In industrial process control,Mass flow meters have become key instruments in fields such as petrochemicals, food and pharmaceuticals due to their unique advantage of directly measuring fluid mass flow rate.However, to ensure its measurement accuracy and stability, the requirement for straight pipelines is a crucial link that cannot be ignored during the installation process.

　　1、 The necessity of straight pipeline requirements

The mass flow meter operates based on the Coriolis force principle and determines the mass flow rate by measuring the phase difference of the fluid inside the vibrating tube. Its measurement accuracy is highly susceptible to the influence of fluid flow conditions. If there are turbulence elements such as elbows and valves upstream of the installation location, it will cause non ideal flow states such as vortices and asymmetric velocity distributions in the fluid, resulting in measurement errors. Research has shown that when the requirements for straight pipelines are not met, measurement errors can be as high as 5% -15%.

　　2、 Specific requirements for straight pipelines

1. Upstream straight pipe section: Generally, the length of the upstream straight pipe section is required to be no less than 10 times the diameter of the pipeline (10D). If there are strong turbulence devices such as regulating valves and pumps installed upstream, it is recommended to extend to 20-30D. For large-diameter pipelines or high viscosity fluids, the requirements for straight pipe sections may be more stringent.

2. Downstream straight pipe section: A straight pipe section with a diameter of 5 times the diameter of the pipeline (5D) is usually required to ensure that the fluid returns to a stable state after flowing out of the flowmeter. In special situations where space is limited, the downstream straight pipe section may be appropriately shortened, but not less than 3D.

3. Pipeline layout: The straight pipe sections before and after the flowmeter should be kept concentric and coaxial to avoid pipeline misalignment or inclination. When connecting flanges, it is necessary to ensure that the sealing gasket does not protrude into the pipeline to prevent changes in the flow cross-sectional area.

　　3、 Handling of special circumstances

1. Space limited solution: When the standard straight pipeline requirements cannot be met on site, it is possible to consider installing flow regulators (such as bundle rectifiers) to shorten the straight pipe section requirements to 5D upstream and 2D downstream. However, it should be noted that the flow regulator itself will increase pressure loss by about 1-2%.

2. Multiple instruments sharing a straight pipe section: When multiple instruments share a straight pipe section, it should be ensured that the mass flowmeter is located closest to the turbulence element and that its straight pipe section is not affected by other instruments.

　　4、 Installation verification method

After installation, the effectiveness of the straight pipeline can be verified by observing the stability of the flowmeter output signal. Under normal circumstances, the zero drift should be less than ± 0.1%/℃ of the range, and the output response time should be stable within 1-3 seconds when the flow rate changes step by step. If necessary, a portable ultrasonic flowmeter can be used for comparative verification.

The straight pipeline requirements for quality flow meters may seem simple, but they are the cornerstone for ensuring measurement accuracy. Strictly following the specifications for straight pipelines not only ensures measurement accuracy (up to ± 0.1% - ± 0.5%), but also extends the service life of instruments. Careful planning of pipeline layout before installation is the first step in unleashing the outstanding performance of quality flow meters.