Some technical aspects of marine fuels testing
Some technical aspects of marine fuels testing

Some technical aspects of marine fuels testing


Ships use the cheapest liquid fuels available on the market, hence the fuel quality varies greatly. The safe operation of ships depends on knowledge of the quality of the fuel used.

Fuel Testing

It is estimated that only one third of all marine fuels delivered to ships trading internationally is tested. Even so, the experience from the testing services indicates that things are far from perfect. The comparison of a car filling up with fuel at a petrol station with a ship lifting bunkers via a barge does not apply. And for good reasons, which will be explained later.

Marine fuels
Marine fuels

Marine fuels are practically all custom blended to a buyer or ISO specification. The supplier may or may not have detailed information on the quality of the components he is using in the blend. Satisfactory quality components in themselves may well result in an unsatisfactory blend, unless you know exactly what you are doing, and we all know that blends are made directly to the vessel bunkering, either through line blending from shore installations, blending on board barge, or in-line blending from the bunker barge. The only way to ascertain the quality of the product actually received on board is through representative sampling and testing by specialised laboratories.

It is true that any analysis result is only as good as the sample analysed. If the sample is not representative of the average quality of the product transferred from supplier to buyer, then the analysis result is of little or no value. Therefore, there should be rules and routines on board to ensure that every bunkering is properly sampled, including fuels for the auxiliary engines. Each and every vessel should have fixed routines describing in detail the bunkering operation, including the stages before, during and after bunkering, and listing the responsibilities of each individual involved. It is the owner/operator’s responsibility to set up such an instruction manual. It is also his responsibility to provide the ships with suitable samplers. Prior to placing the order, it is his responsibility to agree on a joint sampling procedure with the supplier, including where and when the sampling shall be carried out. If the vessel does not have a fuel sampler acceptable to the supplier, the buyer is not likely to be in a position to stipulate sampling at the point of custody transfer, i.e., at the ship’s fuel manifold.

Proper sampling during a bunker transfer operation is extremely important, because continuous drip sampling at the point of custody transfer is the only secure way to ascertain the quality of the product received by the buyer. Sampling either before or after the event will not, for obvious reasons, bear the same weight. It is good news that Singapore, being by far the largest bunkering port in the world, has decided to introduce legislation requiring all bunkerings taking place by barge to be sampled continuously during the bunkering operation at the receiving vessel’s manifold. The bunker barges will all be required to fit a defined quality sampler at the receiving vessel’s end of the bunker delivery hose. The new law will become effective on 1st January 2002.

The Marine Environment Pollution Committee (MEPC) of the IMO (International Maritime Organization) has also recently drafted guidelines indicating where and how samples should be taken in connection with the bunkering of ships. The “Guidelines for the sampling of fuel oil for determination of compliance with ANNEX VI of Marpol 73/78” state: “For the purpose of these Guidelines a sample of the fuel delivered to ship should be obtained at the receiving ship’s bunker manifold and should be drawn continuously throughout the bunker delivery period”. It is hoped that these guidelines will be adopted by all the major shipping nations, because they make good sense.

Even if the bunker industry has come a long way in its endeavour to safeguard the interests of the various parties involved, there are still strong objections from some supplier quarters to accept joint sampling by buyer and seller, despite the obvious fact that this is only fair and square. The practice of multiple sampling by both parties makes dispute resolution difficult, and is always costly and time-consuming to all involved. The sophisticated buyer, who sees the benefit of fuel quality control, should always insist on joint sampling at the point of custody transfer. If declined by the supplier, then he should make a reference to this in the ship’s logbook.

Testing services provide their customers with sound and practical advice relating to bunkering operations. Following them is good practice.

It is customary in some ports to request the pre-signing of documents relating to the bunkers being transferred, including the signing of labels for the bunkering samples. This is not acceptable, as the buyer has no control over which sample bottles the labels will be placed on.

Sample transport

The operator pays good money to the testing service for speedy analysis results. The chief engineer must therefore arrange for a courier company to pick up the sample immediately after collection. It is advisable to inform the courier company of the sample’s whereabouts by e-mail or fax, with copy to the agent and owner/operator.

This will put pressure on the ship’s agent and courier, and will enable the operator to follow up in order to avoid delays.

Use of new fuel

The ship should avoid using the new fuel until its quality has been confirmed to be satisfactory by the laboratory report. It has been customary to bunker just prior to leaving port. However, analysis results on the new bunkers may not be available until a few days after leaving port, so some operators have started to bunker when entering port, whenever possible (draft, cargo, timing, etc., permitting). This allows the analysis results of the new fuel to be available prior to leaving port, which of course is the ideal situation. Should the fuel be unfit for use, then the operator will be able to take appropriate action while the ship is in port, which will be a lot cheaper for all involved.

A number of operators give clear instructions to their ships not to use new, untested fuel until the analysis report is at hand, indicating satisfactory fuel quality. These ships carry larger reserves of the “old” and tested fuel, or may even change to the more costly MDO or gasoil. Such measures may be considered as extra insurance, naturally at a cost. However, avoiding delays and/or engine damage will enhance the ship operator’s reputation in the market, and influence the premium paid for insurance.

Having said that, as ships frequently may have to set sail prior to receiving the fuel analysis report, operators will be well advised to provide fuel test kits for their vessels, thus enabling their chief engineers to verify the fuel’s density, viscosity and water content, plus the nature of the water, whether fresh or salty. The issue of seaworthiness is likely to arise if a vessel leaves port with fuel having a density higher than the ship’s fuel separators are designed to handle, a viscosity too high for the heat available on board, or a density/viscosity relation indicating that the fuel may be deficient in ignition quality (CCAI), since this could result in ignition delay, severely hampering the ability of the main engine to provide propulsion. A too high water content speaks for itself, particularly if it is sea water.

While fortunately most fuels delivered are of satisfactory quality, every operator knows from experience that mistakes are made and problem fuels are supplied. Such products will be discovered at an early stage through proper sampling and professional analysis of representative samples.

While at sea, a ship having received the report indicating a satisfactory fuel quality can optimise the fuel treatment, knowing the precise values of important fuel parameters, such as density (selection of the correct gravity disc for the purifier), the viscosity (adjustment of temperature), water content (checking of water content in the fuel after treatment in order to decide on the use of an emulsion breaker additive) and so on.

However, if the analysis report indicates an unsatisfactory fuel, the fuel testing service will also provide recommendations on how to optimise its treatment and use, if necessary. Through communication with all parties involved, including supplier, testing service, perhaps also class and/or insurer, sound decisions can be made based on facts. The problem may be related to the separation of a high-density fuel. The advice could then be to modify the purifier into a clarifier, by installing the smallest gravity disc of the set, thus converting the separator into a clarifier, frequent shooting of the clarifier bowl, possibly operating two clarifiers in parallel, depending on other fuel parameters such as water, sediments or catalytic fines (al+si). Provided you know exactly the quality of the fuel received on board, the operator will be in a position to make the right decision.

Now imagine a vessel also having received inferior quality bunkers, but without any sample sent for testing. She will carry on until engine damage of some sort occurs, resulting in delay and extra cost, usually far exceeding the cost of regularly using a testing service.

Marine Fuels Specifications

The operator who realises that the quality of marine fuels varies considerably, being “the bottom of the barrel”, the “leftovers” at the refineries, a “low priority product” in the eyes of the manufacturer, accepts that fuel quality control is required for safe ship operation. He realises that even though “highly priced”, marine fuel is priced way below the crude oil from which it is derived.

Marine fuels are in the main produced to company specifications, which are normally stricter than or at least equal to ISO specifications.

The purpose of fuel specification is to stipulate a product quality which, when meeting the requirements of the specification, should perform satisfactorily in the application for which it is intended, provided that application (the diesel engine/boiler) is in normal good condition. However, fuel specification can not safeguard every aspect of satisfactory fuel quality, otherwise it would be far too detailed to be of practical use. And remember, we live in a competitive world. It is naturally in the supplier’s interest to deliver a product which just meets the requirements of the specification at the highest possible price. Independent, third party testing is therefore very important, a must for safe and effective ship operation on today’s fuels.

Know the limitations of your fuel treatment plant

The only way to effectively treat marine fuels on board is to use centrifuges. But even centrifuges can not remove 100 per cent of all the sludge and particles detrimental to engine components. Centrifuge manufacturers may claim that some 70 to 80 per cent of catfine particles will be removed when their machines are operated optimally. Documented reports, however, show that during manufacturer-controlled tests at their factory, the removal of catfines was just over the 50 per cent mark. But even if one accepts a figure of 70 per cent removal of particles and sludge, it still leaves 30 per cent of the particles and sludge in the treated fuel entering the vessel’s daily service tanks.

Is it customary to re-centrifuge the fuel in the service tank? Some vessels have a fuel piping arrangement to enable this to be done. Still, not all carry out this very important operation regularly.

Are bunker fuel tanks cleaned from time to time? The answer is only very occasionally. Tank cleaning may be on the list of items to be carried out during docking, but it is frequently the item that is dropped either due to cost or time, or both. Settling and daily service tanks (or at least the daily service tank) should be cleaned annually. Just imagine what happens to the sludge and particles accumulated in the tank bottom when the ship runs into stormy weather! This is almost certainly the time when excessive engine components wear occurs.

How effective is the fuel treatment plant on your ships? Most operators probably have no idea. The centrifuges are spinning, the fuel is separated at the throughput matching the engine consumption, the fuel temperature and flow are kept as constant as the fuel treatment plant auxiliary components will allow. The fuel quality is known through testing, and hopefully the correct gravity disc has been installed in the purifier. The chief engineer, having done his best to optimise the fuel treatment, will have little or no idea as to the quality of the fuel entering the ship’s engines. He can not see what is going on in the treatment plant and is not supposed to taste, smell or even touch the product. In fact, he has to cross his fingers and hope that satisfactory quality fuel is entering his power units.

In practice it is very simple and easy to ascertain the effectiveness of the treatment plant through sampling and testing. Some sophisticated operators do this in a planned way, and they have an experience factor at hand as to which quality product they can treat satisfactorily. The day such operators receive an off-specification fuel, they will know whether or not their vessel can handle the product in question and whether to arrange an off-lift operation. This does not mean that the buyer must accept off-specification products without having compensation from the supplier. However, in many cases it will be able to avoid a costly deviation and off-lift operation. At least one of the fuel testing services recommends a “Fuel System Check” programme to their customers. They are well advised to make use of it.

Read more : Marine Engine Breakdown After Repairs; Hull and Machinery Incident of Marine Engine breakdown; Breakdown of marine engine due to overspeed; Hull and Machinery Incident Engine Breakdown


Indonesia Marine Equipment

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