A thermowell is a fitting designed to protect sensors when they are installed in aggressive environments in industrial applications. The thermowell will protect the sensor from impact, corrosion, oxidation, pressure and general damage. The most common designs of thermowell are sized to fit thermometers, thermocouples or resistance temperature detectors. The process fluid transfers heat to the thermowell wall, which in turn transfers heat to the sensor. If the sensor fails, it can be easily replaced without emptying the vessel or piping.
A wide selection of materials can be utilised in the manufacture of thermowells, depending upon the operating environment, configuration, lifetime requirements and cost limitations. Ceramics are used where the operating temperatures are very high but the atmosphere is not particularly aggressive.
Carbon steels can be used for slightly lower temperatures, and provide a low-cost solution where corrosion is minimal, such as in reheating or annealing furnaces. However, most applications will combine a degree of corrosivity and elevated temperatures, requiring materials with resistance to oxidation and corrosion. Therefore, stainless steel and nickel alloys are widely used in applications such as power generation, chemical process industries, incinerators, and pulp and paper manufacturing.