This document provides the step-by-step calculation of the design wall thickness of a pipe according to ASME B31.4. It involves determining the allowable stress, internal design pressure and diameter to calculate the minimum required thickness. Additional thickness is then added for corrosion allowance, thread depth etc. to determine the nominal wall thickness. The closest commercial schedule is then selected, which meets the minimum calculated nominal thickness while also considering fabrication tolerances. Finally, the results are analyzed to verify their logical and appropriate order of magnitude and specifications are prepared for procurement.