Thermowells and Protection Tubes

When Thermocouples or RTD's or any other sensors are exposed to harsh atmospheres they are damaged. This damaged due to mechanical or chemical contamination can be avoided by the use of  protection tubes or thermowells. Closed at one end, normally the harsh environment or process end, and opened at the termination end, various methods are used to assemble the tube, sensor, and connection head with termination into the process.

Depending on the chemical or mechanical environment to which the Sensor will be subjected the material for the protection tube is selected. Thermowells are normally used with RTD's, Thermocouples, or Bimetal thermometers where temperatures are to be measured in high pressure (over 150 PSI) or environments that are chemically and mechanically hostile. These thermowells are machined from solid bar stock with high precision and accuracy and have material tracebility.

To design an efficient and safe thermowell pressure, maximum temperature and velocity of the system need to be known. The various designs available are shown on the adjoining page however straight wells are used for low pressures and temperatures, Stepped wells are used for a quick response time and medium strength. 'Tapered thermowells are the most efficient and highly recommended design as they have high pressure ratings, quick thermal response and provide greater strength. These thermowells are more resistant to vibration than straight wells and also work well in high velocity applications as the taper allows fluids to flow without restrictions.

To size a thermowell please indicate the following

Overall length, Process connection, Instrument or Sensor Connection, Type of Material, Maximum Temperature, Maximum Velocity/Pressure.