Erosion-corrosion: causes, high-risk areas and equipment protection

Erosion-corrosion is corrosion accelerated by fluid motion: velocity, turbulence, suspended particles or cavitation strip the protective layer off the metal, which then corrodes much faster. It hits elbows, tees, pumps and valves first. It is controlled by making the flow less aggressive, choosing a more resistant material or adding a wear-resistant coating: ceramic-filled epoxy, rubber or alumina ceramic depending on the mechanism.

This mechanism catches people off guard because it is localized: a pipe in good condition along its full length can fail at a single elbow. This guide is written for maintenance leads in mines, paper mills, process plants and power stations in Quebec and Ontario who want to understand why a part wears out and pick a lasting protection instead of replacing the same part at every shutdown.

What is erosion-corrosion?

Erosion-corrosion is damage where the mechanical action of a fluid and the chemical action of corrosion reinforce each other. Most metals resist corrosion thanks to a thin layer of oxide or corrosion products; the flow strips it, the bare metal corrodes, the new layer is stripped in turn, and the cycle repeats.

The result has a recognizable look: smooth, often bright surfaces, grooves and horseshoe-shaped pits pointing in the flow direction, with no corrosion deposits. Uniform corrosion, by contrast, leaves deposits behind. Our article on types of industrial corrosion places this mechanism among the others.

What factors trigger erosion-corrosion?

Four factors dominate, and they often combine: velocity, turbulence, particles and cavitation. The table summarizes their effect and their signs.

Other conditions make the attack worse: a more corrosive fluid, higher temperature, droplets in a gas (wet steam) or gas bubbles in a liquid. Flow-accelerated corrosion (FAC) of carbon steel in water and steam is a related case tied to water chemistry, handled mainly through material choice and water treatment.

Where does erosion-corrosion show up in a plant?

It shows up wherever the flow changes direction, cross-section or speed. The areas to inspect first are well known:

• Elbows and tees. Especially the outer radius of short-radius elbows and the impact branch of tees.
• Reducers and valve outlets. Acceleration and the jet downstream of a partly open valve attack the wall downstream.
• Pumps. Volutes, impellers, wear plates and rings, where velocity and cavitation meet. See our article on centrifugal pump epoxy repair.
• Valve bodies and seats. Throttling and sudden pressure drop zones; see valve body repair with epoxy.
• Chutes, hoppers and cyclones. In mining, solids impact dominates; see chute and hopper wear repair.
• Heat exchangers. Tube inlets, where the fluid speeds up.

Ultrasonic thickness monitoring at fixed points on elbows and tees, repeated at each shutdown, gives the actual wear rate and lets you schedule the repair before a leak. Marking the measurement points and keeping the readings in the equipment file makes the comparison reliable from one outage to the next. Where several identical lines run in parallel, the most worn one usually shows where to look on the others.

How do you tell erosion, cavitation and abrasion apart?

They are told apart by the surface appearance and the service conditions, and that diagnosis drives the choice of protection directly. A mistake at this step leads to a coating that does not last.

• Clean-liquid erosion. Smooth, wavy, often bright surface. The issue is velocity and turbulence.
• Slurry abrasion. Grooves in the flow direction, dull surface. Particle size, hardness and impact angle matter.
• Cavitation. Rough pits clustered in low-pressure zones (back face of vanes, downstream of restrictions). The issue is hydraulic: insufficient suction pressure or operation away from the design point.

For cavitation, no coating replaces fixing the hydraulic cause. The coating extends part life, but a pump that cavitates will keep attacking the surface. When several mechanisms are present on the same part, protection is chosen for the most severe one, and the layer can vary from one zone of the part to another.

Which coatings protect against erosion-corrosion?

The coating is selected by the dominant mechanism: ceramic-filled epoxy for erosion and fine abrasion, rubber for fine-particle slurries, alumina ceramic for severe impact and sliding. The table compares the families.

Filled epoxies are also used to rebuild lost metal before the finish layer, as explained in our guide to metal repair epoxy putty selection. To compare rubber, ceramic and polyurethane, see rubber vs ceramic vs polyurethane wear linings and our comparison of alumina ceramic vs AR steel. Rubber lining is offered as a separate service.

Should you change the material or the design?

Sometimes, yes: when velocity or cavitation exceed what a coating can handle, changing the material or the geometry is the lasting fix. The coating remains useful for existing parts until replacement.

• Material. Stainless steels, duplex, chrome irons or hardfacing perform better depending on the service; against FAC, low-alloy chrome steels are often selected.
• Geometry. Long-radius elbows, gradual reducers, replaceable impact plates, removal of weld protrusions.
• Operation. Velocity brought back within the design range, valves not used for permanent throttling, pumps run close to their design point.

These decisions are made with service data and thickness readings. The diagnosis compares repair and replacement part by part.

How is a worn surface repaired?

The repair always follows the same logic: diagnose the mechanism, prepare the surface, rebuild lost metal, apply the wear layer and inspect. Preparation is the critical point, because wear often leaves metal contaminated by the process fluid.

1. Measurement and diagnosis. Thickness survey, photos, service conditions.
2. Decontamination. Removal of oils and embedded salts, per the specification.
3. Abrasive blasting. A clean, angular profile for adhesion.
4. Rebuilding. Metal- or ceramic-filled epoxy to restore geometry.
5. Protective layer. Fluid ceramic, rubber or tiles depending on the mechanism.
6. Inspection. Thickness, continuity and cure before return to service.

On a pipe that already leaks, a pipe leak repair without shutdown can buy time until the outage. Pipe coating covers complete lines. This work is part of our protective coatings offering.

Frequently asked questions

Does erosion-corrosion affect stainless steel too?

Yes. Stainless resists better thanks to its passive film, but very high velocity, hard particles or cavitation can destroy it locally.

Can a coating stop cavitation?

No. It slows the attack on the surface, but the cause is hydraulic. Suction or operating conditions must be corrected in parallel.

When should you choose rubber over ceramic?

Rubber suits fine-particle slurries better, where it absorbs impact energy. Ceramic is preferable for coarse solids and severe sliding.

Can a pump volute be repaired instead of replaced?

Often, yes, if the casing keeps enough material. It is rebuilt with filled epoxy, then a smooth wear layer is applied, based on the measured condition.

Are your elbows, pumps or valves wearing out faster than expected? Our maintenance and rehabilitation service diagnoses the mechanism and proposes the right repair, carried out by our crews and qualified subcontractors, including in Abitibi-Témiscamingue and Ontario. Send photos, dimensions and service conditions through the request a quote form: pricing on consultation, reply within 24 business hours.