A thermowell is a protective tube installed in a process system to protect a temperature sensor, such as a thermometer or thermocouple, from the process fluid or gas. This allows the temperature sensor to be removed and replaced without having to shut down the process or drain the system. The primary function of a thermowell is to protect temperature sensors from the corrosive, abrasive, or otherwise harmful process fluids or gases that they are exposed to. This ensures that the sensor remains accurate and reliable over time.