The API/GPA Orifice-Plate Data Base
Authors: Fling Wayne A. 
Published: December 2007

API and the Gas Processors Assoc. (GPA) have completed a four-year, $1.4 million program to develop a new archival data base for flange tapped orifice coefficients. This paper describes this project and the results to date.

Introduction

The API/GPA project was designed to develop basic orifice discharge coefficients over a pipe Reynolds-number range of 150 to 16,000,000 and resulted in more than 300 million bytes of data that will be reduced to about 17,000 data points. The flow media used in these determinations consisted of a light 5-cST [5×10-6-m2/s] oil, water, pipeline-quality natural gas, and air at three separate flow facilities. Adequate crossover data were obtained to verify consistency between facilities.

The archival data base was developed with two sets of five different sizes of meter tubes and two sets of seven orifice-plate sizes for each tube size. Two additional plate sizes with 0.25-in. [0.64-cm] orifice diameters for two of the meter tubes were tested. Data were obtained with modern differential-pressure measuring equipment and electronic data logging techniques and were reduced and analyzed with both microcomputers and main-frame computers.

The new standard and equation for determining the discharge coefficient will be available in the last quarter of 1988.

History

The orifice meter is perhaps the oldest known device for measuring or regulating the flow of fluids. The Romans have been credited with using it for regulating the flow of water to houses in early times. During the past 70 years,1 the orifice meter has evolved into a device for the purchase, sale, or process control of fluids.

The original concept that the pressure of a flowing fluid varies as its velocity changes was discovered in the 18th century through the efforts of three well-known scientists, Bernoulli, Torricelli, and Venturi. When a flowing fluid is caused to "speed up" by restricting the cross-sectional area of the flow stream, a portion of the pressure energy is converted into velocity energy and the pressure drops. This relationship, combined with the fact that the quantity of fluid flowing is equal to the product of the velocity times the cross-sectional area of the flow stream, provides the means to achieve flow measurement in the orifice meter. Of course, these theoretical flow concepts must be related to actual flow concepts. Thus, the need for basic discharge-coefficient research (the ratio of actual to theoretical) required for custody transfer is born.

Since the beginning of the 19th century,2 much has been done to develop the use of the orifice as a custody transfer device. Manufacturers conducted experiments and developed orifice coefficients that were generally proprietary. The proprietary nature of coefficients caused a great deal of uncertainty between buyers and sellers when different manufacturers' meters were used. This prompted the American Gas Assn. (AGA) to establish the Gas Measurement Committee, which undertook a series of orifice research programs. The following highlights the major events in orifice research to date.

1928–32 - A joint American Soc. of Mechanical Engineers/AGA program at Ohio State U. was held to determine the absolute values of orifice discharge coefficients.

1935 - AGA Report 2 was published containing the Ohio State U. values and the Buckingham equation for their calculation.

1955 - AGA Report 3 was published, which was the direct result of research efforts since Report 2 and incorporated the effect of upstream disturbances, the use of straightening vanes and piping configurations, and supercompressibility.

1967 - Intl. Standards Organization (ISO) issued ISO R541 were published that were essentially in agreement with the principles of the AGA Report 3.

1971 - ISO R541 was revised to include ISO R781 and published as an ISO standard on orifices, nozzles, and venturis.

1975 - A joint API/AGA committee was formed to re-establish the basic orifice coefficients through restudy of original Ohio State U. data, to evaluate all published data in the interim, and to correlate and identify the data base for gasp and extensions.

1978 - A joint API/AGA committee report was issued that identified only 303 data points as defendable for coefficient evaluation, indicating that new data are required.

1978 - J. Stolz of France developed a universal equation for orifice plates.

1978 - A joint API/GPA committee obtained funding for development of an enlarged data base for orifice-coefficient determination.

1978 - AGA/API submitted to the American Natl. Standards Inst. (ANSI) AGA Report 3 for designation as a national standard. Standard document ANSI/API 25303 was published and submitted to ISO for consideration as an international standard.

1980 - ISO 5167,4 which was greatly different from ANSI/API 2530, was published. The U.S. delegation to ISO could not accept these differences, rejected the ISO document, and continued to petition the ISO for adoption of ANSI/API 2530 in lieu of ISO 5167. The stalemate still exists.

1982 - A research program for the determination of basic orifice coefficients began at the flow test facilities of the Natl. Bureau of Standards in Gaithersburg, MD.

1982 - A joint API/GPA research program for determination of basic orifice coefficients began at the flow test facilities of the Natl. Bureau of Standards, Gaithersburg.

1983 - Gas-orifice-meter discharge coefficients as determined by mass flow measurement data were released by the Natl. Bureau of Standards, Boulder, CO. GRI was the sponsor.

1984 - Facilities of the Natural Gas Pipeline Co. at Joliet, IL, were contracted for testing with high-pressure natural gas.

1984 - Facilities of the Colorado Engineering Experiment Station at Nunn were contracted for testing with light 5-cSt [5×10-6-m2/s] oil.

1985 - A committee was formed to regress and evaluate the API/GPA data base after completion of testing.

1986 - Experimental data for the determination of basic 4-in. [100-mm] orifice-meter discharge coefficients (European program) were released. The Commission of the European Economic Communities was the sponsor.

Research Design

The API/GPA project was designed to investigate the following parameters of orifice meters: pipe size, beta ratio, Reynolds-number range, different fluids (viscous oil, water, and natural gas), and commercially manufactured meter tubes. The overall project was directed by the Orifice Steering Committee as a subcommittee to the Committee on Gas Measurement under the auspices of the Committee on Petroleum Measurement. The Section H Committee, the technical research group of GPA, was the liaison for GPA.