Thermowells are closed tubes design to insert directly in the process and used to protect the temperature sensing element from pressure or aggressive media. This principle allows the maintenance and replacement of a temperature sensing element without shutting down the process. Due to the fact the thermowells are inserted directly into the process there are different types of designs to fit each process. Variations in process connections from hygienic designs to bar stock forged solid machined thermowells for high pressure conditions. To make sure the thermowell does not break in process the products needs to be engineered specifically to the running process conditions with the flow, temperature and viscosity are main input of the calculations. There are several calculation methods available. At Badotherm the ASME PTC 19.3 is followed to engineer the thermowells. The rules described in the ASME PTC 19.3 standard are converted in the in-house developed software Thermocal.
The thermowell will be exposed to various factors and conditions influencing the performance and lifetime. There are three different sets of variable in the design stage that influence the performance and lifetime. On he process side the variables such as media velocity, media viscosity, density and process temperature. On the piping side the diameter of the main pipe and the size of the nozzle in which the thermowell is mounted. As these two sets are pretty fixed and difficult to change these sets are seen as fixed variables and used as input. The variable set of the thermowell that include thermowell material, diameter of root and tip as well as the bore and radius can be influenced on order to reduce the frequency of the thermowell in process conditions. The outcome of engineering is a thermowell sizing that fits the process conditions and is within the pressure specification of the material and the standards such as the ASME PTC 19.3 and the ASME B31.3.