What is the smallest size iron pipe you can use for a 170′ length of a .5 psi piping system designed to carry 1600 cu.ft./hr of gas, gravity is .6 with a total pressure drop of ½” water column?

What is the smallest size iron pipe you can use for a 170′ length of a .5 psi piping system designed to carry 1600 cu.ft./hr of gas, gravity is .6 with a total pressure drop of ½” water column?