FORM 155.32-ICOM2.EN.UL
SECTION 7 – MAINTENANCE
ISSUE DATE:1/10/2018
JOHNSON CONTROLS
147
Table 40 -
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, or other toxic
gases)
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
), or other gases)
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
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, and
other forms of solid matter)
in water in cooling tower
Scales are generated easily.
Solid matters set. Slime is
generated.
────
Sea wind (District by sea)
Scales are easily generated.
Tubes are badly
corroded.
Reddish brown-
Black
