Within the petroleum industry centrifugal pumps are necessary in order to process fluids especially hydrocarbons. Another important application within the petroleum industry is in the mud circuit on a drilling rig. On drilling rigs, mud which consists mainly of water and bentonite as well as of several different additives depending on many different factors is used. The heart of the mud circuit is the mud pump which is in general a high pressure piston pump. It provides the major part of head to overcome the system’s resistance. The mud is pumped through a piping system to the derrick and through the standpipe to a definite high. Now through the kelly hose via the gooseneck into the upper kelly cock. It flows through the Kelly and the lower kelly cock into the drill string down the borehole. At its end, the mud leaves the drilling collars through the drilling bit.
In addition to selecting the proper suction pipe diameter and having adequate NPSHA, the submergence level and suction pipe configuration must be considered. Submergence level is the depth of the suction pipe inlet below the liquid surface. If an inadequate submergence level exists, an air vortex will form that extends from the liquid surface to the inlet of the suction pipe. This will introduce air into the system, resulting in either turbulent flow patterns or vapor locking of the pump. Amount of submergence required varies with velocity of the fluid. Fluid velocity is controlled by flow rate and pipe diameter. Refer to Figure 1. to determine submergence required based on fluid velocity (fluid velocity can be found in Friction Loss (Centrifugal Pumps Velocity Measured), in the column ‘‘V (ft/sec)’’).
Net Positive Suction Head ( NPSH ) is extremely important to the operation of a centrifugal pump. Factors that affect NPSH are atmospheric pressure, suction line friction loss, elevation, fluid temperature and SG.