Routine Inspection
- Record furnace voltage, current, power, temperature and element-group resistance at regular intervals. Compare trends rather than relying on a single reading.
- Inspect terminal straps, clamps, ceramic holders, furnace-wall openings and support points. Look for loose connections, discoloration, local overheating, contamination, abnormal deformation, cracks or uneven heating.
Common Causes Of Shortened Service Life
- Electrical mismatch, excessive surface loading, poor contact, unsuitable transformer adjustment or uncontrolled mixing of old and new elements.
- Mechanical stress from misalignment, inadequate support, restricted thermal expansion, vibration or impact.
- Atmosphere and contamination effects, including water vapor, alkali compounds, metallic vapors, reactive process materials, dust accumulation or rapid thermal cycling.
- Furnace heat loss or process changes that force the elements to operate at a higher temperature than originally intended.
Replacement Planning
- Maintain a record of element drawings, nominal resistance, installation location and replacement date. For grouped SiC elements, resistance aging should be considered when replacing only part of a group.
- When investigating a failure, send photographs of the fracture and surface condition together with electrical records, furnace temperature, atmosphere, operating cycle and installation images. A failed element alone may not reveal the root cause.
Safety
- Disconnect and lock out electrical power before inspection or replacement. Allow the furnace and elements to cool according to the equipment procedure. Maintenance must be performed by qualified personnel.