Thermowells by WIKA
What is the difference between a standard pressure gauge and a safety pattern version?
A safety version (code S3 per EN 837) has an additional solid baffle wall welded between the dial and the measuring system. In addition, the case has a back wall that can blow out completely. The window is typically made of laminated safety glass. ...
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How do thermowells work?
The heat-resistant pipe, usually made from stainless steel or ceramic, is immersed in the medium of which the temperature is to be measured. The temperature probe positioned in the thermowell measures the temperature of the medium.
What are thermowells needed for?
Thermowells or protection tubes are an important component in temperature measurement. They isolate the process from its surrounding and thus protect operating personnel and the environment. Thus, exposure of the temperature sensor or temperature probe to process pressures and flow rates, as well as aggressive media, is avoided. Furthermore, using a thermowell allows the removal of the thermometer during the running process. A replacement, repair or verification or calibration of the measuring instrument for temperature measurement does therefore not impede the process.
Which variants of thermowells are there?
Due to the different requirements of the respective measuring locations, there are a large number of different variants, e.g. depending on thermowell design or material. In manufacturing, a distinction is made between protection tubes and thermowells. Protection tubes are constructed from a tube that is closed at the pointed end by a welded solid tip.
Another distinguishing feature of thermowells is the process connection.
Why is a non-destructive test/evaluation recommended for thermowells?
In order to ensure the highest level of safety for our customers, WIKA carries out a series of different material tests following the production of a thermowell. With the help of these non-destructive tests (NDT), possible material defects can be detected.
Depending on the design and designated application of the thermowell, different methods can be used:
- Hydrostatic pressure test: Pressure and stability test of the thermowell under operating pressure. The thermowell is loaded with the defined pressure for a specified period of time.
- Dye penetrant test: Used for welding points. With it, typical welding defects in thermowells such as cracks, porous spots, overlaps and laminations can be excluded.
- Positive material identification (PMI test): Serves as proof of the alloying constituents in the material.
- Helium leak test: For testing the leak tightness of the thermowell.
What is the thermowell strength calculation used for?
With the strength calculation, the strength of the thermowell is proven mathematically with respect to the static and dynamic load, taking into account the application temperature and pressure. If the permissible load limit is exceeded, WIKA issues suggestions regarding design modifications.
You can find detailed information in our technical information “Strength calculation for thermowells”.