Operation
0750−1/A1
Winterthur Gas & Diesel Ltd.
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Worn metals, the residual BN, viscosity, fuel components and water are measured.
The quantity of system oil additive metals in the sample gives an indication about the
piston rod gland box condition. It is important to monitor trends and not full values,
and to think about the quantity of drained oil relative to the analysis results.
For data about the procedure to get an oil sample from the piston underside, refer to
8016−1, Lubricating Oil / Servo Oil System, paragraph 2.1 Dirty Oil Samples.
The total iron in the scrape down oil is measured to calculate the corrosion of the
liners and steel parts. A large quantity of system oil can be mixed with the used
cylinder lubricating oil in the piston underside space. To get an accurate view of the
used cylinder lubricating oil, a correction is necessary to remove the effect of the
system oil on the results. The iron and residual BN values are corrected in relation to
the phosphorus and/or zinc content of the system oil in the used cylinder lubricating
oil. This correction analysis must be done carefully because some cylinder lubricating
oils also include phosphorus and/or zinc.
The analyses of many piston underside samples from a wide range of engines that
operate with a high sulphur content in the range 0.5% m/m to 3.5% m/m and cylinder
lubricating oil from BN 40 to Bn 100 has shown:
D The safe corrected piston underside residual BN to prevent piston ring and liner
corrosion is more than 25 mg KOH/g but less than 50 mg KOH/g (see Fig. 1).
D The alert corrected limit for piston underside residual BN to prevent excessive
corrosion is between 10 mg KOH/g and 25 mg KOH/g.
D The danger corrected limit is less than 10 mg KOH/g piston underside remaining
BN. It is possible that there will be too much corrosion, and piston rings and liners
can become quickly worn if not corrected. Scuffing can occur. Piston rings can
quickly become defective. Corrosion to cylinder liners can occur very quickly.
For each engine it is necessary to find:
D The safe value for continuous operation on fuel oil with a low sulphur content (of
between 0.0% m/m and 0.5% m/m).
D A low BN cylinder lubricating oil (between BN 15 and BN 25).
To find this safe value, you monitor the piston underside samples and do regular
checks of the pistons, piston rings and cylinder liners for excessive deposits,
corrosion and wear.
Fig. 1 shows the operation ranges for engines with chrome ceramic piston rings and
fully honed cylinder liners installed. It shows the relation between the piston underside
total oil iron content and the residual BN. If necessary, the cylinder lubricating oil BN
and/or feed rate must be adjusted to prevent excessive corrosion or magnetic iron in
the piston underside oil.
2016−11
Lubricating Oils
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