Pipe roughness related to pipe material at complete turbulent flow, as per Crane appendix A-23.

Piping Material mm inch
Drawn tubing, pipe roughness 0.0015 0.00005905
Commercial steel, pipe roughness 0.05 0.001968
Cast iron, pipe roughness 0.12 - 0.3 0.004724  -   0.01181
Riveted steel, pipe roughness 0.91 - 9.1 0.035827  -   0.35827