A Guide To Water Well Casing and Screen Selection   -   22

8.0  END CONNECTIONS AND ACCESSORIES

No discussion of water well casings and screens can be considered complete without giving proper attention to the connections through which they are joined in the field. The tensile strength of any column is limited by the strength of the connections between its components. Observation of well failures shows that most involve casing or screen rupture, collapse or deformation. Frequently the problem originates in the connecting joints.

In addition to mechanical strength requirements, the following factors should be considered in connecting joint design: smoothness of internal wall, minimization of external diameter, alignment, ease of installation, and economy.

The four major types of connections used in the water well industry are threaded and coupled joints, joints with square or beveled plain cut ends, bell and spigot joints for lap welding and joints with welding collard for lap welding.

8.1  Threaded and Coupled

Threaded and coupled connections are commonly employed in four inch and smaller diameter wells where they provide relatively inexpensive, fast and convenient connections. Strength requirements in such domestic low production wells are not critical. In larger diameter the cost of threaded and coupled joints increases, and they are not generally available larger than 12 inches.

8.2  Plain Ends

Casing and screen joints prepared with square ends for welding are generally satisfactory up to .1875 inch wall thickness. With heavier wall thicknesses the ends should be beveled to facilitate weld penetration, leaving approximately .125 inch flat. Advantages of these connections are economy and smoothness of the external diameter, which minimizes tendency of gravel to bridge in gravel envelope wells. Disadvantages lie in greater assembly time and the difficulty of properly welding casing in the vertical position. A further problem occurs if removal and reassembly is required. The connection must be cut with a torch as withdrawn, and the joint prepared for proper reassembly by machining, if possible, a time-consuming and expensive process.

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