scope:

This Standard specifies the geometry and method of use (installation and operating conditions) for pressure differential devices (including, but not limited to, orifice plates, flow nozzles, and venturi tubes) when installed in a closed conduit running full and used to determine the flow-rate of the fluid flowing in the conduit. This Standard applies to pressure differential devices in which the flow remains subsonic throughout the measuring section and where the fluid is considered as single-phase. The Standard is limited to single-phase Newtonian fluid flow in which the flow can be considered sufficiently free from pulsation effects. It gives information for calculating the flow-rate and the associated uncertainty when each of these devices is used within specified limits of pipe size and Reynolds number.

This Standard covers flow meters that operate on the principle of a local change in flow velocity and/or flow parameters caused by meter geometry, resulting in a corresponding change of pressure between two set locations. Although there are several types of differential pressure meters available, it is the purpose of this Standard to address the applications of each meter and not to endorse any specific meter. The operating principle of a pressure differential flow meter is based on two physical laws: conservation of energy and conservation of mass, realized when changes in flow cross-sectional area and/or flow path result in a change of pressure. This differential pressure, in turn, is a function of the flow velocity, fluid path, and fluid properties.

Included within the scope of this Standard are devices for which direct calibration experiments have been made, sufficient in number and data coverage, to enable valid systems of application to be based on their results and coefficients to be given with known uncertainties.

The devices installed in the pipe are referred to as primary devices, primary elements, or simply, primaries. The primary device may also include the associated upstream and downstream piping. The other instruments required for the flow measurement are often referred to as secondary devices or secondaries. For further information on secondary instrumentation, see ASME/ANSI MFC-8M.

The different primary elements covered in this Standard are as follows:

(a) orifice plates (Part 2) that can be used with the following pressure tap arrangements:

(1) flange pressure taps

(2) corner pressure taps

(3) D and D/2 pressure taps

(b) nozzles (Part 3), each of which differs in the following shape and position of the pressure taps:

(1) ASME long radius nozzles

(2) Venturi nozzles

(3) ISA 1932 nozzles

(c) ASME venturi tubes (Part 4), also known as Herschel or classical venturi tubes

Part 1 of this Standard contains general material such as definitions, symbols, and principles that apply to all the devices covered in Parts 2, 3, and 4 of this Standard with respect to the flow measurement of any single phase fluid.

This Standard does not apply to ASME Performance Test Code measurements. This Standard does not address those devices that operate on the principle of critical or choked flow condition of fluids. This Standard does not address issues of safety. It is the responsibility of the user to ensure that all systems conform to applicable safety requirements and regulations.