Oil & Gas Custody Transfer Density Meter Selection Guide

Steps

1. Refined-product pipelines (gasoline, diesel)

   Clean single-phase liquids, generally steady temperature, and often a product interface to detect as batches change. A Coriolis instrument such as the PS7200 suits this well because density and mass flow come from the same sensor and are therefore inherently consistent — there is no reconciliation between two devices with separate calibration histories. Where the requirement is interface detection rather than fiscal measurement, a sound-speed instrument responds sharply to a product change and is a lighter solution. Confirm the line runs full at all transfer rates, including the start and end of a batch, since that is when a partially filled line is most likely.

2. Crude oil storage tanks (automatic API gravity)

   Crude density feeds automatic API gravity calculation and inventory reconciliation. Temperature range is wide and stratification within a tank is real, so a single point measurement may not represent the tank — establish whether the contract requires a representative average or a specific point, because that determines whether one instrument is even the right architecture. Water content is the other complication: free water changes the measured density and is not the property being traded, so confirm how water is handled in the calculation. Wetted materials should be confirmed against H2S content where sour crude is possible.

3. LPG custody transfer

   LPG is measured under pressure and close to its bubble point, which makes this the application where flashing is the dominant risk. If the pressure drops anywhere in the measurement section, vapour forms and the density reading is no longer a liquid density. Design the installation for adequate margin above vapour pressure at the maximum process temperature, and confirm the pressure drop through the instrument itself — a Coriolis meter's bent tubes contribute to that. Composition also varies (propane to butane blends), so establish whether the contract is settled on measured density or on a composition-derived value, because these are not the same and the difference has commercial consequences.

4. Marine fuel (HFO, VLSFO, MGO) and bunker delivery notes

   Bunker measurement is dispute-prone, and density is central because the quantity delivered is settled by mass while the transfer is observed by volume. High viscosity is the practical constraint: HFO must be heated to flow, so the density measurement is made hot and converted to reference conditions, and the conversion is a frequent source of disagreement. Specify the instrument at the heated condition, confirm the viscosity limit against the worst-case grade, and confirm the conversion standard against the delivery note format. Entrained air is the other recurring issue — the "cappuccino effect" is a known bunkering dispute, and an instrument that cannot indicate the presence of gas leaves you without evidence when it is alleged.

5. High-accuracy metering where disputes are frequent

   Where a measuring point has a history of commercial disagreement, the useful investment is usually not a tighter accuracy specification but a better evidence trail. Consider: continuous logging with timestamps so a disputed period can be examined rather than reconstructed; a diagnostic output that shows whether the instrument was healthy at the disputed time; a documented verification schedule with results retained; and a sampling protocol that both parties agreed to before the dispute. Where two instruments of different principle are affordable, running both makes disagreement visible immediately rather than at settlement. Most custody disputes are settled by records, not by the accuracy line of a datasheet.