It behavior is the same in two or more heaters, then look for common factors: feed quality is the first everybody thinks about, but there are others like velocity steam or water quality (any possible contamination added, especially chlorides, caustic)… If it is an isolated event, then look for recent changes, especially if an upset happened before the sudden rise…Good luck

what about the drop pressure for this pass? are you measure the skin temperature with some pyrometer?

what about the others variable, flow,inlet pressure, delta P, COT, fuel gas , burner behavior, the other skin temperature because if this real you have near to do an online spalling; must be a coke up the pass if this only happened in this only pass, can be a loss a flow, velocity steam or BFW , pattern burner,etc

Dear Espana,
Others variables like  flow (constant),inlet pressure (raising with delta P), delta P (raising with COT), COT (constant), fuel gas (raising with skin) , burner behavior (ok). We did online spalling for this pass, but not successful;
This pass some time gives 4 month run length & some time 25 days. We doubted feed quality, but other pass & heaters are normal. Any other reasons???? like Na deposits only in this passs?? is it possible?///

Dear Espana,
Others variables like  flow (constant),inlet pressure (raising with delta P), delta P (raising with skin), COT (constant), fuel gas (raising with skin) , burner behavior (ok). We did online spalling for this pass, but not successful;
This pass some time gives 4 month run length & some time 25 days. We doubted feed quality, but other pass & heaters are normal. Any other reasons???? like Na deposits only in this passs?? is it possible?///

Is the temperature real on that pass?  Loose Thermocouple Connection?

I would check the instruments (again) to check if the pass flow is correct. A lower flow in one pass can make it coke up faster than the others. Also check the burner fuel gas flow, you might be heating up the coil more in this pass than the others.You said this pass has given you problems in the past, have you done infrared imaging of the radiation section coils ? Have you compared the termocouple temps to infrared imaging temps in the same tube section ? If your spalling was not succesful you could have a spalling steam/ velocity steam flow problem in that pass, again check your instrumentation.
 
Hope this helps
 
CG

all thermocouples in the radiation box is increasing for this pass. Temperature rise also not from the start of run, for two or three weeks it will run normally (0.5 to 0.7 deg C/day) then suddenly it will rise like anything (40 degC/day). then we r forced to reduce passflows and COT to improve the runlength

How many tubeskin thermocouples does your heater have per pass ?
 
In what locations ?
 
Regards
 
CG

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