WÄRTSILÄ 41508, Инструкция по эксплуатации

Страница: 19 / 161

Corrosion rate as a function of nitrite concentration Corrosion rate as a function of nitrite concentration
Nitrite based cooling water additives are so called anodic inhibitors and Nitrite based cooling water additives are so called anodic inhibitors and
require proper dosing and maintenance in order to serve as intended.
require proper dosing and maintenance in order to serve as intended.
The nitrite of the additive is as such a salt and it will increase the
The nitrite of the additive is as such a salt and it will increase the
conductivity of the water. The conductivity is on the other hand one of
conductivity of the water. The conductivity is on the other hand one of
the main parameters affecting the corrosion rate once a corrosion
the main parameters affecting the corrosion rate once a corrosion
process gets started, the higher the conductivity the higher the corro-
process gets started, the higher the conductivity the higher the corro-
sion rate.
sion rate.
If the conditions (nitrite level, chlorides, pH, etc.) in the systems are
If the conditions (nitrite level, chlorides, pH, etc.) in the systems are
such that the nitrite based additive is no longer able to protect the
such that the nitrite based additive is no longer able to protect the
entire surface of the system there may occur a rapid, local corrosion in
entire surface of the system there may occur a rapid, local corrosion in
the areas that are not protected. The corrosion rate at the attacked
the areas that are not protected. The corrosion rate at the attacked
areas will even be much greater than it would be with no additive at
areas will even be much greater than it would be with no additive at
all present in the system, see schematic graph of the corrosion rate as
all present in the system, see schematic graph of the corrosion rate as
a function of the nitrite dosage in Fig 02-1. Observe that the position
a function of the nitrite dosage in Fig 02-1. Observe that the position
of the curve peak on the x-axis (= dangerous condition for corrosion) is
of the curve peak on the x-axis (= dangerous condition for corrosion) is
not stable, but will shift depending on temperature, pH, chlorides &
not stable, but will shift depending on temperature, pH, chlorides &
sulphates contents, etc. in the cooling water.
sulphates contents, etc. in the cooling water.
The table below shows shows examples of the most common cooling
The table below shows shows examples of the most common cooling
water additive types.
water additive types.
B B
A A
C C
o o
r r
r r
o o
s s
i i
o o
n n
r r
a a
t t
e e
X ppm X ppm
Nitrite Concentration Nitrite Concentration
T T o give full o give full protection the protection the Nitrite level Nitrite level
should be kept should be kept above X ppm. above X ppm. The The
actual concentration is additive actual concentration is additive
supplier dependent. supplier dependent.
A permanent lower level will lead to A permanent lower level will lead to
an accelerated corrosion rate. an accelerated corrosion rate.
Fig 02-1 Fig 02-1
3202602002 3202602002
34SG-200303-03 34SG-200303-03 Fuel, Fuel, Lubricating Lubricating Oil, Oil, Cooling Cooling Water Water