JOHNSON CONTROLS
109
SECTION 7 – MAINTENANCE
FORM 155.33-ICOM2.EN.GB
ISSUE DATE:12/4/2017
7
TABLE 22 -
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 pH low
Hard scales are generated
and iron bacteria grow
Corrosion of iron and
copper pipes
Dark brown
~ Pale
greenish
blue
Water pH high
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 carbonate ion CO
3
2-
combine together to generate
hard scales.
Pale
yellow
──
Water contains many
chlorine ions (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.
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 deposits ferric
dioxide (Fe
2
O
3
). Iron bacteria
grow.
Reddish
brown-
Black
Fe
3+
corrodes iron
and copper tubes
badly.
Reddish
brown-
Black
Environmental
Factors
Water smells bad
(Contains sulfuric acid,
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
+
corrode 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 and inorganic
nitrogen are contained, algae
grows. SO
2
+ O
2
becomes
SO
4
and combines with Ca
2+
and Mg
2+
to generate scale.
Algae:
Green
Pale
yellow
Exhaust gas from
automobiles,
factories, sewage
treatment
plants, ammonia
refrigerators, etc.
lower or raise the
pH. As SO
4
2-
, Cl
-
and
NH
4
+
increase, tubes
get corroded and
pitted very quickly.
Solid matter (Mud, sand,
fibers, dust, insects) 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
