1. Introduction
1.5 DD-Containing Proteins in the TLR/MyD88/IRAK System
15.1 PROBLEM AREAS
There are four key areas which must be considered when treating diesel engine cooling water systems.
15.1.1 Scale
Scale results when a compound precipitates from the water phase because its solubility has been exceeded. Scale is a dense, adherent deposit of minerals and is tightly bonded to itself and to metal surfaces.
Scale forming on metal surfaces requires four simultaneous factors:
A. Exceeding the solubility of the compound in water.
B. Formation of small nuclear particles.
C. Adequate contact time for crystal growth.
D. Scale re-deposition exceeds the rate of dissolution.
One primary factor influencing scale adherence is surface roughness.
The rougher the surface, the greater the probability of adherent scale forming. Also, scale forms more readily on corroding surfaces than on non-corroding surfaces. Easily corroded metals (mild steel) result in significantly more scale than metals that do not corrode (stainless steel).
In addition to the four primary factors influencing scale deposition, there are other factors that offset the formation of scale. Wildly fluctuating pH is a significant cause of scale deposition in closed loop systems. Unitor uses Borates to buffer and control this fluctuating pH.
As the pH of the system increases, so does the scaling potential for almost all common scale. This would include Calcium Carbonate, Calcium Sulphate, and Iron Oxide. Low pH extrusions can accelerate corrosion, provide nucleating sites and increase the potential for some forms of Silica scale.
Scale formation in diesel engine cooling water systems can be controlled by various methods. Removing scale-forming Ions from the water before that water enters the cooling system is the most effective method. Almost all engine manufacturers recommend the use of distilled water. Distilled water is free of minerals. However, it is aggressive water and, if untreated, can lead to corrosion.
15.1.2 Corrosion
Corrosion is the phenomenon that returns metals to their native states as chemical compounds or minerals.
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In diesel engines containing dissimilar metals, our concern is galvanic corrosion. When exposed to water, one metal becomes anodic and the other cathodic, setting up a galvanic cell. For example, when Copper and Mild Steel are connected in water, the Mild Steel becomes the Anode, because it will give up electrons more readily than the Copper. The metal loss occurs at the anode, so the Mild Steel corrodes.
Unitor recommends the use of a corrosion inhibitor containing Nitrite, Borate and Azole. Nitrite protects Mild Steel and Iron, while Azole protect Copper from corrosion. Nitrite acts by forming a protective metal oxide (passivating film) on the metal to be protected.
15.1.3 Fouling
Fouling is different from scaling in that fouling deposits are formed from material suspended in the water, while scale deposits are formed from minerals in solution. Materials that cause fouling in cooling water systems are suspended solids and oil leaking into the system. We must control fouling in a diesel engine cooling water system, as it interferes with the effectiveness of corrosion inhibitors.
15.1.4 Microbiological activity
Nitrites act as a food source for some types of bacteria. While the presence of bacteria is not as widespread in diesel engine cooling water systems as in other cooling water systems, it is a potential problem. The problem becomes apparent when conducting chemical tests of the cooling water. If the personnel on the vessel are dosing Nitrites and do not get a reading and the pH begins to fall, there is a possibility of microbiological activity. This can be verified by simple test methods (“dip slides”), or by sending a sample of the water to Unitor.
15.2 UNITOR COOLING WATER TREATMENT PRODUCTS
Diesel engines have almost completely replaced turbines as the main propulsion unit in ships. These engines need to be cooled and water is used for this purpose. This water must be conditioned to ensure that scale does not deposit on the heat transfer surfaces in the cooling system.15.2.1 The System
The water is circulated around the engine and any loss due to leaks, etc. is made up from the expansion tank. As it circulates through the engine cooling spaces, the water picks up the engine heat, and this hot water goes to a heat exchanger where it is cooled.
The steam heater is used to warm the engine up from cold. An air separator is normally installed to get rid of entrained air in the system.
The water added to the expansion tank is termed “make-up” water.
Distilled water shall preferably be used for these cooling systems.
This is normally made onboard by a fresh water evaporator (or generator). A useful way of increasing the plant efficiency is to utilise the heat taken from the engine to provide a heat source to the evaporator.
If evaporated water cannot be used for make-up, then fresh shore water will have to be used. This is normally much higher in impurities.
The engine water temperature is in the region of 65 °C to 75 °C at the inlet to the engine. It is maintained at this temperature by controlling the cooling. The cooler is bypassed if the temperature drops.
15.2.2 Corrosion
As mentioned above, this is the main problem in diesel engine cooling systems. The water contains some Oxygen, and if it is untreated, an ideal environment will exist for all types of corrosion.
15.3 DIESELGUARD NB AND ROCOR NB LIQUID
15.3.1 How do they work?All the information is contained in the relevant product data sheets but can be summarised as follows:
They provide a very thin coating to all metal surfaces to prevent the corrosion from starting. The water is also made alkaline by the treat-ment to ensure that there is no acid corrosion.
It is important that there is an excess of treatment in the system to replace any breakdown in the coating and to treat the makeup water as it enters the system.
The testing for this is quickly carried out by the Spectrapak 309 Cooling Water Test Kit.
Some points to note:
– All cooling water treatments must be approved by accepted Government bodies for use where the water is used as a heat source for an evaporator making drinking water.
– The treatments must also be accepted by the engine manufacturer.
The Unitor products are covered in these areas.
15.3.2 Dieselguard NB dosage chart Unitor Dieselguard NB
– Initial dosage for an untreated system is 2 kg/1,000 liters of makeup water. This will bring the treatment level up to a minimum level of 1000 ppm.
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– The chart below can be used to determine the dosage requirement necessary to achieve a nitrite residual level between the minimum and maximum specification range limits.
Nitrite (as ppm NO2) 0 180 360 540 720 900 1080 1260 1440 1620–2400 Dieselguard NB Kg/1000 L 2.88 2.52 2.16 1.80 1.44 1.08 0.72 0.36 0 0
15.3.3 Rocor NB liquid dosage chart Unitor Rocor NB Liquid
A. Initial dosage for an untreated system is 9 litres/1,000 litres of distilled water. This will bring the treatment level up to a minimum level of 1000 ppm.
B. The chart below can be used to determine the dosage require-ment necessary to achieve a Nitrite residual level between the minimum and maximum specification range limits.
Nitrite (as ppm NO2) 0 180 360 540 720 900 1080 1260 1440–2400 Rocor NB Liquid L/1000 L 13.0 11.3 9.7 8.1 6.5 4.9 3.3 1.7 0
Note: When initially dosing a cooling water system, it is typical that the initial dosage may vary from vessel to vessel, or system to system.Total passivation of the cooling water system will consume more product than when making Nitrite up as mainte-nance dosages. The quality of make-up water will also affect initial dosage rates.
15.4 TESTS FOR DIESEL ENGINE COOLING WATER TREATED WITH DIESELGUARD NB/ROCOR NB LIQUID
The following tests are recommended to maintain cooling water within the prescribed limits when using Dieselguard NB/Rocor NB Liquid:
1. Nitrite 1000–2400 ppm as NO2
2. pH 8.3–10.0
3. Chlorides 50 ppm maximum
15.4.1 Nitrite – Recommended Limits 1000–2400 ppm as NO2
The Nitrite concentration should be maintained within the above recommended limits to effectively inhibit any corrosive or scaling action within a closed cooling system. Over-concentration should be avoided to minimise the cost of maintaining the system. Under-dosage can set up a condition where accelerated corrosion can occur in areas which become unprotected. Dieselguard NB/Rocor NB Liquid is dosed according to the recommended nitrite level.
15.4.2 pH – Recommended Limits 8.3–10
The effectiveness of a corrosion inhibitor is restricted to within a certain pH range. Treatment with Dieselguard NB/Rocor NB Liquid ensures that this pH range is observed when the Nitrite level is sufficiently maintained to prevent corrosion. Under certain conditions because of external contamination, the pH may not fall into the range usually found with the correct Nitrite dosage. In such cases, Unitor recommends dosing 50 ml of Unitor’s Alkalinity Control per tonne of cooling water to raise the pH value when the pH is below 8.3. Re-test pH after dosage to prove that the pH value is being maintained between 8.3 and 10.0.
15.4.3 Chlorides – Recommended limit max. 50 ppm
The Chlorides value of the cooling water should be kept as low as possible. Any increase in value whether sudden or gradual, will be an indication of sea water contamination. Check with the engine manu-facturer for other specified limits.
If the Chloride level exceeds 50 ppm, the possibility of corrosion in the system increases because Chlorides have a negative effect on the passivation film created by nitrites. Therefore, until corrective action has succeeded in bringing the Chloride level back down below 50 ppm, the nitrite level should be kept close to the upper limit (2400 ppm).
15.4.4 Sampling and testing of cooling water
Samples should be drawn, tested and results logged for each system at least of once per week and if possible six times per month.
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15.5 SAMPLING OF DIESEL ENGINES:
Accessible sampling cocks should exist on all cooling systems for each diesel engine. This including, but not limited to, main jacket water, piston cooling, fuel oil valve, auxiliary engines, low temperature systems, etc. A representa-tive sample must be taken from each cooling water system to be tested.
To minimise the effort in obtaining cooling water samples, a sample cock located in a position to draw a sample/having access to draw the sample quickly and easily will make the task of drawing samples a simple one.
In each case of drawing a sample, the container should be filled with the water to be tested, then sealed and labelled. It is advisable to conduct the appropriate tests within 30 minutes of drawing the sample, although this time limit can be extended when sample container is completely filled and sealed.
15.5.1 Sampling Procedure:
The suggestion is for one sample bottle for each system to be tested.
Mark each bottle clearly for each system.
A. Provide a clean bottle for each sample drawn:
The bottle should contain 0.5 litre, should be made of glass or plastic, have a screw cap that seals air-tight and a label indicating pertinent data:
a. Nature of water sample:
1. High temperature system
B. Allow effluent to flush through sampling line a minimum of three to five minutes.
C. Cool effluent to less than 25 °C before commencing to draw sample.
D. Rinse bottle at least three times with sample water.
E. Secure cap on bottle air tight.
F. Be sure sample is representative of total coolant in system.
G. Draw sample from same point in the system each time.
H. Sample should be analysed as soon as possible after securing.
15.6 TEST EQUIPMENT – UNITOR SPECTRAPAK 309 TEST KIT TEST PROCEDURES
15.6.1 Sample preparation:
A. Cool sample to 21–25 °C B. Filter if necessary to clarify.
15.6.2 Spectrapak 309 content:
A. Reagents:
a. Nitrite No. 1 tablets b. Nitrite No. 2 tablets c. Chloride tablets d. pH test strips (6.5–10.0) B. Equipment:
a. Syringe
b. Plastic sample container 15.6.3 Test methods:
A. Nitrite test
a. Take a 5 ml water sample with the syringe and put into the container provided.
b. Make the sample up to 50 ml using distilled water.
c. Add two Nitrite No. 1 tablets and shake to disintegrate (or crush with the rod provided). Sample will be white.
d. Add one Nitrite No. 2 tablet and shake to disintegrate.
e. Continue adding the Nitrite No. 2 tablets one at a time until a pink color persists for at least one minute.
Calculation:
Nitrite(ppm) = number of No. 2 tablets x 180
For example: If 9 tablets are used Nitrite = 9 x 180 = 1620 ppm.
f. Mark the result obtained on the log sheets provided against the date on which the test was taken.
B. Chloride test
a. Take a 50 ml water sample in the container provided.
b. Add one Chloride tablet and shake to disintegrate; sample should turn yellow if Chlorides are present.
c. Repeat tablet addition one at a time until the yellow colour changes to orange/brown.
Calculation:
Chloride ppm = (number of tablets used x 20) –20 For example:
If 3 tablets are used, Chloride ppm = (3 x 20) –20 = 40 ppm
d. Mark the result obtained on the log sheets provided, against the date on whichthe test was taken.
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C. pH test
a. Dip one of the test strips into the water sample so that the colour zone is completely immersed.
b. Compare the colour obtained with the reference, and read off the printed pH value.
c. Mark the result obtained on the log sheet provided, against the date on which the test was taken.
15.7 TEST RESULTS
15.7.1 RecordingThe test results should be recorded on the Spectrapak 309 Rapid Response log forms.
15.7.2 Reporting
Completed monthly log should be distributed as shown:
A. White copy – Send to Unitor Rapid Response Centre.
B. Pink copy – Vessel’s head office.
C. Yellow copy – Retain for ship’s records.
15.7.3 Evaluation
A. Logs will be reviewed for adherence to specification requirements by Unitor’s computerised RAPID RESPONSE system and staff.
B. A log review indicating the status of the system, problems and recommendations will be issued to the ship’s operator.
15.8 DESCALING LOW SPEED MARINE DIESEL ENGINE COOLING WATER SYSTEMS
Note: Be careful – use protective glasses and gloves
Connect a thin (1/3”–1/2”) transparent hose to some low point of the system and run it up to the level of the top of the expansion tank. You now have a level indicator for the system.
Drain the system and fill up with clean tap water to the lowest level in the expansion tank sight glass.
Connect the pressure side of the chemical cleaning module to the cooling water inlet manifold. Make return connection from the bottom of the expan-sion tank to the mixing tank of the module.
The ship’s fresh cooling water pump should be isolated from the system and not used for circulation, i.e. suction and pressure valves closed. The same applies to auxiliary machinery such as evaporators, generators, etc. These should be boiled out separately if necessary.
Sufficient Descalex to mix up a 5–10 % solution is gradually filled into the mixing tank, well dissolved and fed into the inlet manifold.
Take a sample of the solution for later colour comparison.
The solution should be heated to 60 °C using the engine’s cooling water pre-heater.
Circulate the system for 1/2hour, then close the shut-off valves on all cylinders except one, and circulate for 15 minutes. Continue to circulate one cylinder at a time for 15 minutes each, over a period of 4 to 6 hours, checking the solution colour and temperature regularly. If the solution colour changes from red to orange or yellow, indicating acid neutralisation, add sufficient Descalex to the solution to return it to its original colour (usually 25 g per liter of solution). This reinforcement of the solution should not be done more than twice. If after two reinforcements the acid is still neutralised, the solution should be drained off and the process started again with a fresh solution. This will usually only be necessary when dealing with very thick deposits.
When the cleaning solution retains its red colour for one hour, the cleaning operation may be considered complete and the solution can be drained off.
Fill up the engine with clean fresh water and circulate each cylinder for ten minutes. Then drain each cylinder separately in order to get the highest possible dumping speed.
Open all inspection covers and check that all debris that has formed during descaling is flushed out. Close covers. Fill up the engine again and add 0.5 % Alkalinity Control.
Circulate the solution to remove any remaining acidity and passivate steel surfaces. Circulation must be maintained until sufficient level of pH value is obtained. This should be tested through the whole engine. Drain the engine.
Adding the inhibitor – DIESELGUARD NB – ROCOR NB LIQUID.
Refill the engine with fresh water produced by the evaporator to the lowest level in the expansion tank sight glass. Add sufficient cooling water treatment for the initial dosage through the cleaning module.
Disconnect the cleaning module.
Put all valves in normal operating position and circulate the system with the main cooling water pump for 15 minutes. Vent the system thoroughly during this time.
Check the treatment concentration and adjust to 1500 ppm nitrite content.
Fill the expansion tank to the normal operating level using water from the evaporator production.
Check the acid content of the system lubricating oil directly after the descaling operation and repeat after 24 hours.
Virtually the same procedure as above can be followed when descaling 4 or 2 stroke trunk engines. However, this kind of engine seldom has shut-off valves on the individual cylinders and therefore all cylinders must be circulated simultaneously.
Medium-speed engines of this kind often have a drain bore “Tell Tale Bore”
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from the space between the upper (water) and the lower (oil) cylinder liner O-ring. This is to check for leakages.
The bores should be inspected when the engine is running. If leaks are indicated, NO descaling should be performed unless the engine can be dismantled and the cylinder liners pulled out immediately after the descaling operation. Otherwise, you cannot be sure that all acid is flushed out/
neutralised, and corrosion of the sealing surface may occur.
15.9 DEGREASING MARINE DIESEL ENGINE COOLING WATER SYSTEMS
When diesel engine cooling water systems become contaminated with oil and and grease, the system should be cleaned to remove oily deposits, as they can interfere with the cooling water corrosion treatment.
In Service Cleaning
This method may be undertaken with engine running at normal speed.
1) Take a 0.25 litre cooling water sample for future comparison and let it stand in a clear glass container.
2) Calculate the amount of Tankleen Plus required for solution of 0.5 % i.e.
5 litres per 1000 litres cooling water. Drain off similar amount of cooling water from engine if necessary. Slowly and intermittently add the cleaner to the cooling system via either the expansion or return tank.
3) After 5 hours, take a 0.25 litre cooling water sample. This should be allowed to stand in a clear glass container until any oil has risen to the top. The progress of the cleaning operation can be gauged by comparing thickness of this oil level with that of the first sample. A sample should be taken after 5–6 hours to monitor cleaning progress.
4) The cleaner can be left in the engine for a few days until a convenient port
4) The cleaner can be left in the engine for a few days until a convenient port