Fire Protection: Stress Corrosion Cracking

While researching leaks in fire sprinkler and hydrant water supplied, I came across a new term, that I was initially unfamiliar with - Stress Corrosion Cracking ("SCC").

Wikipedia: Stress corrosion cracking
Stress corrosion cracking (SCC) is the growth of crack formation in a corrosive environment. It can lead to unexpected sudden failure of normally ductile metals subjected to a tensile stress, especially at elevated temperature in the case of metals. SCC is highly chemically specific in that certain alloys are likely to undergo SCC only when exposed to a small number of chemical environments. The chemical environment that causes SCC for a given alloy is often one which is only mildly corrosive to the metal otherwise. Hence, metal parts with severe SCC can appear bright and shiny, while being filled with microscopic cracks. This factor makes it common for SCC to go undetected prior to failure.

SCC is the result of a combination of three factors;

  • a susceptible material;
  • exposure to a corrosive environment; and
  • tensile stresses above a threshold.

Precautionary Warnings for Corrosive Environments
…The improper use of corrosive agents such as flux, or other products that contain chloride ions, whether applied internally or externally to the sprinkler system, may result in corrosion of the sprinkler heads, or stress corrosion cracking, which in turn may cause the sprinkler heads to develop leaks, operate unexpectedly or improperly.

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