Issuing body
ASME
Latest edition
2016 Edition
Region
USA, Global
Equipment items
3
Scope
Strength and stability calculation of thermowells (vortex shedding, frequency, stress).
Key requirements (8)
- Thermowells — design and stress analysis (also as ASME PTC 19.3 TW).
- Velocity-induced vibration: avoid resonance (natural frequency ≥ 80% of vortex shedding frequency × scale factor).
- Strouhal number: 0.22 typical for cylinder in cross flow.
- Stress check: bending + drag + axial — combined < material allowable.
- Wake frequency formula (Strouhal): fw = St·V/D where D = thermowell tip diameter.
- Frequency ratio limit: scaling factor 0.4 (lock-in zone) to 0.8 (resonance).
- Mounting: threaded, flanged, socket-weld, welded.
- Insertion length (U): immersion depth into pipe; balance of response time vs vibration.