The process and instrument diagram (P&ID), in some sectors also called a piping

and instrument diagram, is vital to documenting the design, engineering and

operational ‘flow’ of processes in all types of facilities, installations and components.

There is not an industrial process in the world that does not have this valuable document

associated with it. Some large, complex facilities may require dozens or hundreds of P&IDs to

document all of their processes. These P&IDs are useful and effective if they provide

the desired levels of content, quality and accuracy. Recent innovations by plant design software companies are elevating

P&IDs to increasingly important roles in these realms.

Simple flow diagramsMany use the term ‘flow diagrams’ in engineering and design

applications. While this term describes the family of diagrams to which P&IDs belong, it does not accurately describe the P&ID. The flow diagram

family originated with the block flow diagram and the process flow diagram (PFD).

The block flow diagram is a very simple diagram that condenses the whole process onto only a few sheets. Its aim is to show major processes and

equipment. Interconnecting process lines in block flow diagrams typically offer only generic key data, such as flow rates, commodities, temperatures and pressures.

These diagrams are typically very simple and have limited symbols to indicate the form of the equipment being represented.

The PFD was the precursor of the modern P&ID. The PFD carries more information than the block flow diagram, including more detail about major equipment and

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| HydrocarbonEnginEEring | Reprinted from July 2010

subsystems and the flow of product between them. It shows pressures and temperatures for the feed and product lines to and from major vessels, heat exchangers, main headers and other pieces of equipment, and it shows the points of pressure, temperature and flow control, plus main shutdown points in the system. A typical PFD will also show process piping, flow direction, symbols for major equipment, major bypass and recirculation lines, critical control and process valves, system names of processes, system ratings, operational values, composition of fluids and intersystem connections. For rotating equipment, they carry important information such as pump capacities and pressure heads and pump and compressor horsepower, and for tanks, vessels, columns, exchangers and heaters, PFDs sometimes show design pressures and temperatures.

However, when compared to the P&ID, PFDs are fundamentally different in appearance, content and use and play a different and more limited role in the design process in the areas of their content and use.

P&Ids containing more informationP&IDs take things to a much higher level by providing much more information. As true multidiscipline documents, they define and document the processes that allow engineers and designers to produce viable and efficient designs based on process requirements. P&IDs are the best way of accurately documenting the operation of the process and of coordinating these processes among multiple disciplines.

P&IDs take the conceptual aspect of the PFD and expand them much further, with such things as:

ª Detailed symbols.

ª Detailed equipment information.

ª Equipment process order and sequence.

ª Process and utility (non-process) piping.

ª Process flow direction.

ª Major and minor bypass lines.

ª Line numbers, pipe specifications and pipe sizes.

ª Isolation and shutoff valves.

ª Maintenance vents and drains.

ª Relief and safety valves.

ª Instrumentation.

ª Controls.

ª Connection types of process components.

ª Vendor and contractor interfaces.

ª Skid and package interfaces.

ª Hydrostatic vents and drains.

ª Hazardous operations design requirements.

Not only are they effective, but they are required. The US Department of Labor Occupational Safety & Health Administration (OSHA) mandates P&IDs as health and safety documents, so they must be accurate and up to date throughout the life of the plant. Similar requirements are in place in other countries. So, for process plants, the P&ID is the centre of facility operations and product life cycle management.

Expansion of computer aided designOver the past 20 years, technology has shaped the way that the P&ID has evolved in use and has raised expectations for the P&ID. Much of the increase in importance of the P&ID is directly linked to the expanded use of increasingly sophisticated computer aided design (CAD) systems for process design deliverables, including in design engineering and in the management of operations. This began in earnest in the early 1980s and continues unabated. Consisting of lines, arcs and standard symbols, one may sometimes view these as simple CAD drawings but the reality is much more sophisticated.

As CAD became more widely used across diverse industry sectors, larger engineering and engineering procurement and construction (EPC) firms began to move toward CAD for their 3D design work. At that time,

Figure 2. intelligent P&iDs allow important component and process information to be stored and associated with each item. With intergraph CADWorx P&iD Professional this is achieved without any programming. (image courtesy of intergraph Corporation.)

Figure 3. P&iDs carry valuable information that is used during all phases of a project. Here intergraph CADWorx Plant Professional gathers information and places components directly from the P&iD, ensuring the model and P&iD are always in sync. (image courtesy of intergraph Corporation.)

Figure 1. The benefits of intelligent P&iDs are realised when all stakeholders can access the important information they contain. Here intergraph® CADWorx® internet Publisher publishes password protected project information that can be viewed and accessed using a browser. (image courtesy of intergraph Corporation.)

Reprinted from July 2010 | HydrocarbonEnginEEring |

CAD was the domain of the minicomputer, and many of these drafting systems ran on expensive PRIME and DEC VAX systems. These companies were not going to spend hundreds of thousands of dollars on computer systems just to draw P&IDs. So for many companies, the 2D side of their CAD systems was a low cost addition to the 3D modelling systems they had already deployed.

Enhancements in accuracy and legibilityBecause of the simplicity of P&IDs and the ease with which they could be created, early adopters, including engineering companies and owner/operators, expected only two things from them: accuracy and legibility. While these demands may seem simple today, at that time they were quite pleased with their P&IDs when compared to their old PFDs of years earlier because they provided greater efficiencies for clients and engineering design companies alike. They were more than adequate for the vast majority of companies. In fact these firms were seen as being on the cutting edge of technology and often came out on top when it came to the awarding of contracts.

a double edged sword When viewed on a computer screen or in paper form, these CAD produced P&IDs were more legible than their hand drawn counterparts, and they were easier to update and maintain. Even though they were much easier to generate, they still offered no more information than their hand drawn counterparts.

And it soon became apparent that CAD used in this way was not foolproof because operators could still cheat! The power of CAD, which enabled users to quickly modify drawings and enact global changes, also led to abuses for the same reasons. This compromised accuracy, so legibility was about the only advantage that remained. These P&IDs still required the same degree of exhaustive checking for accuracy as those created by hand on the drawing board. And there was no intelligence.

Promise of intelligent P&IdsIn the 1990s new, more affordable, PC based CAD systems came on the market. These systems allowed smaller companies to develop CAD based P&IDs, which often consisted of symbol libraries they developed in house. Because these systems were more open than the minicomputer systems that preceded them, developers began to use the inbuilt programming languages for these CAD platforms to develop packages for the specific purpose of creating P&ID drawings. While many of these systems claimed to produce intelligent P&IDs, which they did to some extent, they still had a way to go to achieve full intelligence.

defining P&Id intelligenceOne of the challenges is that the term ‘intelligent P&ID’ can mean something different to different people. What makes a P&ID truly intelligent? The test of a system’s true intelligence can be answered by asking these two questions:

ª How many differing stakeholders can easily access the information input into the P&ID system and benefit from doing so?

ª And, for how long during installation, operation and the entire lifespan of the project or facility can stakeholders access and add information to the P&ID?

So there are two main ways to identify intelligent P&IDs. One involves the creation of the drawing and the other the additional information that the P&ID holds.

On the creation side, one of the benefits of these intelligent P&ID systems is that they automate as much of the drafting functions as possible. These systems automatically break process lines when they cross over one other; they break out sections of process lines when a valve is inserted and heal up those same lines when a valve is removed. They also check that a valve is the same size as the line into which it is being inserted. They make global changes, such as changing the size of

a line and prompting for those changes to be applied to all inline components, and they change line types without redrawing.

In the area of adding information, intelligent P&ID systems allow for the input of information that is not visible on the printed P&ID. As an example, for a valve one can insert information such as vendor name, material, port size and top works. For process lines, one can add design pressures and temperatures, operating pressures and temperatures, and more.

Being able to add extra information for each component was a key step toward intelligence because, for the first time, valuable information could be held in the P&ID to be accessed at any time or to produce bills of material, valve counts, equipment and instrument lists directly from these P&IDs. And the information was all in one place.

Figure 4. Bidirectional links between the external database, P&iDs and the design model, make sure that project teams always draw from the latest information. (image courtesy of intergraph Corporation.)

Figure 5. Specification driven P&iDs are a valuable check that what is placed on a P&iD conforms to piping specifications. Using the same specs for P&iDs and the model allows for further integration, synergy and accuracy of design. (image courtesy of intergraph Corporation.)

| HydrocarbonEnginEEring | Reprinted from July 2010

Specification driven P&IdsEven though P&IDs had become more intelligent, they were still an autonomous drawing in that all information the operator placed in the sheet was information pulled from sketches, equipment datasheets and piping specifications. There was no readily available electronic data that the P&ID automatically referenced during its creation.

One of the great promises of CAD in 3D plant design was the ability to perform specification driven designs to check the work of humans. Although there are things a P&ID does not need to contain, there is still great benefit in having P&IDs that, like the 3D model, are specification driven. With a specification driven P&ID, once a designer sets the size and piping specification for a line, the CAD system would check the piping specification each time a component was selected to ensure accuracy and fit. For example, the system would make sure that someone did not place a plastic tee in a high pressure carbon steel line or use an unreinforced stub in branch connection when a welded reducing tee was specified.

With specification driven P&IDs, users can also set their pipe sizes and specifications and place inline items onto process lines with the knowledge these items are inserted correctly. With this capability, they know they are receiving the same benefits as their downstream colleagues.

Interoperability with 3d modelsThe real payoff in having a specification driven P&ID is when they use the same specifications as in the 3D model. The 3D designers could now verify their designs against the P&ID and do so with confidence. They could do line checks much more quickly as the system identifies which valves or other inline items on the P&ID are or are not present on the model and if the model contains extra or incorrect items.

Another way specification driven P&IDs aid in modelling is allowing the 3D designer to have both the P&ID and the model up on the screen at the same time and to ‘drag and drop’ a valve or inline item from the P&ID and place it directly into the model. By doing this, the designer knows that the P&ID and model both contain the latest information and the system automatically knows that the item is in the model.

The ability of designers to make these integrity checks at any time in the design process was a large step forward in leveraging the power of the P&ID and all of the information associated with it.

Interdepartmental interoperabilityAlthough the P&ID could be the controlling document for the design process, it had no power beyond a reference drawing. Even with its newfound intelligence, all it had become was a document that was easier to edit, more complete, and that more accurately reflected the design and specifications for the 3D phase of the design.

It was good that a valve could be recognised as, for example, Valve Type: Gate, Size: 6 in., Tag No: VG101 etc., but was that really what was represented by those items? What about the relevant datasheets, purchase orders, external and internal memos, hours of change order notices, safety reports and maintenance records?

What was still not being addressed by these intelligent P&IDs was everything these items truly represented in the real world. There needed to be another step in the P&ID's journey for it to become a broadly useful document and focal point for information. They had to be able to attach external pieces of information to any P&ID component and to allow designers, engineers and other stakeholders access to this information from as broad a base as possible.

distributive intelligence and document managementIn the early 1990s, the rage for many companies was document management. They saw this as the ideal way to access documents and

the information they contained. Most of these systems worked well and continue to offer a great service. However, in the plant design environment where companies had placed enormous amounts of data into their P&ID systems, document management only delivered half the job. The drawing was there and could be printed out, but what about the underlying information?

It was becoming clear that these systems held the P&ID once again to a supporting role as just another file similar to a fax or scanned document. As projects progressed and document management systems became more widely used, P&IDs no longer functioned as the sole coordinating document they were. Yet engineers and designers still wanted to use P&IDs and find out all they needed to know about the items contained in them.

Ultimately, the fault of access was not that of the document management systems but of the P&ID systems that created these drawings. The reason was that to interrogate these P&IDs and the components they contained, one could only do so using the tool that had produced the drawings. Obviously having all stakeholders learn a CAD system just so they can pull out information from a P&ID is really not feasible. And to keep going back to ask the CAD operator to access this information is highly inefficient for all involved.

Unleashing the true power of the P&IdFortunately, there are now innovative software packages that address this problem. One way they do it is to publish the P&ID project, including all of the linked data, documents and database information, in a format that allows all stakeholders to access this information directly from the P&ID in a browser window. This allows someone to search for a P&ID, or for an item on the P&ID, by inputting the tag number, and the person does not have to know CAD to do so.

To do this, the software first gathers and copies all of the associated linked documents. It also makes a copy of the database and links this copied database to the document files associated with each component. Next, it converts the P&IDs into a neutral web accessible format and adds hyperlinks for each and every tag on the drawing that tie them back to the copied database.

The whole process would take days to do manually for each P&ID. With these automated tools, this process that could include hundreds of drawings and tens of thousands of tags takes just minutes to complete. What it creates is an accurate and faithful facsimile of the project with all of the associated information accessible to any person with the ability to operate a browser and a mouse!

The benefits to the process design environment are profound. For example:

ª The published project includes all information and linked documents and files.

ª Everyone is working with the same data.

ª Everyone is working on the most up to date data.

ª Information is being accessed in read only formats.

ª Updates are quick and easy to perform at any time.

ª The system keeps all native files intact and uncorrupted.

ª Information is accessed on the internet, intranet or extranet much like any website.

conclusionP&IDs have always been valuable and useful tools yet it has taken modern technology to release the true potential of this often overlooked document. In this new world, P&IDs are no longer passive drawings that hold information that only skilled CAD operators can access. For just a little more effort, P&ID systems can take on their true place in the design process.