Shale Shaker Selection
This section provides additional thoughts and considerations concerning solids-control equipment. The practical operational guidelines for equipment discussed here may not apply to all drilling applications. These guidelines (in italics) were developed as part of API RP 13C. The discussion beneath each captures some of the comments by committee members as they debated the guideline before approval.
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)’’).
Turbulent flow is detrimental to a centrifugal pump during handling of abrasive fluids. The drilling industry has standardized centrifugal pumps with concentric casings and wide impellers, a design that has proven to offer less turbulence and greatest pump life. The walls of a concentric style of casing (Figure 1) are an equal distance from the impeller throughout the impeller circumference, resulting in a smooth flow pattern. A volute style of casing (Figure 2) has a cutwater point that disturbs the fluid flow pattern, creating an eddy.