What is a piping isometric drawing?
- A top view of every line in an area, drawn to scale
- A three-dimensional view of one line, not to scale
- A side view of one piece of equipment and its nozzles
- A schematic of the instruments and control loops only
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B. A three-dimensional view of one line, not to scale
An isometric shows a line in three dimensions on one sheet, with horizontal runs drawn at 30 degrees from horizontal and vertical runs drawn vertical. It carries the dimensions and bill of material but is not to scale.
Reference: Piping isometric drawings
What does a piping and instrumentation diagram (P&ID) show?
- The exact routing and elevations of each pipe run
- The cut lengths and weld numbers for each spool
- How equipment, lines and instruments connect
- The locations of pipe supports and their loads
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C. How equipment, lines and instruments connect
A P&ID is a schematic of the process: what is connected to what, line sizes and numbers, valves and instruments. It is not to scale and does not show where the pipe physically runs.
Reference: Piping and instrumentation diagrams
What is a spool drawing used for?
- Shop fabrication of one section of a line
- Showing the overall layout of piping in a unit
- Showing the wiring of instruments on a line
- Setting the locations of anchor bolts for pumps
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A. Shop fabrication of one section of a line
A spool drawing details one shop-fabricated piece: its fittings, cut lengths, welds and material list. Spools are shipped to the site and joined by field welds or flanges.
Reference: Piping spool drawings