Veerasamy Venkatesan Forum Moderator 19 Posts
Re: Do instrument tap-offs on a steam line cause accuracy issues?21 January 2019 at 2:07pm
It is a general practice to locate the flow nozzle in the pipe, with 6 - 8 diameters of straight pipe length on each side of the nozzle.
I have not come across with the impact of inaccuracy due to instrument tap-off within that 6 - 8 diameter pipe length. Maybe I am unaware.
But we always try to verify the flow nozzle readings with other possible measurements, like, steam glow with BFW flow & calculated B/D water flow etc.
Since 650DN pipe is a very large one, (26" diameter pipe), my guess is the impacts of Instruments tap-offs should be minimal. However, there could be several other factors impacting the accuracy of flow nozzles.
Hence, I don't have a clear answer about the % of inaccuracy in a flow nozzle. May be some Flow Nozzle manufacturers, who deal with 20" to 30" diameter steam piping could give a better answer.
On a main steam line originating from steam generator (650DN), a flow nozzle has been located. On the downsteam of it starting from 200mm onwards the nozzle, almost 10 holes or tap offs have been made on the DN650 line for instrumentation related piping. The question is how much effect in percentage does these have on the accuracy of the flow readings?
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