# ISO 5167-5:2016 - Cone Meters for Accurate and Reliable Fluid Flow Measurement

## ISO 5167: A Standard for Measuring Fluid Flow by Pressure Differential Devices

Fluid flow measurement is a crucial task in many industrial processes, such as oil and gas production, chemical engineering, power generation, water supply, etc. Accurate and reliable measurement of fluid flow can help optimize performance, efficiency, safety, quality, and environmental protection. However, measuring fluid flow is not an easy task, as it involves many factors, such as fluid properties, flow conditions, measurement methods, instruments, etc.

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One of the most common methods for measuring fluid flow is by using pressure differential devices. These are devices that create a pressure difference across a constriction in a pipe or a duct where the fluid flows. By measuring this pressure difference, the flowrate can be calculated using a known relationship between the two variables. Pressure differential devices are widely used because they are simple, robust, inexpensive, versatile, and easy to install.

However, using pressure differential devices also poses some challenges. For example, how to select the appropriate device for different fluids and flow regimes? How to ensure that the device is installed correctly and has a good seal with the pipe? How to account for the effects of temperature, pressure, viscosity, density, and compressibility of the fluid? How to estimate the uncertainty and error of the flowrate measurement?

To address these challenges, there is a need for a standard that provides guidance and specifications for the design, installation, operation, and calibration of pressure differential devices. This is where ISO 5167 comes in. ISO 5167 is an international standard that covers the measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full. It consists of six parts, each dealing with a specific type of device. In this article, we will introduce the main features and contents of ISO 5167 and its parts.

## Part 1: General Principles and Requirements

Part 1 of ISO 5167 is the general part that applies to all types of pressure differential devices. It defines the scope and objectives of the standard, the terms and definitions used in the standard, the principles of the method of measurement and computation, and the general requirements for pressure differential devices.

The scope of Part 1 is to specify the geometry and method of use of pressure differential devices when they are inserted in a conduit running full to determine the flowrate of the fluid flowing in the conduit. It also gives necessary information for calculating the flowrate and its associated uncertainty.

The objectives of Part 1 are to promote a uniform practice for measuring fluid flow by pressure differential devices, to ensure consistency and compatibility among different devices and methods, to provide a basis for the evaluation of the uncertainty of the flowrate measurement, and to facilitate the exchange of information and experience among users and manufacturers.

The terms and definitions used in Part 1 are based on the International Vocabulary of Metrology (VIM) and other relevant standards. They include terms related to fluid properties, flow conditions, pressure differential devices, pressure tappings, pressure measurements, flowrate calculations, uncertainty evaluations, etc.

The principles of the method of measurement and computation are based on the conservation of mass and energy for a fluid flowing through a constriction in a pipe. The flowrate is proportional to the square root of the pressure difference across the constriction, multiplied by a coefficient that depends on the geometry and characteristics of the device. The coefficient is called the discharge coefficient, which can be determined experimentally or theoretically. The pressure difference can be measured by connecting pressure tappings on the device to a differential pressure gauge or transmitter. The flowrate can be calculated by using an equation that involves the discharge coefficient, the pressure difference, the fluid properties, and a correction factor called the expansibility factor, which accounts for the compressibility effects of the fluid.

The general requirements for pressure differential devices are related to their geometry, material, manufacture, installation, location, calibration, maintenance, etc. They aim to ensure that the devices are suitable for measuring fluid flow under different conditions and that they have a high accuracy and repeatability.

## Part 2: Orifice Plates

Part 2 of ISO 5167 deals with orifice plates, which are thin plates with a circular hole or aperture in the middle. They are inserted in a pipe perpendicular to the flow direction. When a fluid flows through an orifice plate, it accelerates through the hole and creates a pressure difference between the upstream and downstream sides of the plate. By measuring this pressure difference, the flowrate can be calculated using Part 1.

The scope of Part 2 is to specify the geometry and method of use of orifice plates when they are inserted in a conduit running full to determine the flowrate of the fluid flowing in the conduit. It also gives necessary information for calculating the flowrate and its associated uncertainty.

The types and dimensions of orifice plates are classified according to their shape, size, thickness, edge condition, and position of the hole relative to the pipe axis. The standard specifies the dimensions and tolerances of each type of orifice plate, as well as the methods for marking and identifying them.

The installation and location of orifice plates are important factors that affect the accuracy and reliability of the flowrate measurement. The standard specifies the requirements for installing orifice plates in pipes, such as the alignment, orientation, sealing, and support of the plates. It also specifies the requirements for locating orifice plates in relation to other fittings, such as bends, valves, reducers, expanders, etc., as well as the minimum straight lengths of pipe required upstream and downstream of orifice plates.

The discharge coefficient and expansibility factor of orifice plates are functions of several parameters, such as the diameter ratio of the hole to the pipe, number of the fluid, the edge condition of the hole, the pressure tapping arrangement, etc. The standard provides empirical formulas and tables for calculating the discharge coefficient and expansibility factor of orifice plates for different types and conditions.

The uncertainty of the flowrate measurement by orifice plates depends on the uncertainty of the pressure difference measurement, the uncertainty of the fluid properties, the uncertainty of the pipe and orifice plate dimensions, and the uncertainty of the discharge coefficient and expansibility factor. The standard provides methods and examples for evaluating the uncertainty of the flowrate measurement by orifice plates.

## Part 3: Nozzles and Venturi Nozzles

Part 3 of ISO 5167 deals with nozzles and Venturi nozzles, which are devices that have a convergent section followed by a cylindrical throat. They are inserted in a pipe parallel to the flow direction. When a fluid flows through a nozzle or a Venturi nozzle, it accelerates through the convergent section and reaches a maximum velocity at the throat, creating a pressure difference between the upstream and downstream sides of the device. By measuring this pressure difference, the flowrate can be calculated using Part 1.

The scope of Part 3 is to specify the geometry and method of use of nozzles and Venturi nozzles when they are inserted in a conduit running full to determine the flowrate of the fluid flowing in the conduit. It also gives necessary information for calculating the flowrate and its associated uncertainty.

The types and dimensions of nozzles and Venturi nozzles are classified according to their shape, size, and position of the throat relative to the pipe axis. The standard specifies the dimensions and tolerances of each type of nozzle and Venturi nozzle, as well as the methods for marking and identifying them.

The installation and location of nozzles and Venturi nozzles are similar to those of orifice plates, except that nozzles and Venturi nozzles do not require a seal with the pipe wall. The standard specifies the requirements for installing nozzles and Venturi nozzles in pipes, such as the alignment, orientation, support, and protection of the devices. It also specifies the requirements for locating nozzles and Venturi nozzles in relation to other fittings, such as bends, valves, reducers, expanders, etc., as well as the minimum straight lengths of pipe required upstream and downstream of nozzles and Venturi nozzles.

The discharge coefficient and expansibility factor of nozzles and Venturi nozzles are functions of several parameters, such as the diameter ratio of the throat to the pipe, the Reynolds number of the fluid, the pressure tapping arrangement, etc. The standard provides empirical formulas and tables for calculating the discharge coefficient and expansibility factor of nozzles and Venturi nozzles for different types and conditions.

The uncertainty of the flowrate measurement by nozzles and Venturi nozzles depends on the uncertainty of the pressure difference measurement, the uncertainty of the fluid properties, the uncertainty of the pipe and nozzle dimensions, and the uncertainty of the discharge coefficient and expansibility factor. The standard provides methods and examples for evaluating the uncertainty of the flowrate measurement by nozzles and Venturi nozzles.

## Part 4: Venturi Tubes

Part 4 of ISO 5167 deals with Venturi tubes, which are devices that have a convergent section followed by a cylindrical throat and a divergent section. They are inserted in a pipe parallel to the flow direction. When a fluid flows through a Venturi tube, it accelerates through the convergent section and reaches a maximum velocity at the throat, creating a pressure difference between the upstream and downstream sides of the device. By measuring this pressure difference, the flowrate can be calculated using Part 1.

The scope of Part 4 is to specify the geometry and method of use of Venturi tubes when they are inserted in a conduit running full to determine the flowrate of the fluid flowing in the conduit. It also gives necessary information for calculating the flowrate and its associated uncertainty.

The types and dimensions of Venturi tubes are classified according to their shape, size, and position of the throat relative to the pipe axis. The standard specifies the dimensions and tolerances of each type of Venturi tube, as well as the methods for marking and identifying them.

The installation and location of Venturi tubes are similar to those of nozzles and Venturi nozzles, except that Venturi tubes have a longer length and a larger diameter than the pipe. The standard specifies the requirements for installing Venturi tubes in pipes, such as the alignment, orientation, support, and protection of the devices. It also specifies the requirements for locating Venturi tubes in relation to other fittings, such as bends, valves, reducers, expanders, etc., as well as the minimum straight lengths of pipe required upstream and downstream of Venturi tubes.

The discharge coefficient and expansibility factor of Venturi tubes are functions of several parameters, such as the diameter ratio of the throat to the pipe, the Reynolds number of the fluid, the pressure tapping arrangement, etc. The standard provides empirical formulas and tables for calculating the discharge coefficient and expansibility factor of Venturi tubes for different types and conditions.

The uncertainty of the flowrate measurement by Venturi tubes depends on the uncertainty of the pressure difference measurement, the uncertainty of the fluid properties, the uncertainty of the pipe and Venturi tube dimensions, and the uncertainty of the discharge coefficient and expansibility factor. The standard provides methods and examples for evaluating the uncertainty of the flowrate measurement by Venturi tubes.

## Part 5: Cone Meters

Part 5 of ISO 5167 deals with cone meters, which are devices that have a cone-shaped element mounted inside a pipe. The cone element creates a pressure difference across its base and tip when a fluid flows through it. By measuring this pressure difference, the flowrate can be calculated using Part 1.

The scope of Part 5 is to specify the geometry and method of use of cone meters when they are inserted in a conduit running full to determine the flowrate of the fluid flowing in the conduit. It also gives necessary information for calculating the flowrate and its associated uncertainty.

The types and dimensions of cone meters are classified according to their shape, size, and position of the cone element relative to the pipe axis. The standard specifies the dimensions and tolerances of each type of cone meter, as well as the methods for marking and identifying them.

The installation and location of cone meters are similar to those of orifice plates, except that cone meters do not require a seal with the pipe wall. The standard specifies the requirements for installing cone meters in pipes, such as the alignment, orientation, sealing, and support of the devices. It also specifies the requirements for locating cone meters in relation to other fittings, such as bends, valves, reducers, expanders, etc., as well as the minimum straight lengths of pipe required upstream and downstream of cone meters.

of cone meters are functions of several parameters, such as the diameter ratio of the cone base to the pipe, the Reynolds number of the fluid, the pressure tapping arrangement, etc. The standard provides empirical formulas and tables for calculating the discharge coefficient and expansibility factor of cone meters for different types and conditions.

The uncertainty of the flowrate measurement by cone meters depends on the uncertainty of the pressure difference measurement, the uncertainty of the fluid properties, the uncertainty of the pipe and cone meter dimensions, and the uncertainty of the discharge coefficient and expansibility factor. The standard provides methods and examples for evaluating the uncertainty of the flowrate measurement by cone meters.

## Part 6: Wedge Meters

Part 6 of ISO 5167 deals with wedge meters, which are devices that have a wedge-shaped element mounted inside a pipe. The wedge element creates a pressure difference across its upstream and downstream faces when a fluid flows through it. By measuring this pressure difference, the flowrate can be calculated using Part 1.

The scope of Part 6 is to specify the geometry and method of use of wedge meters when they are inserted in a conduit running full to determine the flowrate of the fluid flowing in the conduit. It also gives necessary information for calculating the flowrate and its associated uncertainty.

The types and dimensions of wedge meters are classified according to their shape, size, and position of the wedge element relative to the pipe axis. The standard specifies the dimensions and tolerances of each type of wedge meter, as well as the methods for marking and identifying them.

The installation and location of wedge meters are similar to those of orifice plates, except that wedge meters do not require a seal with the pipe wall. The standard specifies the requirements for installing wedge meters in pipes, such as the alignment, orientation, sealing, and support of the devices. It also specifies the requirements for locating wedge meters in relation to other fittings, such as bends, valves, reducers, expanders, etc., as well as the minimum straight lengths of pipe required upstream and downstream of wedge meters.

The discharge coefficient and expansibility factor of wedge meters are functions of several parameters, such as the diameter ratio of the wedge base width to the pipe, the Reynolds number of the fluid, the pressure tapping arrangement, etc. The standard provides empirical formulas and tables for calculating the discharge coefficient and expansibility factor of wedge meters for different types and conditions.

The uncertainty of the flowrate measurement by wedge meters depends on the uncertainty of the pressure difference measurement, the uncertainty of the fluid properties, the uncertainty of the pipe and wedge meter dimensions, and the uncertainty of the discharge coefficient and expansibility factor. The standard provides methods and examples for evaluating the uncertainty of the flowrate measurement by wedge meters.

## Conclusion

In this article, we have introduced ISO 5167, a standard that covers the measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full. We have explained the main features and contents of each part of ISO 5167, which deal with different types of devices, such as orifice plates, nozzles, Venturi nozzles, Venturi tubes, cone meters, and wedge meters. We have also discussed how to calculate the flowrate and its associated uncertainty using ISO 5167.

Pressure differential devices are widely used for measuring fluid flow because they are simple, robust, inexpensive, versatile, and easy to install. However, they also pose some challenges, such as how to select, install, calibrate, and maintain them properly. ISO 5167 provides guidance and specifications for using pressure differential devices in a consistent and reliable way. It also facilitates the exchange of information and experience among users and manufacturers.

However, ISO 5167 is not a substitute for good engineering practice and judgment. It is not intended to cover all aspects and details of fluid flow measurement by pressure differential devices. It is also not applicable to all fluids and flow regimes. Therefore, users should always consult with experts and follow relevant codes and regulations when using pressure differential devices.

## FAQs

What is the difference between ISO 5167 and other standards for measuring fluid flow?

ISO 5167 is an international standard that covers the measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full. It is widely accepted and used around the world. Other standards for measuring fluid flow may have different scopes, objectives, methods, and specifications. For example, ASME MFC-3M is an American standard that covers the measurement of fluid flow in closed conduits by means of critical flow Venturi nozzles. It has a different approach and criteria for determining the flowrate and its uncertainty.

How can I download ISO 5167 for free?

ISO 5167 is a copyrighted document that is not available for free. You can purchase it from the ISO website or from authorized distributors. However, you may be able to access some parts of ISO 5167 for free from online sources, such as academic libraries, research papers, or websites that provide samples or previews of standards. However, these sources may not be complete, accurate, or up-to-date. Therefore, you should always refer to the official version of ISO 5167 when using it.

How can I verify the accuracy and quality of pressure differential devices?

You can verify the ac