A Waltron Solutions Brief: Mitigating Flow-Accelerated Corrosion With Water Chemistry

Author: Lukas Staub, Chief Commercial Officer, Waltron

Flow-Accelerated Corrosion Defined

Flow-Accelerated Corrosion (FAC) is a localized, rapidly destructive form of corrosion that occurs when high-velocity water or wet steam erodes the protective internal oxide layer (typically magnetite) on carbon steel components. Because inspecting the interior surfaces of complex piping networks is incredibly challenging, controlling water chemistry is considered the most effective mitigation strategy.

To prevent the dissolution of protective oxide layers, power plants must continuously monitor specific chemistry parameters using advanced online instrumentation..

Essential Chemistry and Control Parameters

• pH and Alkalinity: FAC thrives in low-pH environments where magnetite easily dissolves. Maintaining a slightly alkaline pH using ammonia or amines stabilizes the protective oxide layer, serving as the primary defense in all-volatile treatment (AVT) protocols.
• Dissolved Oxygen (DO): In feedwater systems, trace amounts of DO can significantly reduce FAC. Under oxygenated treatment (OT) protocols, precise amounts of DO are introduced to convert soluble magnetite into a denser, more adherent hematite layer. Because too much oxygen invites general corrosion, DO levels must be tightly controlled.
• Conductivity and Ionic Contaminants: Ionic impurities like chlorides, sulfates, and acetates destabilize oxide layers even at parts-per-billion levels. Monitoring specific, cation, and degassed conductivity strips away CO2 interference to reveal aggressive ions and provides an early warning signal for corrosion risk.
• Sodium and Silica: While not direct drivers of FAC, these act as critical dashboard warnings. Spikes in sodium indicate condenser leakage or the introduction of contaminants, while high silica signals compromised filtration or upstream intrusion.

Analytical Methods and Online Instrumentation

Manual testing is insufficient because it often misses dangerous transient events, such as a 3 a.m. pH dip or a load-shift conductivity spike. Therefore, continuous, real-time water quality monitoring via a modern Steam and Water Analysis System (SWAS) is mission-critical.

An effective online instrumentation suite must include:

• pH Analyzers: To continuously track alkalinity and immediately detect CO2 intrusion or chemical dosing failures.
• Dissolved Oxygen Analyzers: To maintain exact DO parameters for OT conditions or rapidly catch unwanted oxygen ingress in AVT setups.
• Conductivity Analyzers: To measure both specific and cation conductivity, ensuring neutralization chemistry is performing properly and catching acid contaminant ingress.
• Sodium and Silica Analyzers: To provide real-time detection of trace contamination, spotting resin bed exhaustion or condenser leaks before they alter the broader steam-water cycle chemistry.

Smart Systems and Predictive Action

Today’s online analyzers are highly integrated; they feed directly into plant control systems to trend historical data and trigger alarms when parameters exceed FAC-risk thresholds. This continuous data stream empowers operators to react in real-time by adjusting chemical feeds or initiating blowdowns. When combined with inspection data and flow modeling, these continuous analytical insights feed into FAC prediction tools that can map high-risk zones and recommend preemptive maintenance before catastrophic failures occur.

Bibliography

EPRI. (2024). Flow-Accelerated Corrosion Investigation and Mitigation. Electric Power Research Institute. https://dl.asminternational.org/am-epri/proceedings/AM-EPRI2024/84871/418/32724

Mukherjee, N. (2023). Flow-Assisted Corrosion: A Hidden Threat in Power Plants. LinkedIn Article. https://www.linkedin.com/pulse/flow-assisted-corrosion-threat-power-plants-nikhilesh-mukherjee/

Integrated Global Services. (2024). Combating Flow Accelerated Corrosion in Power Plants with HVTS Technology. https://integratedglobal.com/combating-flow-accelerated-corrosion-in-power-plants-with-igs-hvts-technology/

International Association for the Properties of Water and Steam. (2015). Technical Guidance Document: Instrumentation for monitoring and control of cycle chemistry for the steam-water circuits of fossil-fired and combined-cycle power plants (IAPWS TGD1-08(2015)). http://www.iapws.org/techguide/Instrumentation.pdf