Category
Instrumentation & Control
Subcategory
Flow Meter
Applicable standards
4
Issuing bodies
3
Description
Differential pressure flow element — orifice, nozzle or Venturi per ISO 5167.
Applicable Standards (4)
ASME — 2 standards
ASME MFC-3M
Measurement of Fluid Flow in Pipes Using Orifice, Nozzle, and Venturi
DP flow element measurement — US counterpart of ISO 5167.
ASME PTC 19.3 TW
Thermowells — Performance Test Codes
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.
ISO — 1 standard
ISO 5167 (series)
Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full
Orifice plates, nozzles, Venturi tubes, cone meters, wedge meters — flow measurement using DP.
Key requirements (8)
- Differential pressure flow measurement: orifice, nozzle, Venturi.
- Orifice: square-edged; β ratio (d/D): 0.10–0.75 typical; thickness ≤ 0.05·D.
- Pressure tap configurations: corner, D and D/2, flange.
- Discharge coefficient C: Reader-Harris/Gallagher equation for orifice.
- Expansibility ε ≤ 1.0 for compressible flow correction.
- Uncertainty: ~0.5–1.0% of rate for properly installed orifice.
- Upstream straight length: 10–80×D depending on β and disturbance type.
- Reynolds number range: typically Re_D > 5000 for orifice validity.
AGA — 1 standard
AGA Report No. 3 / API MPMS Ch. 14.3
Orifice Metering of Natural Gas and Other Related Hydrocarbon Fluids
Custody transfer orifice metering of natural gas (US/global default).
Key requirements (8)
- Custody transfer orifice metering of natural gas (also as API MPMS Ch. 14.3).
- Concentric square-edged orifice plate per ANSI 2530.
- Flange or pipe (D, D/2) tap configurations.
- Mass/volume flow per equation Q = N·Cd·E·Y·d²·√(ρ·ΔP).
- Beta ratio range: 0.1 ≤ β ≤ 0.75.
- Plate inspection: bore diameter ±0.05%, edge sharpness < 0.0004·d radius.
- AGA-8 used for gas density (compressibility).
- Uncertainty: 0.4–1.0 % when calibrated properly.