To ensure longer thermocouple life and measurement accuracy, additional protection tubes are recommended along the length of the thermocouple exposed to high temperatures. Protection tubes also simplify thermocouple replacement.
A common question is: Which Protection Tube Is Right For My Thermocouple?
While all protection tubes provide some level of protection, performance varies depending on process temperature and media. Ceramic protection tubes are strongly recommended for high-temperature and oxidizing environments, where metal protection tubes are prone to oxidation.
TempoTech offers a full range of ceramic protection tubes for applications such as furnaces, molten aluminum, steel furnaces, heat-treat furnaces, flare stacks, incineration furnaces, and more.
Ceramic Protection Tubes and Their Benefits
Mullite C610
Mullite protection tubes are low-cost ceramic tubes composed of aluminum and silicon oxides (3Al₂O₃·2SiO₂), also known as aluminum silicate. These tubes can be used up to 3000 °F in air and dry hydrogen.
TempoTech manufactures mullite tubes in various lengths and diameters. They are recommended for base-metal thermocouples (Type K, J, T, E) and not recommended for noble-metal thermocouples (Type R, S, B), as impurities in mullite can negatively affect noble-metal performance and lifespan.
Alumina C799
Alumina protection tubes are made from 99.7% pure alumina and offer excellent thermal shock resistance, corrosion resistance, and abrasion resistance. Due to their chemical inertness, they are well-suited for high-temperature applications using noble-metal thermocouples (Type R, S, B).
In many cases, alumina tubes are used as secondary protection tubes in combination with silicon carbide or silicon nitride primary tubes.
Silicon Nitride (Si₃N₄)
Silicon nitride is a high-performance ceramic with excellent non-wetting properties, mechanical strength, and thermal shock resistance. It is widely used in non-ferrous metal processing such as molten aluminum, zinc, and brass.
Silicon nitride tubes can be used with all thermocouple types (K, J, T, R, S, B). When used with noble-metal thermocouples, an inner alumina protection tube is recommended.
Silicon Carbide
Silicon carbide protection tubes are commonly used in metal processing industries, including aluminum foundries and steelmaking. They offer excellent non-wetting properties and can be used up to 1300 °C.
Careful handling is required, and preheating is recommended before immersion in molten metal.
TempoTech offers silicon carbide tubes in multiple configurations:
- Isopressed silicon carbide tubes with metal support pipes
- Nitride-bonded silicon carbide tubes
- Coated silicon carbide tubes
- Silicon carbide tubes with collars
- SIALON Thermocouple Tubes
SIALON
SIALON ceramics are advanced materials composed of silicon, aluminum, oxygen, and nitrogen. They provide excellent thermal stability, corrosion resistance, and mechanical strength.
SIALON tubes resist cracking from abrupt temperature changes and are ideal for molten non-ferrous metal applications, where temperatures exceed 1000 °C and chemical reactivity is high.
Sintered Silicon Carbide (Hexoloy®)
Sintered silicon carbide tubes are non-porous, wear-resistant, corrosion-resistant, and highly thermally conductive. These tubes are suitable for temperatures up to 1900 °C and can be used with all thermocouple types.
When used with noble-metal thermocouples, an inner alumina tube is recommended.
