Field Calibration of Orifice Meters for Natural Gas Flow

Abstract

This paper presents the orifice calibration results for nominal 15.24, 10.16, and 5.08-cm (6, 4, 2-in.) orifice meters conducted at the Chevron’s Sand Hills natural gas flow measurement facility in Crane, Texas. Over 200 test runs were collected in a field environment to study the accuracy of the orifice meters. Data were obtained at beta ratios ranging from 0.12 to 0.74 at the nominal conditions of 4576 kPa and 27°C (650 psig and 80°F) with a 0.57 specific gravity processed, pipeline quality natural gas. A bank of critical flow nozzles was used as the flow rate proving device to calibrate the orifice meters. Orifice discharge coefficients were computed with ANSI/API 2530-1985 (AGA3) and ISO 5167/ASME MFC-3M-1984 equations for every set of data points. The uncertainty of the calibration system was analyzed according to The American National Standard (ANSI/ASME MFC-2M-A1983). The 10.16 and 5.08-cm (4 and 2-in.) orifice discharge coefficients agreed with the ANSI and ISO standards within the estimated uncertainty level. However, the 15.24-cm (6-in.) meter deviated up to − 2 percent at a beta ratio of 0.74. With the orifice bore Reynolds numbers ranging from 1 to 9 million, the Sand Hills calibration data bridge the gap between the Ohio State water data at low Reynolds numbers and Chevron’s high Reynolds number test data taken at a larger test facility in Venice, Louisiana. The test results also successfully demonstrated that orifice meters can be accurately proved with critical flow nozzles under realistic field conditions.