The line symbols for piping shown in figure 8-28 are composed of solid or dashed lines that indicate the type and location of that particular

pipe on the plan. Other line symbols identify the proposed use of the pipes. The size of the required piping should also be noted alongside each route of the plan. Piping up to 12 in. in diameter is referred to by its nominal size, which is approximately equal to the inside diameter (I.D.). The exact inside diameter depends on the classification of the pipe. Heavy types of piping have smaller inside diameters because their wall thickness is greater. Piping over 12 in. in diameter is referred to by its outside diameter (O.D.).