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SECTION 2
VSRT-IOM-2022-0728
INSTALLATION
2-37
Glossary of Water Supply Terms
Dissolved Oxygen
: Oxygen that is dissolved in the feedwater
will cause the steel in the boiler and the feedwater system to
be attacked by the water in a manner described as “pitting”.
The pits that are produced can vary from tiny depressions
to holes large enough to penetrate the boiler metal and are
usually covered with tubercles of iron oxide. Once pitting
starts, it may be extremely hard to arrest. Pitting can proceed
at a surprisingly rapid rate and can occur not only in the boiler
proper, but also in pre-boiler equipment such as economizers,
feedwater tanks, and feedwater lines.
Suspended Solids:
Suspended solids are the undissolved
matter in water, including dirt, silt, vegetation, iron oxides,
and any other insoluble matter. Normally suspended solids
are expressed in terms of turbidity. Suspended solids may
also deposit in low velocity areas and create fouling. In line
filters, or various types of pretreatment can be used to lower
the suspended solids level. Periodic blowdowns will eliminate
suspended solids.
Alkalinity:
Alkalinity is the capacity of a water to neutralize
acids. Common water alkalinities consist of bicarbonate,
carbonates, hydroxide, phosphate, and silicate. These
alkalinities, especially bicarbonates and carbonates, break
down to form carbon dioxide in steam, which is a major factor
in the corrosion on condensate lines. High alkalinity also
causes foaming and carry over in boilers. Both foaming and
carry over cause erratic boiler operation. The reason for the
high alkalinity should be determined. It may result from lack
of sufficient blo
w off. The source of alkalinity may be due to an
overdose of alkaline internal water treatment chemical.
pH:
pH is a measure of the degree of acid or base of solution.
A pH range of 8.5-10.5 will have little influence on the
corrosion rate of carbon steel. A low pH can result in corrosion
of metals, while a high pH can result in scale formation
or caustic embrittlement. In order to control boilers and
equipment used for the external treatment of make-up water,
it is essential that reliable pH measurements be made. RO/
DI water will have a low pH and will require neutralization if
used in a carbon steel vessel. It is critical that the boiler pH be
alkaline (8.5-10.5) whenever water is in the boiler.
Chlorides:
If chloride levels are high enough to cause severe
corrosion, they can be controlled by limiting the cycles of
concentration and increasing boiler blowdowns. Corrosion
from chlorides can also be controlled by increasing the
amount of corrosion inhibitor, or changing to a more effective
inhibitor.
Oil:
Oil is not a natural constituent of boiler water; still it can
frequently enter a system through leaks in a condenser or
other heat exchanger. Oil can also enter a system through
the lubrication of steam driven reciprocating equipment.
Whatever the source, the presence of oil in boiler water is
undesirable. Oil can act as a binder to form scale. In high
heat-transfer areas oil can carbonize and further contribute to
the formation of scale and low pH. Foaming is one indication
of oil in boiler water. Its presence can also be confirmed by
first shaking a bottle containing boiler water. If oil is present
foam will result. Often oil in boiler water will originate in
the condensate. This contaminated condensate should be
directed to the sewer until the source of the oil is determined
and corrective steps taken.
Iron (oxides):
Iron in any of its oxide or complex forms is
undesirable in boiler water. Iron in its various forms can
originate in the raw water makeup, condensate return water,
or form directly in the boiler as a result of corrosion. It can
concentrate in the boiler and it tends to collect in stagnant
areas.
Water Hardness:
Water hardness is the measure of calcium
and magnesium content as calcium carbonate equivalents.
Water hardness is a primary source of scale in boiler
equipment. Hardness is removed by softening.
Periodically, the ion exchange resin bed requires regeneration
by flushing through with a brine solution followed by rising
with fresh water. The interval between regeneration is
dependent upon the raw water hardness and flow rate.
In all cases the water hardness should be tested periodically
and prior to starting the boiler or generator to ensure efficient
operation of the softener. Unsoftened water should not be
allowed to enter the steam boiler or generator unless sufficient
scale inhibitor chemical is used.
Feedwater:
Feedwater is the combination of fresh makeup
and returning condensate that is pumped to the boiler.
Condensate:
Condensate is condensed steam that is
normally low in dissolved solids. Hence, it does not
contribute to the dissolved solid content of the feedwater.
In addition, condensate is very expensive to waste. It’s been
chemically treated, heated, pumped, converted to steam, and
condensed.
Dissolved Solids:
Dissolved solids are salts in the water that
stay in solution. They are invisible to the naked eye. As the
boiler generates steam, dissolved solids will concentrate. If
the concentration becomes too high, they will precipitate,
form a suspended solid, and concentrate in the vessel. Daily
boiler blowdown is recommended to help prevent the
formation of deposits. Consult Blowdown procedure in the
