In a pharmaceutical plant, a copper pipe (kc = 400 W/m.K) with inner diameter of 20 mm and wall thickness of 2.5 mm is used for carrying liquid oxygen to a storage tank. The liquid oxygen flowing in the pipe has an average temperature of -200 oC and a convection heat transfer coefficient of 120 W/m2.K. The condition surrounding the pipe has an ambient air temperature of 20 oC and a combined heat transfer coefficient of 20 W/m2.K. If the dew point is 10 oC, determine the thickness of the insulation (ki=0.05 W/m.K) around the copper pipe to avoid condensation on the outer surface. Assume thermal contact resistance is negligible.