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Re:High Pressure after Online spalling

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Good afternoon Mrkimbrell. Thank you very much for your response.
Our only pressure transmitter is in the entrance of the heater, downstream the flow control valve. We have no other pressure indication between this point and the switch valve, so we can not determine whether the possible plugin is in the heater coils or in the pipe from the heater outlet flange to the switch valve.
We have not done a thermal scan of the heater coils after the spalling, as we are starting to know how our heater behaves when we do the on-line spalling.
Our heater has 18 F.G. burners and quite a lot of skin points from coil 4 at radiation zone to coil 30 at radiation ceiling. All of them show a big decrease in temperature, up to 80ºC before and after spalling, so we feel quite happy and confident at this point that the spalling is being very effective, but the bad point is that pressure increases when we put feed in again.
I will have in mind the possibility of an infrared thermography if the problem remains with more spallings.
When we close the feed valve at the beginning of the spalling we also close the flushing to the pressure transmitter (cold LCGO), and it remains closed until we put feed again once the online spalling is finished.
I know there are coker units where the flushing is not used for instruments to minimize throughput ratio with no measurement problems.
Does someone know if pressure drop mentioned effect after online spalling could be related with instrument flushing?
Kind Regards to everyone.

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