Oil Filter Replacement Interval

[JJPellin]

I work with a number of large industrial process gas compressors and pumps in an oil refinery. These machines have circulating lube oil systems built to API specifications. They have temperature and pressure controls with dual filters and differential pressure transmitters. Many years ago, when I started in this business, I was trained that these filters need to be replaced on a time basis regardless of any increase in filter differential pressure. I was taught that this is necessary because filter elements have a finite life. That is to say, a filter that has been in continuous use for a year will not filter as well as a new filter, even if the differential pressure has not increased. As a result of this thought process, we replace all of these filters every six months. I am getting push back from our operations group on the need for this time based filter replacement. I want to validate if this is necessary. I will give a specific example.

We have a circulating oil system on a large centrifugal charge pump in a hydrotreating unit. The system uses an ISO 32 light turbine oil formulated for compressors (Exxon Mobile Teresstic AC 32). This system lubricates the hydrodynamic bearings in the pump. This machine is in continuous operation for four years at a time between major unit turnarounds. The installed filters are 10 micron nominal pleated paper elements. We sample the oil in this machine every 60 days and perform a complete analysis including particle count. I have already approved extending the filter replacement to once per year. Would it be reasonable to extend it even further? What would be a reasonable maximum time for filter replacement?


Johnny Pellin

 

[gearcutter]

You could perform your own microscopic inspections of the filter elements involved.
Then you might be in a better position to estimate the service interval.

Oil filter patch microscopes are available to perform this analysis, here's one example -

https://www.microscopeworld.com/c-433-filter-patch-inspection-microscopes.aspx

You can purchase a guide from the ASTM -

https://www.astm.org/Standards/D7919.htm

I would suggest you perform inspections with the help and cooperation of the filter manufacturers.

 

[romke]

some remarks:

the figures for wear particles or a particle count as usually done within a oil analysis do in itself not fully indicate the state of the oil or whether the filters are still operating the way they should. a better indication to look at is the wear rate say every 500 hrs (mg/kg/500 hrs) to see whether there is a change in the amount of wear that is generated per unit of time. you might argue that when the per unit of time the amount of wear particles increases after prolonged use there either is increased wear or less efficiency in the filters involved. as far as the particle count is concerned you might argue that as long as it stays the same (or decreases due to efficient filtering) there is no need to change the filters - which is not to say that changing filters occasionally will not be needed because you only measure the present status which cannot predict what might happen in the future.

from your description i get the idea that the filters employed do only filter out smaller particles but not necessarily oxidation products. however, when oxidation occurs oxidation products might cause all kinds of trouble due to localized varnish, impeding heat transfer end causing local overheating. since normal filters do not filter out oxidation products i suggest a added filter that not only collects wear material but also is able to filter out oxidation products. usually those filters combine a standard filter and a bowl where the returning oil is cooled to such a extend that oil soluble oxidation products are settling and collected in the filter bowl. getting rid of oxidation products in this type of application may extend both oil life and the time between overhauls.

as far as the need to change the filters after a prolonged time, even when no pressure drop is indicated to do so, the filter manufacturer should be consulted. after prolonged use and heat input and vibrations internal components within in the filter(cartridge) may become loose, effectively bypassing some of the fluid to be filtered.