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Stress-Corrosion/Cracking

Stress-Corrosion

  • This type of corrosion involves constant or cyclic stress acting in conjunction with a damaging chemical environment. The stress may be caused by internal or external loading.
  •  Internal stress may be trapped in a part of structure during manufacturing processes, such as cold working or by unequal cooling from high temperatures. Most manufacturers follow these processes with a stress relief operation.
  •  The force of stress may be externally introduced in part structure by riveting, welding, bolting, clamping, press-fit, etc. If a slight mismatch occurs or a fastener is over-torqued, internal stress is present.
  • Internal stress is more important than design stress because stress corrosion is difficult to recognize before it has overcome the design safety factor. 
  • The level of stress varies from point to point within the metal. Stresses near the yield strength are generally necessary to promote stress corrosion cracking. However, failures may occur at lower stresses force.

Most Specific environments have been identified that cause stress corrosion cracking of certain alloys.

   1.   Salt solutions and seawater cause stress corrosion cracking of high-strength, heat-treated steel, and aluminum alloys.

   2.   Methyl alcohol-hydrochloric acid solutions cause stress corrosion cracking of some titanium alloys.

  3.   Magnesium alloys may stress corrode in moist air.

  •  Force of Stress corrosion may be reduced by applying protective coatings, stress relief heat treatments, using corrosion inhibitors, or controlling the environment.  
  • Shot peening a metal surface increases resistance to stress corrosion cracking by creating compressive stresses on the surface which should be overcome by applied tensile stress before the surface sees any tension load. Therefore, the threshold stress level is increased.

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