Miscsolutions: P&ID Everything you should know

P&ID- Piping and Instrumentation Diagrams

Introduction-

Really Engineers are not an artistic person but we have done a few process drawings in our academic years as a process engineer. I guess that’s earned to me good grades in semister.Lot time what happens is we draw P&ID but cant remember symbol meanigs or rules to draw an P&ID,Acually we fill it a nutjob,But don't worry hereafter you going to remember it forever.

You say that you are now in having a graduate degree still not sure you really have a good handle on P&IDs? You’re not alone. I know how P&IDs are often poorly understood by those who should know them better. In some cases, they make complex documents that only make boom.. b;coz of that geeks really know how to read.

Ok noe enough chattering,i go to the point-Do i know why a solid understanding of P&ID interpretation is important to virtually every discipline involved in a process plant,(e.g.Thermal Power Plant,Automation industries like automobile industries etc) – from process engineering and detail design through construction, commissioning/start-up, operations and management.

Let’s kick things off by defining what P&IDs are and the types of information they illustrate. Afterwards, we’ll cover some of their limitations. It’s important to know the limitations of a tool so that you don’t apply it in the wrong way.

Do yo know Lead Sheets(Legend sheets)-

We will talk more about the lead sheets (sometimes referred to as legend sheets) - Symbology. If you’ve never encountered lead sheets before, for now, just know that lead sheets are used to define the equipment and device symbols, tags and other notations, abbreviations. If you compare lead sheets from a few dozen companies, you will find that 90% of them are pretty much Copy | Paste. For that last 10%±, there can be distinct differences and company-specific conventions used that are not obvious on P&IDs. Therefore, it is good to know where the lead sheets are in your company so you can quickly track down the meaning of that pipe service label or some other obscure symbol..

What are P&IDs?

Major and minor equipment – the distinction between what is “major” vs. what is “minor” equipment is subjective

Valves, including vents, bleeders, safety relief, sample (all of them!)

Instrumentation, including devices that are used to continuously measure pressure, flowrate, massrate, temperature or some analyzed parameter such as pH, concentration, viscosity…the list goes on.

Stand-alone controllers that may function independently to perform a particular function, like a PID controller or relay timer.

Indicators /Recorder functions as display means,

Buttons used to control motors and devices, be they pushbutton, toggle, or some other type.

Motors and drives – many motors are single speed, non-reversing but there are other kinds that have variable speed drives, and can operate in both directions.

Piping (of course!). All the pipes, tubes and even overflows in the plant. Not just the main process pipes inherent to the particular process, but even the utilities (steam, air, fuel, etc.).

Virtual devices on computer control screens (often as graphical representations real-world objects) that are used to interact with the plant from the control room/panel. This includes things like “clickable” buttons used to start/stop equipment, operate valves, adjust controller settings, setpoint sliders and dials, evaluate alarms, etc. Computer functions and software “links” are generally limited because it is difficult to convey complete control meaning using just symbols.

A P&ID (or engineering flow drawing, EFD) is a type of process engineering drawing that describes all process design aspects of a plant. In this context, “Process Design” means all the stuff that makes up a plant, including:

I probably forgot some stuff in the list above but you get the idea. Clearly there can be a lot of information to show on a P&ID. And for this reason, there are various degrees of detail that a particular company will generally choose to show. There is no formal standard for the various amounts of information a P&ID must include, there are lot books avialable library but really guys who care about that creepy stuff.

P&ID Support Documents-

For those things that are deliberately left off P&IDs for the sake of clarity, other documents are used to provide the details. Common documents that serve vital support functions to P&IDs include:

Process Flow Drawings (PFDs) are simple flow drawings that illustrate the general plant streams, major equipment and key control loops. They also provide detailed mass/energy balance data along with stream composition and physical properties. P&IDs originate from PFDs.
Piping and material specifications. Here, you can dig into all the details about materials of construction, gaskets, bolts, fittings, etc. for each of the services. ( I will talk about this more in a future post.)
Equipment and instrumentation specifications. Modern CAD software used to produce P&IDs are sometimes called “smart” because they can incorporate specifications, standards and details that go into the design. Yea, they are cool but just as you can’t fix stupid.
Functional/process control documents that describe in detail, how the plant operates. A good one will include preferred standards for use on control screens/displays. Folks(People in general) involved in programming the computers used to operate the plant, need these.

How Should P&IDs be Organized?

There is no single good answer to this question and most companies will have a defined precedent or standard that they follow but if you find yourself at File .New with nothing to go on,

Here’s a quick example. Consider a process plant with that receives raw feedstock in a storage area, feeds them into some reactor train(s) to make some product and then includes a storage and packaging back end. This particular process might be sitting inside a larger infrastructure and tank farms.
In this case, you might elect to break the P&IDs down as such:

Raw material receiving and storage
Process trains,carriers for product manufacture
Product storage and packaging
utilities and distribution
Environmental control and specialty unit operations/vendor packages such as thermal fluid,concentration of fluid,pH, complex unit operations, etc.

Some companies like to develop their P&IDs so that if you had a huge wall, you could tape them together and all of the various interconnecting arrows would line up as the parts of a jigsaw puzzle. It’s not uncommon for even relatively simple processes to have a dozen or more P&IDs so you would need a really big wall and then you wouldn’t be able to read anything without getting close.

My advice is to make efficient use of the space provided, use the interconnect arrows as required to link them together and not get caught up on how well they align with the god of geometric continuity .

P&IDs Used For?

P&IDs really do have vital roles. such as

Defines process from which all instrumentation engineering, fabrication, construction and operation is based.
Serve as reference for Process Safety Information (PSI) in Process Safety Management (PSM).
Provide a clear and concise illustration of all equipment, pipes, valves, instruments, sensors, etc. so that anyone involved has a solid understanding of the process.
Provide information to assist in analyzing process hazards, safeguards and potential faults so that all kinds of errors (design, human/operation, etc.) are minimized, ideally eliminated
Support development of operating and maintenance procedures
Serve as an as-built record of the process so that changes can be planned safely and effectively using Management of Change (MOC).

So it’s pretty clear that the P&IDs define the process at a root level. They serve as the foundation upon which the system is designed, built and operated. Anyone who tells you that they can design a plant without first generating P&IDs either is a Superhuman or has endless funds that they enjoy throwing at poorly executed projects during the construction phases.

P&IDs Limitations

At this point, you might be wondering what P&IDs can’t do. Well, there are a few things that P&IDs don’t do well and it’s important that you know what these are so that nobody makes any false assumptions because we all know what happens when one assumes.

They don’t serve as a true model for how things are oriented and placed in the real world-(If you just assume that a pipe is located somewhere because it looks that way on the P&ID, you might be disappointed..!)
They don’t reveal scale or geometry -( scale drawings are the ones used by contractors to build the plant. These include civil and piping plans, sections and/or isometrics, skid/equipment fabrication drawings, instrument location plans, etc.)
Not Definitive – P&IDs do not include complete specifications for all of the equipment in the process.
Not Drawn Consistently – Sadly, P&IDs seldom look consistent between companies. That’s because there is a lot of flexibility in how one can go about drawing a P&ID (due to various standards, CAD systems, etc.) and that leaves them open to company and/or personal preferences. As a result, P&IDs often take on a different “look and feel” from company-to-company or even from job-to-job inside the same company.

OK, so now you have a solid feel for what P&IDs are, the purposes they serve and their limitations. Hopefully, you’ve taken the time to at least glance at the example drawings provided.

Symbols & philosophy -

The meanings of the various symbols used on P&IDs (aka, symbology) are defined on separate drawings called “Lead Sheets” (or Legend Sheets). These are your “secret decoder rings” to P&ID symbology interpretation. Every company that builds process plants should have a set of lead sheets customized to their particular ways and means.

Having seen a number of lead sheets over the years, I can tell you that most of them are just variations on a core set of generally accepted symbols and notations that engineers and industry organizations have settled on standards over the years.

Here’s the good news – these lead sheets include 90% of what you need to know. Seriously. Yeah, I realize some companies have more than two lead sheets, four or five even.

Probably even a few with six or seven just to prove a point I suppose, but the number of lead sheets isn’t important. What is important is that they are logically organized so that the symbols and tags can be located easily. Poorly organized and/or incomplete lead sheets will just frustrate folks who turn to them for help so it’s important to keep them neat, concise and logical. And the two I present here should be up-front-and-center in your set.

Related to the content I include on the example lead sheets, you might have noticed a conspicuous absence of lead sheets for major equipment, i.e., tanks, pumps, boilers,valves,controllers panels items typically included in process plants, etc.

Instrumentation and Controls Symbols-

We’ll kick things off with what has traditionally been viewed as the “hardest part” of P&ID interpretation, that of course being instrumentation and controls. In my experience, this is the area that gives newcomers the most grief. Trust me, it’s not that hard and once you have this area conquered-

The main symbols used for Instrumentation and Control (I&C) are shown in the table

When you spot one of these on a P&ID, you will be able to glean three things from it, including:

What is that device? - determined from shape of symbol.
Where is it located? -determined from shape of symbol & inside line of symbol.
Why is it there? - text placed inside the symbolalso called as "tag number" --> " tag number=abbreviation + loop number " e.g. Pressure indicators have the abbreviation "PI",same for temperature ind TI etc. --> Since most plants can have many instruments of the same type, a unique number is applied so that each one can be individually identified called as “loop number”. (e.g- PI0134 and TI4348,) ** An abbreviation for what the device is (based on ISA S5.1), combined with a Loop number based on your company’s preferred numbering system.

control symbol-

Physical instrument or device in the field or on a panel.
Here 'PI' say Pressure indicator.
If it is a physical device that measures or displays something, it will be illustrated by the use of a circle on a P&ID.

Represent a graphic on a computer screen or control panel that you can see ,possibly interface with via touch panel or a computer mouse.
It might be used to show the level in a tank.
illustrated as circle inside a square on P&IDs.

In the case of the hexagon, it means a “computer” is used. That’s a pretty vague description don’t you think. square with a diamond in it, that means a programmable logic controller (PLC) is used.

Where is the device located?

P&IDs generally aren’t good at showing you where something is located in the field. We aren’t talking about that kind of ‘where’. In this case, we are using where as a relative reference. Relative location is indicated via the presence of a centered, horizontal line , a dual centered horizontal line, or a dashed centered horizontal line placed inside the symbol;

Single horizontal line – located on a main control panel near the control room or some computer screen in the main control room,
No horizontal line – located somewhere in the field, probably close to the general area shown on the P&ID,
Double horizontal line – on some secondary (satellite) local panel in the field.
Single dashed horizontal line – inaccessible or not generally located where it can be easily accessed or viewed. May also be used for hidden or password protected areas of a control system.

Common Instrument Abbreviations-

The hardest part in deciphering the abbreviations inside control symbols is figuring out what the letters designate when there are three or more letters used. Here are a couple rules of thumb:

In the case of abbreviations with four letters, the second letter is a modifier to the first.
When only three letters are used, the second letter probably is not a modifier

Symbol Attributes-

comming soon..

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P&ID Everything you should know