This heat exchanger experienced failure due to cracking of the heat exchanger tubes. A dark red/black deposit covering the ID contained several locations with cracks or pits (Figure
A cross section was made of a typical pitted area. The ID pits were filled with a deposit and contained cracks growing from the bottom of the pit
(Figure 2). This cross section was examined using energy dispersive x-ray analysis (EDS).
EDS clearly showed that the pits were the result of dezincification.
Conditions favoring dezincification are: contact with slightly acid or alkaline water,
not highly aerated, low rates of flow of the circulating liquid, relatively high tube-wall temperatures, and permeable deposits or coatings over the tube surface.
Figure 1. Crack on the ID of the
Figure 2. Dezincification plug (100X