An important variable considered in the sizing and design of pipelines is the absolute roughness of the pipe, which is used to calculate the pressure loss during fluid flow through the pipeline. The default value for absolute roughness of commercial steel pipe, as generally used in the industry, is 1800 micro-inch (or 46 micro-metre). This value appears to have originated from studies carried out by scientists such as Pigott, Colebrook, Moody and Nikuradse, among others, more than half a century ago. However, pipe manufacturing and treatment methods have become more advanced since these studies were performed. Indeed, recent studies have suggested overestimation of the pressure drop across a pipeline during design resulting in less accurate cost estimates for pipeline projects.
In this study, the absolute roughness of various pipeline samples was measured using a Mitutoyo SJ-201 surface roughness gauge. The samples were obtained from commercial steel pipes of different diameters that had been manufactured with various methods including: seamless hot-rolling, cold-drawing, cold pilgering, hot expanding, and welded HFIW and DSAW processes. Absolute roughness values were also obtained for pipes treated differently by: simulated post-weld heat treatments, sandblasting, and ultrasonic cleaning. Recorded average pipe roughness values ranged from 57 micro-inch for stainless steel pipe to 1034 micro-inch for heat treated carbon steel pipe. All measured values were less than the generally used 1800 micro-inch (or 46 micro-metre) value. There did not appear to be any correlation between the diameter of the pipe sample and the absolute roughness observed. The pipes that were manufactured using the hot-rolled method typically showed higher absolute roughness values. Furthermore, simulated post-weld heat treatments at higher temperatures correlated with higher absolute roughness values for heat treated pipe.
This paper also examined the impact of applying a range of measured absolute roughness values during the design of liquid and gas pipelines. The pipeline pressure loss was calculated using different roughness values for case studies involving multiple crude oil pipelines and a natural gas pipeline. The results indicated that gas pipelines are more sensitive to the absolute roughness value. Furthermore, liquid pipelines with relatively high Reynolds number are more likely to undergo noticeable capacity loss because of absolute roughness increases due to pipe degradation.
