Service Related Discontinuities (10) Flashcards
Over-Stress Failure
A mechanical failure of a component to a stress that exceeds its strength.
- Ductile or Brittle
- Based on history of failed component
Fatigue Failure/Cracks
Cracks formed from cyclical stress when the maximum stress value is less than the tensile strength of the material (Fatigue Cracks)
- Starts as small crack and progresses
- Fatigue crack is trans-granular (follow grain boundaries)
Thermal fatigue Failure
Fracture as the result of a temperature change
Creep Failure
Tendency of a material to deform permanently over time under stress, stress lower than strength at high-temp over time.
Corrosion Failure Methods
- General
- Pitting Corrosion
- Inter-Granular Corrosion
- Erosion Corrosion
- Cavitation Corrosion
- Fretting Corrosion
- Crevice Corrosion
- Corrosion Fatigue
General Corrosion
Uniform corrosion (rust)
Pitting Corrosion
Highly localized corrosion, deep penetration at only a few spots on the material.
Inter-Granular Corrosion
Corrosion that follows the Grain Boundaries that may cause a crack to propagate.
Erosion Corrosion
From an aggressive chemical environment and high fluid velocity.
Cavitation Corrosion
Caused by implosion in cavities of a liquid against a metal
Fretting Corrosion
Results corrosion assisted wear from small oscillatory movements between mating surfaces under load.
Crevice Corrosion
Corrosion produced where metals contact with metals, or metals with non-metals.
Corrosion Fatigue
Cracking that is subjected to fluctuating stress in a corrosive environment.
(Corrosion + Fatigue Stress)
Stress-Corrosion Cracking
Cracking that occurs when a metal is subjected to constant low Tensile stresses in the presence of a corrosive environment.
- Can be Inter-Granular or Trans-Granular
Hydrogen-Induced Cracking
Results from a corrosive environment produced by hydrogen media in conjunction with an applied Tensile/residual stress.
