Erosion-Corrosion Testing Analysis: Methods, Standards, and Performance Evaluation

Erosion-corrosion testing analysis is a specialized laboratory discipline that quantifies how the combined action of mechanical wear and electrochemical degradation accelerates material loss in flowing or particle-laden media. This article provides a comprehensive technical overview of erosion-corrosion mechanisms, applicable test samples, evaluation items, standardized testing methods, and industrial applications, helping engineers select appropriate testing strategies for pipelines, pumps, valves, and fluid-handling equipment.

Technical Overview

Erosion-corrosion, also referred to as flow-accelerated corrosion or impingement attack, is a synergistic degradation process in which mechanical erosion from high-velocity fluids, suspended solid particles, liquid droplets, or collapsing cavitation bubbles destroys or thins the protective surface films on a metal, while simultaneous electrochemical corrosion attacks the freshly exposed bare metal. The result is a material loss rate that is typically far greater than the sum of pure erosion and pure corrosion acting independently.

This failure mode is most pronounced at locations of turbulent flow, flow direction change, and high local velocity, including pipe elbows, tees, reducers, pump impellers, valve throats, heat exchanger tube inlets, and turbine components. Erosion-corrosion testing analysis therefore serves two purposes: to rank candidate materials and coatings under realistic hydrodynamic conditions, and to quantify the individual contribution of each degradation mechanism so that mitigation strategies—such as velocity limits, inhibitor programs, or material upgrades—can be engineered on a scientific basis.

Under the framework defined by ASTM G119 (Standard Guide for Determining Synergism Between Wear and Corrosion), the total material loss rate (T) in an erosive-corrosive environment is decomposed into four terms: the pure erosion component (E), the pure corrosion component (C), and the synergistic terms in which erosion accelerates corrosion and corrosion accelerates erosion. Accurate separation of these components is the core analytical challenge of erosion-corrosion testing.

Testing Samples

Metallic Engineering Materials

Flat coupons, cylindrical electrodes, and machined specimens prepared from carbon steels, low-alloy steels, austenitic and duplex stainless steels, nickel-based alloys such as alloy 625 and C-276, copper-nickel alloys, aluminum alloys, and titanium alloys. Specimens are typically finished to a defined surface roughness and cleaned, weighed, and dimensionally documented before exposure.

Weldments and Heat-Affected Zones

Welded joint specimens are tested to compare the erosion-corrosion response of base metal, weld metal, and heat-affected zone, since local differences in composition, microstructure, and residual stress often concentrate attack at the weld fusion line.

Protective Coatings and Surface Treatments

Thermal spray coatings (WC-Co, cermet, and metallic overlays), electroless and electrolytic plating layers, hard anodized films, PVD/CVD coatings, polymer linings, and claddings are evaluated for adhesion stability, film breakdown velocity, and through-thickness penetration under impingement.

Actual Service Components

Prototype or retrieved components—including elbow fittings, pump impellers, valve trims, condenser tube sections, and nozzle inserts—may be tested in flow loops or rig configurations to validate geometry effects and remaining-life assessments. Failure analysis of field-returned parts is also supported through complementary metallographic and fractographic examination.

Testing Items

Depending on the engineering objective, erosion-corrosion testing programs typically include the following measurable quantities:

• Total erosion-corrosion mass loss rate and depth loss rate (mm/y) under defined flow conditions.
• Pure erosion rate, determined with the corrosive electrolyte replaced by an inert medium or with cathodic protection applied to suppress the corrosion reaction.
• Pure corrosion rate, measured under static or identical-flow conditions with the erodent particles removed.
• Synergistic and additive interaction terms calculated per ASTM G119 to quantify how much each mechanism amplifies the other.
• Critical or breakaway flow velocity, above which the protective film is mechanically destroyed and the loss rate rises sharply.
• Effect of impingement angle (typically 30°, 45°, 60°, and 90°) on damage morphology and loss rate for both ductile and brittle materials.
• Influence of erodent variables: particle concentration, particle size distribution, hardness, and angularity of sand or proppant.
• Electrochemical parameters under flow, including open-circuit potential, polarization resistance, potentiodynamic polarization behavior, and electrochemical impedance spectroscopy (EIS) response of the surface film.
• Cavitation erosion resistance, expressed as incubation time and steady-state mass loss rate.
• Post-test surface characterization: 3D profilometry of erosion scars, pit density and depth statistics, SEM/EDS analysis of damaged morphology and embedded particles, and microhardness profiling of the deformed surface layer.

Testing Methods

Jet Impingement Testing

A submerged or free-standing jet of fluid, with or without suspended sand, is directed at the specimen at controlled velocity and angle. This configuration offers precise control of impact hydrodynamics, allows electrochemical measurements to be made in situ during erosion, and is widely used to screen inhibitor performance and rank alloys. Recirculating slurry systems with heated, de-aerated, or CO2/H2S-saturated brines reproduce oilfield service chemistry.

Rotating Specimen and Rotating Cylinder Electrode (RCE) Methods

The specimen is attached to a rotating disc, arm, or cylinder immersed in the test electrolyte, generating controlled wall shear stress. The RCE configuration is particularly valued because the wall shear stress can be calculated analytically, enabling correlation between hydrodynamic conditions and corrosion kinetics measured simultaneously by electrochemical instrumentation.

Flow Loop Testing

Closed-circulation loops carrying single-phase liquid, gas-liquid mixtures, or sand-laden slurries pass through instrumented straight sections, elbows, and test spools. Loop testing reproduces realistic multiphase flow regimes (slug, annular, churn) and permits long-duration exposure, wall-thickness monitoring by ultrasonic probes, and inline corrosion monitoring using ER, LPR, or electrical resistance coupons.

Slurry Pot Erosion Testing

Specimens orbit or rotate within a pot containing a sand slurry, providing an economical method for comparing materials at moderate shear levels. This approach is well suited to coating qualification and material screening studies requiring many specimens per condition.

Cavitation Erosion Testing

Vibratory apparatus testing per ASTM G32 uses an ultrasonically driven horn to generate repetitive cavitation bubbles adjacent to the specimen, while ASTM G134 covers cavitating jet testing. Liquid impingement erosion from droplet-laden streams is evaluated under ASTM G73, which is directly relevant to steam turbine blades and wet gas systems.

Solid Particle Erosion Testing

Gas-borne particle erosion is measured per ASTM G76, in which a controlled stream of abrasive particles impinges on the specimen at specified velocity, angle, and feed rate. Results are expressed as erosion rate in volume lost per unit mass of erodent.

Electrochemical and Analytical Support Methods

Linear polarization resistance (LPR), potentiodynamic polarization, and EIS are integrated with the flow rigs to separate the corrosion contribution in real time. Post-exposure gravimetry follows ASTM G1 cleaning practice, and damage quantification employs optical 3D scanning, scanning electron microscopy, and cross-sectional metallography. Test environments are controlled for temperature, pH, dissolved oxygen, chloride content, and partial pressure of CO2 or H2S in accordance with the relevant NACE and ASTM environmental protocols.

Applications

Erosion-corrosion testing analysis supports material selection, integrity management, and failure prevention across many industries:

• Oil and gas production: sand-producing wells, flowlines, chokes, Christmas tree components, and multiphase transport lines where erosive sand and corrosive CO2/H2S environments coexist, supporting both sand-erosion velocity limits and inhibitor qualification.
• Refining and petrochemical plants: crude unit overhead systems, slurry piping in FCC units, and sour water service where flow-accelerated corrosion thins elbows and fittings.
• Power generation: feedwater and heater drain piping susceptible to flow-accelerated corrosion, steam turbine last-stage blades subject to droplet erosion, and condenser tubes exposed to cooling-water silt and debris.
• Desalination and water treatment: high-salinity brine circuits, high-pressure recovery devices, and pump internals in reverse osmosis plants.
• Mining and mineral processing: slurry pipelines, hydrocyclones, tailings transport, and dredging equipment handling highly abrasive solids.
• Marine and offshore engineering: seawater cooling systems, propulsion components, and splash-zone structures exposed to suspended sediment and cavitation.
• Coating and material qualification: acceptance testing of hard-facing alloys, cermet coatings, corrosion-resistant alloys, and lined pipe systems intended for erosive-corrosive service.

FAQ

What is the difference between erosion, corrosion, and erosion-corrosion?

Erosion is purely mechanical material removal caused by particle, droplet, or cavitation impact; corrosion is electrochemical dissolution of the metal. Erosion-corrosion is the coupled process in which flow mechanically damages or removes protective corrosion films, and the resulting bare surface corrodes at an accelerated rate. The measured total loss usually exceeds the arithmetic sum of the two individual processes because of synergy.

How is the synergy between erosion and corrosion quantified?

Following ASTM G119, the total loss rate is measured under combined conditions, while the pure erosion rate is obtained with corrosion suppressed (for example, in an inert fluid or under cathodic protection) and the pure corrosion rate is obtained without erodent particles. The difference between the total rate and the sum of the two individual rates defines the synergy, which reveals whether mechanical or electrochemical action dominates and guides the choice of mitigation.

Which standards govern erosion-corrosion testing?

Frequently applied standards include ASTM G119 for synergy determination, ASTM G32 for vibratory cavitation erosion, ASTM G73 for liquid impingement erosion, ASTM G76 for solid particle erosion by gas jets, ASTM G134 for cavitating jet testing, ASTM G1 for specimen cleaning and mass-loss evaluation, and relevant NACE test methods for oilfield environments. Test programs in accredited third-party laboratories are designed to combine these standardized methods with application-specific flow conditions.

What test variables most strongly influence the results?

Flow velocity (loss rate commonly scales with velocity to a power of 2 to 3), impingement angle, sand concentration and particle size, fluid chemistry including chloride content and dissolved CO2/H2S, temperature, pH, and material hardness. Because of this sensitivity, tests must closely replicate the service hydrodynamics and chemistry for results to be transferable.

How long does a typical erosion-corrosion test take?

Screening tests using jet impingement or RCE rigs often run from several hours to a few days, sufficient to establish steady-state loss rates. Flow loop validation and coating qualification programs may extend from weeks to months to capture long-term film behavior, inhibitor persistence, and incubation phenomena. Durations are selected to ensure the measured rate has reached a reproducible steady state.

What specimen form is required for testing?

Flat coupons (commonly 20 to 50 mm on a side with a few millimeters thickness), cylindrical electrodes, or thin rings are standard, with surface preparation, weighing to 0.1 mg resolution, and dimensional recording performed before exposure. Custom fixtures can accommodate weld cross-sections, coated panels, or actual component sections when geometry-specific behavior is of interest.