World Bunkering >Articles > Testing > Fuel oil quality: damage limitation

Onboard contamination from unusual, foreign, substances in marine fuel oils can be, at the very least, troublesome for all parties involved. When such contaminants are identified after analyses, fingers can start pointing at the refinery, ship, and anything in between. The effects of “bad bunkers” generally hit those on board the vessel hardest, at least in terms of additional labour consequentially created. As a vessel’s engineer I was personally involved with trying to cope with poor-quality fuels and, in one case, we persevered with the bad bunkers until the next port was reached, although doing so created more work for the engineers both during and after use.

Bad fuel, or bad engineering?

My subsequent shore career, as both surveyor and consultant, has resulted in exposure to a multitude of fuel problems and the damages caused by the use of this fuel. I was also involved in a number of cases where the fuel quality was initially blamed for machinery damage, but after further detailed investigation and analyses, it was determined that the cause of the problem was either poor maintenance procedures or inappropriate handling and operation of the ship’s equipment. In one such case, it was identified that fuel pump barrel and plunger assemblies had been recently mismatched, a practice not recommended by the engine manufacturer. In another case, the scavenge air cooler was found to be leaking sea water into the scavenge air manifold and engine units, resulting in a detrimental effect on the cylinder liner film of a large slow-speed engine. The effect of the sea water contamination in the cylinder units was not too dissimilar to using fuel oil with excessive levels of cat fines, with rapid wear of cylinder liners and piston rings.

Maintenance matters

It almost goes without saying that I have seen numerous examples of situations in which fuel oil of either reasonable or borderline quality could have been successfully handled on board if the treatment system and machinery had been operated and monitored in accordance with good practice, including following the machinery manufacturer’s recommendations.

In a further case, I identified unusual deposits in the scavenge space of a large slow-speed engine. Although the vast majority of the scavenge air spaces had been cleaned prior to my attendance on board the ship, there were sufficient warning signs to suggest that there had been problems before the engine was cleaned. After detailed inspection of the main engine, its systems and the documentation, together with detailed analyses, it was ascertained that the fuel in use was not of substandard quality as had been alleged. The cause was found to relate to excessive quantity of cylinder oil at engine inlet coupled with blocked drains from the scavenge air space; the level of sludge in the scavenge air space had risen until it was level with that of the scavenge air ports, so that the piston rings and cylinder liners were effectively operating with the sludge as the lubrication medium. Again, the effects on the piston, piston rings and cylinder liner were similar to those found when the fuel contains excessive levels of cat fines. As may be deduced from the above, it is far from certain that the quality of the fuel oil is the cause of machinery damage, so it is wise to use the term “alleged” when investigating the merits of a case.

Proving the case

It is generally difficult for an owner to show that machinery damage has been caused by poor quality fuel. Representative samples, and the use of reputable and independent laboratories, are paramount in determining the nature of the “contaminants” in the fuel oil. If analyses do not indicate any specific deficiency, it is difficult for owners to prove that a specific batch of fuel has not been “fit for its intended purpose”. Even in circumstances where the analyses indicate a specific problem, it may be difficult for owners to show that the specific fuel was the sole cause of machinery damage if the maintenance is not in accordance with the manufacturer’s recommendations or the equipment has not been suitably handled.

On a too frequent basis, I have seen poor onboard practices such as operating the treatment system with filtration either by-passed or with large holes in the mesh. Other common operating problems include the use of purifiers with incorrectly sized gravity discs, excessive flow rate or insufficient inlet temperature. The misuse of fuel oil temperature controllers and viscosity controllers also tend to be a relatively common issue where machinery damage is blamed on fuel oil quality. Unfortunately, the competence of the crew is often called into question where it is alleged that bunkers have caused engine operating difficulties. In one particular case, a physical test of all 16 fuel injectors for a medium-speed engine found that 14 had been incorrectly set, with most of those leaking fuel oil at some point in their assembly. When access to relevant documentation was provided, it was ascertained that the injectors had recently been overhauled by the ship’s crew and installed in the engine prior to the commencement of the operational problems. When faced with the full facts, it is generally easier to understand the circumstances of the operational problems and what may have caused them. However, the various parties involved when a dispute arises have their own agenda, and access to relevant information is not available in many cases whilst the initial investigations are underway.

The above shows only one side of the story, that where the fuel oil quality is wrongly blamed for causing machinery problems. Where poor quality fuels are used on board the ship, the results can be devastating. It is not uncommon for “bad bunkers” to result in total loss of electrical or propulsion power, or both. Such circumstances can lead to expensive towage or salvage to a safe port of refuge, legal and surveyors’ costs, and a detrimental effect on the safety of the crew, cargo and the environment.

What can go wrong?

Engine components that are commonly affected if the fuel contains high abrasives include fuel pumps, fuel injectors, pistons, piston rings, and cylinder liners. Damage to these items can cause further problems with scavenge space fouling, exhaust space and turbo charger fouling, reduced engine power output, and physical damage to the turbo charger. The damage caused when the fuel contains high abrasives can be severe and rapid. In one case the clearance between the fuel pump barrels and plungers was 10 to 15 times the nominal value. In another, the depths of piston ring grooves were up to twice that for a new piston crown.

Tank, filter and purifying fouling also tend to occur with certain aspects of poor fuel quality. Fuel oil compatibility or stability problems have a tendency to cause problems in the fuel oil systems prior to entry into the main and auxiliary machinery, although their effects can be just as costly to remedy. It has also been known for exhaust valve or bearing damage to occur if the combustion or injection qualities of the fuel are sub-standard.

In recent times, there have been numerous adulterant substances that have found their way into marine fuel oils. Their effects on the machinery and component parts tend to be fairly wide-ranging, dependent on the nature and extent of the adulterant substances. Such effects can include fuel pump and filter blockages, or a reduction in the lubricity from the fuel itself, resulting in seizure between closely fitting parts.

It is hoped that the quality of fuel oil delivered to a vessel is of satisfactory quality in order to prevent some of the problems discussed in this article. Despite the likelihood of reduced income from investigations in relation to “bad bunkers”, it is hoped that the latest, and subsequent, revisions to marine fuel oil standards will reduce the burden on the owners and ship’s crew.