【Daily Question 20090414】What types of failures have occurred with turbine flowmeters in field use, and how were they resolved?
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What types of failures have occurred with turbine flowmeters during use in the field, and how were they resolved? Format: Installation site: Fault symptoms: Cause of the fault: Solution: Pay attention to the posting format; original posts are encouraged. Spamming is not allowed. Original posts earn 10 points, while copied or spam posts result in a deduction of 10 points.
Competing for a sofa: Installation site: Soft water flow rate. Fault symptom: Unstable data output. Cause of the fault: Debris (film) in the turbine flow meter sensor. Solution: Clean it thoroughly when the machine is stopped.
Installation site: Flow rate of demineralized water from the power plant. Fault phenomenon: After three months of operation, at the same valve opening, the flow rate was low. The flow rate at full open position of the control valve cannot be increased; it meets the design specifications for flow rate. Cause of the fault: During maintenance in accordance with the procedures, it was found that a cable insulation piece measuring 0.5 meters in length was blocking the area in front of the instrument flange ； Solution: Rinsing the pipeline again for replacement; normal operation is restored after installation.
I. No display when the fluid is flowing normally, and the total count does not increase
1. Check for any breaks or poor contacts in the power cable, fuses, function selection switch, and signal lines.
2. Inspect the printed circuit boards and contacts inside the display unit for any issues with connections.
3. Examine the detection coil.
4. Check for internal faults in the sensor. If items 1–3 show no problems or the faults have been resolved, but the issue persists, then the fault lies within the sensor’s flow channel. Check whether the impeller is touching the inner wall of the sensor, whether there are any foreign objects stuck there, and whether there are any obstructions or damage to the shaft and bearings.
Solutions:
1. Use an ohmmeter to locate the faulty point.
2. To check for issues with the printed circuit board, replace it with a “spare board” and conduct a thorough inspection after that.
3. Mark the position of the detection coil on the sensor unit. Remove the detection head and move an iron piece quickly beneath it; if the count does not increase, check for broken wires or loose solder joints in the coil.
4. Remove any foreign objects and clean or replace damaged parts. After restoration, blow air or manually move the impeller to ensure no friction sounds are heard. After replacing parts such as bearings, recalibrate the instrument to obtain a new coefficient.
II. The flow rate display gradually decreases despite no attempt to reduce the flow rate
1. Check whether the filter is clogged. An increased pressure difference across the filter indicates that foreign objects are blocking it.
2. The valve in the flow sensor’s pipeline may have a loose valve core, causing the valve opening to decrease automatically.
3. Foreign objects may be blocking the sensor’s impeller or entering the bearing gaps, increasing resistance and slowing down rotation.
Solutions:
1. Clean the filter.
2. Determine whether adjustments to the valve handle are effective; repair or replace the valve if necessary.
3. Remove the sensor and clean it; recalibrate if needed.
III. The fluid is not flowing, yet the flow rate display shows a non-zero value or the reading is unstable
1. Poor shielding and grounding of the transmission lines allow external interference signals to enter the display unit’s input terminal.
2. Vibration in the pipes causes the impeller to shake, generating incorrect signals.
3. Leaks due to a poorly sealed stop valve cause the instrument to display a false leak rate.
4. Interference may arise from damaged electronic components or wiring inside the display unit.
Solutions:
1. Check that the shielding layer and the display unit’s terminals are properly grounded.
2. Strengthen the pipelines or add supports before and after the sensor to prevent vibration.
3. Repair or replace the valve.
4. Use the “short-circuit method” or check each component individually to identify the source of interference and locate the fault.
IV. There is a significant difference between the display value and the value estimated based on experience
1. Internal faults in the sensor’s flow channel, such as corrosion, severe wear, or blockages caused by foreign objects, can disrupt the impeller’s rotation, leading to changes in the instrument’s coefficient. Corrosion or impact on the blades can also cause deformation at the tips, affecting the ability to properly cut through magnetic fields. This, in turn, leads to abnormal signals from the detection coil and changes in the instrument’s coefficient. High or low fluid temperatures, as well as expansion or contraction of the shaft and bearings, can also cause excessive gaps that disrupt the impeller’s rotation, resulting in changes in the instrument’s coefficient. 2. Insufficient back pressure at the sensor, resulting in cavitation which affects the rotation of the impeller.
3. Issues related to flow within the pipes, such as reverse flow due to the absence of check valves, poor sealing of bypass valves leading to leaks, significant distortions in flow velocity upstream of the sensor (caused by valves not being fully open), or fluctuations in liquid viscosity due to temperature changes.
4. Internal faults in the display unit.
5. The permanent magnetic elements in the detector may lose their magnetism over time; when their magnetic strength decreases to a certain level, it also affects the measurement values.
6. The actual flow rate passing through the sensor exceeds the specified range for that sensor.
Solutions:
1–4. Identify the cause of the fault and devise solutions specific to that cause.
5. Replace the elements that have lost their magnetism.
6. Replace the sensor with an appropriate one
1. Check for any breaks or poor contacts in the power cable, fuses, function selection switch, and signal lines.
2. Inspect the printed circuit boards and contacts inside the display unit for any issues with connections.
3. Examine the detection coil.
4. Check for internal faults in the sensor. If items 1–3 show no problems or the faults have been resolved, but the issue persists, then the fault lies within the sensor’s flow channel. Check whether the impeller is touching the inner wall of the sensor, whether there are any foreign objects stuck there, and whether there are any obstructions or damage to the shaft and bearings.
Solutions:
1. Use an ohmmeter to locate the faulty point.
2. To check for issues with the printed circuit board, replace it with a “spare board” and conduct a thorough inspection after that.
3. Mark the position of the detection coil on the sensor unit. Remove the detection head and move an iron piece quickly beneath it; if the count does not increase, check for broken wires or loose solder joints in the coil.
4. Remove any foreign objects and clean or replace damaged parts. After restoration, blow air or manually move the impeller to ensure no friction sounds are heard. After replacing parts such as bearings, recalibrate the instrument to obtain a new coefficient.
II. The flow rate display gradually decreases despite no attempt to reduce the flow rate
1. Check whether the filter is clogged. An increased pressure difference across the filter indicates that foreign objects are blocking it.
2. The valve in the flow sensor’s pipeline may have a loose valve core, causing the valve opening to decrease automatically.
3. Foreign objects may be blocking the sensor’s impeller or entering the bearing gaps, increasing resistance and slowing down rotation.
Solutions:
1. Clean the filter.
2. Determine whether adjustments to the valve handle are effective; repair or replace the valve if necessary.
3. Remove the sensor and clean it; recalibrate if needed.
III. The fluid is not flowing, yet the flow rate display shows a non-zero value or the reading is unstable
1. Poor shielding and grounding of the transmission lines allow external interference signals to enter the display unit’s input terminal.
2. Vibration in the pipes causes the impeller to shake, generating incorrect signals.
3. Leaks due to a poorly sealed stop valve cause the instrument to display a false leak rate.
4. Interference may arise from damaged electronic components or wiring inside the display unit.
Solutions:
1. Check that the shielding layer and the display unit’s terminals are properly grounded.
2. Strengthen the pipelines or add supports before and after the sensor to prevent vibration.
3. Repair or replace the valve.
4. Use the “short-circuit method” or check each component individually to identify the source of interference and locate the fault.
IV. There is a significant difference between the display value and the value estimated based on experience
1. Internal faults in the sensor’s flow channel, such as corrosion, severe wear, or blockages caused by foreign objects, can disrupt the impeller’s rotation, leading to changes in the instrument’s coefficient. Corrosion or impact on the blades can also cause deformation at the tips, affecting the ability to properly cut through magnetic fields. This, in turn, leads to abnormal signals from the detection coil and changes in the instrument’s coefficient. High or low fluid temperatures, as well as expansion or contraction of the shaft and bearings, can also cause excessive gaps that disrupt the impeller’s rotation, resulting in changes in the instrument’s coefficient. 2. Insufficient back pressure at the sensor, resulting in cavitation which affects the rotation of the impeller.
3. Issues related to flow within the pipes, such as reverse flow due to the absence of check valves, poor sealing of bypass valves leading to leaks, significant distortions in flow velocity upstream of the sensor (caused by valves not being fully open), or fluctuations in liquid viscosity due to temperature changes.
4. Internal faults in the display unit.
5. The permanent magnetic elements in the detector may lose their magnetism over time; when their magnetic strength decreases to a certain level, it also affects the measurement values.
6. The actual flow rate passing through the sensor exceeds the specified range for that sensor.
Solutions:
1–4. Identify the cause of the fault and devise solutions specific to that cause.
5. Replace the elements that have lost their magnetism.
6. Replace the sensor with an appropriate one
Installation site: Inside the oil field transportation and metering station. Fault phenomenon: A large discrepancy exists between the measured quantity of crude oil exported and that measured by the receiving unit. Cause of the fault: The presence of certain decomposed gases, which affects accurate metering. Solution: Adjust the heating temperature of the crude oil to reduce the generation of such decomposed gases
Installation site: Measurement of refined oil flow. Fault phenomenon: Unstable flow, intermittent operation, with fluctuations in flow rate. Cause of the fault: Wear and jamming of the bearings in the turbine flow meter due to prolonged operation. Solution: Replace them； When selecting a turbine flowmeter, special attention must be paid to ensuring that the performance of the bearings meets the requirements of the operating conditions and the properties of the medium
Installation site: Circulating water flow rate. Fault symptom: Unstable data output. Cause of the fault: Too close to the pump outlet. Solution: Add supports for fixing the pipes before and after the transmitter