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Flushing with lube oil is carried out to remove dirt from the system by loosening it from the inside of the system or by dissolving it in the flushing oil. Dirt which is picked up by the flushing oil will be caught in the fine mesh installed in the return line and can be removed.
This article contains an excerpt from the paper, “Save your Centrifugal Machinery during Commissioning” by Arun Kumar and Mohit Sabharwal of HPCL- Mittal Energy Ltd at the 2018 Asia Turbomachinery & Pump Symposia.
Before charging the lube oil inside the tank, it is important to ensure that the lube oil tank & run down tank are thoroughly cleaned. All loose foreign material such as scale, sand,weld splatter particles and cutting chips shall be removed. The inside of the interconnecting piping should be wire brushed where accessible. Thereafter, the interconnecting piping shall be thoroughly cleaned before installation by air or steam blowing.
Lube Oil piping is to be connected and for initial flushing temporary bypass piping is to be connected for bearing housings and Seal Oil supply. The scheme is to be validated by the machinery OEM. Orifices, probes and other flow restrictions must be removed for cleaning and flushing to obtain optimum velocities. All removed items shall be tagged and properly store for reinstallation. All the pressure gauges except lube oil pump discharge pressure gauge, pressure switches and instrument connections shall be isolated. All the PSVs shall be removed and blinded during the flushing.
Ensure Motor power connection is provided and, that the auxiliary and emergency oil pumps are ready for use to circulate lube oil. The entire lube oil circuit is divided into different circuits/loops so as to make the flushing more effective. Flushing of successive loops shall be started after the completion of flushing of preceding loop. Fill the tank with enough oil (up to min. level shown on the level gauge) i.e., up to the level such that the pump suction is fully immersed during flushing. Note that after starting the flushing oil, the level will drop inside the tank so make-up oil arrangement should be ready. Ensure that the lube oil tank heater is commissioned and maintains the temperature between 60-70 deg C.
Make temporary hose connections / jump overs across the bearing housing as per the identified scheme connecting the supply lines to return header with fine mesh (100 mesh plain weave, stainless steel) in-between. Install fine mesh (100 mesh plain weave, stainless steel) in the lube oil return line just before the tank as identified in the scheme. In the first circulation, filter elements should not be installed. Once the clarity of lube oil improves, filter elements should be installed properly seated in the filter housing. Ensure filter element commissioning spares are available. At the time of lube oil flushing through bearing, the dry gas seal should not be in place but if it is already installed then a nitrogen/Instrument air purge shall be provided as a separation gas at design pressure.
Sufficient venting of the oil cooler & filters shall be done while taking inline to ensure no air pockets is left. Once the filter element is installed, periodically check the pressure drop across the oil filter. When the pressure drop becomes too high (As per OEM recommendation) change over to the clean filter element. Remove and replace the dirty filter element.
Initially fine wire mesh should be checked after ½ hr. of circulation for accumulation of dirt/corrosion products. Carry out the flushing of lube oil piping through the fine mesh into the return header for 12 hours for each loop. Periodically strike the piping in an attempt to loosen any foreign material. Vary the oil temperature during the flushing process from hot to cold and vice versa a number of times. Stop the lube oil pump after 12 hours of circulation, allow for oil to drain back in to the tank and check the fine mesh for collected particles. Repeat flushing till no particles are observed visibly and no grittiness in felt by touch. The system shall be considered to be clean when the return line mesh found to be free from any foreign particles.
A Centrifuge/online cleaning system shall be used for cleaning the lube oil in the reservoir during flushing. On the completion of the flushing, lube oil sample shall be taken from the reservoir bottom and checked for water content and dirt contamination. Depending on the results oil shall be conditioned or replaced with fresh oil.