What is a thermowell and what characteristics does it have?


When temperature measurement and control instruments are used, they are not installed directly in the industrial process. The sensors are installed in Thermowells for temperature sensors, which isolates them from the stresses of the process.

Flow, high pressures and corrosive chemical effects can damage our probes, which is why they are protected with metal tubes or process pipes.

In today's post we are going to explain to you what a thermowell is, what its characteristics are and, briefly, what criteria to use to choose the model that best suits our needs.

 Thermowell: what is it

As we have already introduced, a thermowell is a tool used to protect temperature sensors (such as thermocouples or PT100 sensors) against corrosion, elevated pressure and material velocity.

Depending on the inclemencies to which the temperature sensor The thermowell has different characteristics. This is to ensure the durability of the different sensor types, allowing its replacement without the need to empty the system and reducing the chances of contamination.

In conclusion, thermowells protect the sensor against the harmful effects of the environment to be processed, to avoid measurement errors. Thus, all data can be documented with recording devices (such as a pt100 temperature sensor).

 Characteristics of a thermowell

The types of thermowells They are classified according to the design of the thermocouple or sensor. They can be straight, stepped or tapered, depending on the diameter and size of the stem.

  • straight thermowell It has the same diameter throughout its length and protects against corrosion and erosion.

  • The stepped thermowells, on the other hand, goes from a ¾ diameter at the top to ½ the diameter near the tip. This increases resistance to slower speeds and temperature response for sensing devices.

  • He conical thermowell, on the other hand, has a diameter that gradually decreases along its length. With this design, resistance and response times to temperature changes increase.

The use of straight or conical thermowells is therefore recommended, using the latter in conditions with greater mechanical loading, that is, when they are subjected to high speeds, vibrations or pressure.

In addition to the body design, a thermowell can be threaded, the most common in the industry; or have flanged connections, which allows the measuring instrument to be isolated.

  • The threaded thermowells They screw onto the proveso pipe or tank, so they can be easily installed and removed when needed.

  • The flanged thermowells, on the other hand, is welded, which prevents its removal once it is installed in the process, unless it is introduced into a slab without welding.

 Thermowell selection criteria

For the thermowell to fulfill its functionality of extracting calibration data from the industrial process more quickly and easily, we must take into account the requirements of the installation and select the appropriate one.

For this, the characteristics of the temperature gauge with those of our thermowell:

Connection types

The type of connection refers to the nature of the thermowell: is it threaded or welded?

When selecting our model, we must take into account the industry in which we are going to be operating. For example, in the pharmaceutical and food industries, the weldable wires cannot be brought into contact with the product, so it will be relevant to perform a weld.

diameter size

There are Thermowells for temperature sensors designed to measure the dimensions of the digital thermometer that will be used to control the industrial process. However, there are also models with a standard diameter, which allows greater flexibility.

These adapt, thanks to their standard diameter, to the most used devices, with the following measurements:

  • 0.26 inches in diameter.

  • 0.385 inches in diameter.

 Type of material

The next thing we are going to evaluate is the material with which it is made as it will provide longevity to your product, making it resistant to chemicals, temperatures and flow rate.

Chemical corrosion can be increased at low concentrations and high temperatures. In addition, we must add the possible erosion that the particles suspended in the liquid would produce.

Therefore, we highlight the following materials as the most used to produce thermowells:

  • carbon steels

  • Titanium

  • Molybdenum/Chromium Steels

  • Stainless steel

  • Nickel based super alloys (Incoloy®, Inconel ®, Monel®, Hastelloy®, Haynes® Alloy)

Carbon steel has little resistance to corrosive substances and low temperature and pressure applications are limited. Stainless steel, on the other hand, is more resistant to heat and corrosion, which makes it even more interesting.

The rest of the alloys are more expensive than stainless steel although they are much more resistant.

 Find the thermowell you need for your project

Now that we know what Thermowells for temperature sensors are and what we must take into account to choose the one that best suits our needs, we must find the most suitable point of sale.

In SRC.SL We are specialists in temperature measurement equipment. With almost 40 years of experience in the control, regulation and measurement of industrial parameters, we can offer our experience to improve your company.

get in contact with us to resolve any possible doubts that may arise, we will be happy to advise you and satisfy your needs.