Pressure DropAn equation for the flow of liquids in a pipe was developed by Darcy in the early 18th Century and the equations, formulae and standards defined by Darçy are still valid today.
Pressure loss in valves and fittings is made up of both the friction loss within the valve or fitting itself and the additional loss upstream and downstream of the fitting above that which would have occurred in the absence of the fitting. Calculation of the pressure loss in a valve or fitting is based on experimental data. One approach is the use of a resistance factor for a given valve or fitting. The resistance coefficient is normally treated as a constant for a given valve or fitting under all flow conditions.
If the crude cools, excessive wax deposits in the pipeline can lower operating efficiency. In cases of extremely viscous crudes, flow can even be halted if the temperature is allowed to fail too low. Not only is the baiting of flow a problem, but restarting flow after such an occurrence can be difficult. To handle these special crudes, pipelines have been successfully installed and operated simply by insulating the pipelines, but other approaches include: