A Guide To Water Well Casing and Screen Selection   -   7

4.4  Fabricated

Fabricated pipe cylinder forming Generally used for production of large diameter pipe for special end uses, this process is non-continuous and multistaged. Flat sheets or plates are first squared an sheared to the proper diameter requirements. In the second stage, longitudinal edges are preformed to the required pipe curvature. The steel is then driven between rolls, bending it into a cylinder. Seam welding is performed by the SAW process. Longer lengths, when required, are manufactured by welding together the necessary number of cylinders.


4.5  Spiral Weld

Spiral cylinder forming operation A newer pipe manufacturing technology involves fabricating a spiral seam tube. Skelp is first flattened and then formed into a cylinder between rolls or a circular-shaped cage or shoe. The seam is welded at the first point of strip contact. Most spiral tubes today are welded from both the inside and outside, assuring full weld penetration. The spiral system is a continuous operation and individual lengths are cut downstream of the producing equipment.

The spiral process offers special advantages. Wall thickness varies according to the thickness of raw material. Since skelp adheres to very close tolerances, pipe manufactured by the spiral and electric resistance weld processes is more uniform and accurate in wall thickness than pipe produced by the seamless and press forming methods. Spiral pipe mils are flexible, enabling the manufacture of pipe from many Seam stresses grades of steel and non-ferrous weldable metals. Non-scheduled diameters and thicknesses can be economically produced for water well installations where required. Another virtue of this system of pipe manufacturing is high product roundness and straightness. Also beneficial is the greater strength of submerged arc electric welded seams. This results from the reinforcement of the weld, and the fact that hoop stresses in a spiral seam tube are less than those in a straight seam tube due to the "bandage" effect, and distributed forces.

Inherent in the spiral method is the ability to form high strength, heavy wall, large diameter pipes currently required in the petroleum and gas industries. For that reason, most recently built facilities producing such products utilize this process.


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