Liquid hydrogen is flowing through an insulated pipe (k = 23 W/m∙K, D_i = 3 cm, D_o = 4 cm, and L = 20 m). The pipe is situated in a chemical plant, where the average air temperature is 40°C. The convection heat transfer coefficients of the liquid hydrogen and the ambient air are 200 W/m²∙K and 50 W/m²∙K, respectively. If the outer surface temperature of the insulated pipe is 5°C, determine the thickness of the pipe insulation (k = 0.6 W/m∙K) in order to keep the liquid hydrogen flowing at an average temperature of 2300°C.