Flow guidelines, standards and legislation

Our flow measurement library:

Within the world of gas systems and liquid systems there are many agreements, which are actually always about:

• Safety
• Accuracy of settlement
• Standardisation in an industry

Those regulations we face in the flow world are made on 3 levels:

• Global
• United States
• European Union

De regelgevende instanties en instituten streven allemaal naar harmonisatie en nemen veel van de regelgeving van anderen over. Het is handig om te weten waar die normen ongeveer over gaan, daarom hieronder een korte introductie op de meest voorkomende.

OIML: global organisation

The OIML (Organisation Internationale de Métrologie Légale) is an international organisation that tries to harmonise the rules around measurement. They write recommendations for that. Countries can adopt these in their own legislation. For European countries these regulations are therefore less binding than, for example, the PED. But also the European Union strives to harmonize regulations worldwide. The EU therefore tests its regulations against those of the OIML, of which the MID and PED are good examples.

The OIML consists of representatives of countries. Certain international institutions also participate in the consultation, such as ISO and IEC, in order to avoid conflicting requirements. The result is that manufacturers and users of measuring instruments and test labs comply with all regulations at the same time as they comply with the OIML rules.

That is what makes these directives so important for all parties in our industry. Like R117-1 for example.

R117-1: Worldwide rules for liquid measurement

Directive R117-1 of the OIML describes rules for measuring liquids other than water.

R117-1 describes a number of requirements that a MID compliant installation for liquids other than water must meet. It describes tests that are difficult or impossible to carry out in practice. For example, the installation must be climatologically tested. EMC (ElectroMagnetic Conformity) tests are also part of the test programme. It is not practical to test a complete installation in the way described. After all, some installations are large and do not fit in the test rooms. It is also impractical to assemble and disassemble the installation at its final destination.

Therefore, a MID-conform installation is built with instruments and fittings that all have a so-called sub-certificate. The components are tested on the basis of R117-1. The certifying body will then assess the materials used, and can declare the installation MID-compliant.

AGA-3.1: American Standard Differential Pressure Measurements

The American Gas Associciation (AGA) has established several standards. One of them is the AGA-3.1, a very old standard from 1990. It describes the measurement of hydrocarbons with differential pressure flowmeters with measuring plate. It covers gases and most liquids found in the petroleum, petrochemical and natural gas industries. Written as a recommendation, but adopted as legally binding. In the petrochemical world this is the standard that everyone adheres to. It gives specifications for:

• construction and installation of measuring plates
• construction of meter tubes
• contstructions for holding the orifice plate
• equations for calculations

The result is a standardized way to achieve mass flow measurement and volumetric flow measurement with a good statement about inaccuracy. Teesing works a lot with this standard, because it is actually always the prescription of customers. For example in this application of a differential pressure flow meter in a gas line for a power plant of De Jong Combustion.

ISO 5197-1: European Standard Differential Pressure Measurements

The European standardization institute ISO has drawn up its own standard after the AGA-3.1. It goes further than the AGA-3.1 because it is not limited to the petrochemical industry. It does not only describe differential pressure flowmeters, but also standardizes a number of other measuring elements. Such as the:

• ISA 1932 nozzle
• Long radius nozzle
• Venturi nozzle
• Venturi tubes

The result is again a standardized way to achieve mass flow measurement and volumetric flow measurement. With a fixed statement about inaccuracy. If one works according to this standard, calibration is not necessary. This saves time and money. Especially because it often involves large instruments where calibration can only be done by a few calibration organizations. Teesing works a lot with this standard, because it is actually always the prescription of customers.

AGA-9: American standard for ultrasonic natural gas measurements

The American Gas Associciation (AGA) has also created the AGA-9, which is a recommendation, describing the performance of multi-channel ultrasonic flowmeters. In the gas world, and certainly the American world, this is the standard that everyone adheres to. Calibration may be required and the document also makes statements about how to do that. Everything is intended to verify the accuracy of the meter and to minimize measurement uncertainty. The document also makes demands on the electronics, on which an ultrasonic flow meter strongly depends. Finally the document deals with the application of the meter. So flow profile by flow lengths, valves and regulators and environmental factors such as operating temperature and pulsation levels.

MID: European regulation on settlement measurements

The Measuring Instrument Directive (MID) is a European Union regulation that has been adopted by all member states into law. The name suggests that it is a directive on measuring instruments. But the directive is about the entire installation, and the person who builds the measuring system is responsible for ensuring that it complies with MID.

MID applies to installations with:

1. Water meters
2. Gas meters
3. Volume conversion devices (flow computers)
4. Energy meters (Wh)
5. Heat meters
6. Measuring systems for the continuous and dynamic measurement of liquids other than water
7. Automatic weighing instruments
8. Tax gauges
9. Material sizes
10. Dimensional measuring instruments
11. Exhaust gas analysers

For gas applications, MID applies if the flow is less than 170,000 Nm³/year. Above that threshold, MID does not apply and companies are free to agree among themselves how to regulate accuracy and settlement. This rule does not apply to the main pipeline of the Gasunie, but it does to the gas supply of a power station. of As an EU rule, MID is closely related to the regulations of the OIML, in order to facilitate cooperation and international trade.

PED: quality of pressure parts

The European directive PED from 1997 applies to appliances that contain pressure. These are boilers, tanks, but also instruments like flow meters. The directive is aimed at quality improvement. The PED allows manufacturers to test and certify their own products, and not necessarily to involve institutes such as TÜV or Lloyds in the certification process.

The directive is already applicable soon: if the process pressure is higher than 0.5 barg. In practice, this means that almost all professionally used equipment must comply with this standard. And that is what the standard is aimed at, as is apparent from the exceptions made for example for inflatable boats and cans of carbonated drinks.

Like the ATEX directive, the PED is part of the CE marking. A supplier can mark his product with the CE mark if it complies with the Pressure Equipment Directive. An example of such a test is that the device must be able to withstand at least 1.5 times the maximum allowable pressure.

Not all products have to comply with the PED. With a selection chart it can be assessed whether it is applicable.

Which rules apply can also differ. That depends for example on how dangerous the medium is. And a distinction is also made between systems designed for liquids or for gases.

ATEX: European regulations for explosion safety

The ATEX directives are two EU directives that describe the minimum safety requirements for workplaces and equipment used in potentially explosive atmospheres.

• ATEX 114 Directive: Equipment and protective systems intended for use in potentially explosive atmospheres.
• ATEX 153 Directive: Requirements for improving the health protection and safety of workers potentially at risk from explosive atmospheres.

The Atex is part of the CE marking. This means that the CE mark may only be applied by the manufacturer if the equipment has been tested and complies with the Atex standard.