Flow-accelerated corrosion (FAC), also known as flow-assisted corrosion, is a

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

mechanism in which a normally protective oxide layer on a metal surface dissolves in a fast flowing water. The underlying metal corrodes to re-create the oxide, and thus the metal loss continues. By definition, the rate of FAC depends on the flow velocity. FAC often affects

carbon steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...

piping carrying ultra-pure, deoxygenated water or wet steam.

Stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...

does not suffer from FAC. FAC of carbon steel halts in the presence of small amount of oxygen dissolved in water. FAC rates rapidly decrease with increasing water pH. FAC has to be distinguished from

erosion corrosion Erosion corrosion is a degradation of material surface due to mechanical action, often by impinging liquid, abrasion by a slurry, particles suspended in fast flowing liquid or gas, bubbles or droplets, cavitation, etc. The mechanism can be describ ...

because the fundamental mechanisms for the two corrosion modes are different. FAC does not involve impingement of particles, bubbles, or

cavitation Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, cal ...

which cause the mechanical (often crater-like) wear on the surface. By contrast to mechanical erosion, FAC involves dissolution of normally poorly soluble oxide by combined electrochemical, water chemistry and mass-transfer phenomena. Nevertheless, the terms FAC and erosion are sometimes used interchangeably because the actual mechanism may, in some cases, be unclear. FAC was the cause of several high-profile accidents in power plants, for example, a rupture of a high-pressure condensate line in Virginia Power's Surry nuclear plant in 1986, that resulted in four fatalities and four injuries.

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