OSPR issues advice on preventing loss of power due to switch from HFO to MDO/MGO
Craig Eason
Tuesday 20 September 2011
A 100% jump in the number of engine failures and blackouts in Californian waters after the introduction of low-sulphur rules has promoted the issuance of guidelines for vessels to prevent a serious incident happening, writes Craig Eason .
The California Air Resources Board developed rules on ships’ fuels aimed at reducing harmful emissions. These requirements came into effect in July 2009 and require ships to use a fuel of less than 1.5% sulphur content.
Following the implementation of the rules the state saw the number of problems spiral. These problems, says Captain Jeff Cowan at the Californian Office of Spill Prevention and Response, can be broken down into a handful of main causes all associated with the switchover from heavy fuel oil to the lighter, low-sulphur fuels that the California rules force ships to use.
In a detailed assessment of the problem sent to Lloyd’s List, Capt Cowan says engine failures are due to the inability of engines operating with marine gas oil or marine diesel oil to overcome propeller torque when the ship is being manoeuvred within the port waters. The engine stalls at low speeds. Similarly, engines will fail to start after a period at anchor, as more fuel is often required. The adjustment of the fuel rack to allow more fuel into the engine cylinder is an operation that needs to be done from the engine control room or beside the engine, not remotely from the bridge of the ship.
Other problems witnessed by ships manoeuvring in Californian waters after a fuel switch have been related to controlling fuel temperature, loss of fuel pressure or even maintaining the required air pressure.
Heavy fuel oils tend to be heated in order to be combustible, while diesel oils and gas oils do not need such preparations. Pushing lower temperature fuel into a warm engine may cause flashing of the new fuel into a vapour, and multiple flashing could again cause loss of power. In some incidents the loss of fuel oil pressure is related to unwanted clogging due to the marine diesel oil effectively washing HFO impurities, known as asphaltenes, that have adhered to the inside of fuel lines out of the lines, only to clog the filters.
Capt Cowen says the problems can be alleviated by having crews that have never performed a fuel switch from heavy fuel oil to ultra low sulphur fuels, practice it before they enter Californian waters. This way they will get a better understanding of what might happen with their vessel before they have to do it in potentially dangerous situations. He cites one incident where a tanker lost power while leaving San Francisco, almost directly under the Golden Gate Bridge. The vessel had switched to diesel when all the generators tripped and the emergency generator came online. The ship lost power, steering and propulsion, and immediately dropped anchor to avoid running aground. The engineers switched back to heavy fuel oil.
The three-way valves between the HFO tank, the diesel oil tank and the generators appeared to have leaked, allowing HFO to backfeed into the diesel oil service tank. The viscosity of the heavy fuel clogged the feed lines to the generators, thus causing them to fail.
A further problem is the damage occurring to fuel injector ‘O’ rings that erode far quicker than the engine makers would like. While the MAN Diesel recommendation has been to service these every 10,000 hours, many ships have been forced to do so after only 2,000 hours. One US incident saw six crew spend eight hours replacing 22 injector O-rings while in port. In today’s world of reduced manning this is an unwanted distraction from their already heavy workload.
The US and Canadian coastline will soon see all its coastal waters become an emission control area. As of 2015 any vessels entering the US will have to switch to a 0.1% fuel, and the same rule will apply in northern Europe. The hope is that the switch between fuel types will occur far enough out at sea that any incidents will be dealt with safely. However, if the problem is leaky valves and failing O rings that cannot be detected at the immediate time of change, there may continue to be some risks attached to the adjustment of ships engines to run off multiple fuels.