What is erosional velocity in pipeline design?

Erosional velocity is the maximum allowable fluid velocity in a pipe above which erosion-corrosion damage is expected. Per API RP 14E, it is calculated as Ve = C / sqrt(rho_mix), where C is an empirical constant (typically 100-150) and rho_mix is the fluid mixture density in lb/ft3. Operating above this velocity accelerates material loss from pipe walls.

What C factor should I use for API RP 14E?

The C factor depends on service conditions: C = 100 for continuous service with solids present, C = 125 for intermittent service or clean fluids, and C = 150-200 for corrosion-resistant alloys (CRA) or solid-free service. Higher C values allow higher velocities. For sand-producing wells, C = 100 is conservative.

How does DNV-RP-O501 differ from API RP 14E for erosion?

DNV-RP-O501 provides a more detailed erosion model that accounts for sand particle size, sand rate, pipe geometry, material hardness, and impact angle. It calculates actual metal loss rate (mm/yr) rather than just a velocity limit. This allows engineers to predict pipe wall thinning and remaining service life, making it more suitable for sand management programs.

What is an acceptable velocity ratio for erosion?

The velocity ratio (actual velocity / erosional velocity) should be below 1.0 to prevent erosion damage. Best practice is to keep the ratio below 0.7 for long-term continuous service. Ratios between 0.7 and 1.0 require monitoring, and ratios above 1.0 indicate erosion risk requiring design changes such as larger pipe, lower flow rate, or erosion-resistant materials.

Sand/Erosion Velocity Calculator | API RP 14E & DNV-RP-O501

Fluid Type & Flow Conditions

Fluid Type

Gas Flow Rate

MMSCFD

Liquid Flow Rate

BPD

Operating Conditions

Operating Pressure

psig

Operating Temperature

°F

Pipe Diameter (NPS)

inches

Gas Properties

Gas Specific Gravity (Air = 1.0)

Gas Z-Factor (Compressibility)

Use Z-Factor Calculator if unknown

Gas Molecular Weight

lb/lbmol

MW = SG x 28.97 (auto-updated from SG)

Liquid Properties

Liquid Density

lb/ft³

Water: 62.4, Condensate: 40-50, Crude: 50-60 lb/ft³

Sand Parameters

Sand Production Rate

PTB = pounds per thousand barrels of liquid

Sand Particle Size

microns

Fine: 50-150, Medium: 150-300, Coarse: 300-600

Corrosion Allowance

Material & API 14E C Factor

Pipe Material

C Factor (API RP 14E)

100 = continuous w/ solids, 125 = intermittent, 150 = CRA/clean

Design Life

years

Understanding Sand/Erosion Velocity

API RP 14E Method
The erosional velocity equation Ve = C / sqrt(rho) sets a maximum velocity limit. Simple and widely used, but does not account for sand rate, particle size, or material. C factor selection is critical.

DNV-RP-O501 Method
A mechanistic erosion model using particle impact theory. Accounts for sand rate, particle size, material hardness, impact angle, and pipe geometry. Predicts actual wall loss rate in mm/yr.

Design Guidance
Velocity ratio < 0.7: Safe for continuous operation. Ratio 0.7-1.0: Monitor with inspection. Ratio > 1.0: Redesign required (larger pipe, sand screen, or CRA material).

📚 Learn the Theory

Understand erosion mechanisms, API 14E background, DNV erosion models, and sand management strategies

Read Engineering Guide →

Formulas

V_e = C / √ρ_mix

V_e = Erosional velocity (ft/s)

C = Empirical constant (100-150)

ρ_mix = Mixture density (lb/ft³)

E = K · vⁿ · (d_p/d_ref)^0.2

E = DNV erosion rate

K = Material constant

n = Velocity exponent

d_p = Particle diameter

Standards & References

API RP 14E (2007)
Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems
DNV-RP-O501 (2021)
Managing Sand Production and Erosion
NORSOK P-002 (2014)
Process System Design
GPSA Engineering Data Book
Section 17: Fluid Flow and Piping

Engineering Notes

C = 100: Conservative for continuous service with sand production
C = 125: Intermittent service or minimal solids
C = 150-200: CRA materials or solid-free service
Sand screens: Consider when sand rate exceeds allowable
Bends & fittings: Erosion rates 2-10x higher at changes in direction
Multiphase: Slug flow increases peak erosion rates significantly

Quick Reference — C Factor Selection

Carbon steel, continuous, with sand → C = 100
Carbon steel, intermittent, clean → C = 125
13Cr or CRA, with sand → C = 125-150
CRA, clean service → C = 150-200
Inhibited carbon steel → C = 150

Sand/Erosion Velocity Calculator

Fluid Type & Flow Conditions

Operating Conditions

Gas Properties

Liquid Properties

Sand Parameters

Material & API 14E C Factor

Understanding Sand/Erosion Velocity

📚 Learn the Theory

Results

Formulas

Standards & References

Engineering Notes

Quick Reference — C Factor Selection

Related Calculators

Gas Line Sizing

Pipeline Hydraulics

Gas Velocity

Hoop Stress