This standard describes the thickness design of ductile-iron pipe complying with the requirements of ANSI/AWWA C151/A21.51, Ductile-Iron Pipe, Centrifugally Cast, for Water. Sec. 4.1 outlines the design procedure, and Sec. 4.2 gives a design example. Sec. 4.3 explains the basis of design. As opposed to using procedures in Sec. 4.1 or Sec. 4.3, the designer may reference Tables 12 through 14 directly. Table 12 lists thicknesses for standard laying conditions and certain depths of cover. Table 13 lists thicknesses for 150 psi-350 psi (1,034 kPa-2,413 kPa) water working pressure. The greater thickness from Table 12 or Table 13 for given trench load or internal pressure should be used. Table 14 lists working pressures and maximum depths of cover for standard laying conditions and standard pressure classes. Table 15 lists special thickness classes of ductile-iron pipe. Major revisions made to the standard in this edition include the following: added definitions for casting and service allowances, working pressures, and surge pressures.