EPS Leading Restriction Orifice Plates and Flow Conditioners

What Are Restriction Orifices and Flow Conditioners?

A restriction orifice is a plate installed in a pipeline whose bore is calculated to produce the required pressure drop at a given flow rate. It differs from a metering orifice in purpose: a metering orifice generates a differential pressure related to flow so that it can be read, whereas a restriction orifice is used deliberately to reduce pressure or to limit flow and usually has no measuring tappings. As a passive element with no moving parts, it is a lean solution wherever a fixed pressure drop is sufficient.

If the required pressure drop cannot be achieved safely with one plate, a staged solution is needed. A multi-plate restriction spool lowers the pressure step by step across successive plates until the outlet pressure reaches the required value. The more stages there are, the longer the spool becomes, so multi-hole plates are used to keep the spool as short as possible.

Flow conditioners solve a different problem. The accuracy of orifice metering depends on flow arriving at the plate with a swirl-free, symmetrical velocity profile. A flow conditioner plate reduces swirl and redistributes the velocity profile, while a tube bundle only reduces swirl. Both help shorten the straight pipe length required in the meter run.

How Restriction Orifices and Flow Conditioners Work

Because every application is different, restriction orifices are engineered from the process data. The design process consists of the following engineering steps:

1.      Defining the process data: The fluid phase (gas, vapor or liquid), inlet pressure, target outlet pressure or flow, temperature, density and line size are established. For liquids the vapor pressure, and for gases the pressure ratio, set the direction of the design.

2.      Orifice sizing: The bore is calculated so that it produces the required pressure drop at the design flow. For gases, once the pressure ratio falls below a certain limit the flow becomes critical (choked) and no longer depends on the outlet pressure; for liquids, an outlet pressure approaching the vapor pressure creates a risk of cavitation or flashing.

3.      Thickness and deflection calculation: Plate thickness is governed entirely by line size and differential pressure. It is calculated so that the plate neither deflects excessively nor buckles in service; for the same line size, a higher pressure difference calls for a thicker plate.

4.      Noise prediction: Gas and vapor flows across a high pressure difference generate aerodynamic noise and vibration. A noise prediction is made for every plate and compared with site limits; if necessary, a staged or multi-hole solution is adopted.

5.      Defining the configuration: If the calculations show that one plate is sufficient, a single-plate element mounted between RF or RTJ flanges is selected. Otherwise a multi-plate restriction spool is designed, and materials are chosen with long service life in mind.

Staged Pressure Reduction in Multi-Plate Restriction Spools

Placing the entire pressure drop on a single plate can mean excessive noise, critical flow, cavitation in liquids and high mechanical load on the plate. In a multi-plate spool, each stage takes only part of the total drop, and the outlet pressure reaches the value the customer requires at the final stage. Because more stages make the spool longer, multi-hole plates are used to shorten each stage and achieve the shortest possible spool.

Difference Between a Flow Conditioner Plate and a Tube Bundle

The Zanker-type flow conditioner plate, designed to ISO 5167-1:2003, is a solid plate with a specific hole pattern; it reduces swirl in the flow and redistributes the velocity profile, creating suitable conditions for accurate differential pressure measurement. The 19-tube bundle, on the other hand, is intended only to reduce swirl at a defined position upstream of the measuring point and cannot redistribute the velocity profile. Tube bundles are made in pin and flanged versions: the pin type is generally used on lines up to 24 inch inclusive, and the flanged type on larger sizes.

How a Flow Conditioner Affects the Meter Run

Long straight pipe sections are needed for disturbances from elbows and valves to die out naturally. Flow conditioners allow the meter run to be shortened within the framework of ISO 5167 and API MPMS 14.3 (AGA 3, Part 2). Because the Zanker-type plate can be retrofitted in the field to existing lines, it is a practical way to improve measurement quality at stations with limited space.

 Key Features

·         Wide size range: Restriction plates are produced to suit line sizes from ½ inch to 48 inch.

·         Plate thickness matched to the pressure drop: Plates are designed in different thicknesses to match the pressure drop of the application.

·         Three engineering calculations for every plate: Orifice sizing, a thickness and deflection check and a noise prediction are carried out individually for each restriction plate.

·         Single plate or multi-plate spool: Single-plate elements fitted between RF or RTJ flanges, or multi-plate restriction spools for staged pressure reduction.

·         Short spools with multi-hole plates: In multi-stage solutions, multi-hole plates keep the spool length as short as possible.

·         Special trim and a wide pressure rating: Special trim options are offered; the pressure rating spans 150# to 10,000 psi.

·         Field-repairable construction: Restriction plates are designed so that they can be repaired in the field.

·         Zanker-type flow conditioner plate: Designed to ISO 5167-1:2003; machined from solid material for robustness, available in 2–48 inch sizes and suitable for retrofitting in the field.

·         19-tube bundle flow straightener: Produced in pin or flanged versions in 2–48 inch sizes to reduce swirl.

·         Materials for demanding service: A material range from stainless steel to duplex and nickel-based alloys; special alloys are widely used for restriction plates to achieve a long service life.

Technical Specifications

Restriction plates and flow conditioners are designed to project requirements. The table below summarizes the design scope; bore, thickness, number of stages and noise values are calculated from the process data.

The flange standard and flange pressure class of restriction plates are determined per project according to the existing flanges of the line to which they will be fitted.

Key Advantages

·         A lean solution with no moving parts: Where a fixed pressure drop is sufficient, a passive plate provides a reliable solution that is easy to maintain.

·         Project-specific sizing: Because every plate is calculated from the process data, the required outlet pressure and flow target are built directly into the design.

·         Noise and vibration managed in advance: Noise prediction allows acoustic and vibration problems that could otherwise appear on site to be addressed at the design stage.

·         Mechanical integrity: The thickness and deflection calculation ensures that the plate keeps doing its job under operating conditions without buckling.

·         Short, compact spools: Multi-hole plates make it possible to design short spools that fit into the piping layout in multi-stage solutions.

·         Shorter meter runs: Flow conditioners help reduce the upstream straight pipe length while preserving measurement accuracy.

·         Practical on site: Field retrofitting of the Zanker-type plate and field repair of restriction plates shorten downtime.

Application Areas

Restriction orifices are used at points in gas, vapor and liquid lines where a calculated pressure drop is required; flow conditioners are used in differential pressure meter runs.

Controlled Pressure Drop in Gas Lines

A restriction orifice is applied when a defined pressure drop or flow limit is required in a gas flow. At high pressure differences, critical flow and noise are managed with a staged spool.

Steam and Vapor Lines

Single-plate or multi-plate solutions are designed to reduce pressure to a calculated value in vapor flows, including steam; noise prediction is particularly important in these applications.

Flow Limitation in Liquid Lines

Used for flow limitation and pressure breakdown in liquid lines. Where the outlet pressure approaches the vapor pressure, the risk of cavitation is reduced by staged pressure reduction.

Differential Pressure Metering Stations

Flow conditioners installed upstream of orifice fittings remove swirl and profile distortion, so that the differential pressure measurement takes place close to standard conditions.

Improving Existing Meter Runs

At existing stations without sufficient straight pipe, measuring conditions can be improved by retrofitting a Zanker-type plate in the field.

Selection Criteria for Restriction Plates and Flow Conditioners

Because both product groups are designed to project requirements, the technical assessment starts with correct process and installation data:

Process Data for a Restriction Orifice

·         Fluid and phase (gas, vapor, liquid); composition, density or molecular weight

·         Inlet pressure, target outlet pressure or target flow; minimum/normal/maximum operating cases

·         Fluid temperature; vapor pressure for liquids

·         Corrosive or erosive components and particle content

Mechanical Design and Installation

·         Line size, wall thickness and existing flange type (RF or RTJ) and pressure class

·         Spool length that can be made available on site for a multi-stage solution

·         Plate and spool material; need for special trim

·         Access for installation and maintenance

Noise and Mechanical Integrity

·         Permissible noise level on site and the measuring distance

·         Downstream piping arrangement and sensitivity to vibration

·         Plate thickness and deflection limits depending on the pressure difference

Flow Conditioner Selection

·         Fittings upstream of the measuring point and the straight pipe length available

·         Is swirl reduction alone enough (tube bundle), or must the profile be redistributed (flow conditioner plate)?

·         Pin-type or flanged tube bundle depending on line size

·         New line or retrofit to an existing line?

Because the temperature can also change as the pressure falls across a restriction orifice, the downstream material and piping design should be assessed with this effect in mind.

Design and Measurement Standards

Restriction plates and flow conditioners are designed on the basis of the following standards.

Project requirements for flange, piping and pressure-equipment codes, as well as hazardous-area conditions, should be clarified with the TLY Enerji engineering team at quotation stage.

Pressure Reduction and Flow Conditioning Solutions from TLY Enerji

TLY Enerji treats a restriction orifice request not as a plate order but as the solution to a pressure reduction problem on the line. Our engineering team collects your process data, defines the operating cases with you and makes sure the sizing, thickness and noise calculations are based on the right data; together with the site piping layout, it assesses whether a staged spool is needed instead of a single plate.

At metering stations, we analyze the need for a flow conditioner from the existing straight pipe lengths and fittings. In new projects we define the conditioner together with the meter run; at existing stations we plan field retrofit options. We also support your project teams with technical documentation, installation planning and site work, and help your operations teams anticipate maintenance needs from the outset.

Frequently Asked Questions

What is the difference between a restriction orifice and a metering orifice?

A metering orifice is used to generate a differential pressure related to flow and to measure it with a transmitter; it has a standard geometry and pressure tappings. A restriction orifice, by contrast, creates a calculated pressure drop or limits flow at a specific point in a line and has no measuring purpose. Besides sizing, plate thickness and noise are decisive in its design.

When is a multi-plate restriction spool needed?

A multi-plate spool is chosen when one plate cannot safely deliver the required pressure drop. Typical reasons are excessive noise, critical flow in gases, a risk of cavitation in liquids and high mechanical load on the plate. In the spool, pressure is reduced across successive stages, and multi-hole plates keep the spool short.

How is the thickness of a restriction plate determined?

Plate thickness is calculated from the line size and the differential pressure across the plate. The aim is to prevent the plate from deflecting excessively or buckling in service. For the same line size, a higher differential pressure requires a thicker plate. For this reason, a separate thickness and deflection calculation is made for every restriction plate in addition to sizing.

Why is noise calculated for restriction orifices?

Gas and vapor flows across a high pressure difference can generate aerodynamic noise and pipe vibration downstream of the orifice. This affects both workplace noise limits and the mechanical life of piping connections. The noise prediction is therefore made at the design stage, and if necessary a staged or multi-hole solution is adopted.

What does a Zanker-type flow conditioner plate do?

A Zanker-type plate is a perforated flow conditioner designed to ISO 5167-1:2003. It reduces swirl and redistributes the velocity profile so that the flow reaches the orifice plate under suitable conditions. Machined from solid material, it is robust, is available in 2–48 inch sizes and can be retrofitted in the field to existing lines.

What is the difference between a 19-tube bundle and a flow conditioner plate?

A 19-tube bundle is used upstream of the measuring point only to reduce swirl; it cannot redistribute the velocity profile. A flow conditioner plate both reduces swirl and redistributes the profile. Tube bundles are made in pin and flanged versions; the pin type is generally preferred on lines up to 24 inch, and the flanged type on larger sizes.

How much does a flow conditioner shorten the meter run?

The reduction is not a fixed value; it depends on the conditioner type and position, the fittings upstream of the meter and the applicable standard. Both the flow conditioner plate and the 19-tube bundle allow meter run length to be reduced within the framework of ISO 5167 and API MPMS 14.3 (AGA 3, Part 2). The suitable conditioner and position are determined per project from the layout of the measuring point.

Can a flow conditioner be retrofitted to an existing line?

Yes. The Zanker-type flow conditioner plate is designed to be retrofitted in the field. This offers a practical way of improving measuring conditions at existing metering stations that lack sufficient straight pipe. The installation position and flange connection should be determined according to the existing line layout and the requirements of the measurement standard.