Evaluation of clamp-on ultrasonic gas transit time flowmeters for natural gas applications: Fid-Bau Portal

Evaluation of clamp-on ultrasonic gas transit time flowmeters for natural gas applications

Ting, V.C. / Ao, X.S.

This paper presents the results of meter performance tests of the Clamp-on Ultrasonic Gas Transit Time Flowmeter GC868 now manufactured by GE Panametrics. Evaluation tests were conducted during the week of December 3, 2001, at the Colorado Engineering Experiment Station, Inc., (CEESI) Wet Gas Test Facility in Nunn, Colorado, USA. The objective of these evaluation tests was to determine the accuracy of clamp-on gas flowmeters at field operating conditions where gas is dry and/or contains a small amount of entrained liquid. The clamp-on ultrasonic gas flowmeter was introduced commercially in 2001. Its transducers clamp on the outside of the pipe wall and cause no pressure drop despite wide rangeability. Since no tapping or cutting of the pipe wall is required, permanent installation costs are significantly reduced. Clamp-on ultrasonic gas meters are suitable for monitoring, control, and diagnostics applications. Advantages such as shorter tube length requirement, lighter meter weight, zero pressure drop, ease of installation and lower unit cost will contribute to capital expenditure (CAPEX) and operating expenditure (OPEX) reductions. It also appears or has been shown to be useful for metering of erosive, corrosive, and toxic gases, and/or metering in many applications where penetrating the pipe wall is undesirable. In the future, it can also be developed for subsea applications, where cost reduction could be significant. Besides flow velocity V, the meter measures gas sound speed c. Sound speed may be interpreted in terms of gas temperature T or average molecular weight MW in suitable situations. The meter evaluation tests were conducted at the following conditions: One meter was mounted on 10.16 cm (4-inch) schedule 80 pipe and the other meter was mounted on 15.24 cm (6-inch) schedule 80 pipe. Natural gas nominal pressures: 14.5, 41.4 and 75.8 bar (210, 600, and 1100 psia). Gas velocities: 3 to 18 m/s (10 to 60 ft/s). Liquid/Gas mass ratio: 0, O.006 and 0.012. Test results indicated that the meters measured dry gas flow velocities within +-2 % uncertainty. When gas is entrained with low liquid rates at liquid gas mass ratio LGMR < 1.3 %, clamp-on meter measurement uncertainty remains in the same range as a dry gas meter, except at lower pressure and gas velocity.