Requirements for the straight pipe section of flowmeters are specified

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Choosing the correct installation location and installing the flow meter properly are both very important steps. Errors during installation can, in mild cases, affect the measurement accuracy; in more severe cases, they can impact the flow meter’s service life or even damage it. Different flowmeters require different lengths of straight pipe sections before and after them. 1. The general requirements for the straight pipe sections upstream and downstream of flow meters in the \"Code for Construction and Acceptance of Automatic Instrumentation Projects\" - GB50093-2013 are as follows: Mass flow meters – no requirements ； Rotary flow meter---not less than 0～5 times the pipe diameter upstream, no requirements downstream ； Target flow meter – at least 5 times the pipe diameter upstream, and at least 3 times the pipe diameter downstream ； Turbine flow meter – at least 5–20 times the pipe diameter upstream, and at least 3–10 times the pipe diameter downstream ； Vortex flow meter – at least 10–40 times the pipe diameter upstream, and at least 5 times the pipe diameter downstream ； Electromagnetic flowmeter – at least 5–10 times the pipe diameter upstream, and at least 0–5 times the pipe diameter downstream ； Ultrasonic flowmeter—no less than 10–50 times the pipe diameter upstream, and no less than 5 times the pipe diameter downstream ； Positive displacement flow meter---no requirement ； Orifice plate—no less than 5–80 times the pipe diameter upstream, and no less than 2–8 times the pipe diameter downstream ； Nozzle—no less than 5 to 80 times the pipe diameter upstream, and no less than 4 times the pipe diameter downstream ； Venturi tubes, elbow pipes, wedge-shaped tubes – a distance of not less than 5 to 30 times the pipe diameter upstream, and not less than 4 times the pipe diameter downstream ； Volumetric tube – a straight pipe section of at least 3 to 25 times the diameter of the tube upstream, and at least 2 to 4 times the diameter downstream. II. Requirements for the flow meter installation location: 1. If there is a 90° elbow or downward connector upstream of the flow meter, there should be a straight pipe section of at least 20D in diameter upstream of the flow meter, and a straight pipe section of at least 5D in diameter downstream. 2. If there is a 90° elbow in the same plane upstream of the flow meter installation point, there should be a straight pipe section of equal diameter of at least 25D upstream of the flow meter, and a straight pipe section of equal diameter of at least 5D downstream of it. 3. If there is a reducer upstream of the flow meter installation point, there should be a straight pipe section with a diameter equal to that of the flow meter itself, with a length of at least 15D, upstream of the flow meter; and a straight pipe section with a diameter equal to that of the flow meter itself, with a length of at least 5D, downstream of it. 4. If there is a flare pipe upstream of the flow meter installation point, there should be a straight pipe section with a diameter equal to that of the flow meter of at least 18D upstream, and a straight pipe section of at least 5D in diameter downstream. III. Special attention: 1. If a valve is installed near the upstream side of the vortex flowmeter, constantly opening and closing this valve has a severe impact on the flowmeter’s service life, and can easily cause permanent damage to it. 2. Flow meters should be installed as far as possible away from overhead and long pipelines, as the sagging of the flow meter can easily lead to leakage at the seal between the flow meter and the flange. If installation is necessary, pipe fastening devices must be installed 2D distances upstream and downstream of the flow meter. 3. The installation of the mass flow meter has no special requirements regarding the straight pipe sections before and after it. However, the following conditions must be met: (1) For liquid media, the flow meter should be placed at the lowest point of the pipeline. Prevent the medium from vaporizing due to too low back pressure, which could affect the measurement results. For gas media, the flow meter should not be placed at a local low point in the pipeline to avoid measurement errors caused by liquid accumulation in the measuring tube. (2) For liquid media, it is necessary to ensure that the medium fills the pipes during operation. There must be no gas-liquid or liquid-solid two-phase fluid in the measuring tube. If installed in a vertical pipe, the fluid should flow from bottom to top. If flow must occur from top to bottom, a flow-limiting orifice plate can be installed after the flow meter to prevent the measurement tube from being emptied. (3) The flow meter and the connection flange must be perfectly aligned; otherwise, external stress will be applied to the measurement tube, affecting the measurement results. (4) To avoid interference from strong electromagnetic fields on the flow meter, there should be no interference sources such as large motors in the vicinity of the flow meter. (5) When installing mass flow meters of the same model adjacent to each other, it is advisable to stagger their vibration frequencies in order to avoid the negative effects of resonance; moreover, the distance between the two flow meters should be at least 4 times the length of the instrument. (6) Be careful to distinguish between the natural vibration frequency of the flowmeter’s phase measurement and that of the pipeline, otherwise it will cause fluctuations in the measurements. (7) Shut-off valves should be installed before and after the flow meter to facilitate zero-point calibration prior to operation. 4. The rotameter must be installed in a vertical pipe without vibrations, with the flow direction of the medium from bottom to top. During installation, it is necessary to ensure that there is a straight pipe section in front of the flow meter with a length of at least 5 times the inner diameter of the pipe, and this length should be no less than 300 mm ； 5. When the medium being measured contains solid suspensions, the target flow meter needs to be installed horizontally. When a target flow meter is installed in a vertical pipe, the liquid flow should be from bottom to top. The length of the straight pipe section ahead of the inlet of the target flowmeter should not be less than 5 times the inner diameter of the tube, while the length of the straight pipe section behind the outlet should not be less than 3 times the inner diameter of the tube.