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Characteristics of stress corrosion cracking (SCC)

Characteristics of stress corrosion cracking (SCC)

Stress corrosion cracking (SCC) is a form of material degradation that occurs under specific environmental and stress conditions, leading to unexpected failures. Below are the key characteristics of SCC:

1.Caused by Static Tensile Stress

SCC occurs under static tensile stress, often far below the material’s yield strength. It is primarily associated with tensile stresses, which make the material more vulnerable to cracking.

2.Brittle Fracture Without Plastic Deformation

The damage caused by SCC results in brittle fractures with little to no visible plastic deformation, making it challenging to detect before failure occurs.

3.Material and Environment Specificity

SCC only happens when specific alloy compositions interact with particular corrosive environments. This unique combination makes SCC highly selective and situational.

ASTM A312 GR TP347H SMLS Pipes

ASTM A312 GR TP347H SMLS Pipes

4.Gradual Crack Growth

The crack propagation rate in SCC typically ranges from 10-9~10-6m/s, resembling the slow progression seen in fatigue cracks. This subcritical growth continues until the crack reaches a critical size, leading to sudden fracture when the remaining material can no longer support the load.

5.Crack Initiation at Surface Pits

SCC cracks often originate from surface pits or flaws. The cracks usually propagate perpendicular to the applied tensile stress, following paths of least resistance.

6.Fracture Surface Appearance

The fracture surface caused by SCC appears dull gray and often contains corrosion products. These visual characteristics can help identify SCC as the cause of failure.

7.Main Crack Branching

SCC often exhibits branching of the main crack, complicating the failure mechanism and further weakening the material.

8.Intergranular or Transgranular Fracture

SCC can result in either intergranular (along grain boundaries) or transgranular (through the grains) fractures, depending on the material and environmental conditions.

Stress corrosion cracking is a complex and dangerous failure mode due to its sudden and brittle nature, gradual crack growth, and dependence on specific material-environment combinations. Understanding these characteristics is crucial for preventing SCC in industrial applications through proper material selection, environmental control, and stress management.

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