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What is stress relaxation cracking?

Stress relaxation cracking (SRC) is a phenomenon where a material experiences cracking due to the gradual decrease in internal stress over time, often at elevated temperatures. Unlike stress corrosion cracking, which requires both stress and a corrosive environment, SRC primarily occurs due to the relaxation of residual or applied stresses in a high-temperature environment. Key factors contributing to SRC include:

  1. Elevated Temperatures: Typically occurs at high temperatures where materials are more susceptible to creep and stress relaxation.
  2. Internal Stresses: Residual stresses from manufacturing processes or applied stresses during service gradually decrease over time.
  3. Material Susceptibility: Certain alloys and materials are more prone to SRC, especially those used in high-temperature applications like turbine blades and pressure vessels.

SRC is characterized by the formation of cracks that can lead to material failure. It is a significant concern in industries such as power generation, petrochemical, and aerospace, where components operate under high stress and temperature conditions.

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What is stress corrosion cracking?

Stress corrosion cracking (SCC) is a type of failure that occurs in materials exposed to tensile stress and a corrosive environment simultaneously. It is characterized by the development of cracks that can lead to sudden and unexpected failure of the material. SCC is highly specific to the material-environment combination, meaning that certain materials will only crack under specific environmental conditions. The key factors contributing to SCC include:

  1. Tensile Stress: Can be residual stress from manufacturing processes or applied stress during service.
  2. Corrosive Environment: Often involves specific chemicals or conditions, such as chloride ions, caustic substances, or high-temperature water.
  3. Material Susceptibility: Certain materials are more prone to SCC under specific conditions.

SCC typically progresses through the material in a brittle manner, despite the material’s ductility under non-corrosive conditions. This phenomenon is a significant concern in industries such as chemical processing, oil and gas, nuclear power, and aerospace, where both stress and corrosive environments are common.