JOHNSON CONTROLS
152
FORM 155.32-ICOM1.EN.GB
ISSUE DATE: 10/13/2017
SECTION 7 – MAINTENANCE
TABLE 38 -
TENDENCY OF GENERATION OF SCALES AND CORROSION BY QUALITY OF COOLING
WATER
QUALITY OF COOLING
WATER
GENERAL TENDENCY
SCALE AND ITS COLOR
CORROSION AND ITS COLOR
Factors of
Water Quality
Water of low PH number
Hard scales are generated
and iron bacteria propagate
Bad corrosion of iron
and copper
Dark brown
~ Pale
greenish
blue
Water of high PH number
Calcium carbonate scales
are generated easily.
Pale
yellow
──
Water contains many
calcium ions (Ca
2+
) and
magnesium ions(Mg
2+
)
Sulfuric ion SO
4
2-
, silica SiO
2
and 2 carbonate ion CO
3
2-
combine together to generate
hard scales.
Pale
yellow
──
Water contains many
chlorine ion (Cl
-
)
──
Iron and copper
tubes are corroded
badly.
Water contains many
sulfuric ions (SO
4
2-
) and
silica (SiO
2
)
Calcium sulfide (CaSO
4
) and
calcium silicate (CaSiO
3
)
combine together to generate
hard scales.
Gray
SO
4
2-
corrodes
copper tubes badly.
Greenish
Blue
Water contains many iron
(Ferrous ion (Fe
2+
),ferric
ion (Fe
3+
))
Fe
3+
becomes ferric
hydroxide (Fe(OH)
3
) to make
red water and sets red rust
of ferric dioxide (Fe
2
O
3
).
Iron bacteria propagate
remarkably.
Reddish
brown-
Black
Fe
3+
corrodes iron
and copper tubes
Reddish
brown-
Black
Environmental
Factors
Water smells bad
(Contains compounds of
sulfur, hydrogen sulfide
(H
2
S), ammonium ion
(NH
4+
), methane, etc.)
Scales are generated easily,
and slime is generated.
Greenish
Blue –
Dark
brown
H
2
S and NH
4
+
corrodes copper
tubes badly.
Black –
Greenish
blue
Water contains organic
matters (High COD and
BOD)
Scales are generated easily,
and slime is generated.
──
Exhaust gases (Sulfurous
acid gas (SO
2
), nitrogen
oxide (NO
2
), hydrogen
chloride (HCl), ammonia
(NH
3
), etc.) mixed in water
in cooling tower
If organic nitrogen and
inorganic nitrogen are
contained, algae propagate.
SO
2
becomes SO
4
2-
and
combines with Ca
2+
and Mg
2+
to generate scales.
Algae:
Green
Pale
yellow
Exhaust gas from
automobiles,
factories, sewage
plants, ammonia
refrigerating
machine, etc. lower
or heighten PH
number. As SO
4
2-
,
Cl
-
and NH
4
+
are
increased, tubes are
corroded and pitted
very quickly.
Solid matter (Mud, sand,
fibers, dust, insects, etc.)
in water in cooling tower
Scales are generated easily.
Solid matters set. Slime is
generated.
────
Sea wind (District by sea) Scales are generated easily.
Tubes are corroded
badly.
Reddish
brown-
Black
