Testing Time for Bunkers

Ship engineers are sometimes faced with a dilemma when it comes to using new bunkers.

Fuel is delivered on board and samples are dispatched without delay to a laboratory for testing, but the crew might not know the results for several days. What happens if circumstances dictate that the new fuel has to be used before its characteristics and quality are known?

It is widely accepted that the best practice is to make sure the vessel is not placed in such a situation. Ideally, there should be sufficient reserves of old fuel on board to allow time for lab testing of the new fuel. But in reality there will be instances where the crew have to start using the new fuel before knowing the lab results. In these situations the engineers must make best efforts to satisfy themselves that the fuel is safe to use.

The impact and consequences of using poor quality bunkers is well documented. The damage to the main and auxiliary engines can lead to costly and lengthy repairs. These in turn lead to costly and lengthy delays and disputes. There is also the question of liability when the bunkers have been arranged and purchased by the charterer.

Marine fuels must meet certain criteria to ensure it is of sufficient quality to be used on board. The international standard ISO 8217 is stipulated in bunker purchasing contracts and charter parties to ensure these minimum standards are met. When a bunker sample is sent to an independent laboratory, it is to test the fuel against the criteria in ISO 8217.

Quite clearly this testing involves specialist equipment and complex testing techniques that can only be carried out in a lab. But there are some quick and simple tests that can be carried out on board by the ship’s engineers prior to using the fuel.

Some of these tests are well established and have been used by ships’ staff during bunkering operations for decades:

• Water content
• Kinematic viscosity
• Density
• Compatibility

However, it is the compatibility test that is often neglected and a number of incidents could have been prevented if this simple test had been carried out. It checks that a residual fuel is stable and if it is compatible with other fuels. If a fuel is unstable or incompatible with other fuels then it has the propensity to form sludge when mixed. Not only will the diesel engines be unable to burn the fuel, increasing the risk of loss of propulsion and electrical blackout, the sludge formation can lead to a build-up in tanks, blocked filters and choked purifiers. The clean-up operation could be time consuming, labour intensive and expensive. 

The test in its simplest form is easy to do, although special onboard testing equipment is available which speeds up the process. A droplet of fuel (or a droplet of mixed fuel) is applied onto a piece of blotting or filter paper and left to dry. If it is homogenous when dried – i.e. no distinct dark and light areas – then there can be a reasonable degree of confidence it is stable and/or compatible.

Another cause of fuel-related engine damage which results in a significant number of costly claims and disputes is the presence of excessive cat fines. These aluminium and silicon fines, a by-product of the refinery process, acts as an abrasive on engine components. They are present in most marine residual fuels to some degree and the concentration is limited by ISO 8217.

A typical situation might be that the bunkers have a cat fine content well in excess of the limits stipulated in the applicable edition of ISO 8217. The laboratory test identifies the problem, but the vessel had already used the fuel resulting in engine damage.

In the past, ship’s crews were unable to test for cat fines on board. However, new testing equipment has been developed that can allow a rough estimate to be made. These work on the principle of centrifuging a fuel sample that has been treated with reagent. After centrifuging, the cat fines are then held in suspension in clear fluid and a visual comparison can be made against a chart. Although accuracy is limited, it can provide a very effective warning at the time of bunkering or before a fuel is used.

On board testing will not substitute laboratory analysis. But the technology is available to provide an early warning and as well as a level of confidence on those occasions where a fuel has to be used before the lab results are available. On board testing kits can be sourced directly from the manufacturers, but they can often be provided by the major oil suppliers and fuel testing companies if engaged in a service contract.      

Images courtesy of Braemar Salvage Association