Introduction to thermocouple protection tubes

To date, thermocouple protection tubes are widely used in industrial production and scientific research. The material properties of the thermocouple protection tube directly affect various parameters of the thermocouple, including its operational stability and service life. This is especially true for thermocouples operating in high-temperature environments, where the material requirements for the thermocouple protection tube are even more stringent.

Currently, with the rapid advancement of science and technology, temperature measurement technology has developed rapidly, evolving from point to line, then from line to surface, and from surface to interior. From traditional wired temperature sensors to wireless thermocouples, both contact and non-contact types exist. Contact thermocouples, with their large production volume and wide applicability, have gained widespread popularity. Thermocouples offer stable performance, accurate and reliable results, and ease of use. They also boast simple structures, a wide measurable temperature range, and the ability to transmit signals over long distances. These advantages have made them widely used temperature-sensing elements in scientific research and industrial production. In the process of temperature measurement, the thermocouple protection tube plays a crucial role.

The material properties of thermocouple protection tubes directly affect the long-term stability and service life of thermocouples during use, especially under high-temperature conditions. Choosing a high-quality thermocouple protection tube is crucial for normal operation. For example, thermocouple protection tubes used in continuous temperature measurement in molten steel must withstand not only high temperatures but also corrosion and impacts from the hot steel, which can potentially affect the measurement accuracy. In circulating fluidized bed boiler temperature measurement, the environment involves high-temperature corrosion, high-temperature oxidation, and even high-temperature grinding of fluidized powder. Such harsh environments pose a severe challenge to thermocouple protection tube materials, presenting a significant problem for technicians: how to solve the problem of thermocouple protection tube failure under high-temperature conditions. This places higher demands on the performance of thermocouple protection tubes.

To manufacture thermocouple protection tubes for high-temperature applications, the material must possess the airtightness, mechanical strength, stability, and thermal conductivity required for ordinary thermocouples. Furthermore, it must be used within the upper limit of the thermocouple's temperature measurement range without deterioration or deformation, and exhibit good oxidation resistance at high temperatures. It should not soften at the operating temperature of the thermocouple, and should be resistant to corrosion from molten metal, glass, molten salt, and corrosive gases when the thermocouple sheath must be immersed in them. It should also possess certain resistance to sudden temperature changes, comprehensive thermal shock resistance, high thermal conductivity, and low thermal expansion.