Frequent choking of lube oil filters 1

[realit]

We are facing a strange problem of lube oil filter plugging after overhauling of the centrifugal compressors.
We overhauled 6 compressor trains (turbine driven) in Oct'23. All machines are having identical lube oil system. Along with overhauling, lube oil for all machines was drained, tanks were cleaned manually and fresh oil was charged for all machines. Individual System flushing was done until clean mesh screen observed at intel of all bearings.
After machines were started, frequent LO filter DP alarms started coming and frequent changeovers were required. In one of the case alarms were coming within 20-30 minutes of filter changeover and it needed machine shutdown. Now, condition is manageable but still we are not out of the problem, as we are not able to identify the root cause.
Currently, filter DPs remain stable for 2-3 days and then suddenly starts increasing. We drain 2000 liters oil and charge same qty. fresh oil, then filter DP reduces to previous value. If we don't charge fresh oil, DP keeps on raising in changed-over filter also.

We are doubting on lube oil properties, but not able to pin point the exactly which property is causing this. Can someone guide, what we should check in lube oil, to reach the root cause.
Viscosity, TAN, moisture content, flash point are within range.
Your insights would be very helpful.

 

[pierreick]

Hi,
Check for thermal oil degradation or oxidation. Ask support from third party lab or lube oil vendor, share with them the dirt collected on filters.
Pierre

 

[georgeverghese]

What is the process gas here ? Is this gas derived from an oil field or a non associated gas field, or a cracked gas compressor in an ethylene plant?
If you have old fashioned shaft seals with no dry gas barrier between seal gas and lube oil, you'd expect lube oil contamination with compressor process gas. If the process gas has gunky materials like corrosion inhibitor or residual paraffinic wax (or similar), this is what is bunging up your LO filters. Many of these old compressors cannot accommodate modern dry gas seals, but there is nothing to lose if you ask the compressor / shaft seal supplier. Alternatively, see if you can increase LO pressure to be higher than max normal compressor suction pressure, which would prevent reverse flow of contaminated LO into the lube oil tank.

 

[LittleInch]

What is the cause of the filter blocking?

Particles or gel?

Amy pictures of what you find in the filter?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hacksaw]

sounds like most of the debris has been collected.

 

[realit]

Thanks All for your inputs. I am sorry to reply late.
We have collected samples today for RPVOT, MPC, Ruler, IPC tests.
We are not finding filters choked physically, our R&D team did the tests by dissolving the paper filters in Toluene. First time they did find rust particles. Source of which is most probably the coolers. But, second time, they did not find any particles which can choke filters.

@ georgeverghese: yes these machines are in gas cracker plant. But, installed with DGS, with nitrogen as secondary seal gas and separation gas.

Below are images of impurities after toluene wash of filter element. Our R&D team says it is Wax.

 

[georgeverghese]

Does sound like raw cracked gas is finding its way into lube oil somehow. Source of contamination can only be through DGS or from the lube oil cooler.

 

[realit]

Same phenomenon is happening in crack gas compressor, ethylene refrigeration compressor, propylene refrigeration compressor, and other three compressors which handles hydrogen and mixtures of hydrocarbons.

If we agree that particles are coming from cooler, I am not able to find answer why filter DP drops when we drain some oil and charge fresh oil?

 

[georgeverghese]

From what you've said so far, there is no indication of water in this lube oil, so we can rule out this cooler leak possibility.
Is primary seal gas or buffer gas for DGS on all these machines coming from a common unit and source ? Where is your final separation N2 gas at DGS from ?

Is LO for all these machines from some reputable manufacturer?

 

[realit]

1. Yes, the separation gas source is from common header from utility plant which distributes to other points also. So, may be some NRV is passing and some hydrocarbon mixing in N2 - a very hazardous condition. We will get the N2 sample checked immediately.

2. Oil for all machines is from one of the most reputed suppliers in India. However, we are questioning them also on quality of blending and base oil. They have collected the oil samples. Waiting for their reply.