Fractionator overhead temperature simulation mismatching

[ASOTOR]

Hi, folks:
I'm performing a simulation of a Fractionator. Trying to match the simulation to field data, there is only one figure that is out of order: the overhead temperature, that is around 105ºC while the destilate 95% D-86 point is around 170ºC. The fractionator top pressure is around 0,6 barg. It is not clear whether there is an experimental error in this temperature measure although there is another temperature instrument reporting similar readings.
We have made temperature readings with a pirometer and figures are about 90-95ºC on the upper side at several points of the overhead pipe.
Historically, no corrosion or salt deposition was detected in the top of the column.
Does anyone would help me to understand this?
Thanks

 

[georgeverghese]

A D86 test runs at atmospheric pressure, while the column press is 1.6bar abs, so a pressure correction on the D86 end point would be indicated. Moreover, a 95% D86 point may not be close enough to the actual dew point temp - may 99%+ may be better - the error may be greater or smaller depending on the composition of the dewpoint vapor.