## Principles of Gas Pipeline Flow Hydraulics

## By Joe Honeywell

### Introduction

Engineers are frequently asked to size a pipeline diameter, calculate the pressure drop or determine the gas throughput. Computer software is often used and the only thing needed is to input the given conditions. But how accurate are the results? What happens if the given conditions are not accurate or if they change? These questions become major concerns if they result in costly decisions or unacceptable risks.

Another challenge an engineer may face is determining how sensitive the calculated results are to small variations to the input parameters. For example, since the pressure drop is related to the pipe roughness, how accurate should the roughness be to accurately predict the results? How will small variations in roughness affect the flow rate and power requirements? Since there are many input parameters, does each have a similar effect on the results? More importantly, what assumptions and constraints, if any, should be placed on the results? These questions and many more will be evaluated.

This paper will review the principles of gas flow in pipelines. It will examine the assumptions and parameters that affect pipeline performance. The five primary gas flow equations commonly used throughout industry will be reviewed. A comparison of results and applications for which they are best suited will be given. Also reviewed are the principles of sizing pipelines, practicable limitations and economic considerations. A limited number of examples are given to illustrate the calculations procedures.

It is hoped that this review of gas pipeline hydraulics will give engineers a better understanding of the results provided by the computer software. Engineers will better understand the complexities of input parameters, their effect on the results, the limitations they pose on pipeline sizing, gas throughput and pressure drop calculations. Most importantly, engineers will understand the basic principles and assumptions that are part of gas pipeline flow hydraulics.

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