Base number (BN), or the alkaline content of a marine lubricant, looms large in any discussion around operating on low sulphur fuels, and the risks of what could go wrong in the event of a mismatch.
“Currently our recommendation when preparing to transit an emission control area (ECA) is to maintain a 40 BN, which is slightly out of kilter with the long-term recommendations of OEMs to go down in BN,” says Castrol marine lubricants technology manager Paul Harrold.
“Our theory is being proven in practice. Operating on low sulphur fuels is expensive and therefore a disincentive to transit at full speed. Most vessels are preferring to operate at little more than half load in the ECA. This means they are typically burning much less lube oil and operating at much lower temperatures. Our view is that problems occur when using a high BN lubricant at high load in an ECA,” explains Mr Harrold.
For Shell Marine Products general manager Jan Toschka, effective operations are not only about matching BN to sulphur content. “Our intensive research has shown that, in addition to acid stress, the cylinder oil in low-speed, two-stroke engines is exposed to thermal, insolubles and humidity stress. An imbalance between the acid stress a cylinder oil faces and its BN can lead to excessive deposits on piston top lands, rings and ring grooves, leading to scuffing and cylinder liner damage. This means higher maintenance costs and reduced vessel availability.”
Launched in September 2014, Shell Alexia S3 has been formulated for use with low sulphur and distillate fuels up to 0.5 per cent sulphur content. It has secured Letters of No Objection for use from both MAN Diesel & Turbo and Wärtsilä, the shipping industry’s two giants of two-stroke engine production and licensing.
For ExxonMobil Marine global field marketing manager Iain White, a big part of today’s challenge is that crews lack operational experience. “At the other end of the scale, if you are operating new engines or you have recently done a conversion to make a vessel operate more efficiently at a lower speed when slow steaming, you are likely to introduce a cold corrosion problem for your crew to manage as well,’ he says.
The solution, he says, is to have a monitoring programme in place doing the scrape down analysis or what MAN Diesel & Turbo refers to as ‘sweep testing.’ “This is a test that can be done very rapidly. Within five days, you can obtain a clear picture of what is going on in the engine under the operational conditions and the fuel that you are using at the time.”
Chevron Marine Lubricants’ onboard DOT.FAST system uses visible spectroscopy for determining the iron content in drip oil. A complexing agent reacts with the iron present in the lubricant to form a complex of dark violet colour, whose intensity is measured. The absorbance reading measured at a specific wavelength is proportional to the iron content of the drip oil sample.
Total Lubmarine technical director Jean-Philippe Roman says that field trials have shown that owners are often limited by their vessels in fully implementing engine manufacturers’ recommendations. “There might be a lack of a storage tank or daily tank,” he says. “This generates issues in terms of management and handling of the cylinder lubricants on board.”
He sees three options: one is to maintain the status quo, using one product for each operating condition; another is onboard blending of marine fuels; and the third – which Total advocates – is to use a single lubricant capable of functioning across a range of operating conditions.
“We have designed a 100 BN lubricant where a significant part of the calcium carbonate has been substituted in favour of ashfree neutralising molecules,” he explains. The product is currently going through testing and approval.
“Comparing with a conventional 70 BN lubricant on an MAN S35 ME B9 mark 9 derated engine from MAN: following a sweep test after 120 hours, fewer deposits can be seen on the hot part of the engine.
The same results were seen following a field test involving a MAN engine Mark 7 S60 that had clocked up more than 4,000 running hours. Again, when using the new formulation the piston ring belt is quite clean, the deposits on the topland were very limited, and engine wear quite low.
A third field test involved a Wärtsilä RTFlex 96 B engine fitted with a slow steaming upgrade kit. “In this test we ran a ship with a conventional BN 70 lubricant when the ship was using a high sulphur fuel. When the vessel entered an ECA we switched to our high BN product and tested it back-to-back with a BN25 product. After 10 days in the emission control area – 85 hours of operation – we observed that with the high BN product we were able to achieve superior engine lubrication.”
Total, says Mr Roman, has also developed a tool to help our customers to monitor their engines: “an automatic system that does not require a detailed knowledge of chemistry.”
Lukoil Marine Lubricants specialises in 100 BN oils (Navigo 100 MCL). “A conventional full 100 BN oil is only needed with high sulphur levels in the bunker fuel,” says the company’s Hamburg-based technical and marketing director Stefan Claussen.
Earlier this year the company launched its intelligent cylinder oil lubrication system, iCOlube system. This has been designed to optimise the use of Navigo 100 MCL cylinder oil by adding either fresh or used engine oil such as Navigo 6 SO.
“With the engine always remaining at its optimum feed rate, the operator only needs to enter the sulphur content of the fuel,” says Mr Claussen. “In this way iCOlube ensures safe and easy operation while saving oil costs at the same time.” The company is close to completing 100 installations.
For Castrol’s Paul Harrold, the earliest the industry is likely to have a universal lube is 2020. In the short term, vessels will need to carry two lubricants and switch between the two when transiting ECAs.
Mr White believes that the industry is going through an irreversible shift from an era of the single fuel to multi-fuels. “This means we are moving into a more challenging era of multiple lubricants. The idea of one universal solution is wonderful, but the industry is challenged on technology, performance and economics. It is a laudable aim, but not achievable in the near-term.”
For Mr Toschka, the longer term will see a more prominent role for LNG. “As a cylinder oil supplier, our expectation is that gas engines will take a growing share of the two-stroke market. We already have the right products for the four-stroke sector and we have recently developed lubricants to take care of low sulphur content fuel for two-stroke engines, as well.”
Turning to Mr Roman’s second scenario – blending on board – Gulf Oil Marine’s technology and solutions director Don Gregory agrees the idea is ‘seductive’ for operators, but the reality is much more complex and the risks are very high. “And when you consider all the other risks when operating ships today this one seems to be a step too far. I have never seen any published data on how an operator can make or save money using this option.”
Mr Truijens finds he agrees with Mr Gregory “to a certain extent.” “We are actively involved in an experimental project around blending on board. One of the outstanding questions is how a blended lube would impact OEM approvals.”
Mr Truijens adds: “Lubricant base number provides only a small portion of information on the lubricant composition and should not be mistaken for lubricant quality at a certain fuel sulphur percentage.”
For Mr Roman, blending on board poses too great a threat to quality and reliability. Mr Harrold adds that blending on board only addresses one fact of lubrication: the BN number. “But BN is not the only dimension you need to think about. You need to think about detergency and viscosity,'” he adds. “There will be lots of technical challenges and for me the business case is not clear.”