corrosionrate

Corrosion rate is the speed at which a material, typically a metal, deteriorates through electrochemical reactions with its environment. It quantifies the loss of material thickness or mass over time and is used to predict service life, plan maintenance, and evaluate material and protective strategies in a given environment.

Rates are commonly expressed as thickness loss per unit time, for example millimeters per year (mm/y) or mils per year (mpy), or as a mass loss per area per time. Depending on the method and units, rates may be reported as surface thickness loss, mass loss, or as an estimated corrosion current density derived from electrochemical measurements via Faraday’s law.

Measurement methods include weight-loss tests (coupons) that compare initial and final mass, and electrochemical methods such as linear polarization resistance (LPR) and potentiodynamic polarization to estimate corrosion current density and convert to a rate. Field monitoring may use probes and corrosion coupons installed in service. In addition, electrochemical impedance spectroscopy (EIS) can be used to assess protective properties of coatings and the resistive nature of the environment.

Factors that influence corrosion rate include material composition and microstructure, oxide or protective coatings, temperature, pH, ionic species (notably chlorides), dissolved oxygen, solution flow, and mechanical stress. Corrosion can be uniform or localized, with pitting, crevice, or cavitation causing higher local rates and potentially premature failure.

Understanding corrosion rate supports material selection, protective design (coatings, cathodic protection), and maintenance planning. It is an estimate subject to time and environmental variability; real-world rates may differ from laboratory measurements, and rates can evolve as surface conditions change.