Requirements for straight pipe sections when installing electromagnetic flowmeter

Case introduction

​A brief analysis of the requirements for straight pipe sections when installing electromagnetic flowmeters: If the installation of electromagnetic flowmeters can ensure the length requirements of the straight pipe sections, it can ensure the accuracy of measurement. Let’s talk about electromagnetic flowmeters below. Installation requirements for straight pipe sections: The requirements for the installation position of electromagnetic flowmeters are strict, and the requirements for the straight pipe section at the installation position are also very strict. One section is installed with 5 times the pipe diameter in the front section and 3 times the pipe diameter in the back section. , In order to obtain normal measurement accuracy, there must also be a certain length of straight pipe section upstream of the electromagnetic flow sensor, but its length requirement is lower than that of most other flow meters. After 90-degree elbows, T-shaped pipes, concentric reducers, and fully-open gate valves, it is generally considered that as long as the straight pipe section is 5 times the diameter (5D) away from the electrical centerline of the electromagnetic flowmeter (not the sensor inlet connection surface), different openings The valve requires 10D; the downstream straight pipe section is (2~3)D or no requirement; but it is necessary to prevent the butterfly valve disc from extending into the sensor measurement pipe. The lengths of upstream and downstream straight pipe sections proposed by various standards or verification regulations are also inconsistent, and the requirements are higher than usual. This is due to ensuring that the current 0.5-level accuracy instrument requirements are met.

2 Requirements for the straight pipe section of electromagnetic flowmeter installation

Selecting the correct installation point and installation method is the key to using the electromagnetic flowmeter. If the installation is incorrect, it will not only affect the measurement accuracy , will also affect the service life of the flow meter, and even damage the flow meter.

2. 1 Requirements for straight pipe sections

In order to ensure the measurement accuracy of the electromagnetic flowmeter, the inner wall of the upstream and downstream straight pipe sections where the meter is located should be clean and free of obvious dents, scale, and peeling. The upstream and downstream straight pipe sections of the electromagnetic flowmeter installation location generally follow the last five principles, requiring that the front straight pipe section is not less than 10 D and the rear straight pipe section is not less than 5 D; if other chemical substances are injected into the upstream pipe section, it is easy to cause conductance Due to the non-uniformity of the rate, the flowmeter should be at least 20 D away from the main inlet (as shown in Figure 1); if reducers are used upstream and downstream of the electromagnetic flowmeter, the central cone angle α of the reducer should be less than 15° (as shown in Figure 2 ).

In order to ensure accurate measurement of the electromagnetic flowmeter, the installation position must be correctly selected (as shown in the figure below:)

Requirements for the straight pipe section of the electromagnetic flowmeter:

The electromagnetic flowmeter must be installed horizontally on the pipeline (the inclination of the pipeline is within 50 degrees). During installation, the flowmeter axis should be concentric with the pipeline axis, and the flow direction should be consistent.

The length of the upstream pipe of the electromagnetic flowmeter should be a straight pipe section of equal diameter not less than 2D. If the installation site permits, it is recommended that the upstream straight pipe section be 20D and the downstream straight pipe section be 5D.

Electromagnetic flowmeter requirements for piping:

The inner diameter of the upstream and downstream piping at the flowmeter installation point is the same as the inner diameter of the flowmeter.

Requirements for bypass pipes of electromagnetic flowmeters:

In order to ensure that the normal use of the medium is not affected during maintenance of the flowmeter, cut-off valves (cut-off valves) should be installed on the pipes before and after the flowmeter. valve) and should be setBypass pipe. The flow control valve should be installed downstream of the flow meter. When the flow meter is used, the stop valve installed upstream must be fully open to avoid unstable flow of the fluid in the upstream part.