A Guide To Water Well Casing and Screen Selection   -   8

Much water well casing used worldwide is designed and manufactured in accordance with transmission pipe specifications and requirements. Therefor, it is important to understand the different end uses and problems which may result from incorrect selection.

4.6  Corrision

Raw material used in the manufacture of line pipe does not normally contain any added elements to give protection against corrosion. It is easier and more effective to provide safeguards in the form of protective coatings. Insulating coatings must be completely perfect, since a random bare spot corrodes at a greater rate than if the pipe were completely unprotected. The use of protective coatings on water well casing is ineffective or harmful due to abrasion incurred during handling, installing, perforating and use. Coating of the field connection is impossible to ally properly. Consequently, the corrosion resistance of well casing must be built into the steel itself.

4.7  Dimensions

Seamless, ERW and press formed pipe diameters are controlled externally. Accordingly, nominal diameters are measured by the outside diameters (O.D.), and the inside diameters (I.D.) varies with the wall thickness of the pipe. For instance, 16 inch O.D. pipe .3125 inch thick would have an inside diameter of only 15.375 inches. Casing diameter is generally selected according to pump size. Therefore, it is often possible to substitute and I.D. size for the next larger O.D. size; for example, 16 inch I.D. instead of 18 inch O.D. Also, since tools required for the construction and repair of water wells work through the interior of the casing, it is appropriate to standardize on inside diameter rather than on outside diameter.

4.8  Availability

Transmission line pipe is ordinarily stocked in double random (38-45 ft) lengths. Occasionally, single random (16-22 ft) joints are produced. Incompatibility with the handling capabilities of any particular drilling rig can result in additional cost and installation lost time.

Since diameter changeovers in seamless, ERW and press formed manufacturing processes are relatively time consuming and expensive, efficiency requires lengthy runs of a given diameter. Thus, availability to a well drilling contractor depends on existing stocks. Moreover, integrated steel mills usually do not manufacture wall thicknesses less than .1875 inch in 8 inch and 10 inch diameters or less than .250 inch in diameters of 12 inches and larger.

4.9  Substandard Pipe

Substandard pipe manufactured from    laminated steel has substantially    reduced collapsing strength.

Line pipe produced to API and other specifications must be subjected to various tests during and following manufacture. In recent years, some pipe which has failed these required tests has been sold as water well casing. Among the names applied to this product are: reject, substandard, limited service and structural pipe. Since quality often means the difference between success and failure, it is to the users' interest to be aware of the potential danger. Since substandard pipe is distributed at discounted prices, the manufacturer disclaims responsibility for this inferior material.

A large proportion of rejected pipe has failed tests to determine weld soundness. Under these circumstances, the stresses of installation or perforating may cause a seam to split, allowing formation material to enter the well.

Pipe may be rejected for reasons other than faulty welding. Variations in diameter or non-uniform wall thickness are frequently cited. It is to the interest of those concerned to consider the relationship of quality and responsibility to the ultimate cost.

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