Gas pipeline design is greatly affected by the amount of a pressure drop anticipated during different phases of natural gas transportation. The outlet pressure can be computed by a common gas pipeline equation such as Weymouth or Panhandle formulas at the desired flow rate and pipe size. In addition to selecting the proper size of a pipeline, the compressor capacity and the related cost are determined based on the discharge pressure. The flow rate, in these equations, is defined in terms of a turbulent friction factor. The fiiction factor relationship approximates the turbulent behavior as a :fi.mction of surface roughness in the pipe. An efficiency factor is employed in the equations for adjusting deviations in the pressure drop calculations. Existence of a sub layer, due to the pipe surface condition and accumulations of condensate, can generate cases that cannot be defmed properly by the use a single friction factor. The proper sizing of a pipeline can be improved by defming the ranges of errors introduced with the use of different friction factors.

Different correlations exist for the calculation of the friction factor, f, as a function of Reynold's number and the relative roughness of the pipe. The formulas for f either require an iterative procedure or may be solved explicitly. Also, each friction factor correlation exists with its own valid limits regarding Reynold's number and relative roughness. Thus, some equations are simple to use but not accurate and some are accurate but not easy to incorporate into the fmal equation.

In this study, the effect of the friction factor on the pressure drop calculations for gas flow is presented. Various correlations for friction factors are utilized to demonstrate their impact on the design of natural gas pipelines. Also, a summary and a comparison of results are presented for different flow rates, pipe sizes, and for field data.

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