Most element failures are not manufacturing defects. Six causes, and how to tell them apart.
When an element fails, the first question is almost always "was it a bad batch?" Usually it is not. Here are the six causes we see most often, and how each one shows up on the failed part.
If the surface load (W/cm²) is too high for the furnace temperature, the element runs hotter than its grade allows. The oxidation film grows faster, the wire thins, and the element eventually opens.
How it shows: often fails in the hottest zone or where elements are packed closest together. The failed wire is noticeably thinner than the rest.
Every start-stop cycle expands and contracts the element. Expansion of a 2 m element from room temperature to 1000 °C is about 30 mm. If both ends are fixed, that movement becomes stress.
How it shows: brittle fracture, often near a support point, with little or no necking.
If the element is boxed in, buried in charge, or sitting in a dead zone with no airflow, its surface temperature climbs. A 100 °C rise above design can halve life.
How it shows: bright local hot spots, heavy scaling concentrated in one area.
FeCrAl relies on an alumina film. Reducing atmospheres (hydrogen, cracked ammonia), carbon-bearing atmospheres, or atmospheres with sulphur or lead will break that film down.
How it shows: green or black discolouration, pitting, and much shorter life than the temperature alone would predict.
Zinc, lead, tin and copper vapours attack element surfaces. Welding with low-melting solder near the element, or galvanised fixtures in the furnace, can do this.
How it shows: localised corrosion pits, often near joints or terminals.
Vibration, impact during loading, or elements stretched to fit a space that is too small. Stretching changes the wire diameter and therefore the resistance.
How it shows: broken at a fixing point, or a section that has clearly been stretched thinner.
| Observation | Likely cause |
|---|---|
| Brittle break, no thinning | Thermal cycling or mechanical stress |
| Thin, necked break | Surface load too high |
| Local bright spot | Poor dissipation or partial short |
| Corrosion pits | Atmosphere or contamination |
| Uniform scaling | Normal ageing — check resistance trend |
Before replacing elements, ask three questions: has anything about the furnace changed recently, what is the actual surface load, and what is the atmosphere? The answers usually point at one of the six causes above.
If you send us the failed part and the operating data, we will tell you which cause it most likely is — including the cases where it is not the element at all.
