Choosing your Thermowell

In some cases, not using a thermowell can cause irreversible damage to your temperature sensor. In this article we will explain what is a thermowell, why you would need one, and what process you should follow when selecting a well for your project.thermowell
Thermowells are tubular fittings used to protect temperature sensors in industrial processes. They consist of a tube closed at one end and mounted in the process stream. A temperature sensor such as a thermometer, thermocouple or RTD is inserted in the open end of the tube. The process fluid transfers heat to the thermowell wall, which in turn transfers heat to the sensor.


High velocity, or high pressure can cause a thermometer to bend or warp & constant exposure to certain materials may cause the device to corrode or erode. A thermowell is designed to protect your temperature device from these costly occurrences.
A thermowell also ensures the temperature device never touches the materials being measured, protecting the material from contamination. This is vital for many applications such as the brewer, who needs to monitor temperature throughout the fermenting process without contamination to the product.
This also comes with the added benefit of allowing you to service or replace your thermometer without draining the vessel or without leakage of your material.
Useful as thermowell’s are they do come with a disadvantage. Due to the added mass present, the sensors response to process temperature changes is delayed. This makes thermowells not suitable to applications that require measurement of quick temperature changes.

How to select a thermowell

A Flanged Thermowell
Flanged Thermowell
  1.  Your material: This is the first step of choosing your thermowell. The most important factor in selecting your material is to determine the corrosive conditions to which the well will be exposed. For detailed information on our most popular materials and their corrosion resistance, read our blog “the hard facts of sheath material”
  2. Connection: There are different methods to connect your thermowell.
    • A threaded connection provides mechanical strength and allows easy removal of the well if required.
    • Welding a well in place provides the best seal.
    • Flanged thermowells consist of a bar stocks well that is welded to a top quality flange. The Flange is then bolted into place providing strength to the well.
  3.  Insertion Length: The length of the well inserted into the piping is the “U” dimension. This indicates the insertion depth into a process vessel or piping system and is measured from under the thread to the tip of the thermowell. The U-length should equal or exceed the sensitive portion of the temperature instrument.
  4. Bore Size: The bore size should accommodate the sheath diameter of your temperature sensors used.
  5. Tapered or Straight Shank: A straight shank thermowell is the same size all along the immersion length of the well and are normally used in standard duty applications. A Tapered shank provides greater stiffness with no change in sensitivity & should be used for heavy duty applications involving high vibration, pressure, temperature or velocity.

Choosing your Thermowell is a difficult process that involves multiple factors. Contact our sales team and they will be happy assist you in finding the perfect thermowell for your project.
D&N Engineering expertly craft thermowells in-house on our CNC lathes from a range of materials and can manufacture to suit a supplied sample or sketch.