At present, the gas engineers use the simple Campbell’s equation to determine the proper length of parallel gas pipelines. The Campbell’s equation was proposed for horizontal pipelines with assumption that the gas compressibility factor and temperature throughout the pipeline are constant. Therefore the Campbell’s equation has notable error for inclined pipeline. In this paper the Campbell’s equation was extended in a way that it can be used for inclined pipelines. In order to make a comparison between the extended and original equations, a pipeline with different slopes was used. The results show that in the case of using pipeline with more than 2 degrees in slope, the resultant error is increased to 11 percent by using original Campbell’s equation. For validation of the extended Campbell’s equation, the results of this equation are compared to the results of HYSYS software (version 3.1) in which the temperature and gas compressibility factor are not considered constant. The results indicate that the average error of the extended equation is less than 2 percent.

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