Cathodic protection for electromagnetic flowmeters

Cathodic protection means that the flow meter sensor is installed on a pipeline with cathodic protection. Here are several installation methods, including installation on cathodically protected pipelines. You may refer to the following: cathodic protection for electromagnetic flowmeters, installation on pipelines with high stray current levels, and insulating bolts. (3) Grounding of sensors installed on cathodically protected pipelines – Sensors on pipelines that are under cathodic corrosion protection should be insulated from the pipelines. The following points must be considered when installing sensors: (see Figure 6-24) http://www.sensorok.com/tech/tech/dc/images/ld611.1.gif Figure 6-24 Installation of sensors on cathodic protection pipelines 1 – Measurement grounding ； 2 – Ground wire (16mm2 copper wire) 3 – Ground ring ； 4 – Bolt (insulated) ； 5 – Connection wire (16mm2 copper wire) ① The sensor must be insulated from pipes with cathodic corrosion protection, to ensure that the potential in the flowing medium does not affect the measurement results ； ②Appropriate grounding rings must be installed on both ends of the sensor. The sensor and the grounding rings must be insulated from the pipe flanges; the grounding rings on both sides should be connected to each other, but there should be no electrical connection between them and the pipe. ③The flanges of the pipes on both sides are connected to each other using copper wires with a cross-sectional area of 16 mm2 that wrap around the sensor ； ④The connecting bolts passing through the flange should use bushings and washers made of insulating material to isolate the bolts from the flange. (See Figure 6-25) http://www.sensorok.com/tech/tech/dc/images/ld611.2.gif Figure 6-25: “Insulating” bolts on cathodic protection pipelines; E – grounding ring ； 1 – Sensor flange ； 2 – Lining (PTFE) ； 3 – Seal ring ； 4 – Pipe flange ； 5－Bolt ； 6－Nut ； 7 – Washer ； 8 – Insulating bushing (4). Sensors are installed in areas with high stray currents in pipelines. In such situations, for example when measuring the flow rate of electrolyte in pipelines near electrolyzers, the stray currents can cause severe interference. In this case, the installation and grounding methods shown in Figure 6-26 can be adopted. http://www.sensorok.com/tech/tech/dc/images/ld611.3.gif Figure 6-26: Sensor installed on a pipeline with strong stray currents. 1 – Measurement grounding ； 2 – Ground wire (16mm2 copper wire) ； 3 – Ground ring ； 4 – Insulated pipeline ； 5 – Connection wire (16mm2 copper wire): An insulated tube is attached to each end of the sensor, and a grounding ring is installed between the sensor and the insulated tube. As with standard installation and grounding methods, the grounding ring is connected together with the sensor’s flange to a well-grounded grounding rod. The process pipes on both sides of the insulated pipe are short-circuited separately using connecting wires. In this way, the leakage current is mainly diverted through the connecting copper wires, resulting in a **reduction** of the interference introduced into the sensor’s signal circuit by the liquid being tested. When the installation environment is subject to strong leakage current and electric field effects, the sensor must be grounded separately. The ground wire is made of multi-strand copper wire with a total cross-sectional area of not less than 16 mm2, and is connected to a grounding rod buried at a certain depth. (5) Insulated installation of sensors and pipes: As mentioned earlier, on cathodic protection pipes and pipes subject to strong stray currents, an electrically insulated installation method must be used between the sensors and the pipes. Sometimes, when there is a large polarization potential between the pipeline and the fluid, it is also necessary to use a connection method that electrically isolates the sensor from the pipeline.

Theoretically, cathodic protection and protective grounding are contradictory; therefore, electromagnetic flowmeters need to be insulated and equipped with separate grounding electrodes to eliminate induced electric potentials. . . . . . . . . . .