Lubricant changeover strategy for compliant fuel

Malcolm Latarche
Malcolm Latarche

10 April 2019

Deciding on a strategy to meet the 2020 sulphur limit for ships has mostly been centred around the choice of a compliant fuel versus installing a scrubber. The ultimate choice will be down to the shipowner – maybe in conjunction with the charterer if the vessel is on a time charter – and their own financial situation.

If the ship does not have a scrubber and it does not run on LNG, it will more than likely use one or more of the new breed of 0.5% sulphur content compliant fuels that are being introduced. In addition, operation in ECA areas will still require a switch to a fuel with a maximum 0.1% sulphur content. Even ships with scrubbers may be required to switch to very low sulphur fuels in some ports because of local regulations.

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As 2019 progresses, ships must prepare for the 1 January changeover and ensure that only suitable fuels are on board and compliant before the deadline. That this will involve running down non-compliant fuels and cleaning bunker tanks is something that most owners have realised but some may not have given as much thought to the lubricants for ships with two-stroke engines.

If the ship is not scrubber fitted but has previously been running mostly on global cap fuel of up to 3.5% sulphur, it will almost certainly have stocks of lubes of 70BN, 100BN or even 140BN if it was one of those ships with engines prone to cold corrosion. After the 1 January when only 0.5% sulphur oil is permitted, these lubricants will be surplus to requirements. There is one possible exception and that is if supplies of compliant fuel are not available then the ship will be allowed to burn other fuels until such time as it can take on compliant bunkers.

There is a cost to lubricant and shipowners will not want to be left with large stocks of surplus types on board. This potentially means either finding a purchaser, transferring to other ships within the fleet that can still use them, or disposing of them ashore. The other alternative is to blend the BN down with a lower base lubricant i.e. 20% of 100BN + 80% of 25BN = (0.2 x 100) + (0.8 x 25) = 40 BN (mg KOH/g). As vessels transition to a low sulphur fuel with a low BN lubricants or potentially high sulphur fuel with higher BN lubricant, it’s imperative that the shift be monitored through drip oil analysis using an analyser such as Chevron’s DOT.FAST on-board and on-shore program. This will ensure the right lubricant is matched with the correct federate. This will provide data on both corrosive wear and abrasive wear to ensure an optimal operation. The two areas to be aware of when changing fuels and lubricants are;

  • High sulphur fuel + low BN lubricant and/or low feed rate = immediate corrosive wear (avoid at all costs)
  • Low sulphur fuel + high BN lubricant and/or high feed rate = deposits longer term (OK short term, avoid long term)

Vessels fitted with scrubbers will mostly be able to continue with their current practices and lubricant choices. However, the owners should be aware that with the removal of the global 3.5% cap, bunker supplies of HFO may have sulphur content even higher than that which is currently available.

If the ship is currently using a 70BN or 100BN lubricant, then a possible need to have 140BN product available should be borne in mind. The implication of higher sulphur fuels for the scrubber operation may be another factor that needs checking. Early versions of scrubbers occasionally had difficulties in meeting the equivalent emission requirement when using very high sulphur level fuels. Since the average sulphur content has gradually declined to 2.7-2.8% this hasn’t been an issue but if sulphur contents of well in excess of 3.5% are encountered the problem may return. Some advice from the scrubber maker may be a wise precaution.

For scrubber equipped ships, the potential of running occasionally on low sulphur fuels transiting ECA Zones for example, would suggest that a small stock of low BN lubricant is also available. Running on low-sulphur fuels could be necessary for a variety of reasons; While it is now expected that around 25% of all marine fuels used from 2020 will be consumed by scrubber equipped vessels and would therefore be 3.5% or higher sulphur content, availability might be troublesome in some ports. Regulations preventing scrubber use now exist in a small number of ports but could be more widely adopted. In the event of a scrubber malfunction, ships would be obliged to switch to compliant fuels until repairs are effected.

Compliant fuels bring their own problems

For the ships that are going to run on compliant fuels, cylinder lubrication will not necessarily become simpler just because only two grades of fuels (0.5% and 0.1% sulphur content) will be used. Many of the new fuels will be blended and as ships move between ports the available fuels may have very different qualities and characteristics.

Some of the fuels may contain bio-fuels in varying quantities and a very small number of vessels may be run wholly on bio-fuel. Most common biofuel types include Fatty Acid Methyl Esters (FAME), ethanol and Hydrotreated Vegetable Oil (HVO). These fuels can exhibit very different properties than traditional oil fuels and may even have a higher acid content with no sulphur present at all.

Blended fuels and bio-fuels may also have very different viscosities and combustion characteristics which will make the choice of an appropriate lubricant an important factor in operation and maintenance.

Some of the leading lubricant suppliers have spent much time and effort in developing lubricants suited to the new range of fuels that will be used after 1 January 2020 and are gradually introducing these to the market. The full range of new products may currently have limited availability and so gathering experience with them in conjunction with new fuels will not be the easiest of tasks.

For ships that have regular routes or areas of operation, some experimentation of new fuels and new lubes may be possible but involving OEMs, lubricant suppliers and testing services would be a prudent precaution.