A. U-tube down
B. Inverted U-tube
C. Horizontal (parallel to grade)
D. Flag position
Coriolis mass flowmeters in gas service must be completely full of gas to measure accurately. The U-tube down orientation (Answer A) could accumulate liquid and should not be used for gas applications.
The inverted U-tube orientation (Answer B) and horizontal orientation (Answer C) would entail modification of the upstream and downstream piping. The flag position (Answer D) would typically be most practical.
Additional Complicating Factors
Not all Coriolis mass flowmeters have U-tube geometry, and some of these geometries can allow liquid to accumulate in the flowmeter.
For example, a Coriolis mass flowmeter with delta-shaped tubes can accumulate liquid in the upstream (lower) portion of the tubes when mounted in a flag position (Answer D), so the upstream and downstream piping should be modified to mount the flowmeter with its delta-shaped tubes inverted (Answer B) or horizontal (Answer C).
Similarly, a single-path self-filling and self-draining Coriolis mass flowmeter that forms a loop, jumps up (sideways if mounted in flag position) and then forms another loop must be installed in the horizontal plane (Answer C) to remove all liquid from the system because any other orientation can allow liquid to accumulate in the flowmeter.
This article originally appeared in P. I. Process Instrumentation magazine.