Fretting corrosion characteristics

The deterioration of surfaces that occurs when parts supposedly tightly fitted together nevertheless move slightly relative to each other in some sort of cycle under load is called fretting corrosion (see Section 8.7). With ferrous materials the characteristic corrosion product is a finely divided cocoa-coloured oxide. The general state of knowledge of the subject was reviewed in a symposium on fretting corrosion held by the ASTM in 1952 and more recently by Waterhouse . ... 

Fretting is of course not a form of corrosion, but it is often confused with corrosion, and can sometimes be associated with serious corrosion. It is in fact a form of oxidative wear which occurs when solid surfaces, usually metallic, rub together in a low-amplitude oscillation. The damage can be very severe. With metals it is characterized by pitting which resembles corrosion, and with ferrous metals there is a characteristic production of red ferric oxide. 

Any action in mitigating flow maldistribution must be preceded by an identification of possible reasons that may cause the performance deterioration and/or may affect mechanical characteristics of the heat exchanger. The possible reasons that affect the performance are [131,147] (1) deterioration in the heat exchanger effectiveness and pressure drop characteristics, (2) fluid freezing, as in viscous flow coolers, (3) fluid deterioration, (4) enhanced fouling, and (5) mechanical and tube vibration problems (flow-induced vibrations as a consequence of flow instabilities, wear, fretting, erosion, corrosion, and mechanical failure). 

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