Lessons from Marine Accident Reports
The UK MAIB has recently issued latestSafety Digest including lessons learnt from maritime accidents. One case highlights how fuel oil quality is fundamental to safe and reliable operation of engines.
A diesel-electric tanker was operating in the Caribbean. The ship was running at slow speed on one diesel generator, which was being supplied with marine gas oil (MGO) from one of two fuel oil service tanks. Overnight, the ship operated with an unmanned machinery space (UMS).
When the engineer OOW came on duty in the morning, he decided to switch from one fuel oil service tank to the other, which was a daily requirement. Prior to the change over, he opened the drain valve at the bottom of the tank being put into service and started to drain off water. Once the duty engineer was confident there was no further water remaining in the tank, by examining an oil sample in a jar, he switched over the fuel supply.
A short time later, the two running fuel oil service pumps seized. The standby fuel pump started, but this too seized soon after. A fourth fuel pump was started manually, and this also failed. The diesel generator remained running only because of a fuel supply from its emergency header tank. Despite the electrical load onboard being reduced to a minimum and the vessel being stopped, the vessel suffered a total electrical failure once the header tank was empty.
The repairs, which included un-seizing the fuel oil service pumps and removing water from the fuel system, took 14 hours to complete. At this point electrical power was restored and propulsion was available about an hour later. The vessel then proceeded to its intended destination with a tug in attendance.
The ship manager’s investigation concluded that there had been a significant quantity of water in the fuel oil service tank in use. The water had entered the fuel oil system, causing the fuel pumps to seize, and this led to the blackout.
The investigation also identified that, although the vessel was operating in an area with high humidity, the possibility of more water than usual accumulating in the service tanks was not considered. In addition, the tank drain and sample area was poorly lit, which made the sampling procedure more difficult.
More stringent change over and sampling procedures have since been put in place onboard the vessel, including:
- A requirement for service tanks to be drained of water at least 1 hour before the intended time of changeover.
- Oil samples from the service tanks are now collected in a clean glass bottle and taken to the engine control room to be checked.
- The time taken to drain water from the tanks is recorded.
|
Lessons Learnt 1. Oil and water do not mix. Fuel oil quality management is fundamental to safe and reliable operation of main and auxiliary diesel engines. Care must be taken to ensure that there is no water in any service tanks that are supplying machinery. 2. Fuel oil samples must be taken in areas that are well lit, using sample containers that are clean and allow the contents to be accurately verified. If in doubt take another sample and get another engineer’s opinion. 3. Fuel and oil storage tanks should be checked for, and drained of, water at regular intervals -such as during machinery space rounds. This is especially important if operating in areas with high humidity and thus high levels of condensation |
Source: UK MAIB
