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Pipe and Pipe Installation Considerations     171


      Advantages                           Limitations
      1. Good internal and external corrosion   1. Susceptible to impact
         resistance in ordinary soils         damage
      2. Better abrasion resistance than   2. Resin selection is
         cement-based pipes                   important for some
      3. Light weight compared to alternative   chemicals
         materials
      4. Various pressure classes available for
         pressure pipe
      5. Excellent hydraulics due to smooth
         interior
      6. Cast pipe has fixed OD and gasketed
         joints that seal on OD
      7. Dimensionally stable for fluid service
         and weather exposure
      8. Very high compressive strength
         (10,000 to 15,000 psi) so ideal for
         jacking
     TABLE 4.16  GRP Advantages and Limitations



          4.7.5 Metallic Pipes
          Metallic pipes in present-day use include ductile iron pipe and steel
          pipe. The precursor to ductile iron was cast-iron pipe. Metallic pipes
          have traditionally been used in pressure applications, but some areas
          of North America use them for gravity sewer applications also. Most
          metallic pipes used in the past were installed by open-cut methods.
          Recent acceptance of trenchless technologies has led to the manufac-
          ture of metallic pipes with joints suited for pull-in or jacking installa-
          tions. Steel pipe with welded joints is a product of choice for large-
          diameter HDD applications (usually more than 22 in. diameters),
          horizontal auger boring (HAB), and pipe-ramming (PR) projects. See
          specific chapters in this book for more information on these methods.
          Ductile Iron Pipe
          Ductile iron pipe was developed in the 1940s from grey cast iron by
          distributing the graphite into a spherical form instead of a flake form.
          This was achieved by the addition of inoculants such as magnesium to
          molten iron. It resulted in the ductile nature of the new pipe, in addition
          to higher strength, impact resistance, and other improved properties.
          The commercial production of ductile iron pipe begun in 1955, and by
          the 1970s, it had almost completely replaced cast-iron pipe in munici-
          pal applications. Since 1980, gray cast-iron pipe for pressure pipe appli-
          cations (not soil pipe) has not been produced in the United States.
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