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Piping is a specialized engineering field concerned with the design of piping systems used to transport liquids and gases in structures and process plants such as oil refineries. Piping drawings specify the pipe fitting types and locations, and use standard symbols to represent pipes, joints, and fixtures. Piping drawings can be very complicated and hard to visualize, which make the use of real models, such as plastic engineering models, or computer models very important. The use of CAD to build 3-D computer models has revolutionized the design and representation of process plants. This chapter is an introduction to piping components, drawings, and symbols.
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OVERVIEW |
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| 24.1 Piping drafting is a specialized area of technical graphics involved with graphically representing the design of piping systems used in the movement of gases and liquids in industrial plants and municipalities. Though a diverse range of industries and professions use piping drawings, there is the common thread in the basic design of the liquid and gas-carrying piping. Some of the types of piping drawings and the areas using them include: Civil piping Process piping CAD has made a tremendous impact on this area of technical graphics. Like electronic drawings (Chapter 23), piping drawings need to carefully document all flow paths between components. Unlike electronic drawings, this flow has to be managed in three dimensions and 3-D virtual models of proposed piping systems are a powerful tool for evaluating a proposed design. |
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PIPE TYPES |
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| 24.2 Though piping is almost invariably round, it can range in diameter from smaller than 1" to many feet. The types of material used for the pipe depends not only on its size, but also where it is located (e.g. buried in the ground, located in the sub-Arctic, etc.) and what material it is carrying (e.g. high pressure gas, highly purified chemicals, sewage, etc.). Common piping materials include: Steel Cast Iron Copper Plastics |
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PIPE CONNECTIONS |
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| 24.3 The type of connection will depend both on the application and the type of piping material. The most common type of connections include: Weld (socket and butt weld) Screw Flange |
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PIPE FITTINGS |
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| 24.4 Using the types of connections listed in the previous section, fittings are used to alter the direction of the piping. Just as gears are used to alter the speed and orientation of the rotating axes, fittings can change the orientation and diameter (and thus the pressure and flow velocity) of pipes. Common fittings include: Elbow Tee Cross Taper Return bend Fittings can also be used to both divide and combine the contents of one or more pipes. |
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VALVES |
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Valves are used to control flow through the pipes. Like fittings, valves are matched to the pipe type, connection method, and end application. Valves can be binary (on/off) or allow for variable rates of flow. They can be operated manually, controlled remotely with electronic solenoids, or independently controlled with governors. |
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PIPE DRAWINGS |
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| 24.6 Piping drawings use many of the conventions of A/E/C drawings and will typically be drawn in plan, elevation, or isometric. The representation of the piping is usually schematic in nature and drawn in either a single line or double line style. Double line is more time consuming but allows for a more realistic representation of the space the piping will take up. |
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| 24.6.3 Spool drawings are a specialized type of drawing used for sub-assemblies fabricated off site. |
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| 24.6.4 Symbols such as arrows and line balloons are used to specify the direction of flow and specifications for the pipe. At a minimum, a piping drawing should contain the following information: Diameters, lengths, and identification numbers for all pipes Location dimensions for all fittings and valves Specifications for all fittings and valves Pipe flow arrows |
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| 24.7 As with many other types of technical drawings, CAD can be of tremendous assistance in creating piping drawings. Symbol libraries allow for quick placement of standard components such as valves and fittings. Parametric methods allow drawings to be automatically updated when a component is moved or a pipe section is changed. 'Rules' are established which define how components are to be connected and the 'expert' knowledge of the system warns operators of pipes clashing, lack of support for long pipe lengths, etc. As mentioned earlier, 3-D CAD programs allow you to explore the location of piping and other components as they would appear in the constructed system. This can be invaluable not only for identifying spatial conflicts between components, but also for evaluating human factors concerns such as whether workers can reach valves, read pressure gauges, have enough room to service remote equipment, etc. |
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SUMMARY |
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The piping industry requires specialized drawing conventions and standards to represent the layout of piping systems used in the chemical, petroleum, HVAC, and other industries. Graphic symbols are used to represent valves, pipes, and joints. Pipe drawings are used to represent pipes in orthographic plan or elevation views, and for section and pictorial views using single- or double-line drawings. Spool drawings are subassembly piping drawings used to assemble a small portion of a piping system. |