Rarefied gas simulations have been performed to study the influence of sudden expansion and contraction complexities located in conventional tubes. Circular tubes have been modeled with different diameters (4-33.5 mm) and area ratio (12.43-64). A finite volume solver is used for carrying out the simulations at a wide range of Knudsen number from continuum to slip regime (6.46×10^-6 < Kn < 3.95×10^-2) and Reynolds number (74.89 and 177.87) at a wall temperature of 300 K. It is observed that pressure drop (ΔP) in sudden contraction is higher than sudden expansion for the same flow conditions. The eddy formed at junction corner of sudden expansion tube are much greater than that at sudden contraction. This study is applicable for designing low pumping power piping systems.