Figure 5-4.—Double-line pictorial piping drawing.

Draftsmen use single-line drawings to show the arrangement of pipes and fittings. Figure 5-3 is a single-line (isometric) pictorial drawing of figure 5-1. The center line of the pipe is drawn as a thick line to which the valve symbols are added. Single-line drawings take less time and show all information required to lay out and produce a piping system. Double-line pipe drawings (fig. 5-4) require more time to draw and therefore are not recommended for production drawings. Figure 5-4 is an example of a Figure 5-3.—Single-line pictorial piping drawing of figure 5-1. double-line pictorial pipe drawing. They are generally used for catalogs and similar applications where visual appearance is more important than drawing time. CROSSINGS The crossing of pipes without connections is normally shown without interrupting the line representing the hidden line (fig. 5-5, view A). But when there is a need to show that one pipe must pass behind another, the line representing the pipe farthest from the viewer will be shown with a break, or interruption, where the other pipe passes in front of it, as shown in figure 5-5, view B. CONNECTIONS Permanent connections, whether made by welding or other processes such as gluing or soldering, should be shown on the drawing by a heavy dot (fig. 5-6). The draftsman normally will use a general note or specification to describe the type of connection. Detachable connections are shown by a single thick line (figs. 5-6 and 5-7). The specification, a general note, or bill of material will list the types of connections such as flanges, unions, or couplings and whether the fittings are flanged or threaded. Figure 5-4.—Double-line pictorial piping drawing. 5-2