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Bunker sampling

Updated 11 Oct 2019

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During delivery of bunkers samples should be taken for analysis in case of dispute and also for compliance with IMO rules. The samples should be properly labelled and stored safely on board. Because of some highly publicised cases of contaminated bunkers causing damage to engines, some operators have adopted the habit of having all fuel analysed before use.

There are many independent laboratories who offer such services and some of the leading classification societies also have their own fuel testing programmes. If taking advantage of such a service, the method sampling will be determined by the service provider.

There are a growing number of kits that allow the crew to make some types of checks on board as well and these can overcome the need to wait days or weeks before learning if the fuel is suitable for use. It is also good practice to segregate the new fuel and where possible not use it until the result of the sample analysis is available.

This last point looks to become more important from now onward as ships begin using the new 2020-compliant fuels. As well as proving the sulphur level meets the new requirement, stability will need to be checked in some way although as yet there is no quick method of doing this.

Quantity and quality fraud

It is to be hoped that most bunker suppliers are honest but there are far too many cases of fraudulent means of short-delivering and delivering off-spec and contaminated fuels recorded each year to demonstrate that not all are. The contamination cases are sometimes accidental but there are many documented cases of bunker fuel being used as a medium for disposing of hazardous waste chemicals.

Sadly it is also true that some seafarers are also dishonest and willing accomplices in defrauding shipowners by taking bribes to sign false delivery notes. If the vessel is on time charter when such crimes are committed, the owner may not be financially out of pocket by virtue of the short delivery but may find himself on the end of a legal dispute over consumption and performance claims from the charterer.

The advent of Monitoring, Reporting and Verification (MRV) by the IMO and the EU as a means of initially measuring CO2 emissions but potentially as a charging basis for a future market-based measure on shipping is another reason why accurate records of quantities delivered is gaining added importance beyond the commercial considerations alone.

One of the main causes of short deliveries is a failure to recognise or understand the relationship between temperature, volume and mass. Unlike fuelling motor vehicles ashore where volume is the pricing factor, bunkers for ships are almost ordered by mass (tonnage).

However, measuring the ordered quantity on delivery is done by volume taking into account the temperature of the fuel. Fuel expands as temperature increases so for the same mass of fuel the volume will be more at a higher fuel temperature than at a lower fuel temperature.

Bunker delivery notes (BDNs) usually detail both mass and volume but whenever there is any doubt as to the actual quantity delivered, the engineer officer signing for the fuel should always endorse it as being for ‘volume only’ adding a clause along the lines of “actual weight to be determined after testing of representative samples”.

Any question as to the temperature of the fuel also needs to be remarked upon as this will be crucial to determining actual mass. The temperature is often measured on the barge which may make checking difficult but whenever possible the temperature should be seen by a crew member or temperatures of the ships’ bunker tanks taken at intervals immediately before, during and immediately after the bunkering operation.

One usually-deliberate means of bunker suppliers making short deliveries is to pump air into the bunker flow during delivery. This causes the fuel to froth, fooling some types of flow meters into measuring a higher amount of fuel. The frothiness of the fuel has given this practice the nickname of the ‘cappuccino effect’.

Not only does the effect give false flow meter readings, it can also mean that measurements taken by sounding the bunker tanks are inaccurate, at least until all the air dissipates.

The shortage in delivered quantities can be significant ranging from 2% to 5% or more.

There are several ways in which air may be introduced into fuel oil:

  • The bunker barge may inject compressed air into its tanks prior to joint soundings being taken to increase the apparent volume of the fuel oil before it is transferred.
  • Compressed air may be injected into the fuel oil during the transfer, either in the vicinity of the discharge pump, or into the tank or into the discharge line. This may be by using the compressed air equipment designed to blow through the pipelines after discharge, or via a separate system.
  • The stripping of bunker tanks using a positive displacement pump means that air will be drawn into the fuel oil when pumped. Consequently, excessive stripping by the bunker barge may also result in the cappuccino effect.
  • Preventing a short delivery through the cappuccino effect requires vigilance by the crew during bunkering but there are several signs and sounds that are giveaways that something is amiss. These include:
  • Suspect connections on the bunker barge’s supply pump and pipework – these can be quite small as only compressed air is being injected.
  • Check the manifold sampling point at regular intervals for frothing or excessive air bubbles.
  • Look for foam and/or frothing on the surface of the fuel oil on the barge prior to bunkering and on the vessel while bunkering is taking place and on completion.
  • Check for bubbles on sounding tapes.
  • Unusual noises at the manifold, supply line or fuel tank vent head.
  • Unusual movement of the supply hose during bunkering.
  • Fuel density – if too low for its temperature, that may indicate presence of excess air.

The temperature of the fuel oil should be measured before the transfer takes place so that the fuel oil density can be calculated accurately.

If it is suspected that air may have been introduced into the fuel oil, an engineer should board the bunker barge and ask to see the line blowing arrangements and the air compressor. If these have recently been in use, the compressor and its connections will be warm, while the compressed air delivery line will be cold. Empty compressed air bottles may also provide an indication that the fuel oil has been injected with air.

The cappuccino effect cannot be detected by most types of flow meter but mass flow meters (MFMs) using a device known as a Coriolis meter are much more accurate as they do measure mass rather than volume. Very few ships have been fitted with MFMs but they are available from several suppliers. Although they are more accurate, MFMs are not infallible and can be cheated.

Dilution of fuel

Under the ISO 8217 standards, the water content of most residual fuels is limited to 0.5% v/v and in most cases is usually considerably below this level. However, fuel can sometimes contain higher levels as a result of an accident such as a leaking heating coil or as a consequence of fraudulent and deliberate injection of water. If samples indicate a high level of water beyond that allowed by the ISO 8217 standard, then a letter of protest should be issued.

The ship’s fuel treatment system should be able to remove water but if this is not the case then the fuel may have to be landed ashore. Fuel samples provided by the barge may not have any traces of water as the samples may have been taken prior to bunkering and mixing of water. Fuel samples should always be collected during bunkering and not before or after. Samples should only be signed for those actually witnessed. Use of water-finding paste on the sounding tape works with distillate but not with residual fuels.

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