Staff on board vessels may need to adjust lube oil grade and feed rates, while sailing, to account for fuel quality and combustion
As we head into the 2020 sulphur cap era, discussions during Riviera’s Asian Sulphur Cap 2020 Conference showed that ship crew will not only have to be watchful of variations in the composition of bunker fuel batches, but they are also likely to need to monitor lubricant performance.
“No more plug and play. Ship staff have to constantly monitor engine condition and performance and adjust lube oil feed rates and possibly the lubricant grade, too,” said Shell’s regional technical manager for Asia-Pacific, Eddie Chen.
The looming onset of the sulphur cap has also introduced fears into the market that compliant fuels may pose other problems such as the precipitation of cat fines or that mixing two bunker batches from different sources could make fuel blends unstable.
Because fuel quality dictates lube oil grade and feed rate, this uncertainty over fuel in 2020 and beyond has forced engine OEMs to make general – rather than specific – recommendations on lube oil specs for 2020 compliant fuel, said panellists at the session.
“OEMs wish to err on the side of caution before recommending lubricants. They want a large dataset to send out clear recommendations,” said Infineum technology manager Laurent Chambard.
Ultimately, all of these variables require proactive ship staff who can make on-the-spot decisions concerning lube oil. Engineers have to go back to the basics and conduct meaningful engine inspections, said Mr Chen. During the transition period, these inspections should be conducted monthly and reports sent to head office more frequently than once every six months, he said, adding this would help the head office monitor ship operations closely.
The lack of clarity around fuels and lubricants in the maritime market prompted a question from the conference attendees on why lube oil suppliers could not collaborate with engine OEMs ahead of time so there was more clarity regarding lube oil.
Castrol global technical services director Gianluca Marucci recalled how 10 years ago, slow steaming forced the operational profile of the engine to change from high-speed, high-load to low-speed, low-load. Corrosion and wear increased as a result, he said. Scavenge drain analysis is important and lube oil feed rates have to be adjusted, he added.
Suitable additive mix
Mr Chambard discussed how fuel with lower sulphur requires lube oil with a lower alkalinity to neutralise the acidity of the fuel and prevent acidic corrosion. This means lowering the lube oil from a BN index of 70 for heavy fuel oil to 40 for very low sulphur fuel oil, for instance.
The higher alkalinity in the past brought better detergent action too. So if the BN index were to go down, the lube oil’s detergent quality would need to be maintained through suitable additives, said Mr Chambard.
“The next generation of lube oils requires higher surfactant and dispersant content to offset decreased soap levels from lower BNs,” he said.
For two-stroke engines, the cylinder lube oil additives were dominated by those that kept BN high, typically between 70 and 100, while surfactant and dispersant and other type of additives formed a smaller proportion. For the compliant fuel, 40 BN is typical. Besides surfactants and dispersant additives, others such as corrosion inhibitor, anti-lacquer and anti-oxidant ZDDP now occupy a greater proportion of the additive mix.
For the four-stroke trunk piston engine, 30 to 55 BN was typical but now it has come down to 20 to 35. The additive proportions have been rebalanced as a consequence, he said. “Piston cleanliness similar to typical high BN oils may be obtained with lower BN oils, but requires different additive components,” Mr Chambard said.
To a question from the participants on whether a lower BN value would mean lower lube oil cost, Mr Chambard said the amount of additive mix remains the same and that is not disrupted although suppliers have to bear a higher supply chain cost.
Mr Marucci talked about how the BN has to be balanced with the fuel choice of the customer. He said ash deposits on the engine are an important concern if BN were to go down. In trunk piston engines where system oil is splash lubricated onto the liner, BN depletion will be less because of lower sulphur content in the fuel. This would mean the system oil in such engines has to last longer and handle combustion products better. “There would be less of a need for topping up the system oil,” he said.
To a question from the participants on whether users can continue using higher BN oil for low sulphur fuel, Mr Marucci said in that case the oil will have higher BN without much to do, causing hard and difficult-to-remove deposits.
As lube oil suppliers on the panel laid out the broad aspects of how system and cylinder lube oils would need to change for two- and four-stroke engines, conference attendees pitched in with more questions on possible scenarios emerging when the sulphur cap kicks in. One question focused on what ship staff should do if they found higher carbon deposits on the piston after changing over the lube oil to lower BN. Mr Chen of Shell said the BN number could possibly be increased to 70 for some time but brought back to 40 after the deposits are removed.
ExxonMobil’s senior territory manager, Ramaswamy Visweswaran said deposits do not happen overnight. If ship staff had done their due diligence and performed condition monitoring such as inspecting scavenge spaces, then they could have dosed the lube oil with higher BN oil and observed the changes.