Measurements and Evaluation of Internal Wall Surface Roughness of Small Diameter Pipes for High Pressure Natural Gas Systems

The default roughness parameter values used in industry to determine the pressure loss through small diameter pipeline systems are much higher than the values employed in typical large diameter gas transmission and lateral systems. It is uncertain whether these higher roughness values are due to higher topological roughness of the internal wall of the small diameter pipes or if they are a result of other factors. Measurements were taken on 17 small diameter pipe samples in order to evaluate the pipe-wall roughness parameter. A model to calculate the effective roughness parameter, which takes into account pressure losses due to the measured roughness as well as internal welds and scaling, has been developed. The effective roughness parameter of these samples is found to range from 20.4 mu m to 62.911 mu m, an increase of 11.0 mu m to 23.3 mu m over the measured pipe-wall roughness parameter. This range of effective roughness parameters agrees well with the default range of 35 mu m to 65 mu m used in industry, as well as the literature quoted range for clean pipe of 40 mu m to 100 mu m. The measured roughness parameter on average increases with increasing nominal pipe size, a result that may be a characteristic of the extrusion or hot-rolling processes used to manufacture small diameter pipes. Additionally, there is a large variation in the measured roughness parameters of pipe samples of the same nominal pipe size, indicating that surface roughness can vary depending on the manufacturing source of these pipes.