25 May 2005
Figure 4-12. Super-Enhanced Copper Tubes
Figure 4-13. Close-Up of Corrosion Pitting on Super-Enhanced Copper Tube
White Rust. Some cooling towers are constructed with galvanized steel
components and must not be exposed to conditions of high pH (high alkalinity). The
galvanizing process deposits a protective zinc coating on a mild steel metal surface,
resulting in increased resistance to corrosion. Failure to avoid such exposure can result
in production of "white rust" due to the corrosion of the galvanizing coating. Eventually,
this corrosion process exposes the mild steel underneath, which then starts to corrode.
White rust failures have been a common occurrence throughout the country, mainly with
newer cooling towers. Proper protection of the galvanizing material is necessary both
during startup of a new cooling tower and during normal operations. Specific water
treatment chemicals are needed to provide this protection. Examples include
pretreatment with a high level of orthophosphate.
Cooling Tower Film Fill. Small- and medium-sized cooling towers use
film fill, which is a tightly packed media as compared to the splash-type fill used