How Can Buyers Prevent Erosion-Corrosion in Alloy Tubes?
Erosion-corrosion in alloy tubes is not caused by flow velocity alone.
It develops when mechanical surface damage and electrochemical corrosion interact. Flow, droplets, bubbles, or solid particles may remove protective films or deform the tube surface, while the exposed material reacts with the process fluid. The combined material loss can be greater than the damage produced by either mechanism separately.
This is why a tube can perform well in a static corrosion test but lose wall thickness rapidly near an elbow, valve, reducer, tube inlet, injection point, or other disturbed-flow location.
Preventing erosion-corrosion requires buyers and engineers to define the complete operating envelope: fluid chemistry, temperature, pressure, flow regime, local velocity, solids, gas fraction, particle properties, tube geometry, material condition, surface features, inspection method, and expected operating life. There is no universal safe velocity or single best alloy for every system.
![Erosion-corrosion damage caused by solid particles in flowing water](https://emilypipe.com/wp-content/uploads/2026/07/Hastelloy-C276-Pipe12.png")
Image credit: Schmitz Metallographie GmbH, Wikimedia Commons, CC BY-SA 4.0.
The most useful procurement question is not:
“Which alloy has the highest erosion-corrosion resistance?”
It is:
“Which damage mechanism is expected in this system, where will it be most severe, and what evidence shows that the proposed tube and geometry can control it?”
What Is Erosion-Corrosion?
ASTM G119-09(2021) describes the interaction between wear and corrosion as a synergistic process. Abrasion, impact, rubbing, or other mechanical actions can increase corrosion, while corrosion can weaken the surface and increase mechanical removal.
A simplified way to think about total material loss is:
Total loss = Mechanical loss + Corrosion loss + Synergistic interaction
The synergistic term is important because total loss may be higher than the sum predicted from separate erosion and corrosion tests.
Mechanisms That Should Not Be Confused
| Mechanism | Main Driver | Typical Evidence |
|---|---|---|
| Erosion | Mechanical removal by fluid, droplets, particles, or impact | Directional wear, grooves, thinning, or impact craters |
| Corrosion | Electrochemical or chemical reaction | General wall loss, pits, deposits, or corrosion products |
| Erosion-corrosion | Mechanical damage and corrosion accelerate each other | Rapid localized loss in a chemically active flowing environment |
| Cavitation erosion | Formation and collapse of vapour cavities | Closely spaced pits, roughened surface, or damaged areas downstream of pressure drops |
| Liquid impingement | Repeated droplet or jet impact | Localized impact damage |
| Flow-accelerated corrosion | Flow increases dissolution or transport of a protective film | Smooth wall thinning, often without solid-particle impact |
| Fretting | Repeated small-amplitude contact motion | Wear at supports or tube-to-component contact points |
Correct diagnosis matters because changing the alloy may not solve cavitation, vibration, or an unsuitable valve arrangement.
There Is No Universal Critical Flow Velocity
Many projects ask suppliers to confirm a “maximum allowable velocity.”
A single number is rarely sufficient.
Velocity limits depend on:
- Material and supplied condition
- Fluid density and viscosity
- Tube ID
- Flow regime
- Temperature
- Gas fraction
- Particle concentration
- Particle size and density
- Geometry
- Surface-film stability
- Corrosive species
- Operating time
- Startup and shutdown conditions
A velocity that is acceptable in clean seawater may be unsuitable in a slurry containing quartz particles.
A velocity that causes limited damage in a straight tube may produce severe loss downstream of a control valve.
Technical reviews of simplified erosional-velocity methods have also shown that one empirical velocity equation cannot reliably address solids, corrosive species, geometry, flow regime, and material behaviour at the same time.
Average Velocity Is Not Local Velocity
The velocity calculated from total flow and nominal tube area is an average.
Local velocities may be much higher near:
- Partially open valves
- Orifices
- Reducers
- Misaligned joints
- Injection nozzles
- Tube inlets
- Blocked passages
- Narrowed areas caused by deposits
The RFQ should provide both normal flow and credible maximum or transient flow.
How Flow Changes Material Loss
Flow can affect erosion-corrosion through several mechanisms.
Mass Transfer
Higher flow may increase the transport of reactants to the surface and remove dissolved corrosion products.
Surface-Film Damage
Flowing fluid, droplets, bubbles, or particles may damage a passive or corrosion-product film.
Wall Shear
Wall shear can influence surface films and deposits, but wall shear alone does not describe particle impact or cavitation.
Turbulence
Turbulence can increase mixing, pressure fluctuations, particle dispersion, and local mass transfer.
It should not be assumed that every turbulent flow causes erosion-corrosion. The effect depends on the material, fluid, geometry, particles, and surface condition.
Two-Phase Flow
Gas-liquid or liquid-solid flow can create impact, fluctuating wetting, slugging, droplet acceleration, and unstable local velocities.
Buyers should identify the actual flow regime rather than reporting only a liquid flow rate.
Why Solid Particles Change the Risk
Solid particles can increase material loss through cutting, ploughing, deformation, fatigue, film removal, or impact fracture.
| Particle Variable | Why It Matters |
|---|---|
| Material | Quartz, catalyst, ore, scale, sand, and soft deposits produce different damage |
| Hardness | Hard particles can penetrate or cut a softer surface more readily |
| Size distribution | Large and small particles follow different trajectories |
| Shape | Angular particles may cut more effectively than rounded particles |
| Concentration | Controls the number of potential impacts |
| Density | Influences inertia and separation from the fluid path |
| Settling tendency | Can concentrate particles at the bottom of horizontal tubes |
| Impact velocity | Controls particle kinetic energy |
| Impact angle | Changes cutting, ploughing, deformation, and cracking behaviour |
| Intermittency | Short high-solids events may control damage even when average concentration is low |
Impact Angle Was Commonly Oversimplified
For many ductile metallic materials, particle cutting and ploughing can produce high erosion rates at relatively shallow or intermediate impact angles.
Brittle materials often experience maximum loss closer to normal impact because cracking and fracture become more important.
These are general tendencies—not universal acceptance rules. Particle velocity, shape, target microstructure, corrosion, and the ductile-brittle transition may shift the peak.
This is one reason bends and tees cannot be evaluated only from a 90-degree impact assumption.
Where Are the Common Erosion-Corrosion Hotspots?
Tube Inlets
Entrance effects, flow maldistribution, sharp edges, and debris can cause localized attack near heat-exchanger tube ends.
Bends and Elbows
Particles do not always follow the fluid streamline exactly. Their inertia may drive them toward particular areas of a bend.
The highest-risk location depends on:
- Bend radius
- Particle Stokes behaviour
- Tube orientation
- Flow regime
- Particle size and density
- Upstream geometry
The outside radius is a common concern, but it should not be assumed to be the only hotspot.
Reducers
Concentric and eccentric reducers can create acceleration, flow separation, particle focusing, and downstream turbulence.
Sudden Expansions
A sudden expansion lowers average downstream velocity but can create recirculation, separation, and high local turbulence. Research on sudden-expansion piping has shown that maximum erosion-corrosion may occur a short distance downstream rather than directly at the expansion.
Valves and Orifices
A partially open valve or restriction can produce:
- High-speed jets
- Pressure drop
- Cavitation
- Downstream impingement
- Unstable flow
Changing the tube alloy without correcting the valve operating condition may provide limited benefit.
Branches and Injection Points
A side stream may strike the opposite wall, change local chemistry, introduce solids, or create thermal gradients.
Welds and Misalignment
A properly specified weld does not automatically cause erosion-corrosion.
Risk increases when the joint creates:
- Internal protrusion
- Root concavity
- Misalignment
- Incomplete penetration
- Surface defects
- Local metallurgical changes
- Preferential corrosion in the weld or heat-affected zone
The important issue is the finished flow path—not merely whether a weld exists.
Cavitation Requires Separate Evaluation
Cavitation develops when local pressure falls sufficiently for vapour cavities to form and then collapse in a higher-pressure region.
Possible locations include:
- Pump suction or discharge
- Control valves
- Orifices
- Sudden restrictions
- High-speed jets
- Poorly designed reducers
- Steam or condensate systems
ASTM G134-17(2023) provides a cavitating liquid-jet test for comparing material resistance.
However, ASTM states that the standard test should not be used directly to rank materials when electrochemical corrosion or solid-particle impingement is a major part of the service condition.
This means a cavitation test, slurry test, and corrosion test answer different questions.
Why Hardness Alone Cannot Select the Tube Material
Hardness may influence indentation, cutting, and abrasive wear.
It does not independently establish:
- Corrosion resistance
- Passive-film stability
- Toughness
- Ductility
- Fatigue resistance
- Cavitation resistance
- Weldability
- Formability
- Crack resistance
- Performance after heat treatment
A harder surface can still fail rapidly if the alloy corrodes after the surface film is damaged.
A highly corrosion-resistant alloy can also lose material if particles repeatedly remove the surface faster than it can recover.
Material selection should therefore balance:
- Resistance to the process chemistry
- Resistance to the dominant mechanical damage
- Ability to recover or maintain the protective surface
- Mechanical properties at temperature
- Manufacturing and joining requirements
- Availability in the required tube dimensions
How Should Nickel Alloys and Titanium Be Screened?
The following table provides preliminary questions, not universal rankings.
| Candidate | Possible Reason to Consider | Important Limitation |
|---|---|---|
| Alloy 625 | Corrosion resistance, strength, toughness, and availability in tube forms | Does not automatically resist severe abrasive slurry or cavitation |
| Alloy C-276 | Candidate for severe mixed chemical environments | Corrosion resistance does not prove wear resistance |
| Alloy C-22 | Candidate in selected oxidizing and chloride-containing media | Dynamic performance must match the exact fluid and particles |
| Alloy 825 | Candidate in selected acid and chloride services | Grade condition and specific chemistry must be reviewed |
| Alloy 400 | Candidate in selected marine and reducing environments | Aeration, sulfides, solids, and velocity can alter performance |
| Alloy 600 | Candidate in selected high-temperature or chemical environments | SCC mechanism, chemistry, and flow damage require separate review |
| Titanium Grade 2 | Strong candidate for many clean, oxidizing seawater services | Reducing media, fluorides, heavy solids, cavitation, and hydrogen conditions require review |
| Titanium Grade 7 | Enhanced corrosion resistance in selected severe conditions | Palladium addition does not automatically improve particle erosion resistance |
| Titanium Grade 12 | Candidate where strength and selected corrosion behaviour are useful | Exact service data and product availability remain necessary |
Titanium industry data report strong performance in many flowing seawater systems, but those results should not be applied automatically to acidic slurries, high-solids streams, cavitating jets, or reducing environments.
For broader material screening, buyers may also review the related guide on selecting corrosion-resistant alloy tubes and bars for harsh environments.
Which Laboratory Tests Are Relevant?
No single ASTM test reproduces every erosion-corrosion environment.
| Standard or Method | What It Helps Evaluate | Main Limitation |
|---|---|---|
| ASTM G119-09(2021) | Synergism between wear and corrosion | Requires separate wear, corrosion, and combined measurements |
| ASTM G31-21(2025) | Laboratory immersion corrosion | Does not reproduce most dynamic particle conditions |
| ASTM G76-18 | Gas-entrained solid-particle impingement | Not a liquid-slurry or corrosion test |
| ASTM G73-10(2021) | Repeated liquid-drop or liquid-jet impact | Not intended for slurry washing or solid-particle impingement |
| ASTM G134-17(2023) | Cavitating liquid-jet erosion | Standard conditions do not include every corrosion or solids effect |
| Flow-loop testing | Combined liquid chemistry, flow, particles, and tube geometry | More expensive and still limited by test scale |
| Jet-impingement testing | Local impact and high mass-transfer conditions | May not represent long piping systems |
| Field spool or coupon | Actual process exposure | Requires sufficient time and reliable monitoring |
| CFD with particle tracking | Local velocity, turbulence, pressure, and particle trajectory | Material-loss model requires experimental or field validation |
Test specimens should match the proposed:
- Alloy
- Heat treatment
- Surface
- Weld condition
- Temperature
- Chemistry
- Particle type
- Particle concentration
- Particle size
- Velocity
- Impact angle
A supplier’s generic static corrosion table is not representative erosion-corrosion evidence.
How Should Existing Tube Damage Be Investigated?
A failure investigation should preserve evidence before cleaning or grinding.
Information to Collect
- Exact damage location
- Tube orientation
- Distance from valves, bends, inlets, or branches
- Wall-thickness map
- Internal and external surface morphology
- Deposit composition
- Particle composition and size distribution
- Fluid chemistry
- Operating and upset flow
- Pressure fluctuations
- Temperature history
- Pump and valve operating position
- Weld location
- Material certificate
- Microstructure and hardness where relevant
- Evidence of cavitation or vibration
Damage Patterns Can Provide Clues
| Observation | Possible Mechanism to Investigate |
|---|---|
| Smooth directional wall thinning | Flow-accelerated corrosion or fine-particle erosion |
| Grooves or cutting marks | Particle abrasion or oblique impact |
| Local craters downstream of a jet | Impingement |
| Dense rough pits near a pressure drop | Cavitation |
| Damage concentrated at tube supports | Fretting or vibration |
| Attack only at a weld or HAZ | Weld geometry, metallurgy, or preferential corrosion |
| Outer-radius bend loss | Particle inertia or local flow concentration |
| Bottom-of-line wear | Particle settling or sliding bed |
| Damage under deposits | Under-deposit corrosion rather than pure erosion |
Several mechanisms may operate at the same location.
Monitoring Should Focus on Hotspots and Trends
A single final inspection may not be enough for systems with changing solids or flow.
Possible monitoring methods include:
- Baseline ultrasonic thickness mapping
- Repeat UT at fixed reference points
- Automated corrosion or erosion probes
- Coupon exposure
- Eddy-current testing for suitable heat-exchanger tubes
- Visual inspection
- Borescope examination
- Process solids monitoring
- Flow and pressure trend review
- Particle sampling
- Vibration monitoring
The monitoring interval should reflect:
- Measured loss rate
- Remaining wall
- Failure consequence
- Process variability
- Access
- Inspection uncertainty
Average thickness across a long straight section may miss a small high-loss area downstream of a valve or bend.
What Should Buyers Ask the Supplier?
A technically useful supplier response should distinguish what the tube manufacturer can verify from what requires system engineering.
The Supplier Can Normally Confirm
- Alloy and UNS designation
- Product standard
- Seamless or welded construction
- Supplied condition
- OD, wall, length, and tolerance
- Heat treatment
- Mechanical properties
- Surface condition
- NDT and pressure testing
- MTC and traceability
- Previous production capability for the size
The Supplier Cannot Confirm From the Alloy Name Alone
- Safe system velocity
- Cavitation-free operation
- Acceptable particle concentration
- Exact service life
- Final erosion-corrosion rate
- Suitability of valve or reducer geometry
- Adequacy of system monitoring
Those decisions require complete operating and design data.
What Buyers Should Include in the RFQ
| RFQ Category | Required Information |
|---|---|
| Fluid | Complete chemistry and phase |
| Corrosive species | Acids, chlorides, sulfides, oxygen, CO₂, H₂S, and impurities |
| Temperature | Normal, design, startup, shutdown, and cleaning |
| Pressure | Operating, design, and local pressure drop |
| Flow rate | Minimum, normal, maximum, and transient |
| Tube ID | Needed to calculate average velocity |
| Flow regime | Single-phase, gas-liquid, slurry, slug, or flashing |
| Solids | Type, hardness, density, shape, and composition |
| Particle size | Minimum, average, maximum, and distribution |
| Solids concentration | Weight, volume, or mass flow basis |
| Geometry | Bends, valves, reducers, tees, nozzles, and inlets |
| Cavitation | Known or suspected pressure-collapse conditions |
| Existing damage | Photographs, location, thickness, and failure analysis |
| Material | Proposed grade and UNS number |
| Tube form | Seamless or welded |
| Dimensions | OD, minimum or average wall, length, and tolerance |
| Condition | Annealed, solution annealed, cold worked, or other |
| Surface | ID and OD condition and weld-bead requirements |
| Testing | Product NDT, pressure test, and project-specific dynamic test |
| Documents | MTC, dimensional report, NDT, heat treatment, and traceability |
| Inspection | Third-party or buyer witness points |
| Quantity | Pieces, length, weight, and spare allowance |
Providing these data allows the tube supplier to identify material or manufacturing conflicts before quotation.
Frequently Asked Questions
Is high flow velocity always the main cause of erosion-corrosion?
No. Velocity is one input. Local geometry, particles, gas fraction, chemistry, surface-film behaviour, pressure drop, and flow regime may be equally important.
Is there a universal safe velocity for nickel alloy tubes?
No. A safe velocity cannot be established from the alloy name alone. It depends on the fluid, solids, temperature, geometry, and failure mechanism.
Is Alloy 625 resistant to erosion-corrosion?
Alloy 625 may be a useful candidate when both corrosion resistance and mechanical properties are required. It is not automatically resistant to severe slurry erosion, cavitation, or high-energy impingement.
Is C-276 better than Alloy 625 for abrasive fluids?
Not necessarily. C-276 may offer better corrosion resistance in some chemical environments, but that does not establish better particle-erosion resistance. Representative dynamic testing may be required.
Is titanium suitable for sand-containing seawater?
Titanium performs well in many flowing seawater systems, but the acceptable condition depends on sand loading, particle size, local velocity, geometry, temperature, cavitation, and titanium grade.
Does a harder alloy always resist erosion better?
No. Hardness is only one property. Toughness, ductility, passive-film stability, corrosion resistance, microstructure, and impact conditions also influence performance.
Are bends always the worst locations?
Bends are common hotspots, but the exact maximum-loss location depends on particle trajectories, bend radius, flow regime, orientation, and upstream conditions.
Can reducing flow velocity solve erosion-corrosion?
It may reduce impact energy or shear, but excessively low velocity can allow particles or deposits to settle. The complete transport and corrosion behaviour must be reviewed.
Can a smoother internal surface prevent erosion-corrosion?
A suitable internal surface can reduce disturbances from burrs, weld protrusions, and defects, but ordinary surface roughness alone does not control the full mechanism.
Can ASTM G31 corrosion data predict slurry performance?
No. ASTM G31 is an immersion-corrosion guide. A slurry system may require combined flow, particle, electrochemical, and geometry testing.
Can ASTM G76 be used for liquid slurry tubes?
ASTM G76 uses gas-entrained solid particles. It can support comparative particle-erosion screening but does not directly reproduce a corrosive liquid slurry.
Can CFD predict tube service life?
CFD can help locate velocity, pressure, turbulence, and particle-impact hotspots. Service-life prediction also requires a validated material-loss model and field or experimental data.
What inspection is useful after installation?
Risk-based UT thickness mapping, eddy-current examination where suitable, visual inspection, probes, coupons, process monitoring, and repeat measurements at defined hotspots may all be useful.
What should be sent with an erosion-corrosion enquiry?
Send the fluid chemistry, temperature, pressure, flow, tube ID, solids data, particle size, geometry, existing damage, proposed alloy, dimensions, testing, and documentation requirements.
Conclusion
Erosion-corrosion in alloy tubes is not solved by selecting the hardest or most expensive alloy.
The damage depends on the interaction of:
- Corrosive fluid
- Local flow
- Solid particles
- Gas or vapour
- Impact angle
- Pressure drop
- Tube geometry
- Surface condition
- Material properties
- Protective-film behaviour
A reliable prevention strategy should first identify whether the dominant mechanism is particle erosion, corrosion synergy, cavitation, liquid impingement, flow-accelerated corrosion, or fretting.
The next steps are to:
- Define the complete operating envelope.
- Identify local flow and particle hotspots.
- Screen materials against both chemistry and mechanical damage.
- Use representative testing rather than static corrosion data alone.
- Improve geometry where practical.
- Establish baseline and repeat inspection.
- Monitor process changes in flow and solids.
- Preserve manufacturing and material traceability.
For nickel alloy or titanium tube enquiries involving erosion-corrosion, buyers should provide the process fluid, temperature, pressure, flow, solids, geometry, dimensions, product standard, material condition, testing, and document requirements.
Emily PIPE can review whether the requested alloy tube grade, product standard, size, wall, condition, surface, NDT, certification, and packaging scope are manufacturable. Final system velocity, geometry, material approval, and service-life assessment should remain with the responsible process, mechanical, or corrosion engineer.
