Discussion: Reasons for the decrease in lubricant viscosity
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In the gearbox lubrication system of the large-scale unit, the viscosity of the lubricating oil has been dropping frequently since it started operating. The lubricant has been replaced several times, but the problem has not been resolved; the viscosity can drop from over 300 to half of that value. There are no obvious mechanical impurities in the filter; initially there was some greasy substance, and recently black sludge was detected. The color of the oil has also turned dark and it has an unpleasant odor. Has anyone encountered a similar situation or can someone explain the cause? How should this issue be addressed?
The decrease in viscosity is due to two main factors: prolonged operation time, and water entering the lubricating oil! In your case, there’s a high possibility that water has gotten into the lubricant!
Under normal circumstances, the viscosity increases; I’ve really never seen a case where it decreases like in your situation. It is recommended to check for leaks, and also to have the oil analyzed carefully.
It was analyzed that apart from the decrease in viscosity, all other parameters were normal, including acidity, mechanical impurities, flash point, and moisture
Due to the decrease in viscosity, the equipment runs very little – it’s basically always shut down. No moisture was detected in the analysis, but could there be reasons for this outcome as a result of the long period of inactivity?
Based on your description, the foul smell of the oil is definitely due to something getting mixed into it; could it be the effect of that substance on the oil’s viscosity? Low oil viscosity is generally caused by shear of macromolecules; it is recommended to conduct a comprehensive analysis of the oil sample
Which type of lubricant is being used? Does the lubricant come with a certificate of conformity and inspection reports? Is there any possibility that other substances have mixed into the oil circuit system? Is the lubricant analyzed before use? After how long does its viscosity start to decrease? Have you reviewed the results of regular sampling analyses?
There is a strong suspicion that there is a problem with the lubricant.
The first three batches of oil were imported; the certificates of conformity were in order. The model number needs to be checked – I can’t remember it. The oil circulation system is relatively simple, with no other substances entering the pipes. The rate at which the viscosity decreases is getting faster and faster; previously it decreased by about 10% per month, but now the decrease is much more rapid. I suspect that there are foreign objects at the bottom of the gearbox, which could be causing this issue. Are there any impurities that can lead to a decrease in viscosity? For example, metal debris such as rust or that resulting from testing may settle at the bottom, or there may already be other debris there; due to the complexity of the gearbox, it’s not possible to see this without disassembling it
What kind of engine is that in yours? What is the process medium? What grade is the lubricating oil?
It’s not clear whether your gearbox bearings are lubricated by forced lubrication or non-forced lubrication Is it an independent lubrication system, or does it share the lubrication system with other systems? You mentioned the issue of changing engine oil brands; have you conducted compatibility tests between two different brands? This is because the additives in lubricants from different brands may react with each other, resulting in abnormal values for one or more performance indicators. Generally, when changing the lubricant brand, it is necessary to thoroughly clean the unit and pipelines. Furthermore, is the lubricant for your new brand one that has been recommended by the manufacturer after 4,000 hours of compatibility testing? For some large-brand bearing housings in Europe, the brand and type of lubricant are sometimes specified, requiring only lubricants that have passed compatibility tests – by compatibility is meant compatibility between the lubricant and the equipment, in order to avoid chemical reactions.