Predicting Metal Loss
Corrosion rate prediction is the foundation of asset integrity management. Every pipeline, pressure vessel, and structural member has a finite corrosion allowance — the extra wall thickness designed to be consumed during the expected service life. Accurately predicting how fast this allowance is consumed determines inspection intervals, maintenance budgets, and ultimately whether a structure is safe to operate.
The Electrochemical Basis
Uniform corrosion is an electrochemical process where anodic dissolution (metal to ions) is balanced by cathodic reduction (typically oxygen reduction in near-neutral water, or hydrogen evolution in acid). The corrosion rate equals the current at which anodic and cathodic polarization curves intersect — the corrosion current density. The Butler-Volmer equation describes how each reaction's rate depends on potential, temperature, and reactant concentration.
Oxygen, Temperature, and pH
Dissolved oxygen is usually the rate-controlling factor in near-neutral water: more oxygen means faster cathodic reaction and higher corrosion rate. Temperature accelerates kinetics (Arrhenius behavior) but also reduces oxygen solubility at high temperatures, creating a maximum corrosion rate around 80°C in open systems. Below pH 4, hydrogen evolution adds a second cathodic reaction that increases corrosion exponentially with decreasing pH.
Flow and Erosion-Corrosion
Flow velocity affects corrosion in two competing ways: moderate flow increases oxygen transport to the surface (increasing rate), but also promotes formation of protective iron carbonate or oxide films. Above a critical velocity, shear forces strip these protective films away, causing erosion-corrosion with rates many times higher than static conditions. This simulation models how these interconnected factors combine to determine the overall dissolution rate.