Mass Flow Meters (MFM) in Bunkering
How a Coriolis meter works, a worked comparison with tank measurement, port requirements, verification and what a buyer should check.
A mass flow meter (MFM) measures the mass of liquid passing through a pipe directly. The type used in bunkering is the Coriolis meter, which reports the quantity delivered without any calculation from tank level, temperature and density. It has been mandatory in Singapore since 2017 for fuel oil and since 1 July 2019 for distillates, and in Rotterdam and Antwerp-Bruges since 1 January 2026.[1][2] The Singapore standard sets an overall measurement uncertainty of 0.5% for the system, which on a 1,000-tonne delivery equals 5 tonnes.[3]
Working Principle of the Coriolis Meter
One or two tubes inside the meter vibrate at a fixed frequency. With no flow, the inlet and outlet legs move in phase. When liquid flows, the Coriolis force acts on the mass moving through the vibrating tube: F = 2m(ω × v), where m is mass, ω the angular velocity of the vibration and v the flow velocity. This force twists the two legs in opposite directions and creates a time difference (Δt) between them, which sensors on the legs pick up. Mass flow is that difference multiplied by a factor set in calibration:
ṁ = K × Δt
The same tube also gives density. Its natural frequency depends on the mass of the liquid inside, and since the tube volume is fixed, a change in frequency converts to density. A heavier liquid lowers the frequency. Dividing mass flow by density gives volume flow, so one instrument records mass, density and temperature together. That is valuable in bunkering because density can shift during a delivery.
Tank Measurement and Its Sources of Error
The traditional method sounds the barge tanks before and after delivery, reads volume from a table and converts it to tonnes with temperature and density:
Weight = observed volume × volume correction factor (VCF) × (density at 15 °C − 0.0011)
Subtracting 0.0011 converts to weight in air in tonnes per cubic metre. For example, 1,000 m³ of fuel with a density of 0.991 at 15 °C, at 50 °C with a VCF of about 0.979, comes to about 969 tonnes. Each input moves the result.
| Source of error | Assumed deviation | Effect on 969 tonnes |
|---|---|---|
| Temperature reading | 5 °C | About 3 tonnes |
| Density at 15 °C | 1 kg/m³ | About 1 tonne |
| Volume (level, trim, list, table) | 0.5% | About 5 tonnes |
| Entrained air | 2% by volume | About 19 tonnes |
These are worked examples using the formula above.
The last line is what the trade calls the cappuccino effect. Air mixed into the fuel creates foam and makes the volume in the tank look larger than it is.[4] The shortfall appears once the foam settles, and by then the barge may have left. Tank measurement is exposed to this because it derives mass from volume, while an MFM reads mass with no conversion step. Recurring quantity problems were the rationale for the Rotterdam and Antwerp-Bruges rule.[2]
System Components and Records
An MFM is a metering system on the barge's delivery line, made up of the sensor holding the measuring tube, a transmitter, a recording unit and a printer. The pipework around it is sealed so that flow cannot bypass the meter, which is why certification covers the whole installation. The printout gives opening and closing totals, delivered mass, average density and temperature. Meter density is at flowing temperature and must be converted to 15 °C before comparison with a laboratory result.[2][3]
Port Requirements
| Port | Status | Basis |
|---|---|---|
| Singapore | Mandatory: fuel oil 2017, distillate from 1 July 2019 | MPA, SS 648-1:2024 |
| Rotterdam, Antwerp-Bruges | Mandatory from 1 January 2026 | Port rule, ISO 22192 |
| Fujairah | Port said in 2023 it was considering a mandate | Port statement |
Source: MPA; Port of Rotterdam; Port of Antwerp-Bruges; Ship & Bunker.[1][2][5]
In Singapore, the system is approved under SS 648. SS 660:2020 covers loading from terminal to bunker tanker, and TR 80:2020 covers verification with a master meter.[3] If a meter fails during delivery, tank measurement can finish the job with permission. In Rotterdam and Antwerp-Bruges, the rule covers all bunker vessels delivering conventional fuels and biofuels. The system must be certified to ISO 22192, and breaches can bring fines or loss of the bunker licence. When the rule was announced in 2023, only 40 of the 170 bunker vessels at those ports had meters.[2]
Elsewhere, the measurement method should be set out in writing at the quotation stage. Information on Turkish and Mediterranean ports is on the Ports page.
Measurement Uncertainty and Verification
Aeration
Two-phase flow is the best-known weakness of a Coriolis meter. Air bubbles in the liquid disturb the tube's vibration and reduce the reliability of the reading, especially near the tank bottom and when the hose is being cleared. Designs differ in how well they cope. Some systems detect aeration and print it on the delivery record, so that information should be read together with the quantity.[3][4]
Calibration and Zero Checks
The measurement depends on the vibration of the tube and so on its stiffness. The instrument compensates for temperature and pressure. What it cannot compensate for is wear, corrosion and coating on the tube over time, which is why regular verification matters. Periodic zero checks are common, though they do not show how the meter performs under real operating conditions, and the industry has therefore pressed for in-situ verification with a master meter.[3] In the EU the Measuring Instruments Directive (MID) applies to the instrument, and OIML R117 is the international reference.
Mass and Weight
A meter reads true mass, that is mass in vacuum. Commercial tonnage is usually weight in air, and the 0.0011 correction above represents the difference. At a density of 991 kg/m³ the gap is about 0.11%, or about 1.1 tonnes per 1,000. The contract and the fuel documents should therefore state clearly which basis applies.
Checks on the Buyer's Side
Before delivery, the buyer's representative checks the meter's certificate, seals and last verification date. After it, the system printout is compared with the quantity on the bunker delivery note. The ship still takes its own soundings, since this is the second record if a dispute arises. Receiving meters on ships are described in ISO 21562:2020.[6] Watching the flow and density display during delivery is useful as well, because a sudden drop in density is often the first sign of aeration.
A meter settles quantity and says nothing about quality. Sulphur content and conformity with ISO 8217 are shown by samples, which is why surveyor demand in Singapore continued after the MFM mandate.[7] Sulphur limits are covered in IMO 2020, and the fuels Bunkerist supplies are on the Fuel Oil and Gas Oil page.
Frequently asked questions
What is a mass flow meter?
A mass flow meter (MFM) measures the mass of liquid passing through a pipe directly.
Is an MFM more accurate than a volumetric meter?
It measures mass directly, so it avoids the errors in converting volume to mass. Aeration, installation and calibration still affect the result.
Are samples still needed with an MFM?
Yes. The meter gives quantity. The MARPOL sample and commercial samples are a separate obligation and show quality and sulphur content.
What is the cappuccino effect?
Air mixed into the fuel creates foam, which makes the volume in the tank look larger. Once the foam settles, the buyer can find less fuel than invoiced.
Sources
- Maritime and Port Authority of Singapore. Bunkering Standards; FreightWaves. Singapore Mandates Accurate Distillate Fuel Meters as of July 1.
- Port of Rotterdam and Port of Antwerp-Bruges. Mass Flow Meter Bunker Measurement System Mandatory as of 1 January 2026; Ship & Bunker. Rotterdam and Antwerp-Bruges Mass Flow Meter Mandate Enters into Force.
- Enterprise Singapore. SS 648-1:2024, SS 660:2020, TR 80:2020, catalogue entries; Tanks and Terminals. Autumn 2021; Emerson. Improving Bunkering Operations by Using Coriolis Mass Flow Meter Technology.
- Ship & Bunker. Tricks of the Bunker Trade: The Cappuccino Effect; Can You Beat the Coriolis Flow Meters; ExxonMobil Marine. The Fuel Measurement Challenge.
- Ship & Bunker. IBIA Convention: Port of Fujairah Mulls Mandatory Mass Flow Meters for Bunkering, 2023.
- ISO. ISO 21562:2020, catalogue summary.
- Ship & Bunker. IBIA Convention: Viking Marine Saw Increased Surveyor Demand in Singapore After MFMs.
