Maintenance of the Oily Water Separator — the Twelve Points and the Compliance Items
The routine that keeps the separator capable of holding 15 p.p.m., and the checks that keep the installation legally compliant.
Key Principles at a Glance 5 points
- The twelve points come down to removing internal contaminant, preventing corrosion, preserving the bilge pump, checking and renewing the coalescer, testing the monitor and cleaning the oil sensor probe.
- The conical plates are largely self-cleaning, but the top of the vessel must still be removed periodically to examine them for sludge build-up and corrosion — that inspection is where most internal faults are found early.
- All test cock lines must be clear: a blocked test cock is worse than no test cock, because it tells you the vessel is fine when you cannot see.
- The compliance items count as maintenance too — the overboard valve chained and locked, the bilge connection blanked, filter element spares carried on board, and the USCG notice displayed on the separator itself.
- Before initial operation, and after any internal work, the separator must be filled with clean water: the automatic controls need a water interface to work against.
1. The twelve points
The maker's instructions and the PMS override these notes. Obey the maker's instructions — the twelve points below are the general requirements, and the manual gives the clearances, the element part numbers and the intervals for the particular machine.
The general maintenance requirements for an oily water separator are:
- Routine attention is needed for satisfactory performance. A separator that is left alone will degrade quietly until it can no longer make the grade.
- Obey the maker's instructions.
- Removal of internal contaminant. Sludge on the plates costs plate area.
- Prevention of corrosion by removal of sludge. Sludge holds moisture against the steel.
- Check for deteriorated anti-corrosion coating, and apply anti-corrosive painting.
- Preservation of the bilge pump — the separator is only as good as the pump feeding it.
- If the coalescer is disposable, check and renew it.
- If the coalescer is renewable, check and clean it.
- Check and test the oil discharge monitor.
- The oil sensor probe must be cleaned.
- Clean and coat the catch plate.
- All test cock lines must be clear. A blocked test cock is worse than no test cock, because it tells you the vessel is fine when you cannot see.
The short working list
For day-to-day purposes the same requirements reduce to a shorter list: clean the chamber surfaces, because oil sticks to them; check the oil monitoring system; check the sensor; regularly change the oil-absorbing material; and check the flow regulating valves.
The plates
The conical plates are largely self-cleaning, which is why the separator does not need the plate pack stripped every few weeks. But they are not entirely self-cleaning, and periodically the top of the vessel must be removed and the plates examined for sludge build-up and corrosion. That inspection is the point at which most internal faults are found early.
Before initial operation
Before initial operation the separator must be filled with clean water. This applies after any internal work as much as after a new installation — the automatic controls need a water interface to work against, and starting dry gives them nothing to sense.
2. The compliance items
These are not machinery maintenance, but they are just as likely to be checked, and their failure is just as consequential:
- The overboard valve is chained, locked, with the key held by the Chief Engineer. The bilge connection is blanked by a blind flange and is absolutely free from oil and sludge.
- Filter element spares are carried on board — a ship with no spare coalescer element can fail a survey.
- The USCG notice is displayed on the separator itself, not merely filed with the Oil Record Book.
At IOPP renewal the surveyor works through these items as part of the survey. The renewal checklist in full, including the alarm test, the stopping device, the valves and the piping, is in When You May Discharge, section 6.
3. What the routine looks like in practice
| Interval | Action |
|---|---|
| Every operation | Check the interface through the test cocks; verify the oil content meter reading against the sampling valve sample; confirm the overboard valve is relocked afterwards |
| Daily / weekly, per PMS | Check the oil content meter and the sensor; check the flow regulating valves; confirm no oil leaks in the machinery space |
| Monthly, per PMS | Test the alarm and the automatic stopping device; clean the oil sensor probe |
| Per maker's interval | Renew or clean the coalescer element; change the oil-absorbing material; clean and coat the catch plate |
| Periodic, on survey or as found | Remove the vessel top and examine the conical plates for sludge and corrosion; check the anti-corrosion coating |
| At IOPP renewal | The compliance items in section 2 above, together with the alarm test, the stopping device, the valves and the piping |