Thermowell calculation to ASME PTC 19.3 TW-2016
A thermowell standing in a steam line is excited by the flow. If the vortices are shed in time with its natural frequency, it resonates — and breaks. The part that breaks off travels on through the plant with the medium.
ASME PTC 19.3 TW-2016 is the procedure that rules this out. We calculate it for our thermowells and supply the verification as a report.
When a verification is needed
- steam, gas or liquid at high flow velocity — as a guide, from around 10 m/s in liquids and 40 m/s in gases
- long installation lengths, with thin tubes especially
- plants in which a thermowell breaking off causes consequential damage
- where the operator or the plant builder asks for it — increasingly standard in process engineering
Behind the thermowell vortices are shed alternately and excite it transverse to the flow. If the shedding frequency meets the natural frequency, it builds up.
What is checked
| Criterion | What lies behind it |
|---|---|
| Vortex shedding and natural frequency | The excitation frequency from the flow has to keep a sufficient margin from the natural frequency of the thermowell. This is the criterion on which most designs fail. |
| Static stress | Bending stress from the flow pressure against the permissible stress of the material at operating temperature. |
| Dynamic stress | Alternating stress from the vibration, with a safety factor against the fatigue strength. |
| Permissible pressure | Internal pressure load on the tube and the tip. |
What we need for it
- medium, operating temperature and operating pressure
- flow velocity or volume flow together with the pipe inside diameter
- density and viscosity, if not water, steam or air
- installation length, preferred form, material
- process connection and the nominal size of the line
That is all it takes. If something is missing we calculate with the unfavourable value and say so in the report.
What you get
A report in the GHI test layout with input data, intermediate values and the result for each criterion, passed or not. If a design fails, we propose the change straight away — usually a larger root, a shorter installation length or a change from form 2 to form 4 is enough.
Limits of the procedure
ASME PTC 19.3 TW applies to straight and tapered thermowells from solid material as well as to drilled tubes with a defined root. Thermowells with a weld seam on the shank, ceramic tubes and supported versions are not covered — there we work with the limit values from DIN 43772 and the experience from comparable plants.
Send us your process data
We will calculate your thermowell to ASME PTC 19.3 TW-2016 and send you the verification — also for thermowells that are already installed.
When a verification is needed
What is checked
What we need
What you get
Limits of the procedure
Question about the design?
Tell us the medium, temperature and installation situation — you will have a proposal within one working day.