Introduction: LNG export terminals move a boiling-cold liquid whose density and pipe dimensions shift with temperature, so measurement has to follow mass rather than volume assumptions.
A loading operation at an LNG export terminal is a race against heat. The liquid sits near -162°C, the transfer line is long, and every hour of pumping pushes large volumes of cold fluid into a carrier's tanks. During that transfer, the LNG warms slightly, its density changes, and the steel around it contracts. Engineers who compare loading totals at the end of a shift often find that the volume figures moved more than the mass figures did. Understanding why that happens is the first step toward understanding how cryogenic Coriolis mass flow measurement behaves in terminal service.
LNG is natural gas cooled until it becomes a liquid, which shrinks its volume by roughly 600 times and makes it practical to ship by sea. The U.S. Department of Energy describes LNG as a cryogenic liquid that has to stay cold through liquefaction, storage, and transport, and an export terminal sits in the middle of that chain. The number that matters commercially once a carrier is loaded is how much gas, measured as mass, actually left the terminal. Volume alone is a moving target in that setting, because LNG density depends on temperature, pressure, and composition, and all three can shift while the pumps are running. Continuous measurement matters because loading is not a batch process that can be weighed afterward. Flow starts slowly, ramps to a high rate, holds there for hours, and then tapers as the ship's tanks fill. Cool-down, line packing, and topping off each produce a different flow profile. A meter that only performs well at a steady rate will miss part of the total, and any gap in the record has to be reconstructed later. Direct mass measurement keeps the record continuous across the whole loading sequence instead of only during the stable middle.
LNG density is not a fixed number. Colder liquid is denser, and liquid that has picked up heat is lighter, so the same mass of gas occupies a larger volume. Terminal lines, storage tanks, and the ship's tanks all leak heat into the fluid, and the composition of the LNG itself — how much nitrogen or heavier hydrocarbon it carries — shifts its boiling point and its density curve. If a terminal bills on volume at observed conditions, converting that volume into a mass figure requires a density reference, and small temperature errors propagate straight into the result. A Coriolis meter measures mass directly while also reporting density and temperature, which turns those variables into useful cross-checks rather than inputs the calculation rests on.
Steel shrinks as it gets colder, and the temperature swing from a warm day to liquid methane is enormous. A long cryogenic transfer line changes length between ambient and operating conditions, and that movement travels through supports, flanges, and anything bolted rigidly into the run. A mass flow meter sitting in that line is part of the mechanical chain, so when pipework pulls on it, the vibrating tubes inside can pick up stress that appears as a zero offset. Installation that lets the line contract, plus a zero check at operating temperature, is what keeps that effect small.
A Coriolis meter works by vibrating a tube, or a pair of tubes, and watching how the flowing fluid distorts that vibration. Mass moving through the tube adds inertia that twists the oscillation, and the phase difference between the two pickup sensors is proportional to mass flow. Tube frequency reveals the density of whatever is inside, and an integrated temperature sensor reports the fluid temperature. The KROHNE OPTIMASS 6400 uses a twin bent tube sensor and measures mass flow, density, volume flow, and temperature together in one device. That combination is what makes cryogenic LNG service workable. Because the meter reads mass directly, a density change during loading does not corrupt the mass total; density simply becomes another live reading, which is useful for spotting a composition shift or a warm slug arriving from the shore line. The harder problem in cryogenic service is phase behavior. LNG sits close to its boiling point, so a small pressure drop across a valve, a heat leak through insulation, or a change in tank pressure can flash a fraction of the liquid into vapor. Bubbles change how the tubes damp and can interrupt the drive system if the meter is not built for it. Instruments designed to keep running with entrained gas hold a continuous signal instead of dropping out, which keeps the loading record intact when flow briefly becomes two-phase.
Orientation is the first practical decision. In cryogenic service, meters are usually installed so the sensor stays full of liquid and drains naturally when the line is emptied. Upward flow through a vertical run helps trapped gas escape rather than collect in the measuring tubes, and it also lets the sensor self-drain during maintenance. Horizontal installation can work, but only when the layout guarantees the tubes stay flooded and no vapor pocket forms at the top of the sensor body. Because the pipe is contracting and moving at the same time, supports and expansion loops have to absorb that travel without pushing stress into the meter. The second set of choices concerns how the meter is built. The published media temperature range for the OPTIMASS 6400 runs from -200°C to 400°C, and KROHNE lists cryogenic LNG among the applications for this model. Actual cryogenic performance depends on device configuration, installation, and calibration conditions, so sensor material, tube wall construction, and options such as heat tracing or purge ports are selected against the specific line rather than assumed. Wetted materials offered for the sensor include duplex stainless steel and Alloy 22, and the insulation detail around the meter body affects how much heat reaches the fluid inside it. Calibration and traceability complete the picture. NIST Standard Reference Materials support the reference chain that flow laboratories build on, and the BIPM's working group on gravimetry coordinates mass flow calibration standards internationally, which is what gives a factory or laboratory certificate weight when terminal figures are compared. Where the meter is calibrated, and how closely those conditions match the line's product and temperature, shapes what the instrument can deliver in service.
Cryogenic LNG measurement at an export terminal is a case where the fluid and the hardware both move. Density tracks temperature and composition, steel contracts across a huge temperature span, and loading runs for hours under flow profiles that never sit still. A Coriolis meter fits this picture because it measures mass directly, reports density and temperature alongside flow, and can hold a continuous signal when the liquid briefly flashes. What it delivers in practice still depends on the configuration ordered, the way the sensor sits in the line, and the conditions it was calibrated under. For terminal projects, those three points are worth pinning down before a general-purpose flow assumption is carried into a cryogenic line.
A：Because the commercial value of a cargo is defined by mass, not by the volume the liquid happens to occupy at a given moment. LNG density shifts with temperature, pressure, and composition throughout a loading operation, so a volume reading needs a density reference to become meaningful. A Coriolis meter measures mass directly and reports density, volume, and temperature at the same time, which keeps the loading record continuous from cool-down through topping off and gives operators live cross-checks on product quality.
A：It means the sensor is published as suitable for media temperatures down to -200°C, which covers LNG service and leaves margin below the roughly -162°C at which LNG is normally handled. On the KROHNE OPTIMASS 6400, that rating runs from -200°C to 400°C, and cryogenic LNG appears among its listed applications. The rating describes the temperature the sensor can be built for, while the accuracy actually achieved on a given line still depends on configuration, installation, and calibration conditions.
A：Going from ambient to LNG temperature makes steel shrink, so a long transfer line changes length between standby and operating conditions. That movement travels through supports and flanges, and if the meter is bolted into a rigid run, the vibrating tubes can carry mechanical stress that shows up as a zero offset. Installation that allows the line to move, combined with a zero verification at operating temperature, keeps that effect small and protects the accuracy of the mass total.
Liquefied Natural Gas (LNG) | Department of Energy
Standard Reference Materials | NIST
CCM Working Group on Gravimetry - BIPM
