Cooling Water Additives and Treatment

In order to prevent corrosion, scale deposits or other deposits in closed circulating water systems, the water must be treated with additives.
Before treatment, the water must be limpid and meet the specification found in the end of this chapter. Further, the use of an approved cooling water additive or treatment system is mandatory.


Distilled water without additives absorbs carbon dioxide from the air, which involves great risk of corrosion.

Sea water will cause severe corrosion and deposit formation even if supplied to the system in small amounts.
Rain water has a high oxygen and carbon dioxide content; great risk of corrosion; unsuitable as cooling water.
If risk of freezing occurs, please contact the engine manufacturer for use of anti-freeze chemicals.
Fresh water generated by a reverse osmosis plant onboard often has a high chloride content (higher than the permitted 80 mg/l) causing corrosion.


The use of glycol in the cooling water is not recommended, if it is not necessary. Since glycol alone does not protect the engine against corrosion, additionally an approved cooling water additive must always be used!

As additives, use approved products from well-known and reliable suppliers. In marine applications suppliers’ wide distribution networks makes it easier to get the same product in different geographical locations.


The use of emulsion oils, phosphates and borates (sole) is not accepted.

In an emergency, if compounded additives are not available, treat the cooling water with sodium nitrite (NaNO2) in portions of 5 kg/m3. To obtain a pH value of 9, add caustic soda (NaOH), if necessary.


Sodium nitrite is toxic. Handle with care and dispose all possible residuals in accordance with valid environmental regulations.

Nitrate oxidation curve

Corrosion rate as a function of nitrite concentration
Nitrite based cooling water additives are so called anodic inhibitors and 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 conductivity of the water. The conductivity is on the other hand one of the main parameters affecting the corrosion rate once a corrosion process gets started, the higher the conductivity the higher the corrosion rate.
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 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 areas will even be much greater than it would be with no additive at all present in the system.

When changing the additive or when entering an additive into a system where untreated water has been used, the complete system must be thoroughly flushed and if necessary chemically cleaned and rinsed before fresh treated water is poured into the system. If, against our recommendations, an emulsion oil has been used, the complete system must be absolutely cleaned of oil and greasy deposits.
Evaporated water should be compensated by untreated water; if treated water is used the content of additives may gradually become too high. To compensate for leakage or other losses, add treated water.
In connection with maintenance work calling for drainage of the water system, take care of and reuse the treated water.


Ask the supplier of the treatment product for instructions about treatment procedure, dosage and concentration control.

Most suppliers will provide a test kit for the concentration control. Additionally a frequent laboratory analysis of cooling water at 3 months interval is recommended to ensure safe engine operation.


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  1. Hi all,

    Water cooling is commonly used for cooling automobile internal combustion engines and large industrial facilities such as steam electric power plants, hydroelectric generators, petroleum refineries and chemical plants. Thanks a lot!


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