The Guide provides additional information on rightly opting for complaint fuels, due to a wider variability of fuel formulations and characteristics.
First of all, the constituents of a residual fuel however include asphaltenes, resins and liquid hydrocarbons.
In order for a fuel to be stable, the nature of the liquid hydrocarbons will determine the fuels capability to maintain the asphaltenes in suspension and remain in a stable condition allowing this important source of energy to take part in the combustion process.
Yet, there is a high possibility that the fuels may be unstable; Unstable fuels are unusable since the precipitated asphaltenes, together with the entrained fuel, forms excessive sludge concentration in tanks and can readily choke purifiers, filters, fuel injection equipment and even fuel lines themselves.
Thus, the Guide provides practical steps, mitigating the risk of the fuel becoming unstable onboard:
- Order the fuel to the ISO 8217:2017 specification which includes the stability test method ISO 10307-2.
- Select supplier considering recommendations in the guidance document MEPC.1/CIRC.875 ‘Best practices for purchasers.’
- Request the Certificate of Quality (CoQ) from the supplier prior to receiving bunker and compare characteristics with that of fuels already on board. Widely diverse characteristics to one another, such as density, viscosity and carbon residue may indicate potential incompatibility issues.
- Be proactive in minimising mixing of fuels especially fuels with widely different properties.
- Perform compatibility tests between all fuels, even if segregation is applied, either on board and/or in laboratories on shore.
- If mixing in tanks is anticipated, ensure compatibility checks are made between the two fuels in accordance with the anticipated ratio and in the order of mix prior to commingling (see Chapter 4). For each compatibility test run, ratios of around 10/90, 50/50 and 90/10 are recommended as a minimum. If the mixing ratio is known, compatibility testing should be done using the actual ratio between existing fuel in the tank and the new fuel to be loaded on top.
- Maintain a record of the compatibility between fuel tanks.
- Apply “first-in first-out” fuel inventory principle.
Moreover, the shipping industry has a variety in confirming the stability of the fuel and test for the compatibility between fuels. Whilst stability requires just the one fuel to undergo the test, the compatibility test to date has always required a sample of both fuels to be available in the laboratory or on board the ship for the test to be carried out.
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