Find the most economical diameter of Sch. 40 commercial steel pipe that would be needed to transport a petroleum fraction with a viscosity of $60 \mathrm{cP}$ and $\mathrm{SG}$ of 1.3 at a rate of $1500 \mathrm{gpm}$. The economic life of the pipeline is 30 years, the cost of energy is $\$ 0.08 / \mathrm{kWh}$, and the pump efficiency is $60 %$. The cost of pipe is $\$ 20 / \mathrm{ft}$ of length, per in. ID. What would be the most economical diameter to use if the pipe is stainless steel at a cost of $\$ 85 / \mathrm{ft}$ per in. ID, all other things being equal?