Find some explanations to be able to better evaluate the examination of your wiper oil both with the on-board measuring devices and by our qualified laboratory. Our experts will be happy to help you if you have any further questions.
Abrasion or chemical degradation provide important information about the condition of the machine.
Acid and base are gene players in every liquid. The stable relationship is crucial here.
Water in oils is not visible to the naked eye but can produce visible rust.
Is, beside the base number, the most important indication for any problem in the liner. It can indicate corrosive or abrasive wear. Corrosive wear is due to acid condensation on the liner wall. Abrasive ware is most probably due to liner or ring wear. The reading from your on-board device might be different from your laboratory oil report. This is not because of inaccuracy of either device but because of the different measuring methods.
The lab device does measure the chemical element Fe with either ICP or XRF which gets reported as Iron. This will also report any iron which is chemically bounded like corrosion. On the other hand ICP will not report particles bigger than 5 µm but XRF will. Therefore it is important to understand which method is used in the lab. In most labs (also in the CMT lab) the ICP method is used which will only see smaller particles. In many labs also the PQ method is used. This method is based on magnetometry and will therefore only see abrasive iron. Corrosive wear metal is no longer magnetic and cannot be seen by this principle. However, this principle allows seeing also large particles so that it is a useful addition to the ICP method.
For onsite there are different devices available. The CMT device similar to the Chevron DOT.FAST ® device will see the total iron (abrasive and corrosive). This method is therefore recommended by MAN and Wartsila. There are also other on-site devices on the market like the Mobile Scrapedown Analyser (MSA) or the Shell (or Kittiwake) Analex Alert. Those devices are based on magnetomety similar to the PQ technology in the lab which will see only the abrasive wear. The corrosive wear, which is these days of much more concern, cannot be seen with this technology.
Is a very important indication for corrosive wear because of acid condensation. The acid will condense at the liner wall when the temperature gets below the dew point of the acid. In modern engines this can happen already at temperatures around 280 °C during the combustion process. Also slow steaming does reduce the temperature to a point, where cold corrosion can happen.
BN can vary between units due to different fuel being injected, higher cylinder pressure or lower liner wall temperature. Also system oil leakage will reduce the BN reading in the under piston space.
During combustion the sulphur from the fuel and the water from the air will form sulphuric acid. This acid needs to be neutralised by the additives in the cylinder oil. The amount of additives is indicated by the BN (base number) of the fresh oil. A too low BN in the drain oil can result in acidic corrosion whereas a too high BN will result in deposits creating abrasive material. An optimum BN will be around 25 mg KOH/g. Please make sure that the BN in your cylinder drain oil is always above BN 15 mg KOH/g as minimum.
Water does come into the cylinders because of the humidity of the inlet air. Most of it should be collected by the water catchers. However, in high humidity areas sometimes the water catchers cannot cope with the amount of water in the air. It can also indicate a possible cooling water leakage. If the air cooler does run with sea water the sodium reading will be high as well. The water level should stay below 0.5% water. High water levels may be causing emulsification and disruption of cylinder lubrication. It will increase the viscosity of the lube oil and contribute to wear. In case of high water we recommend that the air coolers and water catchers serving the respective units are inspected and drains are checked for obstructions in order to eliminate water ingress. Sampling procedure should be followed carefully as incorrect sampling can cause high water in the oil sample which is not in indication for unusual water ingress into the combustion space. Note that the first liquid from the sampling cock should be drained to waist as water may accumulate in the line prior to commencement of sampling.
Aluminium and Silicon
Is an indication of high cat fines level in the fuel. High cat fines level is causing abrasive wear. This should be confirmed by high iron readings as well. According to ISO 8217 fuel must have a cat fines level below 40 ppm when delivered. However, the engine manufacturers specify cat fines levels of about 15 ppm and below when the oil is injected into the engine. High cat fines levels in the drain oil indicate to an inadequate performance of the fuel oil separators.
High Chromium indicates wear of the piston ring groove coating. Levels below 10 are within normal range. Higher levels are expected during running in.
Low values combined with low iron indicate normal free movement of the piston and that abrasion between piston skirt and liner wall is insignificant. High levels point to a disturbance of piston alignment. Higher levels are expected when running in. Tin levels up to 20 ppm are normal.
Nickel / Vanadium
Is an indication of fuel contamination because of blow by. You should also see an increase of viscosity. Vanadium levels around and above 300 ppm does indicate a possible blow by.
Higher levels are an indication of skirt and / or stuffing box wear. In case of alu-coated rings the level will also be higher during running in of new rings.
High soot indicates an unstable combustion. Soot level should be below 0.4%
Sodium / Manganese
If Sodium is high and at the same time the water is high this would be an indication for seawater. If there is seawater around usually the Manganese value would be increased as well. Sodium and Manganese should be in the ratio 1:5 in case of seawater. Sodium can also be found in cooling water. However, cooling water leakage into the cylinder drain oil is not seen very often.
High readings indicated that the cylinder oil is contaminated with fuel and lubricant debris. It is important to have an adequate dispersant reserve to maintain piston cleanliness.
Zink and Phosphorus Level
Is an indication of system oil leakage through the stuffing box into the scavenge air space. Zinc levels up to 30 ppm are within normal range.