ASHRAE Journal - June 2022 - 25

COLUMN ENGINEER'S NOTEBOOK
FIGURE 1 Small simplex softener. (Courtesy of
IMEG Corp.)
FIGURE 2 Small duplex softener. (Courtesy of
BAC)
FIGURE 3 Large duplex resin beds. (Courtesy of
IMEG Corp.)
Where Jeff lives with 22 grains (376 ppm) of hardness,
residences tend to soften all potable§ water except for
hose bibbs (which is a waste of salt) and the kitchen
sink (which makes it taste worse and adds a little
sodium to your diet). A client in the Madison, Wis.,
area had a problem with copper-tube steam water
heaters corroding. They were softening all domestic
hot water. After doing the analysis (Madison has a great
utility that lets you look up your client's address, tells
you what percentage of their water comes from each
well, and gives you a water analysis for each well), we
realized water was far too corrosive and recommended
softening only 7% of the hot water and bypassing 93%.
Jeff told them that he was surprised they weren't having
trouble with other copper pipes failing. The reply
was that they had pinhole leaks they had been fi xing in
the tunnel between their central utility plant and their
main facility.
These calculations can be done in a workbook, or you
may have a vendor who will provide this service.
Anaerobic and Under Deposit Corrosion
Microbially infl uenced corrosion (MIC),# Figure 4,
and other anaerobic microbiological attacks have been
FIGURE 4 MIC vs. oxygen corrosion . (Courtesy of BAC)
a major issue in sprinkler systems and in open water
cooling systems due to corrosion under deposits. Often
sulfate-reducing bacteria (SRB)II are part of the problem.
Preventing MIC in sprinkler systems is diffi cult because
water treatment can minimize the black, stinky water,
but it also means high levels of biocides and/or corrosion
inhibitors could be sprayed on occupants. System cleanliness
is key to reducing anaerobic corrosion, especially
in open water systems and those with equalizer lines.
Reference 1 is a great source for water treatment information.
Search for " microbiologically infl uenced " and
" anaerobic, " as information appears in many locations.
Pure Water Systems
Many ASHRAE members design laboratories, dialysis
§Potable: Safe to drink. Pronounced with a long " o. " In the U.S., this normally means water that complies with the National Primary Drinking
Water Regulations (NPDWR) (Reference 2). The NPDWR document is also an excellent source of information about the adverse
effects and sources of each regulated contaminant. Some states may also adopt the National Secondary Drinking Water Regulations,
which are shown at the end of the NPDWR document and affect cosmetic issues and taste, but not health.
#Microbiologically infl uenced corrosion (MIC) is corrosion in water systems that is accelerated due to the presence of biological organisms.
As biological organisms live and die, they directly affect the electrochemical conditions on the surface of the metal, due to several
factors, such as acidic or basic conditions, and under deposit corrosion. This is most commonly an issue in sprinkler systems.
II Sulfate-reducing bacteria (SRB) are bacteria that can obtain energy by oxidizing organic compounds or molecular hydrogen (H2) while
reducing sulfate (SO42-) to hydrogen sulfi de (H2S). Interaction of water and metal creates a layer of molecular hydrogen on the metal
surface, and sulfate-reducing bacteria can oxidize the hydrogen and create hydrogen sulfi de and sulfuric acid, which contribute to corrosion.
Microbiologically infl uenced corrosion (MIC) is an issue in some metallic piping systems, and one common cause in iron/steel
systems is sulfate-reducing bacteria.
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ASHRAE Journal - June 2022

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