The use of Environmentally Acceptable Lubricants (EALs) is on the rise as many shippowners and operators consider them as a way to meet environmental regulations and reduce risk. However, new research indicates that they may be having adverse effects on bearing and seal performance, damaging critical components and compromising oil-tight integrity. A new industry initiative by DNV GL in association with The Swedish Club, Norwegian Hull Club and Gard & Skuld to evaluate the effect of biodegradable lubricants, has been welcomed by manufacturer of seawater-lubricated propeller shaft bearings, Thordon Bearings.
According to Terry McGowan, President and CEO of Thordon Bearings, shipowners and operators are beginning to favour cleaner, more reliable lubricants, such as EALs over mineral oil-based lubricants, but there is still little evidence on EALs that shows they do what they’re supposed to do without damaging machinery or the environment.
EALs are mostly biodegradable, non-toxic, and non-bioaccumulative and all ships over 79 feet operating in US waters must use them in all oil-to-sea interfaces of the ship, switching over before the next dry-dock in order to remain in compliance with the 2013 Vessel General Permit (VGP) for Discharges Incidental to the Normal Operation of Vessels in US waters.
There are four major types of lubricants that can meet the VGP requirements, which complicates matters further, says McGowan, whose company provides seawater lubricated propeller shaft bearings, completely removing the need for any oil at all. He says that vegetable oils, synthetic esters, polyalkylene glycols (PAGs), and seawater can all be used to lubricate equipment, but their operational performance is another matter.
“Not all of these EALs perform in the same way,” says McGowan. The International Marine Contractors Association warned in a 2014 paper, Understanding Biodegradable Lubricants, that “choosing the correct type of lubricant for a particular application can be problematic, given that most types offer some degree of biodegradability, but differ in performance and regulatory compliance”.
It is therefore confusing for shipowners and operators to select a lubricant that is compliant and does the job without damaging machinery over time. EALs have a reputation for being much better for the environment than mineral oil-based lubricants, but according to McGowan, who is a chemical engineer by training, “the real concern is when biodegradable oils mix with water. Their viscosity can deteriorate with water ingress, resulting in reduced lubricating capacity and potential damage to seals and bearings.”
Furthermore, some EALs are incompatible with the sealing material, resulting in hydrolysis. This phenomenon weakens the sealing material, significantly reducing the lifespan of the seal.
In addition, the environmental impacts of EALs are not always known. They were originally introduced to limit the environmental impact of shipping, but Thordon Bearings’s Director of Marketing, Craig Carter, says that just because EALs state they are biodegradable does not mean they are environmentally safe to aquatic life. He believes that the technology was introduced to the market quickly and without sufficient research. “Unlike seawater lubricated propeller shaft bearings which have been around for many decades, there are no guarantees these new EAL lubricants actually work as mineral oils have.”
“We issued a statement in 2015 calling for more research on biodegradable lubricants regarding their operational and environmental performance, so are pleased to hear there is now a concerted effort to provide shipowners and operators with the information they need to make better informed lubricant decisions.
The new research on EALs under supervision of DNV GL will take place at the University of Sheffield, UK, testing EAL lubrication performance in stern tube bearings. According to Thordon Bearings, this type of research could influence future Class Society rules on EALs.
Images courtesy of Thordon Bearings.