Calculate the API RP 14E erosional-velocity screening limit, compare actual pipe velocity, and estimate maximum flow in field or SI units.
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Erosional Velocity Formula
- Ve = erosional velocity screening value, ft/s
- C = empirical constant (field units)
- rhom = mixture density at flowing conditions, lb/ft³
For the pipe check, actual velocity is V = Q / A, with A = pi * D² / 4, using the line-condition volumetric flow rate. For multiphase, the no-slip mixture density is the volumetric-flow-weighted average at line conditions:
Gas density at line conditions uses rho_G = 2.699 * SG_g * P / (Z * T) with P in psia and T in °R. The metric form of the API 14E equation uses C ≈ 1.22 × the field value when ρ is in kg/m³ and Ve is in m/s.
Reference Values
Historical C values associated with API RP 14E and descriptive utilization ranges are shown below. These are not a universal safe-design rule; the governing C factor and method require engineering selection.
| Service | C (field) | Notes |
|---|---|---|
| Continuous, solids-free, non-corrosive | 100 | Historical screening value; verify applicability |
| Intermittent, solids-free | 125 | Short-duration flow |
| Solids-free; corrosion-free or controlled service | 150–200 | Requires engineering assessment and monitoring |
| Solids present | Not established by this screen | Use an applicable sand-specific erosion model |
| Utilization | Interpretation |
|---|---|
| < 90% | More than 10% below selected screen; does not establish safety |
| 90–100% | Within 10% below selected screen; does not establish safety |
| > 100% | Above selected screen; engineering review required |
Worked Example
Gas-condensate line, C = 100, mixture density 12 lb/ft³, nominal 4-inch pipe with 4.026-inch inside diameter, flowing 8 ft³/s.
- Screening velocity: Ve = 100 / √12 = 28.9 ft/s
- Pipe area: A = π × (4.026/12)² / 4 = 0.0884 ft²
- Actual velocity: V = 8 / 0.0884 = 90.5 ft/s
- Utilization: 90.5 / 28.9 = 313% — well above the selected screen; review line sizing and operating conditions.
FAQ
Is API 14E conservative? It is an empirical screen with limited applicability. A below-screen result does not establish safe operation. Solids, corrosion, flow regime and geometry may require a more appropriate erosion model.
Which density do I use for multiphase? The no-slip mixture density at flowing pressure and temperature, not standard conditions.
Why does the metric C differ? The 1.22 factor reconciles units when ρ is in kg/m³ and Ve in m/s. The underlying limit is the same.
Does the limit account for elbows or fittings? No. Local velocities at bends and chokes can exceed the line value; assess those points with an applicable flow and erosion model.
