OEM impressions on operational performance post-sulphur cap

“So far so good. We prepared for the transition, communicated clearly with our customers and have heard of few problems,” Konrad Räss, Director of R&D for WinGD told The Motorship. “While it’s too soon to make a definitive judgement, we certainly have not seen the catastrophic switchover that some people outside the industry were expecting before December.”

Dorthe Jacobsen, head of emissions reduction, fuels and lubricants at MAN Energy Solutions’ two-stroke business in Copenhagen offered a similar analysis, adding that MAN had received “sporadic” reports of issues related to cylinder condition, ranging from high wear to scuffing, as well as some issues in the cylinder lubricators.

“In the most serious case I have heard about, the ship operator reported scuffing on all of their cylinders,” Jacobsen said.

“We heard from a containership with damage to a couple of cylinder liners, which was confirmed to have been caused by cat fines,” Räss said.

Such incidents have been reported by ship operators, from across the market ranging from small to larger size. But it was too soon to draw conclusions from the limited number of incidents reported. “We should be able to form a more accurate picture about what is happening by April,” Räss said.

Cat fines

Engine manufacturers had warned about the need to maintain cleanliness of the fuel and in the fuel tanks well ahead of the switchover, warning about the potential impact of cat fines. “We supplied service letters [SL2019-674, SL2019-670] on the need for due care when cleaning the fuel tanks in 2019,” Jacobsen noted.

Nevertheless, a number of ship operators have reported issues presumably related to cat fines. Some ship operators did delay the cleaning of the fuel tanks until shortly before the global sulphur cap entered force. Some of the crews used chemicals, such as fuel additives, to dissolve the high sulphur fuel oil residue from the side of the fuel tanks. However, the use of fuel additives had unexpected consequences further down the fuel cleaning system.

“The fuel additives were effective cleaning the tanks, but reduced the cleaning efficiency of the separator,” Jacobsen said, adding that this led to an increase in the proportion of cat fines reaching the engine. MAN had seen a number of high wear cases linked to cat fines passing through separators.

“We have heard of a number of cases where tank cleaning of years of accumulated sediment has released more cat fines into the system. Where the separators were insufficient, this has resulted in damage when the cat fines reached the engine,” Räss noted.

Lubricators and feed rates

Some of the sporadic incidents of high wear have been seen in engines that had consistent operational records before January, Räss noted. “We’ve heard feedback from more engines that were ‘silent’ previously.”

Jacobsen noted that that older lubricators on these ships could be one of the potential causes, particularly when the vessels had no experience with operating at low feed rates.

“If the fuel lubricator had slowly lost efficiency over time, and then the vessel shifted from its previous feed rate to a minimum feed rate, this could have led to excessively low lubrication feed rates,” Jacobsen said.

MAN recommends that the feed rate be reduced incrementally from 1.0g/kWh (or the existing feed rate) rather than shifting immediately to a low feed rate.

Cold corrosion

Jacobsen also noted that high wear caused by cold corrosion has also been a factor since January. The combination of HSFO residues in the fuel tanks with 0.50% sulphur fuels may lead to fuel supplies to the engine exceeding 0.50%. “In this circumstance, low-BN cylinder oils (40 BN) may not offer sufficient protection, leading to cold corrosion,” Jacobsen added.

A second cause of cold corrosion was inadequate mixing of low and high BN cylinder oils in a vessel’s storage tank. “When cylinder oils are not mixed properly, they will separate, leaving the heavier high BN cylinder oils to fall the bottom. At a certain point, the high-BN supply will be exhausted and the engine will begin running on low-BN lube oil,” Jacobsen said.

Piston rings

Jacobsen also noted that MAN had recommended in 2019 that the piston rings aboard all vessels operating on 0.50% sulphur fuel be replaced with Cermet coated piston rings.

“In the newest recommendation for cermet coated rings (SL2019-685), the crew must monitor the thickness of the cermet layer on the piston ring,” Jacobsen noted.

“We recommend that once the cermet coating thickness falls below 100 microns, ship operators plan to overhaul the piston ring pack. Once the thickness falls below, 50 microns, this overhaul should be carried out at the first opportunity,” Jacobsen said.

Where the cermet layer has been worn down and the piston ring substrate has been exposed, wear rates between the liner surface and the piston ring can accelerate rapidly, particularly when elevated levels of cat fines are present.

Fuel system sensitivities

Jacobsen also noted that a number of issues had been reported from fuel systems. These included cases of seizures of high-pressure fuel pumps, caused by temperature variations when changing between fuels with different viscosities.

“We have seen some problems with seizures in high pressure fuel pumps,” Jacobsen said.

Another problem connected with temperatures in the fuel system was that of gasification of low viscosity fuels. This had been seen in fuel systems during stand still periods.

At the other end of the temperature scale, there were issues related to the cold flow properties of newer fuels, as well as the engine room arrangements for heating cylinder oils and fuels to potentially different operating temperatures.

While the number of incidents related to fuel supply incompatibility reported to OEMs had been relatively limited, both Räss and Jacobsen noted that ship owners and crews needed to remain aware of potential risks. “While the tank cleaning is likely to be a one-time risk, crews need to pay attention as the other risks remain,” Jacobsen noted.

The Motorship has heard some operators have postponed switching to VLSFO from MGO during the transition, while bunker suppliers and ship operators have told The Motorship that the composition of VLSFO fuels might slowly evolve over the course of 2020.