How to Read Pipe Schematics
In 1984, the International Society of Automation began publishing standards to regulate widespread use of flow diagrams. Pipe schematics, falling into this category, must now be created according to these standards to allow for seamless interpretation without confusion of language or notation styles. Though guides may still be of use, especially in the early stages of deciphering such diagrams, learning the primary symbols and methods used in pipe schematics will ensure comprehension of these consistent diagrams for years to come. Does this Spark an idea?
Things You'll Need
- Guide to ISA S5.1 symbols and identification
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Instructions
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Learn the four basic graphical symbols defined by the ISA and what they represent. Differentiate between circular symbols, which represent discrete instruments, and circles within squares, which represent shared controls or displays. Identify hexagonal shapes as computer functions and triangles surrounded by squares as programmable logic controllers, also known as PLCs.
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Discern between the three location categories set forth by ISA standards. Look for the device in its primary location if a horizontal bar appears across the graphical symbol used to represent the device. Expect the device to be in an auxiliary location if two horizontal lines are used. Determine that the device is field mounted if no line appears through the symbol. An inaccessible device may be marked by a dashed horizontal bar.
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Determine the measured variable of a device by reading the first identification letter represented on a particular diagram symbol. Identify a "T" as temperature measurement, "F" as flow rate measurement and so on. Consult an ISA guide for a full list of viable letters and their corresponding meanings.
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Use the second letter notated in a symbol to discern the device's readout function or output function, if any. Be sure to consult a guide to differentiate between secondary letters and modifiers -- such as D, F, K and Q -- which change the meaning of the first letter rather than indicating output or readout functions.
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Understand the numbers listed after the letters on a graphical symbol. Interpret the first number as the line number, and read the following number as the pipe size in inches. Make sure you are familiar with the numbering system used for your schematic; these numbering systems are not universally standard, as they are not explicitly defined by the ISA standards, and they may differ between schematics.
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Learn what is symbolized by each of the types of connecting lines between devices. Interpret a solid line as an instrument supply or connection to a process. View a solid line with double dashes through it as a pneumatic signal and a completely dashed line as an electrical signal. Find a full list of connecting lines in an ISA standards guide.
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Consult a guide to ISA symbols to identify those in your diagram. Locate the group in which your symbol belongs -- a pipe schematic will likely include symbols for pumps and tanks -- as there are many into which ISA graphic symbols can be categorized. Browse to find the symbol along with any descriptors or relevant information about the part. Be sure to match very small or detailed symbols, such as valve representations, to precise detail for accuracy.
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Tips & Warnings
Do not interpret symbol size as a scaled representation of actual piping.
References
- Photo Credit Stockbyte/Valueline/Getty Images
