How to unlock design efficiency, standards for P&ID development

P&ID standardization insights

• Understand the importance of standardization in P&ID development.
• Become familiar with key areas for P&ID standardization.
• Learn how to apply some best practices in P&ID development.

In a multidiscipline design and process-driven project, automation design documents may consist of several items, such as equipment or instrument specifications, input/output (I/O) lists and process control descriptions. The process piping and instrumentation diagram (P&ID) ties these elements together for the contractor, systems integrator and owner. These drawings can contain a plethora of information, and although there are some industry standards, designers can customize the look and feel of them to fit their project needs.

P&IDs communicate the instrumentation and controls (I&C) design. They have their own dictionary that updates over time. With so much information that could go into these drawings, it’s important for designers to develop standards for them:

•  To complement and support the rest of the design documents and disciplines (in particular, electrical and process mechanical).
• To provide relevant information to the contractor to facilitate project bidding, construction and control system documentation.
• To support existing client philosophies, standards and maintenance management systems.

A brief history of piping and instrumentation diagrams

P&IDs have gone through an evolution mirroring the shifts in technology, industry standards and ever-evolving demands of modern projects. The origin of P&IDs is not completely clear, but there are a couple of noteworthy people who deserve credit for developing the symbols and systems that are used in modern-day P&IDs.

Frank and Lillian Gilbreth published their 1921 paper “Process Charts” with the American Society of Mechanical Engineers (ASME) (see Figure 1). In this paper, the Gilbreths “point out the place of the process chart in management and present established working data used successfully in numerous working installations for many years.”

Figure 1. Process chart symbols presented by the Gilbreths in their 1921 paper. Courtesy: Library of Congress.

Many of the symbols presented in the Gilbreths’ paper were later adopted and further developed by different organizations, and they are incorporated into many of the standards used today in P&ID development. In particular, the International Society of Automation’s (ISA) RP 5.1, Instrument Flow Plan Symbols, is widely used for P&ID development. It was first published in 1949 and is still in use today, updated in 2022, as American National Standards Institute (ANSI)/ISA 5.1, Instrument Symbols and Identification.

In addition to the progress of symbology and nomenclature, the ways in which P&IDs are developed and used have changed. From hand-drawn diagrams in the 1960s and 1970s to computer-aided design (CAD) diagrams in the 1980s, the evolution of software has allowed more flexibility and options for displaying information (see Figure 2).

Figure 2. Portion of a hand-drawn P&ID (1974). Courtesy: CDM Smith.

Since the software technology advances at the turn of the 21st century, we’ve seen the rise of 3D and 4D designs, which have placed P&ID front and center in a multidiscipline process design. This includes an emphasis on integration of instrumentation and control system data that aid in not only construction but future operations and maintenance for the owner after system commissioning is completed (see Figure 3).

Figure 3. 3D process model built from intelligent P&ID data. Courtesy: CDM Smith.

The quest for P&ID standardization

The integration of P&ID data with current 3D models requires seamless coordination and interoperability between P&ID design and process modeling. Engineers must balance the standardization of key elements of P&ID development with accommodations for unique project requirements. Areas such as vendor/packaged systems, instrumentation symbology, control system input/output (I/O) representation and pipe/equipment identification demand standardized conventions to ensure consistency and interoperability.

Navigating the path to standardization is no easy feat, and there is no one-size-fits-all approach. It’s a worthwhile journey with complexities and nuances that demand careful consideration and require involvement from all stakeholders to strike the proper balance between customization and industry standards. While professional voluntary organizations like the ISA offer invaluable guidelines, such as ISA 5.1, there are many standards that can be considered depending on industry, geography and preference (see Table 1).

Table 1. Common Sources for P&ID Nomenclature and Symbology. Courtesy: CDM Smith.

This table organizes the standards and their descriptions in a clear format for easy reference.

In addition, balancing the level of detail in P&IDs is crucial to meeting project requirements without overwhelming the reader and causing confusion. Standardizing the level of detail ensures that P&IDs convey necessary information effectively and efficiently. What is behind the scenes of a P&ID can be just as important as what is on the P&ID. Modern P&ID development software allows us to take advantage of new 4D data-driven enhancements to generate tables and lists for valves, I/O signals and instrument lists that provide another useful layer of information to the project team throughout the system life cycle. Project-specific guidelines, customizable software tools and stakeholder collaboration are key elements of standardizing the level of detail. What follows is a sampling of items worth considering when developing a program for P&ID standardization.

Input/output signals and their significance on P&IDs

Standardizing the representation of I/O on P&IDs is crucial to ensure clarity and consistency throughout the design and maintenance processes. Clear and standardized I/O symbols improve communication among stakeholders, such as electrical engineers for their riser diagrams and cost estimators for determining quantity of controller I/O cards. They also streamline design workflows and enhance maintenance and troubleshooting activities.

By adhering to established conventions for I/O symbols, teams can effectively interpret and work with P&IDs, leading to more efficient project execution and enhanced overall quality. Options for standardization include adhering to international standards such as ISA symbols, following company-specific guidelines or using digital tools with standardized symbol libraries.

In traditional P&IDs, the process portion showing piping and instrumentation is typically depicted on one mechanical sheet and I/O details are depicted separately for each system by loop number, often on several different sheets. This separation makes it difficult to understand the entire plant process. This approach could lead to confusion among stakeholders, design errors and coordination issues between different contractors during construction (see Figures 4 and 5).

Figure 4. Portion of a legacy P&ID, circa 2000. Courtesy: CDM Smith.

Figure 5. Matching instrumentation loop drawing associated with Figure 4, circa. 2000. Courtesy: CDM Smith.

In modern P&IDs, one drawing typically depicts the entire scope of the process, including primary mechanical equipment, instrumentation and I/O signals. I/O signals can be shown to and from the control system, typically situated in the top quarter of the drawing. This comprehensive representation ensures that all essential components, from equipment to control signals, are clearly illustrated on a single sheet, facilitating seamless understanding and coordination among stakeholders throughout the project lifecycle (see Figure 6).

Figure 6. Portion of a modern P&ID. Courtesy: CDM Smith.

Standardizing I/O across the automation elements from the back end, 4D, CAD database to frontend graphics is essential for consistency, efficiency and reliability of process control systems. By ensuring that the input and output mechanisms adhere to established standards and conventions, such as those defined by industry protocols or system interfaces, application engineers can streamline communication between the database, graphical user interface and field devices. This standardization enables seamless data exchange, improves system interoperability and simplifies maintenance and troubleshooting tasks by incorporating additional details such as fail-safe wiring, pulse signals, three-wire analog and resistance temperature detectors (RTD)/thermocouple inputs and any other signal elements to enhance the clarity and comprehensiveness of system representation (see Figure 7).

Figure 7. Portion of I/O signals from a modern P&ID. Courtesy: CDM Smith.

Extra detail can provide valuable information about the functionality and characteristics of the I/O components depicted in the diagram. For instance, indicating fail-safe attributes, such as normally open or normally closed contacts, informs users about the system’s response in the event of a failure or emergency, enhancing safety and reliability in both hardwired control circuits and control system programming.

Similarly, specifying an RTD card or pulse I/O offers insights into the sensors or devices being used, aiding in system configuration, calibration, and troubleshooting activities. Furthermore, this information can assist in performing calculations to generate an I/O list in an Excel spreadsheet when integrated with modern intelligent modeling tools to refining control system I/O card designs for system architectures and control panel sizing. Additionally, it supports cost estimation teams in accurately interpreting details from P&IDs.

Differentiating between I/O that is hardwired versus software over communication cables with distinct line types and/or symbology an important visual distinction to make. This helps contractors understand how each instrument is wired, and which I/O is required to be programmed in the control system. It is crucial to coordinate this aspect closely with the customer as well as electrical discipline or electrician and note the different symbology on P&ID legend sheets. By clearly indicating these differences on P&IDs, contractors can efficiently plan and execute wiring tasks and programming, enhancing overall project coordination and execution.

The importance of instrumentation in P&IDs

To ensure clarity regarding the division of responsibility (DOR) of an instrument during construction, P&IDs should indicate which pieces of equipment are to be provided by specific trades. One option for achieving this is by assigning a two-digit number next to the device to indicate the design specification division number under which it is specified. For instance, a flow switch associated with an eyewash shower could be labeled with an ISA tag and a “22” next to it, indicating it is to be provided by a plumbing supplier and not the control system supplier shown as “40” in this example (see Figure 8). This approach helps contractors understand their responsibilities, streamlining construction coordination and ensuring efficient project execution.

Figure 8. Instrument supplier designations example. Courtesy: CDM Smith.

For many projects, there is a need to differentiate between existing instruments, new instruments and future work on a drawing. Existing instruments could be represented using standard symbols with a grayed-out appearance and italicized text, without DOR annotations. However, for future work, showing the text in italics within the bubble or adding a distinctive marker next to the instrument bubble, such as an asterisk or a specific abbreviation, can indicate that it pertains to future installations or modifications. This subtle differentiation effectively distinguishes the existing instruments from future and/or proposed work on P&ID. This ensures clarity and understanding which components require attention or action in a contract, facilitating smoother project management and accurate bidding and execution of work by a contractor and owner (see Figure 9).

Figure 9. Differentiating between current, existing and future work. Courtesy: CDM Smith.

ISA and other standards may not provide guidance for all types of instrumentation representation and their symbology. Therefore, additional details can be added to standard instrument symbols to include the instrument type acronyms and power requirements. For instance, a flow switch could be vane-activated (designated with a “V”) or a thermal dispersion type (designated with a “TD”), and it could be loop powered or externally powered (see Figure 10).

Figure 10. Incorporating instrument variations into symbology, such as type and power source. Courtesy: CDM Smith.

These additional details aid the cost estimating team in determining costs, support electrical teams in creating their risers and help the design team coordinate and cross-check installation details or hookup diagrams. Including this extra information enhances overall project quality by ensuring accurate communication and alignment across the project.

Vendor panels in P&IDs

Vendor control panels accompanying major mechanical equipment play a crucial role in industrial processes alongside the plant’s control system designed by the I&C discipline. Vendor control panels in P&IDs, in addition to the control system control system designed by the automation discipline, need differentiation to guarantee clarity.

It is crucial to coordinate any vendor panels (i.e., panels typically provided by a subcontractor, not the general contractor) shown on P&IDs with the appropriate specification division to ensure proper coordination of signals with the control system, communication medium and panel devices.

Additional information that could be depicted on vendor control panels includes their power source, such as a centralized plant-wide uninterruptible power supply (UPS) system, a power feed from a control panel or a power feed from an electrical power distribution panel. Any vendor panels depicted on P&IDs must align with the appropriate specification sections to ensure comprehensive coordination. This coordination includes hardwired I/O signals to the control system, communication medium used to connect to the control system and requirements for panel layouts. Standardizing drawing elements by showing key details such as DOR and power sources helps coordinate between disciplines during design, prevents discrepancies during construction and assists with programming coordination between the vendor’s system and the plant’s control system (see Figure 11).

Figure 11. Vendor panel representation. Courtesy: CDM Smith.

[subhead/h2] Loop numbering in a P&ID

Organizing control loops with standardized numbering schemes enhances clarity and efficiency in P&IDs. Every instrument on a P&ID should have a unique loop number to ensure that all instruments and equipment are accounted for in a design and follow a logical sequence from the start to the end of the process (see Figure 12).

Figure 12. Portion of loop numbering sequence for water treatment plant by process area. Courtesy: CDM Smith.

These unique loop numbers are then carried through into construction and provide consistent documentation between the field equipment, system documentation, control system programming and asset management systems. Standardized loop numbering conventions enable efficient maintenance, modification, and troubleshooting of a control system throughout its lifecycle. Plants can implement industry-standard loop numbering practices, develop their own guidelines or use loop numbering tools within design software for standardization.

The importance of P&ID standardization

P&ID standardization benefits the entire system’s lifecycle, and there are many elements that should be considered. The challenge lies in developing a framework that strikes a balance between adherence to industry standards and flexibility to accommodate client-specific preferences. Standardization is not just about conforming to a set of rules; it’s about forging a common language that bridges the gap between different project stakeholders.

In today’s world dominated by data, P&ID development faces a unique set of challenges. Off-the-shelf software solutions promise efficiency but often fall short in handling the nuances of P&ID data. Engineers find themselves wrestling with data manipulation, striving to massage raw information into formats that benefit both their organization and their clients. Moreover, the growing demand for data integration necessitates a paradigm shift in P&ID development. Modern P&IDs that have a thoughtful approach to standardization, from capturing real-time process data to facilitating predictive maintenance, provide the backbone needed to create the dynamic documents capable of supporting the modern-day control system they assist in developing.

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