A cast iron pipe of diameter $600\: mm$ and length $400\: m$ carries water from a tank and discharges freely into air at a point $4.5\: m$ below the water surface in the tank. The friction factor of the pipe is $0.018$. Consider acceleration due to gravity as $9.81\: m/s^2$. The velocity of the flow in pipe (in $m/s$, round off to two decimal places) is ________.