Reasons for inaccurate steam flow rate
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This post was last edited by kbx_a_b on 2010-5-28 00:01. There is a steam flow measurement: temperature is 200, pressure is 0.4 MPa; the measuring element used is a V-cone flow meter. The phenomenon observed is that initially, with some condensate present, the indication was basically normal, but it gradually decreased over several hours until eventually no indication was left. What’s going on exactly? I checked the positive and negative chambers of the V-cone flowmeter – they are correct, and the pressure lead pipes also have the right polarity. Please give me some advice! Thank you!
Could it be a problem with the three-valve assembly, or some other process-related issue?
Based on the provided parameters, since the medium is superheated steam, temperature and pressure compensation must be performed. Also, if the flow rate gradually decreases and reaches zero, there must be a problem with the measurement system. Check the pressure guiding tubes, valve assemblies, differential pressure transmitters, and other components; if everything is normal, then there is a problem with the V-cone. To be honest, I’ve never been a fan of V-cone flowmeters; although their principle is reliable, there are too many issues related to the reliability of the manufacturers.
This post was last edited by ROSEHOOD on 2010-5-28 09:36. Differential pressure flow meters generally have many issues related to their pipelines; it is necessary to examine the pipelines carefully, as well as the balance valves and condensation tanks. Everything must be done in accordance with the specified requirements. Nozzles are a better choice for measuring steam flow – V-type elements are not the best option, as they result in similar pressure losses to orifice plates, and they are also less safe
Such low-pressure nozzles are not suitable; orifice plates or vortex flow meters will do, and temperature and pressure compensation is necessary. Based on the phenomenon, it is estimated to be a problem with the measuring element. Please also share the final result, so that we can learn from it as well
I’d like to ask gently: could it be that there’s a leak in the positive and negative pressure chambers? Once the pressures in these chambers become equal, there will be no flow indication anymore
The V-cone differential pressure is too low; check if there is any leakage or blockage somewhere
After ruling out leaks, the problem could be: 1. The medium is low-pressure steam with a high water content; if the pressure measurement point is not positioned properly, this can cause the reading to increase or decrease gradually. 2. The instrument heating is unreasonable, causing the pressure transfer tube to overheat and leading to the evaporation of condensate. 3. Instrument drift. 4. The pressure guiding piping is unreasonable. The problem in question must lie within the measurement circuit; there should be no issues with the pressure-sensing elements. By following this line of thought and eliminating problems one by one, it is definitely possible to resolve the issue.
It is clear that you are a very experienced engineer. What are the main problems with the V-cone? I only know that the cone falls off when in use; what other disadvantages are there?
Reply to 9# backhamm1982: The main issue is the low reliability of the hardware; moreover, when a problem occurs with the cone inside the pipeline, it’s practically impossible to carry out maintenance. It is also very inconvenient to use in pipes with smaller and larger diameters.
We had an issue here where a conical flow meter kept showing zero readings. We’ve tried all the methods mentioned by the colleagues above; now we’ll take it apart during a shutdown to inspect the cone, and we’ll let everyone know the results once we have them!