The most common form of excess in oil treatment is to treat the acceptance limit as a target that can be approached without end. The machine has reached NAS 1638 class 5, so it seems worth going further; the water content has reached ≤3 ppm, so it seems worth seeing how much lower it will go. Pushing further in that way usually brings three results: the treatment takes longer, the energy and the consumables go up, and the user gains almost nothing at the other end.
The limit is a condition of entry, not a target value
The main indicators each have a defined test basis and a defined limit: water content by GB/T 7600, ≤3 ppm; gas content by GB/T 423, ≤0.01%; breakdown voltage by GB/T 507, ≥65 kV; cleanliness by NAS 1638, class 5; filtration accuracy ≤1 μm.
Those figures are the thresholds that decide whether the oil can go into use. Once the machine holds the oil steadily at those levels, the process task is finished. The part beyond them is an improvement rather than compliance, and the ratio of what is spent to what is gained changes noticeably there.
Two different kinds of non-compliance have to be told apart. Some indicators fall short because the capability of the machine is not enough, and a machine with more capability puts that right. Other indicators fall short because of the oil itself, either because the oil has oxidised and broken down or because the water content is so high that neither the filter material nor the degassing stage can bring it down in a reasonable time. Both need the cause established, rather than more treatment intensity applied to force them through.
Where the return starts to fall away
Take water content as an example. Taking the water content from 5 ppm down to 3 ppm is the move from non-compliant to compliant, and this is where the return is largest, because the difference decides whether the oil is usable. Taking it from 3 ppm down to 2 ppm returns much less, but the difficulty does not fall in the same proportion: the way the water exists in the oil means that the further it goes the harder it is, the driving force for separation falls away, and the treatment time grows.
Gas content is the same story. The ≤0.01% of GB/T 423 is the decision line, and below it the further reduction is limited, while the error of the sampling and testing steps themselves becomes relatively noticeable. At that point the difference between two readings is already smaller than the resolving power of the test method.
Breakdown voltage works the other way round. It is one of the few indicators with useful margin above the limit. ≥65 kV is the floor, different voltage classes of equipment require different insulation levels, and if the actual operating environment calls for a higher breakdown voltage, then continuing to raise it above the limit still has a clear purpose. Whether that is worth spending on depends on whether the user has such a requirement at all.
When pushing further pays
| Condition | Carry on treating | It is reasonable to stop |
|---|---|---|
| The user has a requirement above the standard | Run to the higher target | There is no extra requirement |
| The oil is to be stored for a long time or takes part in another process | Leave margin | Treated and used straight away |
| The machine reaches the limit steadily and has margin | Adjust as needed | The limit is held steadily |
| The indicator that fails comes from the oil itself | Look at the oil first | More intensity achieves nothing |
| The treatment time is limited by the window | Give the key indicators priority within the window | Do not extend the window |
An order of judgement that can be followed
Test once against the stated basis and confirm which indicators are out. Then decide whether the failure is a matter of machine capability or a matter of the oil. Next, put the treatment intensity only into the items that need improving and leave the rest running steadily. Finally check once more and decide whether the intensity can be brought down.
The value of this order is that it turns the treatment intensity into a parameter that can be adjusted against the result, rather than a fixed set point. When the conditions on site change, adjusting the intensity with them costs less than holding the highest setting all the time.
The limit decides whether the oil can be used, and the part beyond the limit is only worth spending on when the user has a requirement for it.
