Figure 2-12 provides several representations of pipe as it may appear on a drawing. When pipe is represented on a drawing, typically the pipe's nominal size dimension is used to identify pipe size. One would find it difficult to draw a 4'' pipe to its actual outside diameter of 4' -0 ½'' especially on such a small scale as 3/8'' = 1'-0''.
There are certain applications, however, when the pipe's true outside diameter dimension is used to represent the pipe on a drawing. Drawings created with most software packages are an example. Piping software programs draw with such accuracy that pipe is drawn using the actual outside diameter.
Note : Pipe created by means other than a piping soft ware program in this text will be drawn using nominal sizes. Be aware that drawings created with a piping soft ware program use actual outside dimensions and will differ slightly from manual and AutoCAD generated drawings.