Fretting corrosion factors

Modeling fretting corrosion. An equation has been used for steel to evaluate the loss of weight W caused by fretting corrosion based on a model that combines the chemical and mechanical effect of the corrosion by fretting. The chemical factor concerns the oxidation that occurs at the time of wear, corresponding to adsorption of oxygen to form the oxide. The mechanical factor concerns the loss of particles, at the asperities on the opposite surface. 

There are some corrosion cases where other factors, i.e. stress, or other mechanical factors are involved. For example, stress corrosion cracking, corrosion fatigue, hydrogen embrittlement, erosion corrosion, cavitation corrosion, fretting corrosion, etc. can be mentioned. 

Another type of corrosion promoted by mechanical factors is fretting corrosion, which occurs on a metal surface that repeatedly touches another solid [17]. 

Mechanical factors Avoidance of excessive stress (internal or applied) when using metals known to be susceptible to stress-corrosion cracking avoidance of conditions leading to corrosion fatigue or fretting corrosion... 

Another special case of erosion-corrosion, fretting corrosion, occurs when two heavily loaded metals rub rapidly together, causing damage to one or both metals. Vibration is usually responsible for the damage, but corrosion is also a factor because the frictional heat increases oxidation. In addition, mechanical removal of protective corrosion products continually exposes fresh metal. Fretting corrosion occurs more frequently in air than in water. 

Mechanical effects Corrosion can often be initiated or intensified by the conjoint action of mechanical factors. Typical examples include the presence of inherent or applied stresses, fatigue, fretting or cavitation effects. Inhibitors that are effective in the absence of some or all of these phenomena may not be so in their presence. In fact it may not always be possible to use inhibitors successfully in these situations and other methods of corrosion prevention will be required. 

Other factors are fretting and cavitation in a liqnid (impact of the liqnid). Corrosion can also occnr dne to electric cnrrents (stray cnrrents in soils). 

If the factor of safety against fatigue f, is less than ff = 1, then the shaft will fail. The suitability of factors of safety ff > 1 will depend on the operating conditions, i.e. the likelihood of corrosion, fretting or stress concentrations near the bottom bearing. The fatigue life of a shaft will be strongly dependent on environmental conditions and material properties. It is recommended that a materials specialist be consulted for advice on this matter. 

The term "erosion" applies to deterioration due to mechanical force. When the factors contributing to erosion accelerate the rate of corrosion of a metal, the attack is called "erosion corrosion." Erosion corrosion is usually caused by an aqueous or gaseous corrodent flowing over the metal surface or impinging on it. The mechanical deterioration may be aggravated by the presence of a corrodent, as in the case of fretting or corrosive wear. 

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