Handling and Maintenance

Ease of transport, handling and installation are important considerations. These not only influence cost, but also are relevant to the selection of the type of casing and screen field connections.

Casing and screen should be designed to facilitate future rehabilitation, including cleaning, incrustation removal, redevelopment and repair. Another consideration is the possibility of future well deepening. Casing and screen diameter, as well as type and material selected, are influenced by the parameters.


Economy
Economy plays an important role in the engineering of any ground water producing installation. Considering water well materials, however, lower cost does not necessarily mean the least durable or efficient. On the other hand, the most expensive materials do not always produce the best results. Optimum balance between design and price requires a knowledge of those special conditions pertaining to the well, and comparison of available products. An example is analysis of the required well life. This is becoming more important, particularly in the case of municipal wells. Inflation, the lack of proper sites and the difficulty of transporting, setting up and operating water well construction equipment in restricted urban locations, have dictated the use of better well designs, and, in many cases, more durable materials for extra longevity.


Steel Casing

By far most common casing and screen material is steel. Steel is easily formed into tubes – the ideal casing and screen configuration. When exposed to the atmosphere, water or soils, steel builds up a protective oxide coating that assures long life under mildly corrosive conditions. Under more extreme conditions, steels with special chemistries or alloys, such as the stainless steel grades, are available for greater life or permanent protection. Steel possesses the high yield and tensile strengths required for water well use. Of particular importance are the characteristics of elasticity and resiliency inherent in steel. Casings and screens may be subjected to underground external forces after installation. Earthquakes or subterranean earth movements tend to displace them. Steel permits absorption of many forces with maintenance of structural integrity. Another important quality of steel is its weldability. This facilitates proper field installation.


Non-ferrous Materials
In some areas, non-ferrous materials have been used with some success in wells. The most common are cement, plastic and fiberglass. Concrete casing can be used in some shallow installations, but its weight, difficulty in handling and special connecting-joint requirements have rendered it impractical for general use.

Plastic has been used successfully in shallow domestic wells up to 8 inches in diameter. Connection, collapsing and tensile strength requirements are relatively modest in these types of installations. Plastic has not yet been found to be a suitable material for large-diameter or deep wells because of cost and strength considerations.

Fiberglass has found use in some areas where waters are known to be corrosive. Again, connecting-joint limitations have restricted its use to shallow and medium depth wells. While mechanical joints designed for this end use have been adequate for installation purposes, they have been known to present difficulties in well rehabilitation. Fiberglass also is costly, particularly for the larger diameter, heavier wall fiberglass tubes required in high production wells.
This article series is provided through the courtesy of Roscoe Moss Co., a leading manufacturer of water well casings and screens. Courtesy National Drillers