The relation between dynamics pressure and velocity is pd = ρf v2 / 2       where rohf is the density of fluid, pd is the dynamics pressure , v2 is square of fluid velocity. (use the units as you want but the units in both side of the equation must be equal), So you can obtain velocity from the previous equation since you know the pressure, the the discharge= velocity x area of pipe= velocity x (3.14/4) x square of diameter. (m3/sec or ft3/sec or wahtever you want according to the used unit system.(note that 1kg/cm2=98.0665 kpa and density of water is 1000 kg/m3)

Mamdouh El Haj Assad answer is correct. You have a pipe diameter of 300mm. If the flow is laminar, it is relatively easy to compute the flow rate once you have the pressure drop \Delta P over a given length of pipe L with radius R, based on Poiseuille's formula: Q=\frac{\pi \Delta P R^4}{8 \mu L}. If the flow is turbulent the formula is is bit more complicated and is called the Darcy–Weisbach equation. Saad El-Sayed has has referred to the Bernoulli equation which for steady inviscid flow is p+v^2/2=const ( ignoring gravitational effects). This will not hold if the flow in the pipe is laminar, and will not hold for dissipative turbulent flows in a pipe, which by definition are not inviscid.

Applying Bernoulli's equation near the pipe end and outside the pipe,you get the exit velocity which when multilied by cross sectional area provides the flow.Here it is around 1.6 m3/sec

I do agree with Dr. Tapan Mandal post.

Regards,

Emad