NEW STANDARD DEVELOPED FOR ORIFICE-METER NGL MEASUREMENT

A new orifice-measurement standard has recently been published by the American Petroleum Institute (API) whose support, combined with that of the American Gas Association (AGA) and the Gas Processors Association (GPA), enabled development of the standard. The standard, contained in Chapter 14, Section 3, Parts 1-4 of the API's Manual of Petroleum Measurement Standards, provides a new coefficient of discharge and fundamental orifice-meter mass flow rate equation set. The chapter deals with

Sept. 2, 1991

2 min read

The standard, contained in Chapter 14, Section 3, Parts 1-4 of the API's Manual of Petroleum Measurement Standards, provides a new coefficient of discharge and fundamental orifice-meter mass flow rate equation set.

The chapter deals with NGL measurement specifically as it pertains to concentric, square-edged orifice meters.

JOINT EFFORT

The standard has resulted from several years' joint effort of the three associations in which a group of technical experts from the U.S., Canada, Japan, Norway, and other European nations developed an equation using the Stolz linkage form that fits the regression data set more accurately than have previously published equations.

The data set utilizes approximately 12,000 data points derived from numerous laboratory and application flow tests on four different fluids-oil, natural gas, water, and air.

By comparison, the previous standard, adopted in 1935, incorporated an equation set based on only 300 data points tested solely on water.

The new standard also addresses the manufacturing and inspection tolerances of orifice fittings, meter tubes, and orifice plates.

For precise metering applications, such as custody transfer, it requires that these products, along with flowmeters and adjacent piping, meet the most stringent specifications of the standard.

The API chapter also encourages the application of the standard to existing equipment in the field because the new calculation procedures and techniques represent significant improvement in accuracy from the previous standard.