Slow steaming has become a standard way for ship operators to save money on fuel, but it comes with a well-known risk: pitting damage to the engine's cylinder liners, a process known as cold corrosion.
When running the engine at a low load, more of the sulfuric acid produced from burning high-sulfur fuel condenses out instead of going up the stack. Over time, this condensate will damage the liners and the piston rings. However, this problem can be prevented by the use of cylinder lubricating oil with the right base number (BN) and the right lubricant feed rate.
Monitoring the state of cylinder scrapedown oil is key to getting the lubrication right and neutralizing the acid. Shell's new LubeMonitor condition monitoring program provides this service to shipowners by combining lab test data with on-board readings of iron content and base number – creating an up-to-the-moment picture of the state of the lubricant.
“OEMs recommend cylinder drain oil analysis as a way for shipowners to optimise feed rates, as it allows them to strike the right balance between corrosion protection and minimized oil consumption,” says Jan Toschka, general manager of Shell Marine. "Our collaboration with OEMs has highlighted a need for better collection of the analysis data. The job demanded on the lubricants is changing, so we need to monitor more closely in order to prevent excessive engine wear. LubeMonitor addresses this need in a comprehensive way.”
ECAs pose additional challenges
With limits on sulfur content in Emissions Control Areas (ECAs) comes another problem for operators: how to match the lubricant to the fuel when switching between HFO and ultra-low sulfur diesel. LubeMonitor helps the ship’s engineers ensure that they are using the right BN and feed rate in all emissions regimes – but there are a variety of alternatives when it comes to the oil itself.
Shell competitor Total Lubmarine has launched a new "universal" lubricant, Talusia Optima, which is intended to work with every fuel from zero to 3.5 percent sulfur content. "No ship operator or engineer wants added complexity [for ECA operations]," says Total Lubmarine global marketing manager Serge Dal Farra. With Talusia, Total says, switching fuels requires no alteration of the composition of the cylinder oil, reducing risk during fuel changeovers.
Toschka understands the appeal of a "universal" product. "Technically it is possible for us to do the same thing, and we have no doubt that it can be done. But the truth is that the product itself needs to be cost-competitive," he says. Shell takes a different approach to solving this problem in an affordable way: it has trialled blending in additives on board to its system oils to achieve the required BN. Its.Alexia 140 is an ultra-high base number oil that is intended for onboard mixing with lower BN oils to accommodate different fuels.
"It's difficult to have a full spectrum of lubricant grades available in all ports at all times, and shipowners are less certain than ever where their vessels will be in the coming months," Toschka says. "With mixing and on-board blending, the crew can create the lubricating oil they need, when they need it."
MAN Diesel and Turbo (MDT) and Shell Marine recently completed trials of an automated cylinder oil mixing system, which directly matches the lubricant's BN to fuel sulfur content. When switching fuels, the system meters in just enough high BN oil to meet the requirements of HFO or ultra-low-sulfur diesel as needed.
As an example, when a vessel’s engine needs a lubricant for burning ultra-low-sulfur diesel, the operator can use a low-BN oil like Alexia S3; when switching to HFO, the crew can mix in just enough Alexia 140 to bring the base number up to 70, or to any other value required.
For those shipowners who do not wish to mix or blend their own oil on board, Toschka says that Shell already offers competitively-priced products which can be used with a wide range of fuels.
"We've found that our BN 100 lubricant, Alexia S6, can be used for a limited number of days on ultra-low-sulfur diesel without any damage – not something that we would advise our customers to do, but it it possible, and that can take away some complexity. In addition, we have millions of operating hours showing that our Alexia S4 covers everything between BN 40 and 70 quite well," Toschka says.
For the future, Toschka predicts that the advent of the global sulfur cap in 2020 will mean that there will be more vessels equipped with scrubbers. Scrubber-equipped ships can burn much cheaper fuels containing as much as four to six percent sulfur, and that means that R&D efforts for cylinder oils may need to focus on a much different BN range than anything offered on the market today.
The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.