Photo Gallery F2: Chill Water
Chill water systems, also termed chilled water, are fundamental to virtually all larger building properties. Unlike condenser water service, they benefit from far lower internal corrosion activity but then have a potential secondary corrosion front occurring externally. The smaller lines to any chill water system are the most vulnerable due to lesser wall thickness, threaded construction, thinner insulation, and their frequent placement in areas of higher humidity – such as within fresh air plenums, mechanical rooms, and at perimeter building columns.
A common issue called CUI, for corrosion under insulation, applies to the failure of the insulation to protect the pipe exterior. This is less a failure of the insulation itself and more of a design, installation, and maintenance issue. Nevertheless, CUI can easily destroy a chill or cold water piping system far in advance of just internal corrosion alone, and is a significant problem for both 2 pipe and 4 pipe HVAC systems. Whereas internal corrosion activity can be controlled to near 0.5 MPY with little effort, an aggressive external corrosion condition can multiply that loss 5 times or more. And unlike the application of chemical water treatment, there are no preventative methods available other than preventing it from occurring in the first place. External corrosion is also quite random and varies widely depending upon insulation thickness, condition, area moisture – thereby making it impossible to predict.
Critical side stream water filtration is almost never installed in its design phase, and only considered once an internal corrosion problem becomes too significant to ignore. Furthermore, the bare carbon steel pipe is never painted or protected against corrosion; instead relying entirely upon insulation well known to fail. For most heavily damaged piping systems, their early retirement has been due to the combination of inadequate internal corrosion control compounded by insufficient insulation which has been inadequately installed.
Copper and brass pipe are the exclusion to this corrosion threat with the possible exception of where soft foam insulation has been installed.
