The use of mass flow meters (MFM) is mandatory for all fuel oil deliveries in Singapore, as of 1 January 2017. However, issues related to bunker quantity remain prevalent, according to Gard P&I Club. In this context, the Club presents some issues faced by operators, when taking bunkers in Singapore, following the implementation of the MFM requirements.
The introduction of mandatory use of MFMs was intended to address frequent quantity disputes arising between the bunker barge and the receiving vessel, although these issues remain.
Causes
- Operational practices by the bunker barge operators
Gard has received reports indicating that some bunker barges were found to syphon fuel back to their tanks via pipe connections between the flow meter and the outlet flange going to the ship manifold. In such circumstances, the MFM reading will be higher than the amount actually received by the ship’s bunker tanks.
The Maritime Port Authority of Singapore is currently investigating these issues and has suspended several barges from operations until completion of the investigation. It is worth noting that an MPA certified bunker barge should have all connections between the flow meter and the shipside blanked off and sealed as part of the certification.
- Limitations of the equipment itself.
Some vessels have recently reported quantity difference exceeding their past experience. Some bunker surveyors have studies the discrepancy between the MFM readings and the vessel received figures for a duration of time. Out of 24 cases of discrepancies over the duration, the maximum discrepancy was 57.24 MT and minimum 6.79 MT. The average discrepancy, in the disputed cases, was approximately 19 MT.
These discrepancies can be due to:
- Errors in the tank calibration tables for the receiving vessel.
- Errors in the MFM’s measurement of the flow rate.
- Any errors in the tank calibration of the vessel would be consistent with or without the MFM. To identify this issue a vessel experience factor (VEF) from her previous bunkering operations should be taken into account.
Errors in the MFM reading can also account for such discrepancies. All MFMs have a maximum and minimum flow rate, commonly known as “Qmax” and “Qmin” respectively. As Gard explains, these limits define the operational accuracy within which the system is qualified to operate. This means that, if the flow rate of the liquid is outside these limits, the calibration of the equipment may not be accurate.
Moreover, the accuracy of measurement can be influenced by MFM parameters such as Damping, Drive Gain, Low Flow Cut Off Value & Air Index, if they exceed the manufacturers’ recommended limits during the bunkering operation.
While stripping of the bunker tanks is allowed under the TR48 (Technical Reference For Bunker Mass Flow Metering), it has been noted that prolonged stripping operations causes frequent fluctuations in the flow rate with several instances of the flow rate falling below the Qmin. It has also been observed that some bunker barges conduct stripping operations in the middle of bunkering which is not permitted under TR48 and can lead to measurement uncertainty.
Recommendations If there is significant discrepancy between the vessel received figures and the MFM figures after having physically verified all the above points, the following actions are recommended: