Water Nucleate Boiling possibility in a fire tube Boiler

jsaidy

Hi guys,
I'm designing a simple waste heat recovery Fire Tube Boiler. The Flue gas inside the tubes has an average temperature of 300 C (572 F).
The tubes are submerged in water at a pressure of 6 atm, this gives us the saturated steam temperature of 158.83 C ( 318 F).
I've calculated The overall Heat Transfer Coefficient of the HX

Uo=50 W/m2.K ( 8.8 Btu/hr.ft2.F) neglecting conductivity and water-tube transfer resistance

The Tube inside Heat Transfer Coefficient is :

hi=55 W/m2.K ( 9.7 )

I know that the nucleate boiling heat transfer coefficient is very High for the tube-water Side and i neglected it in the calculation of U.
I've been wondering if Nucleate Boiling of water is possible IN THE FIRST PLACE!

i appreciate your help