Oil spilled during the bunkering due to leaking valves

What happened

The vessel was taking MGO bunker when approximately 30 Liters overflowed from a vent line into the sea. This vent line is from a non-bunkered tank. Once overflow was discovered the bunkering was immediately stopped. 100 Liters of MGO were collected from the deck into oil spill drums.

Causes

Upon investigation, the following causes found:
1. Valve No. 1 the Butterfly valve (used for bunkering of the overflowed non-bunker fuel tank) failed and leak through to the tank during bunkering operation. Damaged rubber pieces were found in several places of the rubber seat after the line was opened for examination.

2. Valve No. 2 Butterfly valve (used for bunkering of the overflowed non-bunker fuel tank) was found damaged disconnected from spindle shaft drive and valve flap is seen in the closed position, but the valve flap was opened inside and fuel went through from there.

3. Valve No. 3 Quick Closing valve (use for the overflowed non-bunker fuel tank loading and discharging) upon inspection was found with some material trapped between the valve plate and valve seat, so fuel still escapes from there.

4. Manifold strainer was not effective to trap the debris in the line.
5. Bunkering procedures were not covering the monitoring on non-bunkered tanks during bunkering.

Corrective actions

1. During bunkering, ALL fuel storage tanks, including bunkered and non-bunkered, must be monitored for early detection of unplanned filling and possible overflow.
   
2. Periodic pressure test of bunker line must be conducted for early detection of leaking valves.
   
3. All valves which suspected to be leaking must be overhauled without delay.