Steam at T$1=320\backslash$deg C flows in a cast iron pipe $($k $=80$ W$/$m $.\backslash$deg C$)$ whose innerand outer diameters are D$1=5$ cm and D$2=5\mathrm{.}5$ cm$,$ respectively. The pipe iscovered with $3-$cm$-$thick glass wool insulation with k $=0\mathrm{.}05$ W$/$m $\backslash$deg C$.$ Heat is lost to the surroundings at To$2=5\backslash$deg C by natural convection and radiation, with