The oily water separator and 15 ppm bilge alarm: tests and calibration

Which standard applies to your equipment

Resolution MEPC.107(49) applies to equipment on ships whose keel was laid on or after 1 January 2005, and to new installations from that date on older ships as far as reasonable and practicable. Equipment fitted to older ships may instead meet resolution A.393(X) (installed from 14 November 1978) or MEPC.60(33) (installed from 30 April 1994).¹ The IOPP Supplement states which standard each item was approved to, and a copy of the type approval certificate for the separator and the alarm must be carried on board.¹¹ MARPOL Annex I regulation 14 tells the Administration to “have regard to” the IMO specification when approving equipment, which is how the guidelines become binding in practice.⁷

The separator

The separator must work automatically with fail-safe arrangements, need no adjustment of valves to start, run for 24 hours of normal duty without attention, and keep the effluent at or below 15 ppm when its feed changes from bilge water to oil, to emulsified bilge water or to air.² At type approval it is tested with three fluids: a residual fuel (ISO 8217 RMG 35, density not less than 980 kg/m³), a distillate (DMA, not less than 830 kg/m³) and an emulsion containing surfactant and iron oxides.⁶ The emulsion test matters on board: detergents and chemical bilge cleaners create emulsions the separator may not handle, and adding chemicals to get round the discharge conditions is itself banned by MARPOL Annex I regulation 15.8.⁷

The 15 ppm bilge alarm, clause by clause

At type approval the alarm’s accuracy must be within 5 ppm, even with contaminants other than oil present and with the power supply 10% off its design value.⁶³

Installation

The installation rules in section 6 are what an inspector walks along:⁵

• a sampling point in a vertical section of the effluent pipe, close to the separator outlet;
• a recirculating facility after and next to the overboard outlet of the stopping device, so the whole system can be tested with the overboard valve closed, arranged so it can never bypass the separator;
• a feed pump of not more than 110% of the separator’s rated capacity;
• a permanently attached plate with the operating or installation limits;
• the operating and maintenance manuals on board for both the separator and the alarm;
• an overall response time, from effluent above 15 ppm to the stopping device acting, as short as possible and never more than 20 seconds; and
• a sample line that gives a truly representative sample at adequate pressure and flow.

The five-yearly calibration

Since resolution MEPC.285(70) (28 October 2016) replaced paragraph 4.2.11, the rule reads: the validity of the calibration certificate is checked at IOPP annual, intermediate and renewal surveys; the accuracy check is done by “a manufacturer or persons authorized by the manufacturer” at intervals not exceeding five years after commissioning, or within the term in the manufacturer’s instructions, whichever is shorter; the unit may instead be swapped for a calibrated one; and the certificate showing the date of the last check stays on board.⁴ Before 2016 the check was tied to the IOPP renewal survey.³ The resolution “recommends” that governments apply the amendment, and flags such as Liberia have written it into their notices word for word.¹⁰

Working out the due date: take the date on the current calibration certificate (or the commissioning date if there has been none), add 60 months, and compare with the manufacturer’s stated interval from the same date. The earlier of the two is the deadline. Many manufacturers specify a shorter term than five years, so read the manual, not just the resolution. Plan the visit or the exchange unit well before the annual survey window opens, because an expired certificate is a finding at the survey and at any port state control inspection.

On-board testing and maintenance

The manufacturer defines the routine maintenance in the operating and maintenance manuals, and “all routine and repair maintenance” is to be recorded.⁶ That record belongs in the ship’s maintenance system: MEPC.1/Circ.736/Rev.2 says general OWS maintenance does not have to be entered in the Oil Record Book.¹² A typical on-board function test, done to the manufacturer’s procedure, uses the recirculation line with the overboard valve shut: start the system, check that the alarm reads and records, use the manufacturer’s test function or approved test method to make the reading cross 15 ppm, and confirm that the three-way valve diverts within the response time and that the recorder logs the event. Do not open sealed parts of the alarm; if a seal must be broken for repair, it is a job for the manufacturer or its authorised technician, and the repair and resealing should be recorded.

Any failure of the separator, the alarm or the stopping device is entered in the Oil Record Book under code F (items 19 to 21), with a matching code I entry if the overboard valve is sealed shut while the system is out of order.¹²¹³