Corrosion assisted fatigue

Subcritical Crack Growth Environmentally Assisted Fatigue Crack Growth (or Corrosion Fatigue)... 

Table 14-1 shows a summary of some available statistics for both destructive events and nondestructive breaks, the latter include all the cases of fractures discovered in time or which could become destructive and all those minor fractures, probably not potentially destructive, that required intervention because of their size. The principal causes of the reported fractures are fatigue (mechanical, thermal or corrosion assisted) associated with pre-existing fabrication defects, generally corresponding to structural discontinuities such as appendages, penetrations, etc. 

Environment can significantly influence fatigue crack initiation. Environmentally assisted fatigue, often referred to as corrosion fatigue, must be considered when dealing with components in the BWR environment. 

Environmental factors may also affect the fatigue behavior of materials. A few brief comments will be given relative to two types of environment-assisted fatigue failure thermal fatigue and corrosion fatigue. 

Mechanically assisted degradation can consist of the following types of corrosion erosion-corrosion, water drop impingement corrosion, cavitation erosion, erosive and corrosive wear, fretting corrosion, and corrosion fatigue (CF) (Fig. 1.14). Erosion-corrosion consists of the corrosion process enhanced by erosion or wear. Fretting corrosion consists of the wear process enhanced by corrosion. CF consists of the combined action of fluctuating or cyclic stress and a corrosive environment. 

The total cost of material fracture is about 4% of gross domestic product in the United States and Europe (88,89). Fracture modes included in the cost estimates were stress-induced failures (tension, compression, flexure, and shear), overload, deformation, and time-dependent modes, such as fatigue, creep, SCC, and embrittlement. The environmentally assisted corrosion problem is very much involved in the maintenance of the safety and reliability of potentially dangerous engineering systems, such as nuclear power plants, fossil fuel power plants, oil and gas pipelines, oil production platforms, aircraft and aerospace technologies, chemical plants, and so on. Losses because of environmentally assisted cracking (EAC) of materials amount to many billions of dollars annually and is on the increase globally (87). 

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