A pipeline pump serves to overcome height differences (see Geodetic altitude) and pipe friction losses when transporting crude oil through piping (pipelines) from the area of production or tank farms to refineries and when supplying consumer areas with refined products such as petrol, jet fuel, fuel oil and diesel oil (through product pipelines).
They can also be used for pumping alkaline solution in gas scrubbers or as cavern pumps for flushing and filling salt domes. The above pump applications require pumps without a balancing device. See Fig. 1 Pipeline pump
Requirements for pipeline pumps
- Reliable operation: As a simple but robust construction is required, the number of stages is limited. The axial forces are balanced by impellers in back-to-back arrangement or by double-entry impellers (see Back-to-back impeller pump and Double-suction pump). See Figs. 1 and 2 Pipeline pump
- Straightforward assembly and dismantling: Easy access for replacing wear parts is given by the casing being split at shaft level (see Axially split design) and by the nozzles being arranged in the lower casing section. See Fig. 11 Pump casing
- High efficiency across as large an operating range as possible: This condition can be met by selecting multistage back-to-back impeller pumps or, especially for large flow rates, single-stage pumps with a double-entry impeller. The pumps are also suitable for parallel operation or series operation. The viscosity of the fluid handled must be considered at the time of selection.
- Adaptability to pump output requirements of future development stages by means of various internal parts: The pump can be adapted by changing the width or diameter of the impeller.
The crossover channels of pump casings of multistage pumps are hydraulically optimised. Replaceable bushes protect all running surfaces prone to wear. See Fig. 2 Pipeline pump
The shaft seals used are almost exclusively mechanical seals. Gland packings are also an option. The bearings can be rolling element bearings or plain bearings, or pivoted segmental thrust bearings for absorbing the axial thrust.
A flexible spacer-type shaft coupling is used so that the drive-end mechanical seal or the bearings can be replaced without removing the pump rotor. This does away with the need to shift or remove the drive from the baseplate (see Back pull-out design)
In virtually all cases a booster pump is installed, so that generally there is no requirement for an extremely low NPSH value. Pipeline pumps are usually operated fully automatically from a process control station.
Key values of a pipeline pump which require monitoring:
- Inlet pressure
- Bearing temperature
- Shaft seal pressure, leakage
- Fluid temperature
- Oil pressure upstream of the pivoted segmental thrust bearing
- Vibration amplitude for monitoring the bearings and the suction characteristics (with regard to cavitation)
When starting up the pump the sequence and timing of actions must be controlled: opening the suction-side gate valve, the discharge-side gate valve and the main gate valves of the pumping station as well as starting up the lubricating oil pump and the booster pump.