The point at which the pipe changes direction is referred to as the turning point (TP).

When a pipe on a piping orthographic drawing makes a change in direction, that change must also be reflected on the isometric.

Piping drawing symbols used on plan, section, or elevation views dictate whether a pipe turns left, right, up, or down. Notice in Figures 13-3 and 13-4 that the elbow symbols differ in the orthographic views and in the isometric view. To be successful in drawing isometrics, the pipe drafter must be able to interpret the information conveyed by the drawing symbols for fittings, flanges, or valves used on piping arrangement, section, and elevation drawings and transfer that information to the isometric. Drawing an iso proportionally simply means drawing a 10'-0' run of pipe twice as long as a 5'-0' length of pipe. Although piping isometrics are not drawn to scale, drafters should make every effort to draw them proportionally. This information is conveyed through the use of callouts and notes placed on the drawing. No attempt is made to represent a pipe's actual size or pound rating graphically. Isometric symbols for fittings, flanges, and valves represent all sizes of pipe. Isometrics are also drawn as a schematic, which means they are not drawn to scale. Piping isometrics are typically drawn single lines no matter the pipe's size, with each pipe line drawn on a separate sheet of vellum having an isometric grid background. Most engineering and construction companies draw a piping isometric of every piping configuration to be installed in the facility. After configurations are fabricated, isometrics serve as an aid to the construction and erection of the facility by providing workers with the locations of tie-ins, connections, and routings. Once drawn and properly dimensioned, isometrics are provided to fabricators who will build each piping configuration.

Isometrics are also used by many companies as fabrication drawings. This means all piping components (elbows, flanges, nuts, bolts, washers, gaskets, etc.) must be accounted for so that purchases of those items can be made. Material take-off is the process by which each individual component that makes up a pipe configuration is tabulated for purchase or procurement.

Piping isometric drawing symbols