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Iso Plan And Elevation View For Piping
Figure 13-4. Piping isometric view.

Figure 13-3. Piping orthographic views.

Material take-off is the process by which each individual component that makes up a pipe configuration is tabulated for purchase or procurement. 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. Isometrics are also used by many companies as fabrication drawings. Once drawn and properly dimensioned, isometrics are provided to fabricators who will build each piping configuration. 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.

Most engineering and construction companies draw a piping isometric of every piping configuration to be installed in the facility. 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. Isometrics are also drawn as a schematic, which means they are not drawn to scale. Isometric symbols for fittings, flanges, and valves represent all sizes of pipe. No attempt is made to represent a pipe's actual size or pound rating graphically. This information is conveyed through the use of callouts and notes placed on the drawing. Although piping isometrics are not drawn to scale, drafters should make every effort to draw them proportionally. Drawing an iso proportionally simply means drawing a 10'-0" run of pipe twice as long as a 5'-0" length of pipe.

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. Notice in Figures 13-3 and 13-4 that the elbow symbols differ in the orthographic views and in the isometric view. Piping drawing symbols used on plan, section, or elevation views dictate whether a pipe turns left, right, up, or down. When a pipe on a piping orthographic drawing makes a change in direction, that change must also be reflected on the isometric. The point at which the pipe changes direction is referred to as the turning point (TP). To correctly draw the isometric representation of a pipe shown on a plan, section, or elevation view, the pipe drafter must be knowledgeable in the use of piping symbols used for orthographic views and the corresponding symbols used for isometric views.

To make piping isometrics look uniform, most companies use the grid units on the isometric vellum to establish sizes for fitting, flange, and valve symbols. Remember piping isometrics are not drawn to any particular scale. No matter what size or pound rating fittings may be, they are all shown the same size. Figure 13-5 shows the size and shape of manually drawn isometric symbols for fittings, flanges, and valves relative to the isometric grid. These symbols are typical of industry applications and should be used as a guide when drawing piping isometrics.

Piping Isometric Symbols
Figure 13-5. Isometric piping symbols.

iso grid = .125" snap = .0625"

AB •

■ • ■ • ■ • • • • • • • • • • • • • • • • • • •

-30' kw pt. eij f-base pt.

• • •

•-j—base pt.

wb file

lock obj nam e=gat

ect. 'evalh

Figure 13-6. Creating isometric piping symbols using AutoCAD.

STEP 1. Drawing setup. Set the SNAP Style to Isometric. Set the vertical spacing to .125". Set SNAP TO .0625."

STEP 2. Draw the desired symbols. Use the BASE command to place a base point in the location designated in Figure 13-7.

STEP 3. Use the ROTATE command to revolve each symbol -30° about its base point.

STEP 4. WBLOCK each symbol using the name associated with each symbol in Figure 13-7.

Isometric symbols drawn with AutoCAD can be developed so that a single orientation of the symbol can be used in any of the isometric axes. Isometric symbols can be drawn, rotated, and WBLOCKed for repeated use in any drawing at any isometric angle. Initially symbols for fittings, flanges, or valves are drawn on the north/south isometric axis, but, before they can be used in the other isometric axes, they must be rotated -30° about a base point placed on the center of the symbol. Use the step-by-step procedures illustrated in Figure 13-6 to create isometric piping symbols using AutoCAD commands. Figure 13-7 shows the size of the symbols relative to the isometric grid in AutoCAD.

Notice that in Figures 13-1 and 13-2 the height, width, and depth dimensions in the orthographic views are assigned to the isometric view using point A as a point of reference. On piping isometrics, establishing a point of reference becomes even more imperative. The complexity of piping configurations requires a point of reference to establish orientation between the orthographic and isometric views. The north arrow is used as this point of reference. Accurate isometric layout is based on the orientation of the north arrow on the piping arrangement drawing and the north arrow on the piping isometric. Figure 13-8 illustrates the relationship between the piping arrangement drawing north arrow and the north arrow on the isometric.

Knowing that a piping arrangement drawing is a plan view drawing, a pipe can be determined to be turning north, south, east, or west when oriented relative to the drawing's north arrow. So, if a pipe that has been traveling north turns down and then east on the arrangement drawing, it should also be shown to travel north, turn down, and then east on the isometric drawing (see Figure 13-9).

Most companies prefer to draw piping isometrics with the north arrow pointing up and to the right. An alternate position is to draw the north arrow pointing up and to the left. This is done, however, only in exceptional cases to improve drawing clarity. Figure 13-10 uses the configuration from the previous figure to demonstrate how drawing an isometric with the north arrow pointing up and to the left will affect the isometric representation. It is never appropriate to show the north arrow pointing down.

Piping Isometric Symbols
Figure 13-7. AutoCAD isometric piping symbols.
North Arrow Symbols
Figure 13-7. Continued.
Piping Isometric Symbols
Figure 13-8. Orthographic and isometric north arrows.
Isometric North ArrowIsometric North Arrow Isometric North Arrow
+9 0


    4 years ago
  • mirella pugliesi
    What is the reason for giving.north direction in isometrics?
    3 years ago
  • Diamanda
    Why piping is used with north direction?
    2 years ago

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