Introduction to Common Thermocouple Protection Tubes
In industrial production, thermocouples are commonly used temperature measurement elements, and the choice of protection tubes significantly impacts the accuracy and stability of temperature measurements. Common materials for thermocouple protection tubes include stainless steel, high-temperature alumina ceramic, and high-temperature silicon nitride ceramic.
1、Stainless Steel Thermocouple Protection Tubes 
Stainless steel protection tubes are a common material for thermocouple protection tubes, offering good corrosion resistance and high-temperature performance. Due to their relatively low cost, they are widely used in applications where high measurement accuracy is not critical. However, stainless steel protection tubes have lower hardness, making them prone to scratches and wear, thus requiring proper maintenance during use.
2、Alumina Thermocouple Protection Tubes
Alumina thermocouple protection tubes are high-temperature ceramic tubes primarily composed of alumina, known for their high hardness and insulation properties. Alumina ceramics are highly stable in environments such as air, steam, hydrogen, argon, carbon monoxide, and vacuum when temperatures are below 1700°C. However, when manufactured into high-temperature thermocouple protection tubes, the temperature limit may vary depending on the purity of alumina (95%, 99%, 99.5%). Compared to silicon nitride protection tubes, alumina protection tubes have relatively lower high-temperature resistance but are more cost-effective. Hence, they are widely used in medium to low-temperature applications.
3、Silicon Nitride Thermocouple Protection Tubes
Silicon nitride thermocouple protection tubes are primarily composed of silicon nitride, which offers excellent high-temperature resistance, corrosion resistance, and insulation properties. Compared to traditional metal protection tubes, silicon nitride protection tubes have higher hardness and a lower thermal expansion coefficient, making them more suitable for high-temperature, high-pressure, and highly corrosive environments. Additionally, silicon nitride protection tubes exhibit good chemical stability and do not easily react with acids, alkalis, and other chemicals, ensuring long-term stability and accuracy of thermocouples in complex environments. Due to their superior insulation properties, silicon nitride protection tubes paired with thermocouples are also suitable for use in environments with strong electromagnetic fields.
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