Skeleton Corrosion

Definition - What does Skeleton Corrosion mean?

Skeleton corrosion refers to graphite formation in low-alloy steels or iron. This takes place when the elements are exposed to high temperatures throughout a significant period of time.

Graphite formation can be very dangerous, as it weakens a material, causing localized corrosion damage that could potentially affect the entire structure or material.

Skeleton corrosion is also known as graphitization.

Corrosionpedia explains Skeleton Corrosion

Skeleton corrosion involves the formation of free carbon or graphite that is usually brought about by the growth process and nucleation that takes place when metal or a steel is exposed to temperatures higher than 800°F (1470°C).

Free carbons are very weak with low levels of resistance and ductility to certain factors such as mechanical or thermal fatigue. Due to this, there can be localized weakness on the structure, which spreads out to the entirety.

Steel that is exposed to extremely high temperatures for an extended period of time undergoes metallurgical degradation and forms graphite as well as iron. At high temperatures, the graphite or free carbons shift to grain boundaries, resulting in graphite nodule formation that can make the metal brittle.

Skeleton corrosion may be intentional, such as in the production of graphite electrons intended for arc furnaces, as well as cast irons. However, in most cases it is unintentional, like in low-alloy steels and carbon. Unintentional skeleton corrosion leads to loss of toughness and strength in the affected surface, producing low ductility, creep resistance and low levels of tensile strength.

This phenomenon is commonly seen in:

  • Boiler tubes
  • High-energy pipes
  • Steel pipes
  • Gray cast iron pipings
  • Coal plants

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