A Guide To Water Well Casing and Screen Selection   -   6

4.0  MANUFACTURING PROCESSES AND END USE COMPARISONS

Water well use represents a very small percentage of the production of steel tubular products. Practically all steel pipe manufactured worldwide falls into two categories:

  1. Transmission (line) pipe for the conveyance of water, oil, or gas.
  2. Oil country tubular goods such as heavy wall tubing and drill pipe.

It is useful to review the major manufacturing processes of these materials and relate them to their primary purposes, as well as their potential for use as water well casing


4.1  Electric Resistance Welded

Electric resistance welded pipe forming Generally transmission pipe of diameters from 4 to 16 inches is produced by the electric resistance weld (ERW) process. First raw material in coil form (skelp) is unrolled and flattened. The skelp then moves through a series of forming rolls which stage by stage shape it into a cylinder. The seam is welded as it passes beneath rotating electrodes. Resistance encountered by the current at the seam edge heats the metal to a plastic state. Simultaneously pressure is applied, forging the edges together. The pipe then travels through a series of finishing rolls. These stages reduce the diameter slightly, assuring proper size and roundness. Since resistance-welded pipe use, it is manufactured in approximate 40-foot lengths for convenient field assembly.


4.2  Seamless

Oil country tubular goods, such as high pressure tubing and drill pipe, require thicknesses and chemistries which are difficult to weld by ordinary procedures. These products and other special purpose pipe and tubing in diameters 20 inches and smaller are usually manufactured by the seamless process. A billet of steel is heated to a plastic state and pierced by a spear or lance. The hollow billet is then gradually elongated as it is shaped over mandrils and sized by rollers until pipe is produced. For water well applications seamless pipe has no inherent advantage over welded pipe, and its higher cost is not justified. Furthermore, wall thickness uniformity is not as consistent as pipe or casing produced by other methods of manufacture.


4.3  Press Formed

Final stage press formingA substantial portion of transmission pipe 18 inches in diameter and larger is manufactured by the press forming process. This method is a three stage operation.

  1. In the first stage the edges of a flat steel plate are curved upward.
  2. The plate is then pressed by dies into the shape of a "U".
  3. In the final stage a third press closed the "U" to form a cylinder.
The seam is then welded by the submerged arc electric weld (SAW) process. SAW welding required the use of a bare wire electrode and a granular flux. Contact of the electrode and the seam to be welded creates an electric arc. As a welding head traverses the seam, wire and flux are continuously added. The function of flux is to shield the molten weld from atmospheric contamination and add alloys to the weld deposit. This process allows the weld puddle to be molten long enough to purge impurities.

SAW welds are strong, ductile and uniform. Their mechanical properties are equal to or superior to those of the base metal.


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