Short answer: bunker samples are drawn continuously throughout the delivery at the receiving vessel’s manifold, then divided, sealed and labelled. One sample, the MARPOL sample, stays on board for at least 12 months. Another is usually sent to an independent laboratory, which tests it against the ISO 8217 grade purchased so problems are found before the fuel is used.
Why sampling is the foundation of quality
If a dispute arises, the samples are the evidence. A sample that was not drawn properly, not sealed, or not recorded on the bunker delivery note is easy for the other side to challenge. Getting sampling right at delivery matters more than anything that happens in the laboratory.
How bunker samples are taken
- Continuous drip sampling collects a small, steady flow throughout the whole delivery, so the sample represents the entire quantity, not just one moment.
- Location: the sampling point is typically at the receiving ship’s bunker manifold.
- Witnessing: the sampling should be witnessed by the vessel’s representative and the supplier’s representative, and by a bunker surveyor if one is appointed.
- Division and sealing: the collected sample is mixed and divided into bottles, sealed and labelled with vessel, product, date, location and seal numbers.
Who keeps which sample
- MARPOL sample: retained on board under the ship’s control until the fuel is substantially consumed, and for not less than 12 months. Used by authorities to verify sulphur compliance.
- Supplier’s sample: kept by the supplier.
- Vessel’s retained sample: kept on board for commercial purposes.
- Testing sample: sent to the buyer’s chosen laboratory.
Since 2022, MARPOL also requires designated sampling points on board for in-use and on-board fuel samples, which authorities may take to check what the ship is actually burning.
What laboratories test
A standard residual fuel test covers density, viscosity, sulphur, water, flash point, total sediment, carbon residue, ash, pour point, acid number, metals (vanadium, sodium, aluminium, silicon), CCAI and used lubricating oil indicators. Distillate tests add cetane index, appearance, oxidation stability and lubricity. For biofuel blends, FAME content and stability are added. Where contamination is suspected, GC-MS screening can identify chemical compounds not covered by ISO 8217’s table.
Reading the results
Each test method has a stated precision. ISO 4259 sets out how results are interpreted against specification limits, so a result marginally above a limit is not automatically off-specification. A good laboratory report explains this.
If the fuel is off-specification
- Segregate the fuel and avoid burning it if the parameter affects safety or engine reliability.
- Notify the supplier promptly in writing, within any time bar in its terms.
- Propose joint testing of a retained sample at an agreed laboratory.
- Keep the BDN, sample receipts, seal numbers, test reports and engine room logs.
In Singapore, the MPA’s Bunker Quality Advisory Panel provides a procedure for reviewing test results and giving technical advice in off-specification cases.
Frequently asked questions
How much fuel is in a MARPOL sample?
IMO guidelines call for a sample of not less than 400 ml, sealed and labelled, kept on board for at least 12 months.
When should bunker fuel be tested?
As soon as possible after delivery, and before the new fuel is used where practicable. Early results give the vessel time to segregate fuel and the buyer time to raise a claim within the supplier’s time limits.