York YHAU-CW - TABLE 30 - Tendency of Generation of Scales and Corrosion by Quality of Cooling Water

JOHNSON CONTROLS
146
FORM 155.31-ICOM2.EN.UL
ISSUE DATE: 12/21/2018
SECTION 7 – MAINTENANCE
TABLE 30 - 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
Water Quality
Factors
Low PH of the water
Hard scales are generated
and iron bacteria propagate
Bad corrosion of iron
and copper
Dark brown
~ Pale
greenish
blue
High PH of the water
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 chlorine
ions (Cl
-
)
──
Iron and copper
tubes are corroded
badly.
Water contains many
sulfuric ions (SO
4
2-
) and
silica (SiO
2
)
Calcium sulde (CaSO
4
) and
calcium silicate (CaSiO
3
)
combine together to generate
hard scales.
Gray
SO
4
2-
corrodes
copper tubes.
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
(Containing compounds
of sulfur, hydrogen sulde
(H
2
S), ammonium ion
(NH
4
+
), methane, or other
gases)
Scales are generated easily,
and slime is generated.
Greenish
Blue –
Dark
brown
H
2
S and NH
4
+
corrodes copper
tubes.
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 attributing
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, or other
environmental
elements, 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,
bers, 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 heavily
corroded.
Reddish
brown-
Black