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Erosional Velocity Calculator (API RP 14E)

API RP 14E gives a simple erosional velocity limit for oil and gas piping: Ve = C / sqrt(rho). This calculator converts the units for you, compares it with your actual velocity and tells you the smallest bore that stays under the limit.

Your numbers

Total flow rate (actual conditions)

m3/h

Pipe inside diameter

Mixture density at flowing conditions

kg/m3

Use the no-slip mixture density for two-phase flow.

Empirical constant C

Your results

Erosional velocity limit

11.1361

In m/s.

Actual velocity

3.4432

In m/s.

Density in lb/ft3

7.4914

Erosional velocity in ft/s

36.5359

Ve = C / sqrt(rho), with rho in lb/ft3.

Velocity as percent of limit

30.9%

Minimum inside diameter to stay at the limit

112.711

In mm.

API RP 14E is an empirical guideline. Many operators use lower limits in corrosive or sand-laden service. Confirm design limits with your project specification.

Save results:

Actual velocity vs erosional limit (m/s) by flow rate

Sweeps Total flow rate (actual conditions) from 50 to 1000, holding your other inputs fixed.

Link line lists to ERP item data

Optional review of how to connect process line data to pipe and fitting records.

Optional. The tool and every export work without this. No spam.

How to use it

Enter the flow at flowing (actual) conditions, the pipe inside diameter and the mixture density at flowing conditions. Choose the C constant that your project specification allows. The limit uses the API form in US units internally, then converts to metres per second. The ratio of actual to limit velocity shows how much headroom you have. If it is above 100 percent, either increase the bore or reduce the flow. The minimum diameter output gives the smallest inside diameter at which the actual velocity equals the limit.

Formula and background

The recommended practice gives Ve = C / sqrt(rho_m), where Ve is in feet per second and rho_m is the gas-liquid mixture density at flowing conditions in pounds per cubic foot. C is 100 for continuous service and up to 125 where solids are absent and corrosion is controlled, with higher values for intermittent service. The method is conservative and was written long before modern sand and corrosion monitoring, so some operators apply their own more detailed erosion models.

Lower density gives a higher limit, so gas lines tolerate higher speed.
Sand, corrosion products and bends lower the true safe velocity.
Check also noise, vibration and pressure drop criteria.

Worked example

A line carrying 400 cubic metres per hour of a mixture at 120 kg per cubic metre has a density of 7.49 lb per cubic foot. With C of 100 the limit is 100 / sqrt(7.49) = 36.5 ft/s, or 11.1 m/s. In an NPS 8 schedule 40 line the actual velocity is 3.44 m/s, about 31 percent of the limit. The line is comfortably under the erosional limit.

Common mistakes

The usual error is using standard-condition flow rather than the actual flowing volume, which understates velocity. Another is using liquid density when gas is present: the mixture density is what counts. Remember that the limit is an upper guide for continuous service, and that vibration and noise criteria often govern in gas lines first. In the ERP, keep the line list with flow and bore data linked to the pipe item so spec breaks are visible.

Frequently Asked Questions

What is C in the erosional velocity equation?

C is an empirical constant. API RP 14E suggests 100 for continuous service, and notes that values up to 125 may be used for solids-free, non-corrosive fluids. Higher values apply only where adequate studies exist.

Which density do I use?

Use the mixture density at flowing pressure and temperature. For two-phase lines, calculate the no-slip density from the gas and liquid volumetric fractions. For single-phase liquid lines, use the liquid density.

Is the limit a safe velocity?

It is a screening guideline, not a guarantee. Sand, abrasive solids, corrosion and flow disturbances can erode piping below the limit, so many operators apply lower values or use more advanced erosion modelling.

Why show the minimum diameter?

It gives the smallest inside bore for which the actual velocity equals the limit at your flow. Choose the next standard pipe size with an inside diameter above that value and allow margin.

If your line lists and pipe specs sit in spreadsheets, we can help you connect them to ERP item and BOM data so spec changes stay visible to purchasing.

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