How Often Should the Oil Circuit of a Compressor Be Cleaned

To ensure the safe operation of turbocompressor units, the oil circuit must remain clean and free of contaminants. Even trace impurities entering high-speed bearings, seals, regulating valves, 

as well as turbine bearings and governors sharing the same oil system may trigger serious failures, such as burnt bearings and malfunction of regulating valves and governors, 

which endanger the safe operation of the whole unit.

Therefore, newly installed oil systems must be thoroughly cleaned to remove oil sludge, iron filings, welding slag, oxides, dust and other impurities trapped inside pipelines and fittings. 

This guarantees unobstructed oil flow, accurate and responsive actuation of regulating mechanisms and safe unit operation. The oil circuit shall also be cleaned every time the machine undergoes an overhaul.

The general oil flushing method is to circulate the unit operating oil within the system under normal operating pressure, 

and subject the oil to rapid heating and cooling within a specified temperature range. 

The temperature range for thermal cycling can be determined according to the specific oil system. One plant specifies heating the syngas compressor oil system to 75°C followed by rapid cooling to 50°C, 

while other facilities adopt lower temperature swing parameters.

In general, the heating and cooling duration should be as short as possible. Nevertheless, due to the large oil volume, extensive heat dissipation area of the oil system and capacity limits of heating and cooling equipment, 

sufficient time is required to achieve thermal cycling. Typically, the oil is heated from low temperature to high temperature within 1–2 hours, held at high temperature for 2 hours, 

cooled down to low temperature within 1 hour, kept at low temperature for another 2 hours, and then reheated repeatedly to generate thermal shock.

During cooling, strike the pipe walls sequentially along the oil circuit with a wooden mallet, especially welds and elbows to create vibration and dislodge oxides, welding slag and other deposits.

To achieve efficient and effective oil flushing, the following measures can be adopted in addition to the above basic method: 

intermittently start and stop oil pumps and open/close oil circuit valves to generate swirling flow of flushing oil inside pipes; inject nitrogen into pipelines to create turbulent flow and improve flushing efficiency; 

raise oil flow velocity and increase flushing flow rate by installing an additional oil pump of suitable specification to boost flow inside piping.

Oil can be heated by heating coils at the bottom of the oil tank, yet these coils have limited capacity with low heating rates and often fail to reach required temperatures by themselves. 

Apart from tank bottom coils, parallel oil coolers can be used for alternating heating and cooling: one set supplied with hot water and the other with cooling water.

If hot water is unavailable, a low-pressure steam line can be connected to the cooling water inlet of the coolers to heat cooling water by introducing steam. 

The cooling water flow rate must be controlled properly to achieve sufficient water temperature for heating the oil.

The steam feed rate shall be strictly controlled. Especially when all components remain at ambient temperature, excessive steam input at once will cause excessive temperature difference across the cooler, 

generating high thermal stress and resulting in cooler damage.

Strainers shall be fitted at all main oil supply lines and oil inlets of bearings, seals and other components to block contaminants and serve as inspection points during oil flushing. 

A debris catcher shall be installed at the return oil main line inlet to the oil tank to capture impurities in return oil and prevent large volumes of contaminants from flowing back into the tank.

1. Manually clean the interior of the oil tank thoroughly, wipe dry with lint-free cloths, and remove dirt using oil-dough (dough mixed with oil). After cleaning, 
2. fill the tank with flushing oil accounting for over 60% of the tank’s rated capacity.
3. Disassemble and manually inspect all detachable oil system equipment including oil coolers and filters, and conduct manual cleaning. 
4. Special care shall be taken for dead flow zones where contaminants are difficult to flush out. Inadequate cleaning of these areas will compromise flushing quality and may require rework of disassembly and inspection.
5. Field-fabricated piping must be cleaned in advance. Carbon steel pipes require acid pickling; stainless steel pipes shall be purged with steam and then blown dry with air. 
6. Appropriate flanges shall be incorporated during pipe fabrication to avoid fully welded piping that cannot be cleaned.
7. Remove all filter elements from lube oil, seal oil and control oil filters. Original elements will be reinstalled after oil flushing, 
8. and temporary filter cartridges wrapped with two or more layers of 100-mesh stainless steel wire shall be fitted instead.
9. Formal operation will commence immediately after oil flushing, so all pipelines shall undergo oil flushing. Main oil pumps, auxiliary oil pumps and drivers shall complete individual trial runs and be kept on standby before flushing. 
10. Both pumps shall be operated alternately during oil flushing to remove residual contaminants inside piping and pump casings.
    Install temporary pipelines and blind plates in accordance with requirements of each flushing phase.
11. Fit the aforementioned strainers and debris catcher.

1. Phase One: Circulate oil through all oil supply lines, return lines, bearing housings and seal oil chambers, while isolating governors, trip valves and automatic regulating valves.
   Remove upper bearing shells and sealing components, retaining lower bearing shells to provide rotor support inside the cylinder. 
2. Dummy bearing shells specially designed for oil flushing can also be used to replace lower shells.
   For some automatic regulating valves isolated from oil flow, manual bypass valves can be opened to connect inlet and outlet pipelines. 
3. Where no bypass is available (such as governors and trip valves), temporary oil-resistant rubber hoses shall be routed to bypass these components.
   The number of sealing elements to be removed depends on specific structure, with a strict requirement to prevent oil from entering the cylinder.

After every 8–12 hours of oil flushing, remove filter cartridges for inspection and collect filter residues for comparison. 

Continue flushing until acceptance criteria are satisfied.

No unified standard exists for oil flushing cleanliness inspection. Generally, this phase is deemed acceptable if no visible debris can be observed on each inlet strainer, 

or only isolated fine particles exist; temporary filter cartridges contain fewer than 2–4 impurity particles per square centimeter.

2. Phase Two: Reinstall all bearings and seals per normal operation requirements and allow oil to circulate through the entire system. Fit original formal filter cartridges. 
3. Maintain lube oil and control oil pressure at normal operating values, and ensure seal oil achieves required oil-gas differential pressure.