EPS Leading Orifice Meter Runs

What Is an Orifice Meter Run?

An orifice meter run is the complete set of pipe sections connected to the inlet and outlet of a differential pressure meter, produced to the lengths and tolerances called for by the measurement standard. It is also known as a meter tube. Its task is to deliver the fluid to the measuring element with a fully developed, swirl-free and axisymmetric velocity profile, and to limit how far disturbances downstream of the meter can feed back to the pressure tappings.

In orifice metering, the discharge coefficient is valid on the assumption that the plate sits in a pipe of standard geometry. If the internal diameter, ovality or internal surface roughness of the run — or a step between the run and the fitting — departs from this assumption, measurement uncertainty increases. For that reason a meter run is not treated as an ordinary pipe spool: it is designed, manufactured and verified as an inseparable part of the metering system.

EPS Leading meter runs can be combined with every EPS differential pressure meter and can also be supplied as run sections without a meter. Connection points for instruments such as thermowells and densitometers can be provided on the run, and the flow conditioner, transmitters and flow computer can be defined within the same scope — creating an integrated metering system under single responsibility.

How a Meter Run Determines System Accuracy

An orifice meter run prepares the flow for the measuring element and takes the measured values from the right points. Following the direction of flow, its functions can be described in this order:

1.      Upstream straight pipe section: Flow arriving from an elbow, valve or header loses its swirl and develops its velocity profile as it travels along straight pipe. The required length is set as a multiple of the pipe diameter according to the beta ratio, the type of upstream fitting and the applicable standard.

2.      Flow conditioner or straightener: Where the site layout does not allow enough straight pipe, a flow conditioner placed in the upstream section reduces swirl and corrects the profile, helping to shorten the run. Its position follows the distances defined in the standard.

3.      Alignment between meter and run: Axial offset or a bore step between the orifice fitting and the upstream and downstream pipes distorts the profile arriving at the plate. On flanged versions, dowel alignment keeps the assembly concentric even after it has been reassembled on site.

4.      Downstream straight pipe section: The section after the plate stops downstream elements such as valves or elbows from influencing the pressure tappings. The temperature measuring point is usually located in this section too, at the position specified by the standard.

5.      Instrument connections and data acquisition: Differential pressure, static pressure, temperature and, where needed, density measurements are combined in the flow computer to calculate flow. Condition-based monitoring (CBM) diagnostics help track the performance of the metering system throughout its operating life.

Dimensional Verification: Radiography, Surface Finish and Concentricity

On meter runs, weld integrity is verified by radiographic examination, while internal surface finish and concentricity are measured against the customer's requirements. These records, together with the measurement verification reports and material certificates, form part of the delivery documentation and provide the basis for auditing the metering system.

The System Accuracy Approach

System accuracy is the combined result of how precisely the meter and the meter run piping are made and dimensioned. It is therefore advisable to obtain the meter and the run from the same production and inspection process, machined to match each other. Joining parts from different suppliers on site raises the risk of bore mismatch and alignment error — and such errors cannot be compensated later by calibration.

Key Features

·         Project-specific design: Each orifice meter run is designed around the customer's metering objective, piping layout and specification; a bespoke design service is offered on request.

·         Complete metering system scope: EPS differential pressure meters, a flow conditioner or straightener, differential pressure and process transmitters, a flow computer, an enclosure and CBM diagnostics can all be included with the run.

·         Instrument connection points: Connections for thermowells, densitometers and similar instruments are integrated into the design on the upstream and downstream sides.

·         Wide pressure range: In addition to ANSI 150#–2500# pressure classes, high-pressure designs up to 10,000 psi are possible.

·         Materials for demanding service: Material options range from standard carbon steels to duplex, super duplex and nickel-based alloys; fabrication to an internal cladding specification is available where required.

·         Flexible end connections: Flange–flange, flange–weld or weld–weld ends, with flat face, raised face (RF) or ring-type joint (RTJ) flange facings.

·         Dowel alignment: On flanged versions, dowel alignment helps keep the meter and the run concentric after installation and maintenance.

·         Verified manufacturing: Radiography, surface finish and concentricity checks are carried out to customer requirements and documented.

·         Run sections without a meter: Meter run sections alone can also be supplied for use with an existing meter.

Technical Specifications

Because meter runs are built to project requirements, the information below defines the design scope. Diameter, length, wall thickness and connection points are determined from the project data.

Pressure class, material and end connection options are not independent of each other; the final combination is confirmed together with the applicable design code and process conditions.

Key Advantages

·         Uncertainty reduced at its origin: Producing the meter and the run to match each other limits, from the outset, systematic errors caused by bore steps and axial offset.

·         Fast, reliable installation on site: Factory-verified, dowel-aligned run sections fit into place on site without additional adjustment.

·         Low maintenance requirement: Precision-machined pipe sections with fixed geometry need very little maintenance over their service life.

·         One responsibility, one documentation package: Supplying the meter, run and accessories within one scope brings quality records and pressure-equipment documentation together in a single dossier.

·         Suited to demanding service: Material and cladding options are available for high pressure, sour service and corrosive fluids.

·         Flexibility at existing stations: The option of run sections without a meter allows only the pipe sections to be renewed while meters in service are retained.

Application Areas

Meter runs form the mechanical backbone of differential pressure measuring points in the gas transmission and distribution, power and process piping covered by the design codes.

Natural Gas Metering Stations

For orifice metering stations on transmission and distribution lines within the scope of ASME B31.8, upstream and downstream meter runs are designed together with the flow conditioner and instrument connections.

High-Pressure Production and Gathering Lines

With API 6A flange options and designs up to 10,000 psi, measuring points can be built on high-pressure lines.

Power Plants

Meter runs can be manufactured for flow measuring points on lines covered by ASME B31.1 power piping.

Process Plants and Corrosive Service

On lines within the scope of ASME B31.3 process piping, duplex, super duplex or clad constructions give long service life with corrosive fluids; sour service is assessed under NACE MR0175.

Renewal of Existing Metering Stations

In projects where the installed meters are kept, dimensional compliance can be restored by replacing only the meter run sections.

Meter Run Design Criteria

To size an orifice meter run and define its manufacturing scope, we recommend clarifying the following data at the start of the project:

Measurement and Flow Conditions

·         Meter type to be used, line size and expected beta ratio range

·         Fluid, flow range, operating pressure and temperature

·         Fittings upstream and downstream of the measuring point (elbow, valve, header, reducer)

·         Straight pipe length available on site and the need for a flow conditioner

Mechanical Design and Codes

·         Piping design code to be applied and pressure-equipment requirements

·         Pressure class, wall thickness and corrosion allowance

·         Material, sour service requirement and need for internal cladding

·         End connection type, flange standard and flange facing

Instrumentation and Connection Points

·         Thermowell location and connection type for temperature measurement

·         Connections needed for a densitometer or additional process measurements

·         Mounting arrangement of the differential pressure and static pressure transmitters

·         Scope of flow computer, enclosure and CBM diagnostics

Quality and Documentation

·         Radiography extent, surface finish and concentricity measurement requirements

·         Type of material certificate and expected measurement verification report

·         Need for conformity with PED or regional/customer codes

·         Transport, installation clearance and ease of removal for maintenance (favoring flanged ends)

Hazardous-area requirements for the electronic instruments on the meter run are assessed per project according to the area classification of the station.

Design Codes, Flange and Measurement Standards

EPS Leading meter runs are designed and manufactured to the following standards and codes, as required by the project.

Additional customer- or region-specific codes are assessed per project; which codes apply should be clarified at quotation stage.

Meter Run Engineering from TLY Enerji

TLY Enerji treats the meter run as the mechanical and metrological backbone of the metering station. Our engineering team reviews the existing or planned piping layout, assesses the need for straight pipe and a flow conditioner according to the fittings upstream of the meter, determines the positions of the instrument connection points and defines the run scope together with the meter, transmitters and flow computer.

We support your project teams in preparing the technical specification, following up the manufacturing quality plan and delivery documentation, integrating the measurement into the control system and commissioning. In renewal projects, we assess with you whether the installed meters can be retained, the dimensional condition of the existing orifice meter run and the installation sequence that will shorten station downtime. The new run then becomes part of a system that delivers traceable, auditable metering data from the first day of operation.

Frequently Asked Questions

What is a meter run?

A meter run is the set of pipe sections connected to the inlet and outlet of a differential pressure meter, manufactured to the lengths and tolerances specified by the measurement standard. It ensures that flow reaches the measuring element with a well-formed velocity profile and that disturbances downstream of the meter do not affect the measurement. In orifice metering it is one of the basic building blocks of system accuracy.

Why should the meter run be supplied together with the meter?

System accuracy combines the manufacturing and dimensional precision of both the meter and the meter run piping. Machining the meter and the run to match each other minimizes bore mismatch and axial offset. When parts from different suppliers are joined on site, these errors are harder to control and usually cannot be corrected afterwards.

How much straight pipe is needed upstream and downstream of an orifice?

The required length is not a fixed value; it is calculated as a multiple of the pipe diameter according to the beta ratio, the type of fitting upstream of the meter (single elbow, elbows in different planes, valve, reducer) and the applicable standard. A separate minimum length is also defined for the downstream side. These values are set per project on the basis of ISO 5167 or API MPMS 14.3.2.

Does a flow conditioner shorten the meter run?

Yes. A suitable flow conditioner reduces swirl and corrects the velocity profile, allowing the upstream straight length required by the standards to be shortened. How much shorter depends on the conditioner type, its position and the applicable standard. At stations with limited space, the flow conditioner should be considered as part of the meter run design.

Which instruments can be connected to a meter run?

Connection points for thermowells, densitometers and similar instruments can be added to the upstream and downstream sides of the run at the design stage. Transmitters, a flow computer, an enclosure and condition-based monitoring diagnostics can also be included in the metering system delivery. The positions of the connection points are set according to the relevant measurement standard.

Should a flanged or a welded meter run be chosen?

Flanged ends make it easier to remove the run for inspection and maintenance, and dowel alignment preserves concentricity on reassembly. Welded ends reduce the number of potential leak points and may be preferred on high-pressure or critical lines. A flange–weld combination is also possible; the choice depends on the design code, the maintenance strategy and site constraints.

What documentation is supplied with a meter run?

Meter runs are delivered with detailed measurement verification records and material certificates. Radiography, surface finish and concentricity checks are reported according to customer requirements. Where applicable, documentation of conformity with PED 2014/68/EU and with customer- or region-specific codes is also provided; the scope is clarified at quotation stage.

Can only the meter run section be replaced at an existing station?

Yes. Meter run sections can also be supplied without a meter. However, the bore and alignment compatibility of the new run sections with the existing meter must be verified. Using the dimensional data of the existing meter and the station layout, TLY Enerji evaluates the renewal options and helps you decide whether the meter and run should be renewed together.