The fundamental equations which describe the flow through gas and liquid pipelines are formally identical. However, the wide gap between the compressibility ranges of gases and liquids leads to quite different transport characteristics for both kinds of media. While for oil pipelines and pump stations specific topics like batch operation, surges, and possible slack line scenarios have to be considered, a detailed design calculation for gas pipelines and compressor stations require substantial knowledge of real gas thermodynamics. The general relationship between pressure difference along a pipeline section and volume flow is given through the combination of mass conservation and the force balance. An extension of Bernoulli´s law applies to steady-state liquid flow with non-constant density profile (e.g. batch operation), whereas Ferguson´s formula is valid for gas flow through pipelines. The dynamic behaviour of a pipeline system is calculated by real time simulation of a complete model including all existing station elements like pumps, valves, etc. in terms of a one by one mapping of the real world. The energy equation is the link between flow mechanics and thermodynamics and is the basis for the temperature model which again is formally identical for liquid and gas pipelines. Especially for gas pipelines a realistic temperature model turns out to be essential. Heat exchange with the environment shows considerable differences for onshore and offshore pipelines.
This article briefly outlines some layout and design considerations for transport capacity and power consumption of oil and gas pipelines. The impact of uncertainties of assumptions on the results is shown with examples.