Flow Accelerated Corrosion (FAC) Testing
Flow-Accelerated Corrosion (FAC), also known as flow-assisted corrosion, is a phenomenon that happens when the protective oxide coating on the metal surface is broken down by swiftly moving water, causing metal loss from pipelines, vessels, and equipment composed of carbon steel. FAC testing is done to identify FAC before failure occurs.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
Material deterioration caused by high-velocity fluids interacting with metal surfaces is assessed using Flow Accelerated Corrosion (FAC) testing. Because of the combined impacts of flow dynamics and electrochemical processes, FAC is a corrosion mechanism that causes carbon steel and low-alloy steel components to thin more quickly.
In contrast to normal erosion or general corrosion, FAC causes protective oxide layers to dissolve under flowing circumstances, resulting in fast wall weakening without visible localised pitting. FAC is critical in boiler systems, power plants, oil and gas pipelines, and feedwater lines where steam or high-temperature water is constantly flowing.
FAC testing supports preventative maintenance plans, evaluates susceptibility under simulated service conditions, and forecasts material loss rates.
Scope, Applications, and Benefits
Scope
Procedures for assessing corrosion rates under regulated flow, temperature, pressure, and chemical conditions are defined by FAC testing. The test assesses metal dissolution rates, oxide stability, and wall thinning in dynamic settings that mimic actual service conditions.
Applications
- Power plant feedwater and condensate systems
- High-temperature steam pipelines
- Oil and gas transport systems
- Boiler tubes and heat exchangers
- Nuclear plant secondary systems
- Material qualification for high-flow environments
Benefits
- Quantify corrosion rates under flowing conditions
- Identify susceptible materials and system areas
- Predict long-term wall thinning and service life
- Optimize water chemistry control strategies
- Reduce risk of catastrophic pipe rupture
- Support regulatory and safety compliance
Test Process
Specimen Preparation
Machine carbon steel or alloy specimens to the required dimensions and surface finish. Clean thoroughly and record initial thickness and weight.
1Flow Loop Setup & Installation
Install specimens in a controlled-flow loop system that simulates operating velocity, temperature, pressure, and water/steam chemistry conditions.
2Controlled Exposure & Monitoring
Circulate water/steam at controlled velocity and chemistry; monitor flow, temperature, pressure, dissolved oxygen, corrosion rate, and wall thinning.
3Post-Test Evaluation
Remove specimens after exposure; evaluate thickness loss, oxide morphology, and surface condition via microscopy and profilometry to determine corrosion performance.
4Technical Specifications
| Parameter | Details |
|---|---|
| Standard References | ASTM G31 (general immersion), ASTM G170 (flow-assisted corrosion guidance), industry-specific protocols |
| Fluid Medium | Deoxygenated water, wet steam, or process fluid |
| Flow Velocity | Typically 1–10 m/s (or as per service simulation) |
| Temperature Range | Ambient to 300°C (depending on system simulation) |
| Exposure Duration | Weeks to months |
| Measurement Accuracy | Thickness measurement ±0.01 mm |
Instrumentation Used for Testing
- High-pressure flow loop systems with corrosion-resistant piping
- Precision flow meters and pressure control systems
- Temperature control units and heating elements
- Ultrasonic thickness gauges for in-situ monitoring
- Analytical instruments for water chemistry control (pH, dissolved oxygen meters)
- Scanning Electron Microscopy (SEM) for oxide layer evaluation
- Data logging systems for continuous monitoring
Results and Deliverables
- Corrosion Rate (mm/year) under dynamic flow conditions
- Wall Thinning Measurements
- Oxide Layer Characterization
- Surface Morphology Analysis
- Flow Velocity vs. Corrosion Rate Correlation
- Failure Risk Assessment
- Recommendations for Material Upgrade or Chemistry Control
Frequently Asked Questions
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