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Instructions for Silicon Nitride Thermocouple Protection Tubes

Thermocouple protection tubes are primarily designed to safeguard the internal metal wires of thermocouples, ensuring these wires remain undamaged by the environment being measured. Silicon nitride (Si₃N₄) tubes exhibit key properties such as no infiltration with molten fluids, high-temperature resistance, corrosion resistance, oxidation resistance, and non-pollution. To extend their service life, please review the following guidelines before use.

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1, Fragility Note

Handle the tubes with care during transportation, installation, and disassembly. Avoid subjecting them to strong impacts, as they are fragile.

2, Installation Buffer Requirement

When installing, use heat-resistant rubber gaskets at the contact points between the thermocouple protection tubes and metal components, or bond these areas with adhesive. This prevents damage to the Si₃N₄ tubes.

3, Hot and Cold Loading Operations

If the installed thermocouple is to be used in a hot-loading scenario, preheat it to 300–500°C before operation.

For cold-loading, the thermocouple can be heated gradually along with the furnace. Both methods help extend the tube’s service life.

4, Maximum Operating Temperature

Under aerobic conditions, the maximum operating temperature of Si₃N₄ tubes must not exceed 1400°C to avoid oxidation.

In a vacuum or protective atmosphere, the maximum operating temperature should not exceed 1800°C.

5, Storage Conditions

Store Si₃N₄ tubes in a dry environment to prevent moisture from impairing their performance.

6, Surface Cleaning Guidelines

Regularly clean aluminum oxide deposits from the surface of Si₃N₄ tubes. Use preheated tools for cleaning—cold tools are not permitted.

7, Impurity Removal Timing

When removing impurities adhering to the surface of Si₃N₄ tubes, it is advisable to perform the process while the tubes are at a high temperature.