Correct cooling water treatment and follow-up of the cooling water condition
are of utmost importance for keeping the cooling water systems of the
engines in good condition. The corrosion processes that could occur due to a
bad cooling water quality may under certain circumstances be local and by
their nature proceed very rapidly. This may cause unexpected operatingproblems or engine failures even within relatively short periods of time, for
example in the cylinder head exhaust valve seat pockets and other areas
prone to corrosion (see further comments in the “Worth noticing” chapter
below) in the cooling water systems of the engines.
Most of the cooling water additives which are approved by Wärtsilä are nitrite
(typically NaNO2) based and today themajority of the installations in
operation are also using nitrite based additives. There is a slow trend towards
more environmentally friendly alternatives. These operating instructions and
recommendations are mainly intended for installations using nitrite based
additives but certainly contain useful information for users of other types of
To avoid unnecessarycorrosion damages and operating problems in the
cooling water systems of the engines.
Instructions & Recommendations
Raw water quality
The raw water quality for the cooling water circuits of an engine must meet
the following specification:
pH Minimum 6.5
Total hardness Maximum 10 °dH*)
Chlorides (Cl) Maximum 80 mg/l
Sulphates (SO4) Maximum 150 mg/l
*) Atotal hardness of 10 °dH (German degrees) . 178 mg/l (as CaCO3).
Soft waters (like distilled, ion exchanged, reverse osmosis and rain water)
with a total hardness close to 0 °dH have the ability to dissolve oxygen and
carbon dioxide from the air, which quite rapidly lowers the pH levels and
increases the corrosive effect of these waters.
Suitable amounts of calcium and magnesiumcompounds (= total hardness)
participates in forming a thin, corrosion protective layer on the heat
exchanging surfaces of the cooling water system. Correct additive dosage
and careful follow up of the dosing levels are thus even more important with a
very soft water compared to a normal quality tap/drinking water with a total
hardness of 2 – 10 °dH. The use of raw water qualities with a toohigh total
hardness may on the other hand result in excessive deposit formations and
reduced heat transfer properties. Water produced by one (1) stage reverse
osmosis processes may sometimes contain too high chloride (and sulphates)
contents, and are in those cases not suitable as cooling water. Two (2) stage
RO processes usually achieve satisfactory chloride and sulphate levels.Additive dosing
The cooling water additive dosage recommendations may vary, depending
on additive type and manufacturer. The dosage recommendations for the
cooling water additives approved by Wärtsilä are presented in table 3. There
exists no general dosage recommendation for the approved additives.
Observe that these recommendations apply for normal raw/cooling water
properties, see alsothe “Worth noticing” comments below. Generally a slight
overdosing is better than under dosing, but an excessive additive (nitrite)
dosage is not to be recommended economically, nor technically. Large (> 2 –
3 times the maximum recommendation) overdosing may cause corrosion on
copper, brass and other “soft alloys” in the system and possibly also
problems with precipitation and depositformations.
Table 3 presents the currently approved cooling water treatment products,
their suppliers of these and the dosage recommendations (presented as
some different units).
Aggressive compounds and conditions
Sulphates, sulphides, halides and especially chlorides are extremely
aggressive (corrosive) against iron. If there are high amounts of these...