Flow-Accelerated Corrosion (FAC)

Definition - What does Flow-Accelerated Corrosion (FAC) mean?

Flow-accelerated corrosion (FAC) is a type of corrosion where a normally protective film oxide present on surfaces like metal undergoes dissolution in fast-flowing liquid, such as water.

In this mechanism, the metal undergoes corrosion in order to regain the oxide. Therefore, the metal loss or damage continues. This is often mistaken for a simple type of corrosion. However, industries should be mindful of FAC as it could lead to serious problems.

Flow-accelerated corrosion is also known as flow-assisted corrosion.

Corrosionpedia explains Flow-Accelerated Corrosion (FAC)

FAC entails a process where a metal's protective oxide film dissolves when exposed to fast-moving water, steam or a combination of the two. For instance, in carbon steels, this phenomenon takes place under well-organized and specific parameters. Some of the major parameters include the following:

  • pH
  • Oxygen content
  • Temperature
  • Water velocity

This corrosion mechanism can take place whenever a metal that is susceptible is exposed to certain environmental conditions involving the parameters mentioned above. This often attacks carbon steel that carries pure wet steam or deoxygenated water. By nature, FAC decreases when pH increases.

Industries must understand FAC so that they can differentiate it from simple erosion, since the mechanisms of these two are dissimilar. Essentially, flow-accelerated corrosion does not entail particle impingement, cavitation or bubbling, which produce crater-like wear. FAC engages the dissolution of oxide that is usually poorly soluble through various means like the combination of mass transfer, water chemistry and electrochemical actions.

FAC is one of the leading causes of high-profile industrial accidents, such as ruptures in condensate lines at power plants. Thus, measures to prevent this from happening should be carried out by industries.

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