A new industrial plant requires a supply of water at a rate of $5.7 \mathrm{~m}^{3} / \mathrm{min}$. The pressure in the water main is $800 \mathrm{kPa}$, and it is $50 \mathrm{~m}$ from the plant. The line from the main to the plant will have $65 \mathrm{~m}$ of galvanized iron pipe, four standard elbows, and two gate valves. If the water pressure at the plant must be no less than $500 \mathrm{kPa}$, what diameter pipe must be used?