Heat exchangers may be subject to various modes of deterioration associated with flow such as erosion- corrosion, fretting, and fatigue, and they may suffer stress corrosion cracking (SCC) due to preexisting or imposed stress. These mechanically induced problems will be discussed first, and then some of the fluids that give rise to corrosion in exchangers will be considered.

A. Mechanically induced damage

There are three main types of wastage directly associated with liquid flow, as illustrated in Figure 1: cavitation, impingement, and erosion-corrosion.

Figure 1 Wastage due to stress. (a) Cavitation: collaps of bubbles at metal surface sets up a stress oscillation transverse to the surface,causing localized fatigue failure. (b) Impingement: a similar effect produced by liquid drops impinging on a surface. (c) Erosion-corrosion: transverse stress due to fluid flow causes rupture or thinning of protective film

(a) Cavitation