Harun Ar Rashid of DNV Petroleum Services warns against relaxing precautions relating to bunker fuel quality. If samples taken from a bunker delivery are tested and found to meet the required quality specification, it does not mean the crew can relax other precautionary measures. Improper fuel sampling, poor maintenance of machinery, crew negligence and lack of technical knowledge can still result in engine problems.
DNV Petroleum Services has encountered cases of damage to engines reportedly incurred after using bunker fuel that conformed to the ISO 8217 marine fuel specification.
Whereas the off-specification results of a tested fuel will raise the necessary alarms, investigations have suggested that many problems with fuels that had in fact met the ISO 8217 quality requirements involved the improper operation of onboard fuel cleaning equipment, such as the centrifuge.
As a result of poor fuel cleaning, contaminants such as highly abrasive catalytic fines have been allowed to accumulate in the settling and service tank bottoms over time.
If this accumulation is unsettled – for instance, when the ship sails in rough weather – catalytic fines in the fuel are found in quantities far beyond the capability of any separators or filters to reduce sufficiently before the fuel enters the ship’s engine. Should this happen, the catalytic fines can seriously damage machinery.
The ship’s crew tends to pay more attention to the fuel filter, as this cleaning device literally sounds an alarm whenever it is not functioning effectively. The centrifuge, though similarly equipped with an alarm system, may not give off the same warning if its operation is not at an optimal level.
It must be emphasised that the centrifuge provides the ultimate protection for the engine, while fuel filters are merely a secondary requirement in the onboard fuel cleaning process. To determine whether the fuel treatment plant is functioning at an optimal level, the crew should periodically check the quality of the fuel being cleaned by analysing representative specimens drawn at specific locations along the fuel treatment system.
Taking representative fuel samples is the key to accurate assessments of both fuel quality and efficiency levels of machinery operations.
When investigating an engine problem, it may not be easy to ascertain whether the problem is fuel-related. An engine may already be on the verge of collapse due to excessive wear and tear, and the act of consuming a fuel, albeit one of acceptable quality, simply pushes the engine over the limit. Drawing and analysing representative fuel samples routinely will, in this case, help verify if the eventual engine failure is due to the fuel used.
Several other issues can lead to confusion over the quality of the bunker fuel delivered to the vessel.
A clean and stable fuel can produce excessive sludge and sediment, particularly if left at an unnecessarily elevated temperature in the ship’s storage tanks for prolonged periods of time or if mixed with other incompatible products.
Incompatibility can occur when mixing one residual fuel with another, although this problem predominantly occurs when residual fuels are blended with marine diesel. As a rule of thumb, we should avoid mixing two fuels of dissimilar origins.
In a recent investigation, a ship could not start its main engine after having stayed in port for a week. This problem was subsequently attributed to the crew’s lack of experience in changing over from residual fuel to marine diesel before the vessel came alongside. Apparently, insufficient flushing of the fuel booster system had led to a mixture of incompatible blends in the de-aerating tank. Sludge began to form and accumulate in this tank, and this prevented the main engine from restarting successfully.
Ship operators must also be aware that ISO 8217, the most commonly used marine fuel specification, is only a baseline and does not cover every possible quality issue.
Poor fuel ignition and combustion properties may give rise to piston ring breakages and scuffing of engine liners. Such parts failure is exacerbated by poor engine maintenance and operating conditions.
In the past, the Calculated Carbon Aromaticity Index (CCAI) has been relied upon as a method for predicting marine fuel ignition quality.
Unfortunately, this mathematical formula is no longer as reliable, since bunker fuels today are not manufactured in the same way as when it was introduced.
Fortunately, there is now an approved test method – IP 541/06 – for evaluating marine fuel ignition quality and combustion quality using the Fuel Combustion Analyzer.
CIMAC, the International Council on Combustion Engines, is currently also developing recommendations on FCA-based testing for marine fuels.
Meanwhile, studies undertaken by DNVPS show that FCA analysis results do not correlate well with the CCAI, thereby confirming the latter’s inability to predict fuel ignition quality accurately.
Another example of inadequate technical knowledge contributing to engine issues relates to the increasingly popular 500 cSt grade fuel, which is cheaper than the 180 cSt or 380 cSt grade. But if the ship does not have adequate heating or separator capacity, it must avoid using 500 cSt fuels since insufficient heating adversely affects fuel atomisation and subsequent combustion. This, however, should not be perceived as an issue of inferior fuel quality.
The ship staff must also be mindful of the possibilities that the fuel in use may have been contaminated by waste material un-screened by a routine analysis of ISO 8217 quality parameters.
Waste contaminants in bunker fuel may immobilise the ship. In many cases, the fuel pump plunger and barrel in the engine stick, resulting in excessive wear of the fine clearances. Ships which have used these fuels have also reported damage to the injector needle valves and excessive sludge formation in the centrifuges.
Detecting and identifying waste products in marine fuel require the use of high-end analytical instruments as well as considerable diagnostic time and expertise. The complexities involved are one of the reasons why waste contamination is not usually a part of the standard fuel quality testing service offered in the market.
That said, the presence of waste contaminants in bunker fuel does not comply with Clause 5.1 of ISO 8217:2005.
While many ship management decisions are made in the office, it is the ship’s crew who handle the operations on board. How well the ship is run will determine her physical condition in the long term.
Maritime safety and efficient ship operations are possible only if we succeed in maintaining a consistent level of competency among shipboard staff. This is clearly a function of adequate and continuous training.
The time and money spent on crew training can help avoid costlier damage to machinery, which, in many cases, has little to do with the quality of fuel delivered to the ship.
Harun Ar Rashid is a technical adviser with DNV Petroleum Services and can be contacted at Harun.Rashid@dnvps.com.
For more information on DNVPS fuel management services, please email singapore@dnvps.com.
This article is adapted from a write-up published previously in Lloyd’s List.
Date: 2008-03-14