erosive-wear

name	erosive-wear
description	Erosive wear — solid particle erosion, slurry erosion, liquid impingement, Finnie/Bitter models, erosion angle dependence (ductile vs. brittle), material selection, ASTM G76/G73, protection strategies.
metadata	{"priority":7,"promptSignals":{"phrases":["erosive wear","erosion wear","solid particle erosion","slurry erosion","liquid impingement","erosion resistant","ASTM G76"],"minScore":3}}

Erosive Wear — Complete Skill

Erosion Mechanisms

Solid Particle Erosion

Solid particles carried by gas/liquid strike surface at velocity → material removal Two primary mechanisms:

Cutting/plowing (ductile materials): particle slides along surface at low angles → microchips; like micromachining Deformation/brittle fracture (brittle materials): particle impacts form cracks at Hertzian contact → lateral cracks → spalling

Erosion Rate — General Form

Volumetric wear rate: W = K × C_p × V^n × f(α) [cm³/g erodent; or mg/g]

C_p = erodent concentration [g/cm³ gas]; V = impact velocity [m/s] n = velocity exponent = 2.3–3.0 (ductile metals); 2.5–3.5 (ceramics, brittle) f(α) = angle function K = material/erodent constant

Mass erosion rate: ṁ_erosion = W × ṁ_erodent [mg/s or g/s]

Impact Angle Dependence — Critical Distinction

Ductile metals (Al, Cu, mild steel): Maximum erosion at α = 15–30° (oblique impact; cutting mechanism dominant) Minimum at α = 90° (normal impact; energy absorbed by deformation, not cutting) f(α) ≈ sin(2α) - k sin²(α) [Finnie model; k = 1/3 for hard particles]

Brittle materials (ceramics, glass, WC-Co): Maximum erosion at α = 90° (normal impact; maximum Hertz pressure → most cracking) Minimum at oblique; f(α) ≈ sin^n(α) [n ≈ 2]

Elastomers: Low erosion at all angles; resilient deformation absorbs energy; cut resistance good at low angles

Finnie Model (Ductile Erosion)

Cutting mode (α ≤ α; α ≈ arctan(ε/3)):** W = (m V²)/(2p) × (cos²(α)/3 - sin(2α)/3) ÷ ... [simplified Finnie]

Deformation mode (α > α):* W = (m V²)/(2p) × (sin²(α)) [for larger angles where plowing fails to cut]

p = plastic flow stress (hardness); m = particle mass Key insight: minimizing cutting wear → maximize surface hardness; brittle erosion → toughness matters

Bitter Model (Energy-Based)

Separates elastic (deformation) and plastic (cutting) contributions: W_total = W_deformation + W_cutting Each mode has velocity exponents: W_deformation ∝ V^2 × (cosα)^2 × K_el W_cutting ∝ V^2 × sinα × (cosα) × K_cut

Extended: allows prediction over full angle range; more accurate than Finnie

Material Behavior vs. Erosion

Material	Max erosion angle	Mechanism	Relative erosion rate
Mild steel (as-rolled)	20–30°	Cutting	Reference = 1.0
Hardened steel (HRC 60)	20–30°	Cutting reduced	0.3–0.5
Rubber	20–30°	Cut resistance	0.1–0.3
WC-Co (12%Co)	80–90°	Brittle	Low at oblique; high at 90°
Al₂O₃ ceramic	90°	Brittle fracture	0.05–0.2 at oblique
UHMWPE	20–30°	Viscoelastic	0.05–0.15

Slurry Erosion

Particles suspended in liquid; lower velocity than gas erosion (liquid drag reduces impact V) Slurry erosion rate: W_slurry = K_s × C × V^n × f(α) × d_p^m

d_p = particle diameter; m ≈ 0.3–1.0 Higher particle size → more inertia → higher erosion despite drag

Miller number / SAR (Slurry Abrasion Response): ASTM G75; measures relative material erosion in specific slurry SAR < 10: excellent; 10–50: good; > 100: poor

Pipe bend erosion: most severe at outer wall; α ≈ 20–40° for slurry bends Pump impeller erosion: suction side leading edge; inlet angle relative to flow direction

Liquid Impingement Erosion

High-velocity liquid droplets (steam + water; jet pump nozzles; rain impingement on aircraft) Mechanism: water hammer pressure → compressive shock on impact → tensile reflected wave → fatigue pitting Water hammer pressure (first impact): P_hammer = ρ_liquid × c_liquid × V_droplet = 1000 × 1500 × V [Pa; V in m/s for water]

Erosion onset velocity: V_threshold ≈ 30–50 m/s for steel in water Below → no erosion; above → incubation period then mass loss

Materials resistant: high-strength stainless (17-4PH); Stellite alloys; PVC (compliant); rubber

Cavitation Erosion (Related)

Collapse of bubbles near surface → high-velocity micro-jets → pitting Intensity: related to collapse pressure P_c = P_v × (R_max/R_min)^3 Most damaging: in pump impellers, throttle valves, marine propellers ASTM G32: vibratory cavitation erosion test; compares MDR (mean depth of erosion rate)

Erosion Testing Standards

ASTM G76: solid particle erosion test; air jet with particles; measure mass loss vs. impingement angle ASTM G73: liquid impingement erosion test; rotating arm with specimens ASTM G75: miller number for slurry abrasivity ASTM G32: vibratory cavitation test ISO 5167 (nozzle): relates to velocity calibration for erosion

Protection Strategies

Material Upgrade

• Hardened steel (HRC 45–65): reduces ductile erosion 50–70%
• White iron (Ni-Hard, ASTM A532): for sand-slurry pumps; very high hardness
• Stellite alloys (Co-Cr-W-C): hard + tough; excellent for steam erosion
• WC-Co thermal spray: excellent for oblique-impact gas erosion

Coatings

• HVOF WC-Co coating: 0.2–2 mm; wear resistance; high bond strength (>70 MPa)
• Electroless Ni-P + PTFE: reduces adhesion; good for mild slurry
• Rubber linings: excellent for sand-slurry at < 50°C; very low erosion at acute angles
• Ceramic tiles (Al₂O₃): slurry chutes; pipe liners; brittle so use at near-normal angles only

Geometry Changes

• Avoid sharp bends: use long-radius elbows (R/D > 10); ceramic-lined bends
• Reduce velocity: larger diameter pipe; lower pump speed
• Use swirl-flow: redirect particle trajectories away from wall
• Sacrificial wear pads: replaceable wear plates at highest erosion zones

Process Controls

• Reduce particle size: fine grinding before slurry transport
• Reduce solids concentration: dilute slurry
• Add viscosity modifiers: reduces particle impact velocity

Output

Provide: erosion mechanism (cutting/brittle fracture/slurry), maximum erosion angle α* [°], relative erosion rate normalized to reference steel, velocity exponent n, material recommendation (with Vickers hardness and expected erosion reduction %), coating type (if applicable), ASTM test method for material qualification, and slurry pipeline geometry recommendation (R/D ratio of bends, liner material).