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to prevent acidic corrosion of boiler tubes and plates
and to provide for the precipitation of scale forming
salts.
Below a Ph of 5.0 the water is acidic enough to
dissolve the steel boiler plates. Under these
conditions the steel gradually becomes thinner and
thinner until it is destroyed. At a Ph between 5 and
9.4 pi=ing of steel plates will occur at a rate
dependent upon the amount of dissolved oxygen in
the boiler.
Dissolved Oxygen
Aeration of city water supply is frequently used
to remove other noxious gasses, however, e:cient
aeration results in saturation of the water with
oxygen.
e majority of corrosion problems are
directly related to the quantity of dissolved oxygen
in the boiler water. Elimination of the corrosive
e<ect of dissolved oxygen can be accomplished
either directly or chemically.
Direct or mechanical removal of dissolved
oxygen is done through the use of a deaerator.
Chemical deaeration is done through the
introduction of speci9c chemicals in the boiler to
react with the oxygen.
content should be maintained at as low a level as
possible. At no time should it exceed 0.007 mg/l.
Sulfites
Sodium sul9te is generally used for the chemical
removal of dissolved oxygen within the boiler water.
To assure the rapid and complete removal of the
oxygen entering the boiler feed water system the
concentration of sul9te in the boiler must be
maintained at a minimum of 120 ppm. (parts per
million).
Solids (Steam Boilers)
Solids can be broken up into two categories of
both suspended and dissolved. Suspended solids are
those that can be removed by 9ltration while
dissolved solids are in solution with the water.
e best test for the determination of the solids
content of the boiler water is through a conductance
test.
e conductance value of boiler water varies
by the various ionized salts present.
conductance can be used to measure the total
dissolved solids in the boiler water and to serve as
e dissolved oxygen
e
an accurate means for the control of solids through
the use of blow down.
Another test that is sometimes used as a measure
of solids is to measure the chloride present in the
boiler water.
e ratio of chlorides in the boiler
water to that of the feed water can be used as a
means to determine the amount of blow down
required.
e chloride test is unsuitable for feed
water with low incoming concentrations, and the
concentrations in the feed water must be averaged
over time for accuracy.
High boiler solids will lead to foaming, priming,
surging, and carry over.
be overcome by proper blow down of the boiler.
Alkalinity
e alkalinity of boiler water should be
su:ciently high enough to protect shell and plates
against acidic corrosion, but not so high as to
produce carryover. A minimum value for alkalinity
for adequate protection is 200 ppm.
High boiler alkalinity (in excess of 700 ppm)
should be avoided. Values higher than this can
cause the steel to become bri=le.
Phosphates
Phosphates are used to react with calcium
hardness in the boiler water. In order for this
reaction to take place it is important to maintain a
Ph at a minimum value of 9.50. It is desirable to
keep the concentration of phosphates in the water to
30-50 ppm to enable the complete reaction of the
phosphates with the calcium hardness entering the
boiler through the feed water.
Hardness
e hardness of water is caused by calcium and
magnesium ions. Water hardness will vary greatly
throughout the country depending on the source of
the water.
Hard water in boilers and hydronic heaters can
cause the formation of scale and sludge or mud.
hardness must be removed in the makeup water to
the return system. Total hardness should not exceed
50 ppm.
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ese conditions may only
e
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