API RP 14E Erosional Velocity Calculator (Line Sizing) — Sample Report

1 · Design inputs

A clean, solids-free water line: NPS 6 schedule 40 (6.065 in bore) carrying 800 gpm at 62.4 lb/ft³. The project applies an erosional constant of C = 100 for this continuous, solids-free service.

2 · Method

Two velocities are computed and compared. The erosional velocity limit, API RP 14E ¶2.5:

V_e = C / √ρ_m

and the actual line velocity from volumetric flow and inside diameter, in the standard gpm/inch form:

V = 0.4085 · Q / d²

ratio = V / V_e → PASS when ratio ≤ 1

Units are fixed: ρ_m is the flowing mixture density in lb/ft³, Q the volumetric flow at flowing conditions in gpm, d the inside diameter in inches, and both velocities come out in ft/s. The 0.4085 constant is a pure unit identity converting gpm and inches of bore to ft/s — it is not a code value and carries no empirical content, unlike C, which carries all of it.

The word mixture in the density term is where most misuse of this equation begins. For a two-phase line, ρ_m is the density of the flowing gas–liquid mixture at the pressure and temperature at the point being checked, not the liquid density and not the gas density — and it changes along the line as pressure drops. A line that passes at the separator outlet can fail at the low-pressure end, because the mixture density there is lower, the limit is therefore higher, but the actual velocity has risen faster still as the gas expands. Check the demanding end, which for gas-bearing service is normally the outlet.

Entering Q = 0 puts the card in limit-only mode: it returns V_e and suppresses the operating check and the verdict, which is what you want when you are establishing a velocity ceiling before a line size exists. With a flow entered, a second warning fires when the actual velocity falls below roughly 3 ft/s — the low-velocity failure mode of liquid holdup and slugging in two-phase lines, which oversizing produces and which the erosional limit alone will never catch.

3 · Calculation

1. Density term: √ρ_m = √62.4 = 7.89937.
2. Erosional limit: V_e = C / √ρ_m = 100 / 7.89937 = 12.659 ft/s.
3. Bore squared: d² = 6.065² = 36.784225 in².
4. Actual velocity: V = 0.4085 · Q / d² = 0.4085 · 800 / 36.784225 = 326.8 / 36.784225 = 8.884 ft/s.
5. Ratio: 8.884 / 12.659 = 0.7018 — the line runs at about 70% of the erosional ceiling.
6. Verdict: PASS, with 3.775 ft/s of velocity headroom before the limit is reached.

4 · Results PASS

5 · Verification statement

The result values above are locked as fixture erosional-velocity.json, case “C=100 water, NPS 6 sch 40, 800 gpm — passes”, tolerance 0.001, in the calc-core continuous verification gate (see https://pipingtoolset.com/trust/validation.html). Allowable-stress and factor data are user-supplied inputs; citations: API RP 14E, Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems — ¶2.5, erosional velocity Ve = C/√ρm, including the C values by service; those values are user-supplied and not reproduced here. · DNV-RP-O501, Managing Sand Production and Erosion — particle-based erosion modelling for solids-bearing service, where the RP 14E screen does not apply. · ASME B31.3, Process Piping — ¶300.2 and ¶302, where erosion allowances enter as a mechanical allowance c in the wall thickness calculation rather than as a velocity limit. · Constants: 0.4085 converts gpm and inches of bore to ft/s and is a unit identity, not a code value.