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176    Cha pte r  F o u r

          availability of various pressure classes and diameters makes it easily
          desirable to engineers and specifiers. The pipe itself is highly resistant
          to chemical permeation. Also, there are various internal and external
          corrosion protection systems available.
             Ductile iron is susceptible to internal and external corrosion.
          Although there are a variety of corrosion protection systems, they do
          not all perform equally. Cathodic protection is too cost prohibitive for
          use in the municipal systems. The internal cement-mortar lining pre-
          vents the deflection of the pipe beyond 3 percent, even though ductile
          iron is a flexible conduit. External polyethylene encasement is easily
          damaged, for example during tapping, and is subject to careful instal-
          lation. The heavy weight of ductile iron pipe raises the cost of labor.
          Although the pipe itself resists chemical permeation, the gasket at the
          joint does not.

          Steel Pipe
          Steel pipes, made from a versatile refinement of iron, have seen a wide
          range of usage for more than a century and a half. The development
          of high-strength steel pipes has made it possible to transport fluids
          such as natural gas, crude oil, and petroleum products over long dis-
          tances. Initially, all steel pipes had to be threaded together, which was
          difficult for large pipes, and they often leaked under high pressure.
          The development of electric arc welding machines in 1920s made it
          possible to construct leak-proof, high-pressure, large-diameter pipe-
          lines. One of the earliest steel water pipe installations in the United
          States, still in service today, was in San Francisco in 1863. Develop-
          ments in technology have given way to riveted steel pipes evolving
          to the automatically welded steel pipes of today. Various other devel-
          opments have resulted in the creation of different types of joints as
          well as effective mechanisms for prevention of corrosion, making
          steel more versatile for trenchless and open-trench applications.
             In municipalities, steel pressure pipes are used today in large-
          diameter potable water transmission applications. In municipal
          trenchless construction, steel pipes are used as casing pipe in pro-
          cesses such as microtunneling, jacking, boring, and pipe-ramming
          because of their high stiffness and compressive strengths. There have
          even been several large-diameter spiral-welded steel pressure pipe
          installations in Texas, Washington, and Hawaii via horizontal direc-
          tional drilling.

          Corrugated Steel Pipe  Corrugated steel pipes have been used for
          more than a century in gravity applications such as drainage and
          storm sewers. Though corrugated steel pipes have been used in
          some sanitary sewers, this is not the case today. Due to their rela-
          tively low-compressive and tensile strengths, corrugated steel pipes
          are not used in trenchless or pressure applications. Therefore, a
          detailed discussion of corrugated steel piping products has been
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