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ASME Y32.11-1961 — Graphical Symbols for Process Flow Diagrams in the Petroleum and Chemical Industries
🏭 ASME Y32.11-1961, originally approved as ASA Y32.11-1961, is the American standard that defines graphical symbols for process flow diagrams (PFDs) in the petroleum and chemical industries. It was developed under the joint sponsorship of The American Society of Mechanical Engineers (ASME) and the American Institute of Electrical Engineers (AIEE). The copy covered here is a scanned edition of the original pages; the extracted text is searchable but should be checked against the page images. A process flow diagram is the first drawing made for a project: it shows the basic items of major equipment, their relation to one another in the process scheme, and the principal flow lines connecting them, thereby describing how the process operates.
💡 The PFD is the “first drawing” of chemical and refining design: it conveys the skeleton of the whole process scheme with simple equipment outlines, and it forms the basis for the more detailed engineering flow sheets and final piping layout drawings.
1. Scope of the Standard 📌
The Standard states that this preliminary set of symbols is intended for use on the basic process flow diagrams to represent the major items of equipment used by the petroleum and chemical industries. The PFD serves to:
- show, as the first drawing made, the basic equipment items and their relationships;
- connect these items with the more important flow lines so that the operation of the process is clearly described;
- provide the framework for subsequent detailed engineering flow sheets and final piping layout drawings.
The Standard also warns that, for the detailed design, erection, or operation of a unit, the PFD must be supplemented by more detailed engineering flow sheets and the final piping layout drawings.
⚠️ The 79 symbols in Y32.11-1961 are a preliminary minimum set — by no means all that were suggested or may be required. They can adequately represent the majority of present processes, but special units may still need additional symbols with explanatory notes.
2. Basic Principles of Drafting ✏️
Chapter 2 of the Standard sets out the basic principles for drawing a PFD:
- Simplicity of outline: preserve the general physical appearance of the equipment with the minimum strokes for the draftsman;
- No scale: a process flow diagram is not drawn to scale, but relative symbol sizes should suit the overall size of the finished drawing;
- Logical sequence: arrange symbols in logical order of flow, from charge material to main product, with a minimum of crossover lines;
- Line contrast: draw equipment outlines with heavy lines and the connecting piping with lighter lines;
- No instrumentation: for most PFDs it is not necessary to show instrumentation or electrical symbols.
3. Symbol Code Numbers and Classification 📐
The 79 symbols are organized by symbol code numbers into 14 categories. The table below summarizes each category and its coverage:
| Code Range | Category | Typical Items |
|---|---|---|
| 1–4 | Lines | Feed stock / products (identified by name), connecting lines, crossover lines |
| 5–8 | Valves | Gate, globe, plug (cock), check |
| 9–13 | Process Quantities | Liquid flow, weight flow, gas flow, pressure, temperature |
| 14–18 | Furnaces & Boilers | Box type, radiant (single coil), vertical, fired or waste-heat boiler |
| 19–27 | Heat Transfer | Coolers, condensers, shell-and-tube exchangers, cooling towers, reboilers, superheaters |
| 28–32 | Pumps & Compressors | Centrifugal, reciprocating, rotary, proportioning, blower or fan |
| 33–36 | Drivers | Motor, engine, turbine, steam piston |
| 37–41 | Process Pressure Vessels | Horizontal/vertical drums, jacketed vessels, catalytic and nuclear reactors |
| 42–46 | Dryers | Batch trays, spray, desiccant, continuous tunnel, rotary drum dryer or kiln |
| 47–53 | Material Handling Equipment | Air lift, belt/shaker, bucket/flight conveyor, screw conveyor, roller conveyor, feeders |
| 54–57 | Size Reducing Equipment | Ball mill, grinder, roller crusher, screener |
| 58–66 | Processing Equipment | Blowing egg, extractor, mixer, settler, autoclave, jacketed kettle, jet mixer, thickener |
| 67–73 | Separators | Centrifuge, cyclone, electrical precipitator, filter press, drum settler |
| 74–79 | Storage Vessels | Cone-roof tank, floating-roof tank, gas holder, spherical pressure storage, cone-bottom bins |
💡 Valve-drawing tips: show valves only where necessary to clarify the process flow; if a valve is closed during normal operation, write “CLOSED” directly above it. Place numerical quantities inside symbols and explain the assigned units in the drawing legend.
4. Engineering Practice Essentials 🛠️
- 📋 Legend discipline: state the values assigned to all units in the drawing legend and place the numerical quantities within the symbols.
- 🔥 Furnace drafting: indicate the approximate position of inlets and outlets; for a dual-coil furnace, show the path of both streams; do not indicate fuel type or firing position.
- 🔁 Exchanger views: side views may be shown for exchangers and reboilers; distinguish kettle-type and thermo-siphon reboilers.
- ⚙️ Driver annotations: drivers may be shown attached to the prime mover; specific motor types follow ASME Y32.2; the Standard proposes changes to the corresponding Z32.2.6-1950 symbols.
- 🔄 Sister standards: the Standard references Z32.2.3 (pipe fittings and valves), Z32.2.4 (HVAC), and Z32.2.6 (heat-power apparatus) so the whole drawing set stays consistent.
🚨 Scanned-edition caution: this is a historical scanned standard; some page text carries OCR noise. Verify symbol shapes against the original page images before use, rather than relying on the extracted text alone.
5. Frequently Asked Questions ❓
❓ Q: What is the difference between a PFD and an engineering flow sheet (EFD)?
A: The PFD is the earliest overall concept drawing showing only major equipment and principal flow lines; the detailed engineering flow sheet adds controls, instrumentation, and full line details, and the final piping layout follows from it.
A: The PFD is the earliest overall concept drawing showing only major equipment and principal flow lines; the detailed engineering flow sheet adds controls, instrumentation, and full line details, and the final piping layout follows from it.
❓ Q: Why is a PFD not drawn to scale?
A: A PFD expresses the logic and sequence of the process scheme, not installed positions or dimensions; relative symbol sizes only need to suit the drawing, and exact dimensions belong to the piping and detail drawings.
A: A PFD expresses the logic and sequence of the process scheme, not installed positions or dimensions; relative symbol sizes only need to suit the drawing, and exact dimensions belong to the piping and detail drawings.
❓ Q: Are the 79 symbols all that a designer will ever need?
A: No. The Standard explicitly states the set is a preliminary minimum; most current processes can be represented adequately, but special equipment may require additional, clearly explained symbols.
A: No. The Standard explicitly states the set is a preliminary minimum; most current processes can be represented adequately, but special equipment may require additional, clearly explained symbols.
🔍 Q: How does the scanned edition differ from the printed standard?
A: Content and layout are identical, but the scan has no reliable embedded text layer; use the page images for exact symbol reference.
A: Content and layout are identical, but the scan has no reliable embedded text layer; use the page images for exact symbol reference.
