Gestión del cambio

It is recommended to use EP-gear oils, viscosity 400-500 cSt at 40 °C=ISO VG 460 as lubricating oils for the turning device.

The list of lubricating oils for the engine turning device approved by the turning device manufacturer can be found in the end of this chapter.

02.3 Cooling water

02.3.1 General

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 specifica-tion found in the end of this chapter. Further, the use of an approved cooling water additive or treatment system is mandatory.

Caution! 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.

Caution! 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!

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02.3.2 Additives

As additives, use products from well-known and reliable suppliers with vast distribution nets. Follow thoroughly the instructions of the sup-plier.

Attention! 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.

Attention! Sodium nitrite is toxic.

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.

B

A

Corrosion rate

X ppm Nitrite Concentration

To give full protection the Nitrite level should be kept above X ppm. The actual concentration is additive supplier dependent.

A permanent lower level will lead to an accelerated corrosion rate.

Fig 02-2 3202602002

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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, see schematic graph of the corrosion rate as a function of the nitrite dosage in Fig 02-3. Observe that the position of the curve peak on the x-axis (= dangerous condition for corrosion) is not stable, but will shift depending on temperature, pH, chloride &

sulphate contents, etc. in the cooling water.

The table below shows shows examples of the most common cooling water additive types.

Summary of the most common cooling water additives

Additive Advantages Disadvantages

Sodium nitrite

- good efficiency, if dosage is controlled carefully

- small active quantities, 0.5 % by mass

- cheap

- suitable as additive except in air cooled heat changers with large soft solder surfaces

- toxic

- risk of spot corrosion when too low concentration

Nitrite + borate

- no increased risk of corrosion

at over doses

- innocuous for the skin

- tendency to attack zinc coverings and soft rings

- toxic: lethal dosage 3 - 4 g solid nitrite

- risk of spot corrosion when too

low concentration

Sodium silicate

- not toxic

- harmless to handle

- not active when water velocity exceeds 2 m/s - commercial products very expensive

- increased risk of corrosion when too low tration; spot corrosion - limited suitability

Sodium molybdate

- not toxic

- harmless to handle

- more expensive than toxic additives

- increased risk of corrosion, if unsufficently dosed - can cause deposit formation

(molybdates can collect to ferrous sulphates)

Organic and inorcanic synergistic

based

- not toxic - more expensive than sodium

nitrite and molybdate based

additives

- big active quantitives by mass

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02.3.3 Treatment

When changing the additive or when entering an additive into a system where untreated water has been used, the complete system must be cleaned (chemically) 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.

The list of approved cooling water additives and treatment systems can be found in the end of this chapter.

Attention! 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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