of cartridge heater failures are caused by using the wrong size heater for the application. This includes both the diameter fit we talked about before and the length of the heated part. If the heater is too short, the unheated lead section may rest within the bore, which can make a cold spot. If the heated part is too long and sticks out of the hole, the part that is not covered by metal can't transmit heat, which makes it overheat and break.

Moisture and contamination are the second most common cause of failure. Magnesium oxide powder is used as insulation within a single head electric heating tube. It is hygroscopic, which means it easily absorbs moisture from the air. The internal volume of a cartridge heater changes when it turns on and off, which pulls in air from the outside. If the air has moisture or other things in it, such oil vapour, these things are sucked into the heater. When you switch the heater back on, the moisture converts into steam, which builds up pressure inside the heater and oxidises the resistance wire. This oxidation thins the wire over time until it breaks like a fuse-40. In very bad circumstances, moisture can trigger a short circuit as soon as the power is turned on.

Another typical mistake is using the wrong voltage. A cartridge heater rated for 120 volts will produce four times its rated wattage if it is attached to a 240-volt supply. This is because power changes with the square of the voltage. The heater gets too hot nearly right away because of this big jump in output. On the other hand, running a heater at a lower voltage than it is rated for lowers the output but doesn't hurt the heater; it just takes longer to heat up. Before turning on the heater, always make sure that the supplied voltage matches the rating on the heater nameplate.

The 26mm single head electric heating tube has its own set of rules, especially for units with a big diameter. higher MgO insulation is usually a good thing, but the bigger interior volume also means higher thermal mass. When a 26mm heater breaks because it doesn't fit right, the damage is usually very bad because the heat builds up inside before any indicators of trouble show up. Experience suggests that an air gap as little as 0.3mm can cut heat transfer efficiency by more than 30%, making the heater dangerously hot-12.

Too much temperature cycling also makes heaters last less long. If the control system uses basic on-off switching instead of proportional control, the heater goes through cycles of thermal expansion and contraction over and over. The resistance wire and MgO insulator are put under stress with each cycle. This stress causes micro-cracking and eventually failure over time. Thyristor power controllers that stop on-off cycling can greatly improve the life of high-density cartridge heaters used in high-demand applications.

What can be done in real life to stop these problems from happening? First, always keep the right diametral clearance. For a 26mm big diameter single head electric heating tube, that should be 0.1mm to 0.2mm. Second, utilise sealed termination ends to keep moisture out. Third, make sure the voltage you used is the same as what the heater says it should be. Fourth, be sure that the heated length is completely inside the bore. Fifth, before you install it, make sure the bore is clean and clear of dirt and other anything that could get in the way. Every piece of industrial heating equipment has its own set of working requirements, and knowing these is important for choosing the best heating solution.