Upstream and Downstream Flow Straight Pipe Requirements refer to the length of straight pipe before and after the installation location of the flowmeter.
In order to ensure that the fluid flow state is uniform in the pipeline, the flow field of the fluid can generally be stabilized. It is required that the straight pipe section before and after the installation position of the flowmeter should be long enough. Otherwise, it will cause inaccurate measurement.
The general rule of thumb for straight piping is a five-diameter length of piping upstream and three diameters downstream from the meter (measured from the center of the tube).
Next, we will detail the various flow meters Upstream and Downstream Flow Straight Pipe Requirements.
what is upstream and downstream flow?
For pipelines where fluid flows, we must first understand the upstream and downstream fluids when installing the flowmeter.
The direction of fluid entry is upstream. The direction of fluid discharge is downstream.
The straight pipe section of the flowmeter is the straight pipe section that requires a certain length of the water inlet and outlet of the flowmeter. That is, the pipe in that section needs to be straight. There can be no elbows, valves and the like. Generally, the upstream length requirement will be longer than the downstream length requirement.
Extended reading: Fluid flow meter types
10D Upstream and 5D Downstream
When users use the orifice flowmeter, they generally require 10D Upstream and 5D Downstream for the straight pipe sections before and after the orifice flowmeter. So what does this D stand for? Today I will briefly talk about it.
The D represents the diameter of the pipe. For the orifice plate in the orifice plate flowmeter, the minimum requirements for the front and rear straight pipe sections are 10D Upstream and 5D Downstream. If there is a pump or regulating valve in front of the orifice plate, then the requirements for the straight pipe section are greater.
Read more about: How to Calculate Pressure Drop in a Pipe?
Different Flow Meters Installation Rule of Thumb
Due to the limitation of the structure of the orifice plate flowmeter itself, its measurement accuracy is not high. There are a number of system reasons that can cause errors during installation. And the magnitude of this error cannot be estimated.
But by analyzing the factors that cause the error, the error can be reduced.
When the orifice flow measurement system is installed and used, it must meet the following technical requirements:
- When the orifice plate is installed, the center of its opening and the center axis of the pipe are concentric. And its end face is perpendicular to the axis of the pipe.
- The axis of the pressure taking hole on the orifice plate and the downstream side meets the requirement that the distance from the orifice plate and the downstream end face is 25.4±0.8mm.
- The axis of the pressure taking hole should be perpendicular to the axis of the inner cylinder of the 2D measuring tube length on the downstream side of the orifice plate. The included angle between the axis of the pressure taking hole and the outward inclination angle of the two ends of the orifice plate shall not be greater than 3 degrees. The diameter of the pressure hole should not be greater than 0.08D.
- Orifice plate installation requires front and rear straight pipe sections. The length of the straight pipe section is related to the form and diameter ratio β of the local resistance member on the upstream side of the orifice plate. Its determination method is as follows:
Table. Required Straight Run Lengths Between Orifice Plate and Choke (No Flow Conditioner)
(The value is expressed in multiples of the pipe diameter D)
| Diameter ratio β | Upstream side of orifice plate (inlet) | |||||||||||||
|
Single 90° Elbow Two 90° elbows In any plane (S＞30D) |
Two 90° elbows in the same plane, S shape (30D≥S＞10D) |
Two 90° elbows in the vertical plane, (30D≥S≥5D) |
Two 90° elbows on the same plane, (30D≥S≥5D) |
Two 9° elbows in the vertical plane, (5D>S) | Single 90° Tee | Two 45° elbows on the same plane with a single 45° elbow, S shape (S>22D) | ||||||||
| A | B | A | B | A | B | A | B | A | B | A | B | A | B | |
| 0.2 | 6 | 3 | 10 | 10 | 10 | 10 | 19 | 18 | 34 | 17 | 9 | 3 | 5 | 5 |
| 0.4 | 16 | 3 | 10 | 10 | 10 | 10 | 44 | 18 | 50 | 25 | 9 | 3 | 30 | 9 |
| 0.5 | 22 | 9 | 18 | 10 | 22 | 10 | 44 | 18 | 75 | 34 | 19 | 9 | 30 | 9 |
| 0.6 | 42 | 13 | 30 | 18 | 42 | 18 | 44 | 18 | 65 | 25 | 29 | 18 | 30 | 18 |
| 0.67 | 44 | 20 | 44 | 18 | 44 | 20 | 44 | 20 | 60 | 10 | 36 | 18 | 44 | 18 |
| 0.75 | 44 | 20 | 44 | 18 | 44 | 22 | 44 | 20 | 75 | 18 | 44 | 18 | 44 | 18 |
| Diameter ratio β | Upstream side of orifice plate (inlet) | Downstream side of orifice (outlet) | ||||||||||
| Reducers change from 2D to D over a length of 1.5D to 3D | The expanding tube changes from 0.5D to D within the length of D to 2D | Full bore ball valve or gate valve fully open | Symmetric shrink tube | Thermometer sleeve or socket diameter less than 0.03D | All Front Choke Types and Density Meter Sleeves | |||||||
| A | B | A | B | A | B | A | B | A | B | A | B | |
| 0.2 | 5 | 5 | 16 | 8 | 12 | 6 | 30 | 15 | 5 | 3 | 4 | 2 |
| 0.4 | 5 | 5 | 16 | 8 | 12 | 6 | 30 | 15 | 5 | 3 | 6 | 3 |
| 0.5 | 6 | 5 | 18 | 9 | 12 | 6 | 30 | 15 | 5 | 3 | 6 | 3 |
| 0.6 | 9 | 5 | 22 | 11 | 14 | 7 | 30 | 15 | 5 | 3 | 7 | 3.5 |
| 0.67 | 12 | 6 | 27 | 14 | 18 | 9 | 30 | 15 | 5 | 3 | 7 | 3.5 |
| 0.75 | 22 | 11 | 38 | 19 | 24 | 12 | 30 | 15 | 5 | 3 | 8 | 4 |
Orifice flowmeters use flow regulators if possible in harsh installation conditions. The installation of the thermowell does not change the length of the small straight section on its upstream side.
The length of the small straight pipe section refers to the length between the upstream and downstream baffles of the orifice plate and the orifice plate. The length is measured from the downstream end of the curved portion of the adjacent elbow or tee or the downstream end of the tapered portion of the reducer and expander.
Extended reading: Liquid Bitumen/Asphalt Flow Meter
The length of the straight pipe section required by the differential pressure type is 10-62D. So the difference is big. This is because the required length of the straight pipe section depends on the opening ratio of the orifice plate (ratio d/D of the inner diameter D of the pipe to the inner diameter d of the orifice plate).
The opening ratio (ratio d/D of the inner diameter D of the pipe to the inner diameter d of the orifice plate) is larger. The longer the straight pipe section is required.
Conversely, the smaller the opening ratio, the shorter the straight pipe section required.
- Difficult to give a general range
- Helpful to use impulse lines on either side
- Actual value depends on the type of upstream elements and the beta ratio
- Beta ratio is defined as the diameter of the pipe orifice divided by the pipe diameter
Discover more about: Differential Pressure Flow Meters
The correct selection of the installation point of the electromagnetic flowmeter and the correct installation of the sensor are both very important links.
If there are minor mistakes in the installation process, the measurement accuracy will be affected. Heavy ones will affect the service life of the sensor. Even damage the sensor.
To improve the effects of eddy currents and current field deformities. There are certain requirements for the length of the straight pipes before and after the flowmeter. Otherwise, the measurement accuracy will be affected. A power converter can be installed. But installation must be avoided. Near or after regulating valves and half-open valves.
Extended Reading: Special Magnetic Flowmeter Installation situation
| Pipe Installation Types | Installation Instruction Diagram | Standard-pipe Type | |
| Front straight pipe L | Back straight pipe S | ||
| Bent pipe | Picture a | 10D | 5D |
| Horizontal pipe | Picture b | 5D | 3D |
| Backward position of valve | Picture C | 10D | 5D |
| Flaring pipe | Picture d | 10D | 5D |
| Backward position of mercury | Picture e | 15D | 2D |
| Shrinkage pipe | Picture f | 5D | 2D |
| Mixed liquid | Picture g | 30D | 3D |
Extended reading: What Is Difference Between Rotameter And Flow Meter?
Vortex flow meter has certain requirements on the upstream and downstream straight pipe section of the installation point. otherwise it will affect the flow field of medium in the pipeline and affect the measuring accuracy of the meter. The length of the upstream and downstream straight pipe section of the instrument is required as shown in FIG. DN is the nominal diameter unit of the instrument:mm.
Read more about: Vortex flow meter installation
Since the ultrasonic flowmeter is a velocity flowmeter, it has strict requirements on the flow characteristics of the medium. It must be ensured that the medium is in a laminar flow state during the detection of the transducer.
Therefore, whether it is a split ultrasonic flowmeter with a large pipe diameter or an integrated ultrasonic flowmeter with a small pipe diameter, it is necessary to ensure that there are enough straight pipe sections before and after the instrument before installation.
Although most of the velocity-type instruments have such regulations for the requirements of the straight pipe section, in order to ensure the good use of the ultrasonic flowmeter, the straight pipe section is most likely to be larger than the first 10D and the latter 5D standard, the bigger the better.
Extended Reading: Mechanical flow meter for diesel
Steady flow is helpful for ensuring measurement accuracy.
Standard requests for steady flow are:
1. The pipe should be far away from pump outlet and half-open valve. 10D to upstream and 5D to downstream. (D means outer diameter)
2. 30D to pump outlet and half-open valve.
The requirement of straight pipe section for turbine flowmeter installation is very important. Its detailed requirements are as follows:
- The flowmeter has certain requirements on the upstream and downstream straight pipe sections at the installation point. Otherwise, the measurement accuracy will be affected.
- If there is a reducer upstream of the installation point of the flowmeter, the upstream of the flowmeter should have an equal-diameter straight pipe section of not less than 15D (D is the diameter of the pipe). The downstream should have an equal-diameter straight pipe section of not less than 5D.
- If there is a gradually expanding pipe upstream of the installation point of the flowmeter, there should be a straight pipe section of equal diameter not less than 18D (D is the diameter of the pipe) upstream of the flowmeter. There should be a straight pipe section of equal diameter no less than 5D downstream
- If there is a 90° elbow or downlink joint upstream of the installation point of the flowmeter, there should be an equal diameter straight pipe section not less than 20D upstream of the flowmeter, and an equal diameter straight pipe section not less than 5D downstream.
- If there is a 90° elbow on the same plane upstream of the installation point of the flowmeter, there should be an equal-diameter straight pipe section of not less than 25D upstream of the flowmeter, and an equal-diameter straight pipe section of not less than 5D downstream.
The oval gear flowmeter is a kind of instrument specially for measuring the flow of high-viscosity medium. The instrument plays a very important role in the industry, and the measurement accuracy is relatively high.
Oval gear flowmeter, this kind of flowmeter does not need to use straight pipe sections in the process of use.
This kind of measuring instrument can be easily installed at the valve outlet or turning point of the pipeline. Do not use the original straight pipe section at all. It is also a disguised way to save production costs during use.
The oval gear flowmeter should be cleaned before installation. If the liquid contains solid particles, a filter must be installed upstream of the pipeline; if it contains gas, an exhaust device should be installed.
The oval gear flowmeter does not have certain requirements for the front and rear straight pipe sections. It can be installed horizontally or vertically. During installation, the rotation axis of the oval gear of the flowmeter should be parallel to the ground.
Read more about: Various Types of Mass Flow and Volumetric Flow Meters
Coriolis flow meters directly measure mass flow and density. Their measurements are insensitive to fluid profiles and have virtually no installation restrictions. Therefore, no upstream and downstream straight runs are required.
The main guideline for a Coriolis sensor is to ensure that the sensor tube remains full. If installing in a vertical pipe. Make sure that fluids (liquids and slurries) flow up and gas flows down. And do not use the meter to align misaligned pipes.
Read more about: Mass Flow Meter Types
Read more about: Different Types of Flowmeters – Technical and Application Analysis
There are many professional organizations that provide guidance and standards for most flow techniques used. Some of them are ISA, ISO, API, AGA, ASME and ANSI.
When in doubt, it is recommended that you refer to these guides. As they have been tested and provide a good starting point for ensuring that the flowmeter is performing properly.
Some very common guidelines/standards are listed below:
Coriolis – ISO10790
Critical Nozzle – ISO9300
Differential Pressure – ISO5167
Electromagnetic – ISO6817
Positive Displacement – ISO2714
Thermal Mass – ISO14511
Turbine – ISO2715
Ultrasonic – ISO17089
Variable Area – ISO11605
Vortex – ISO/TR12764
ASME MFC-3M-2004
ASME MFC-6-2013
ASME MFC-11-2006
ASME MFC-5.1-2011
ASME MFC-16-2014
These are some general guidelines to consider when determining the right flowmeter placement for your application. By asking the right questions and having a good understanding of existing guidelines and standards, you should be able to take advantage of a very large investment in flow meters.
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Wu Peng, born in 1980, is a highly respected and accomplished male engineer with extensive experience in the field of automation. With over 20 years of industry experience, Wu has made significant contributions to both academia and engineering projects.
Throughout his career, Wu Peng has participated in numerous national and international engineering projects. Some of his most notable projects include the development of an intelligent control system for oil refineries, the design of a cutting-edge distributed control system for petrochemical plants, and the optimization of control algorithms for natural gas pipelines.