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Mid-year fuel quality review – the numbers do not tell the whole story

Mid-year fuel quality review – the numbers do not tell the whole story
Having reviewed the fuel analysis data on a quarterly basis for a number of years, it is clear that for some time now the general quality, as measured by compliance with the specification limits, has been fairly steady.

This does not mean there have not been instances of non-compliance, sometimes serious in nature. These instances have, however, tended to be localised and relatively few in number.

Clearly there was great interest to see whether the change in the Emission Control Area (ECA) sulphur limit from 1.0%m/m to 0.1%m/m at the beginning of the year would impact this status quo.

Two issues were of interest: 1) The availability and quality of Marine Gas Oil (MGO) and 2) the nature of the New ECA Fuels (NEFs) being offered by a number of bunker suppliers.

During the first quarter of the year there was a rash of MGO deliveries with flash points below the legal limit of 60°C. Interestingly the deliveries occurred in a range of US and European ports and not just from the locations with a longstanding history of delivering non-compliant fuels. Even more interestingly, during the second quarter of the year this problem has virtually disappeared. It is almost as if suppliers were waiting to see how MGO demand developed before committing to stocks of flash point compliant MGO.

A few deliveries of MGO had very low viscosities below the ISO 8217¹ DMA limit of 2.0mm²/s @ 40°C. The majority of deliveries had viscosities above 2.0mm²/s @ 40°C. A large proportion fell within the range 2.0 to 3.0mm²/s @ 40°C. Whilst within the limits for ISO 8217¹ DMA, such fuel has the potential to cause operational problems on some engines. The four -stroke engine OEMs suggest that their engines are less prone to fuel pump leakage issues than the two stroke designs. Time will tell if this will be an issue or not.

The New ECA Fuels (NEFs) are a slight departure from the norm and are causing much comment and, in some cases, alarm. From the samples analysed so far the majority of these fuels are very good, providing they are understood and managed correctly. Ignition and combustion characteristics are, from what we have seen so far, excellent.   The challenge relates to handling and compatibility during storage and the changeover process.

Samples analysed to date show, for the most part, the high pour points are as indicated by the suppliers. If this were the only issue, it would not be a great problem. The low temperature properties of hydrocarbons are, however, quite complex. The ability of a liquid to flow under its own weight (pour point) does not mean that liquid will pass through the fuel systems filters or not form wax deposits in the fuel tanks. Additives, often referred to as cold flow improvers or pour point depressants, modify the way wax crystals interact with each other. They do not prevent the wax crystals forming.

The Cloud Point (CP) and Cold Filter Plugging Point (CFPP) tests can give an idea of when wax crystals start to form and when they will plug a filter under defined test conditions respectively. The problem here is that many NEFs are not clear and bright preventing the CP test from being conducted. Also, the relatively high viscosities and the presence of residual components prevent the CFPP test from being carried out. This leaves a testing issue that needs to be resolved if sound operational advice is to be given. There is a significant number of instances where operators have experienced serious filter blockage problems caused by wax with fuels that meet the supply specification, including MGO.

Residual fuels have almost taken a back seat during this period of transition. Indeed there have not been any significant changes in analysed quality for some time now. The number of fuels seriously exceeding the specification limits is small. On the other hand the number of fuels with measured properties at, or just above, the specification limit is quite high. In a number of locations such as ARA, Singapore and the US gulf and west coast areas, cat fines are consistently high albeit within the specification limits. These continue to represent a significant risk to ships that bunker such fuels.

Given that the majority of fuels analysed meet the respective specifications it would be tempting to suppose that there should be very few problems on-board ship.

However, evidence shows this is not the case. Why?

A common misconception that pervades all corners of the industry is that “On specification equals fit for purpose”. This is most definitely NOT the case.

It is convenient to think that compliance with ISO 8217¹ ensures fit for purpose fuel. Unfortunately the Standard has a number of major gaps that result in on specification fuels giving serious operational problems.

To briefly focus on two weaknesses:

The Standard (ISO8217¹) does not make any mention of the requirement for a fuel to be stable.    
The Potential Total Sediment test and its associated limit is NOT a measure of residual fuels’ stability.
There have been a number of instances this year where vessels have experienced severe centrifuge and filter blockage with fuels that passed the Potential Total Sediment test. It was proved with additional analysis that the fuel was unstable.

These fuels, that fully met the specification, were not in fact fit for purpose.

Pour point is a totally inadequate control for the low temperature properties of distillate fuels in the marine market.
There have been many instances VPS have been consulted on where distillates, meeting the specification for pour point, have given serious operational problems, including engine stoppage, due to filter blockage caused by wax. Clearly unfit for purpose yet on specification.
Adding cloud point as a controlled property is only a partial solution as many marine distillate fuels may not be clear and bright rendering the test unusable.

In conclusion, whilst the data implies no significant downward trend in marine fuel quality, the actual experience of ship operators indicates otherwise. Knowledge of fuel chemistry that goes beyond adherence to imperfect specifications is necessary to help operators avoid or deal with fuels that meet the specification numbers but give serious operational problems.

¹ ISO 8217:2012

Contrubited by Keith Forget, group fuel specialist at Veritas Petroleum Services. Email: [email protected]