The internal surface absolute roughness influences the pressure drop along a gas pipeline significantly. In order to determine the proper roughness value of the pipeline, a numerical inverse calculation method is built. This method is applied to five large-diameter natural gas pipelines, which have different materials, operating pressure, service time and throughputs. As a result, the distribution of the absolute roughness values as well as their variations with service time, pipe material, and pipe diameter are obtained. The results show that the service time is the dominating factor influencing the absolute roughness. In the first five months of service, the roughness shows a value around 20 μm to 28 μm, dropping gradually with increasing service time, and reaching about 12 μm after one year. The findings of this article provide good references for both natural gas pipeline design and operation.
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