A thermowell is a cylindrical fitting typically made of metal (such as stainless steel) or thermoplastic material, designed to protect temperature sensors (such as thermocouples or resistance temperature detectors) from harsh environments, while still allowing accurate temperature measurement. It is commonly used in industrial processes where temperature monitoring is critical.

The thermowell is installed into the process piping or vessel, and the temperature sensor is inserted into the thermowell. This arrangement allows the sensor to measure the temperature of the substance inside the piping or vessel without being directly exposed to the process fluid. This is beneficial because it protects the sensor from corrosive substances, high pressures, or high flow rates that could damage or interfere with its accuracy.

Thermowells come in various shapes and sizes, including straight, tapered, or stepped designs, depending on the specific application requirements. They can also have different end connections such as threaded, flanged, or welded connections for easy installation and maintenance.