July 16, 2003
Claude Ouvrier-Buffet, technical manager of Total Lubmarine, says that despite an imminent new world-wide sulfur cap of 4.5 percent, and lower regional limits of 1.5 percent or less, "there are areas of the world where fuel sulphur content is climbing. Owners and engineers need to pay attention to the possible effects."
"Typical heavy fuels today have a sulfur content of around 3 percent," says Ouvrier-Buffet. "And typically owners use BN 70 lub oils, which provide the right alkalinity to match the fuel sulfur level.Ê But the sulfur content of the fuel is a function of the crude it comes from, and fuels supplied in the Caribbean, for example, may have substantially higher sulfur levels. Paradoxically, as owners adjust to the idea of having to change lub oils to lower BN numbers, that is, with lower alkalinity, to cope with strict fuel sulfur limits in Europe, they will still have to cope with burning very high sulfur fuels in other areas. Sulfur contents up to 4.5 percent will be permitted by IMO Annex VI. Some owners have already been offered fuels with sulfur contents over 4 percent."
Lubmarine say the most important step is to increase monitoring of the engine performance and increase monitoring of the condition of the piston crown and the ring pack through the scavenge ports.
Lube oil feed rates should not be increased initially, as this may lead to increased deposits on the top land and also in the grooves.
"Too much lube oil interferes with the circulation of the lubricant behind the rings leading to lube oil stagnation and deposits," explains Ouvrier-Buffet. "Although the BN70 oils are matched to current average sulfur levels, and if the sulfur level is reduced owners need to switch to lower BN oils, the reverse is not normally true. There is no mathematical or direct link between the BN of the oil and the sulfur content of the fuel, as performance of the lub oil depends also on the engine design, and the ignition and combustion quality of the fuel."
"If high sulfur fuel is to be burned regularly, then the best answer may be to switch to a lub oil with a BN higher than 70. But this step should only be taken after a period of monitoring the engine burning the higher sulfur fuel and after discussion with the engine manufacturers and lub oil suppliers," he concludes." "Unfortunately there is no one simple remedy to the problems of high sulfur fuels."
Lubmarine is the worldwide maritime lubricants network of oil major Total.