Mastering P&ID (piping and instrumentation diagram) symbols is an important part of process industry knowledge, and having resources and legend lists on hand will put you on the fast-track. That’s what we’ve included in the article, below, so that you’ll have plenty of places to turn when you need to decipher (or construct) your next P&ID project. Highly technical? Check. Suited for those committed to the task? Double-check. But it’s an important part of navigating the process and infrastructure construction business, so let’s get started!
From simple designs to hugely complex structures, comprehensive knowledge of P&ID symbols and diagrams is going to be essential. And learning the entire legend of symbols is too large of an undertaking for a short amount of time — if you haven’t seen a comprehensive list of them all, you’re in for a bit of a shock. The resources that we provide below will be something that you can reference as frequently as you need to, and we’ll close out by recommending a few software solutions that are frequently used by process design engineers.
Piping and Instrumentation Diagrams (P&ID)
If you’ve been in the manufacturing process industry, there’s a good chance that you’re going to be familiar with at least a handful of the symbols present in these resources. They’re a standardized collection of graphics that can be recognizable in process diagrams. They’re used for a variety of different purposes, in many different construction processes. It’s this versatility that makes the existence of these types of resources so important.
Combined in a completed diagram, an engineer can look at the P&ID symbols present and know precisely how a particular construction is meant to flow and function. They’re authorized and archived by the International Society of Automation, which means that a comprehensive set of resources is going to set you up for thorough, time-tested knowledge. Like many elements of engineering research, P&ID symbols will remain relevant for as long as professionals continue to use them; and for as long as the processes indicated in the diagram are relevant to future engineering projects.
Process Flow Diagrams (PFD)
PFD and P&ID diagrams, as well as their correlating symbols, are often mistaken for one another. This comes as a result of their being used for largely similar purposes. But each has a different degree of detail that makes them preferable for different situations.
Engineers and manufacturers who only need to understand the flow of operations in a particular project might use a process flow diagram (PFD), instead. This is a type of diagram that’s comparatively lacking in detail when you stack it up next to a P&ID diagram. It lets someone see how one instrument and procedure flows into the next in a particular process, but that’s about where the details end.
A P&ID diagram, on the other hand, is almost limitless in detail. This is why the legend of symbols necessary for interpreting them is so thorough, and it’s why P&ID diagrams are more important for a precise understanding of mechanical functions in a process.
The following collection of symbols is organized based on different categories — Equipment, Piping, Vessels, Heat Exchangers, Pumps, Instruments, Filters, Compressors, Heat Exchanges, Mixers, Crushers, Centrifuges, Dryers, Valves, Motors, Peripherals, and General Processes. This comprehensive collection of symbols will allow you to identify the parts and processes that are diagrammed in a project, and also see how they relate to one another.
For this article’s purpose, we’ll be referencing the symbols as displayed by LucidChart. It’s helpful to click through to the link we’ve provided so that you can easily see each of these groups of symbols as we elaborate on them. Beyond that, however, LucidChart is a particularly useful piece of software for teams that regularly make use of P&ID (and PFD) diagrams.
As we’ve said above, it’s a relatively large set of symbols to understand. This collection from eDrawSoft also displays the entire legend of symbols, for you to view. And they can be downloaded in PDF format, too.
P&ID Diagram Details
First and foremost, P&ID diagrams are meant to be concise. Though most professionals working in process engineering will be familiar with this type of diagram, not everyone understands what information should be included in them, and what should not. When reading (or constructing) a P&ID diagram, keep in mind that it should contain as much information as possible with as little clutter as possible.
This means that symbols should be used from the legend specifically, and marginal notes should be kept to a minimum. Below, we’ll briefly discuss the types of information that you’ll see included in a P&ID diagram, apart from the given symbols that make up most of it.
Understanding how to read the various symbols in a P&ID diagram is the most important part of understanding one, but other information is often included, especially for more complex projects.
Things such as…
- Mechanical and computer input (not manual inputs)
- Flow and process directions
- Equipment sequence
- Mechanical components and functions
- Process piping, valves, etc. and their relevant sizes
- Capacities and limitations of diagrammed equipment
This is by no means an extensive list; some P&ID will include details that might be relevant to a specific project. For the most part, however, the only additional information and data included is always relevant to the process detailed in the diagram.
Though P&ID diagrams might differ significantly depending on the purpose they’re being used for, and the person responsible for making them, most tend to omit the same types of information, all for the sake of remaining concise and straightforward.
While certain data is included in the diagram when necessary, most output data is left out. This is because the process is the critical purpose of the P&ID, rather than any numerical values or variables that emerge from the process itself. It’s not a place for math, speculation, or data collection — it’s a diagram made to inform a process engineer of the mechanical flow in a process. This might seem slightly in contradiction to what we listed above, but there’s always a difference between defining input and output readings and filling empty space in a P&ID with irrelevant information.
Your most accurate information about P&ID is going to come from whoever you’re drafting them for, ironically. Though the legends and symbols used in them are widely recognized, many process engineers — and the firms that they work for — are going to have their own peculiarities that they bring to the table. Therefore, your best bet is to memorize the basics, and have handy resources for those that you don’t know. After all, it’s quite a large legend of symbols to memorize, but you should be familiar enough with the entirety of it to be able to make easy reference when needed.
Below, we’ll provide you with a few online resources, as well as some software solutions that are frequently used by working professionals. If that’s how you’d describe yourself, then it’s all the more important to have access to the right types of information.
Handy P&ID Legends
Many of the best resources are going to be contained in either published materials or installed software. However, many of those information repositories that offers literature or software also provide lists of symbols online. We’ve listed a few of them, below.
Other options are available, but many of them aren’t as comprehensive. And a resource quickly uses up its usefulness once its no longer able to provide you with a way to see the entire collection of P&ID symbols that might be used in a drafted project. Productivity is important, and the more time that you need to spend looking for a reference, the more time is wasted.
Additionally, there are several software applications that are frequently used by professional when drafting P&ID. Chief among these is AutoCAD, which you’re no doubt familiar with if you’re working as a process engineer. It’s the gold-standard for structure drafting and is actually undergoing some interesting changes as of the publishing of this article. Click the link to check out this very powerful software solution.
You can also opt for something like LucidChart, which we made mention of earlier in this article. The company responsible for this software has many free resources available online, including a working legend of P&ID symbols. But the software itself is where the real usefulness is.
Using the above resources, you should be able to learn a vast majority of the most relevant P&ID information. Further literature is available in the links that we’ve provided, and if you need a software solution for your particular team, we’ve provided that as well. Keep in mind that P&ID diagrams are an established facet of engineering process design, and thus following the best practices — especially those required in specific lines of work, or for specific employers — is of critical importance. The extensive symbols available in the legend lists we’ve linked to are proof of this!