Flow meters can sometimes experience troubleshooting after being in normal operation for a period, due to changes in the flow conditions. Although the occurrence of such troubleshooting is not common, it should not be overlooked when analyzing potential causes.
Case Study : Oscillating Rubber Liner Piece in the Liquid Flow
This rare instance involved a rubber liner piece in the pipeline that detached and oscillated with the flow, creating pulsating flow. In a copper mining plant in Jiangxi, several electromagnetic flow meters were used to measure slurry containing powdered solids. The system had been running normally for years. However, in July 1998, one of the DN600 flow meters showed output fluctuations ranging from 50% to 100% of full scale.
Upon on-site inspection, the flow meter itself appeared to be functioning normally. Interviews and checks indicated no changes to the flow source, and no environmental disturbances had been introduced. Overall, the meter, installation, and environmental conditions were all in line with requirements. As it was not possible to stop the flow to inspect the hidden parts of the flow sensor and the surrounding pipeline, the troubleshooting could not be immediately identified.
It was only after over a month, when the plant shut down for maintenance, that the cause was discovered. A large section of the rubber liner in a U-shaped pipe downstream of the flow sensor had detached and was suspended inside the pipe. The liner oscillated with the liquid flow, creating flow disturbances. The flow meter faithfully detected these disturbances, resulting in fluctuating outputs. After replacing the U-shaped pipe, the severe output fluctuations stopped.
Case Study : Fish Swimming in the Pipeline Causing Signal Spikes
This case, reported from the US, involved a large-diameter electromagnetic flow meter monitoring the cooling seawater flow in a thermal power plant’s condenser. The flow meter occasionally showed large spikes on the recorded output. Several site inspections were conducted, but the transient noise causing these spikes could not be captured or traced, and no electrical noise sources were identified.
A suggestion was made that perhaps fish might be swimming inside the flow meter, but this was initially dismissed, as it was believed the fish could not have entered the pipeline due to the fine mesh screen in the discharge gate. However, after conducting an experiment, the flow meter was installed in a small tank, and a goldfish was placed near the sensor. The flow meter immediately registered sharp spikes in the output when the goldfish swam near it. Further investigation revealed that fish had indeed entered the discharge pipe via the mesh screen and had grown into larger fish, causing the fluctuations observed in the flow meter output.
Summary
These cases highlight the importance of considering changes in flow conditions, such as physical objects (like detached liners or fish), that can cause unexpected troubleshooting or signal disturbances in electromagnetic flow meters.
Leave a comment