Incompressible flow\compressible flow and roughness

Hello, i want to do a simulation of methane gas in a pipe in order to determine the loss of pressure in it. However, i have faced two main problems:
1-Although methane gas is compressible, is an incompressible simualtion possible in a good approximation ?
2-I’d like to set a roughness height number for my simulation (initialy 0), however simscale refuse to fix the number chosen (roughness of steel around 0,2 mm 0,008) and stay at 0. Why ? and how can i modify it ?

A post was merged into an existing topic: Methane through a pipe