Importance of Pipeline Roughness in Greenfield and Expansion Projects

Arensman, Dennis (Enterprise Products)



Potential routes, pipeline sizes, pump spacing, and numerous more details are scrutinized when designing Greenfield and expansion pipeline projects. These details are analyzed to create an accurate cost estimate to determine the economics of building a new pipe. Billions of dollars are spent constructing pipelines based on these estimates with detailed studies. However, one important pipeline parameter is generally kept at a default value when designing Greenfield and expansion pipeline projects – pipeline roughness.

Absolute pipeline roughness of 0.0018 inch (0.04572 mm) is often selected by default based on published industry information for hydrocarbon liquids. In practice, default pipeline roughness can be shown to vary based on product when pipeline roughness is used as a tuning factor. Various friction factor equations can be selected to reduce the variation in tuned pipeline roughness. However, light hydrocarbon liquids are not well suited to existing friction factor equations. Pipeline pressure losses will be overestimated if the roughness value of 0.0018 inch (0.04572 mm) is used. Overestimating pressure losses results in overdesigning pipe and pump requirements for new pipelines. Proposed projects may fail to start due to excessive material costs and projects that do get completed may have installed equipment that is not used after construction. More research is needed in order to determine exact correlations between product type and friction factor equation results.

Introduction and background

Greenfield pipelines and expansions of existing pipelines are constantly analyzed. These projects are essential for providing pipeline access to newly developed oilfields and increasing transportation out of existing oilfields. Project budgets became much more restricted during the oil price collapse in 2015. As a result, projects to develop new Greenfield pipelines and to expand existing pipelines came under intensified scrutiny.

One way to improve the chance of a project’s success was to closely analyze the hydraulics of the projects. Close scrutiny of hydraulics from various projects revealed that pipeline roughness, which is used as a tuning factor, has consistently been kept at a default value of 0.0018 inches (0.04572 mm) and used the Colebrook-White friction factor equation for new liquid pipeline projects. Evaluation of existing pipelines showed that a default pipeline roughness value of 0.0018 inches (0.04572 mm) worked well for heavier hydrocarbon liquids. However, Natural Gas Liquids (NGLs) had tuned pipeline roughness values that were lower than the default value by as much as a magnitude of 10 with Colebrook-White. This observation showed that product type needed to be considered when deciding pipeline roughness for new pipeline design.