Hey Nickvil...
It looks like something is not correct.. Its is not possible to have LCO IBP > HVY NAP End point, if your Lab is using same Distillation method to characterise for both.
Check the distillation method your are carrying out on both the products.
Suhas
rgrokkam
Water washing.
The exchangers which you are talking abt are before or after the Desalter. I think this exchanger fouled due to salts depositions from crude and at high temp these salts get precipitates out. So if you put water into it helps in removal of salts.
Find Fouling factor...