In process industries such as petroleum, chemical, and electric power, a set of accurate P&ID drawings is the key cornerstone of project success – it is not only the “engineering language” of construction, but also the “control blueprint” of safe operation. This article will take you to deeply analyze the P&ID symbol system, reveal the differences between international standards such as ISA/ISO/DIN, and master the application of specifications from valves and instruments to pipeline numbers, so that your engineering design can comply with global standards and be accurate and efficient. Whether you are a novice who is just getting acquainted with P&ID or an engineer who needs to optimize drawings, this guide will become your professional assistant.

What is a P&ID?

P&ID (Piping and Instrumentation Diagram) is a crucial technical drawing in engineering design and industrial processes, used to describe in detail the piping, equipment, instruments and control logic of the process system. It is not only a core reference document for plant design, construction and operation and maintenance, but also helps engineers, operators and maintenance teams understand the structure and function of the entire system.

The core role of P&ID

The main uses of P&ID include:

• Design guidance: Provide basis for pipeline layout, equipment installation and instrument configuration.
• Construction Basis: Guide the construction team to correctly install equipment and piping systems.
• Operation reference: Help operators understand the process flow and control logic.
• Safety and Maintenance: For troubleshooting, safety analysis, and maintenance planning.

The main components of a P&ID

A complete P&ID usually contains the following elements:

• Equipment (such as reactors, heat exchangers, storage tanks, pumps, etc.)
• Pipelines (including main process pipelines, auxiliary pipelines, heating pipes, etc.)
• Valves (such as Globe Valves, ball valves, control valves, etc.)
• Instruments and control components (such as pressure gauges, flow meters, sensors, etc.)
• Connection and flow direction (arrow indicates the flow direction of the medium)

Application scenarios of P&ID

P&ID is widely used in many industrial fields, including:

• Oil and gas (refineries, pipeline systems)
• Chemical industry (reactors, distillation tower systems)
• Power industry (boilers, cooling systems)
• Pharmaceuticals and food (clean pipelines, aseptic processes)
• Water treatment (filtration, pumping systems)

The difference between P&ID and other flow charts

• PFD (Process Flow Diagram): More macro, only showing the main equipment and processes, without detailed instrument and valve information.
• P&ID: More detailed, contains all piping, instrumentation, and control components, used for construction and maintenance.
• ISO drawing (isometric drawing): shows the three-dimensional direction of the pipeline, mainly used for prefabrication and installation.

P&ID is the foundation of industrial automation and process control. Mastering its symbols and standards is crucial for engineers. In the following chapters, we will deeply analyze the meaning and usage of various P&ID symbols.

P&ID symbols explained: meaning and usage comparison table

P&ID uses standardized graphic symbols and letter codes to represent equipment, pipes, valves, instruments and other components. Correctly understanding these symbols is essential for reading and drawing P&ID. This chapter will introduce common P&ID symbols and their application scenarios.

P&ID Equipment Symbols

Equipment symbols represent the main vessels, machines and devices in the process flow, usually represented by simplified geometric shapes.

Piping P&ID Symbols

Pipe symbols represent the flow path of the medium, and different line types represent different functions.

Valve P&ID Symbols

Valve symbols use different graphics to distinguish their types and control methods.

Instrument and control symbols

Instrument symbols represent measurement or control functions through letter codes and graphics.

Other common symbols

P&ID symbol abbreviations and meanings

In P&ID drawings, equipment and instruments are usually labeled using standardized letter codes to quickly identify their functions. These abbreviations follow international standards (such as ISA S5.1 and ISO 14617) to ensure that engineers around the world can understand them uniformly.

Instrument function letter code

Instrument symbols usually consist of a letter (indicating the measured variable) and an additional letter (indicating the function), for example:

Equipment numbering rules

Equipment in a P&ID is usually numbered by category, for example:

Pipeline numbering and labeling

The following information is usually marked on the P&ID:

• Medium code (such as PG = process gas, CW = cooling water)
• Pipe diameter (e.g. 6″ = 6 inches)
• Pipeline class (e.g. CL300 = Class 300 pressure class)

Example:
PG-100-6″-CL300

• PG：Process Gas
• 100: pipeline number
• 6″: pipe diameter 6 inches
• CL300: ANSI Class 300 flange pressure rating

Common abbreviation comparison table

Comparison of international standards

Different countries/industries may use different abbreviation standards:

International standards and industry specifications for P&ID symbols

The standardization of P&ID symbols is crucial, as it ensures that engineers, designers, and operators around the world can accurately understand the process flow. Different countries and industries use different standard systems. This chapter will introduce the main international standards and their application scenarios in detail.

Comparison of mainstream P&ID international standards

Key Differences and Selection Recommendations

(1) Differences in instrument symbols

• ISA S5.1: Instruments are represented by a circle with a letter code inside (e.g. PI = pressure indication).
• DIN 19227: Hexagons or squares may be used to represent special instruments.
• GB/T 6567: Similar to ISA, but allows Chinese abbreviations (such as “pressure gauge” instead of “PI”).

(2) Differences in device symbols

• Heat Exchanger:
  • ISA: Add wavy lines inside a rectangle
  • DIN: Rectangle with double horizontal lines
• Pump:
  • ISO: Simplified circle + arrow
  • JIS: Possible to add details (such as blade shape)

(3) Differences in pipeline marking

• North America (ANSI): The “PG-100-6″-CL300” format is commonly used.
• Europe (ISO/DIN): The pressure class may be omitted and PN (nominal pressure) may be used instead.
• China (GB): Chinese characters may be added (e.g. “Process Gas – 6 inches”).

How to choose the right standard?

1. Project Location:
   • North American Projects → ANSI/ISA-5.1
   • European projects → ISO 14617 or DIN 19227
   • China Project → GB/T 6567
2. Industry requirements:
   • Petroleum/Chemical → ISA S5.1
   • Pharmaceutical/Food → Emphasis on cleanliness standards (may be supplemented by ISO 10628)
   • Electricity → Industry-specific symbols (such as special markings for boilers)
3. Customer needs: Some multinational companies will specify standards (such as Shell and BASF’s corporate specifications).

자주 묻는 질문

Q1.What is the difference between P&ID and PFD?

A1：

• PFD (Process Flow Diagram) Displays the main processes and equipment, and does not contain detailed instrumentation, valve or piping specifications.
• P&ID (Pipe & Instrumentation Diagram) is more detailed and contains all piping, control elements, instrumentation and valves for construction and maintenance.

Q2. Can P&ID symbol standards be mixed in different countries?

A2：Mixing is not recommended. While standards such as ISA, ISO, DIN, etc., are mostly compatible, some symbols (e.g., heat exchangers, valves) are represented differently and can lead to misunderstandings. Projects should uniformly adopt the standards specified in the contract (e.g., ANSI/ISA-5.1 or GB/T 6567).

Q3. How do I quickly memorize P&ID letter codes (e.g. PT, FV)?

A3：

• Initials: P = Pressure, T = Temperature, F = Flow.
• Feature Set:
  • PT = Pressure Transmitter
  • FV = Flow Valve
• The ISA S5.1 Standard Alphabetic Code List can be downloaded as a cheat sheet.

Q4. What is the difference between “CL300” and “PN40” in pipe callouts?

A4：

• CL300 (Class 300): American Standard pressure rating, indicating that the flange can withstand a pressure of approximately 300 psi.
• PN40 (Pressure Nominal 40): European standard pressure class, indicating the nominal pressure of 40 bar.
• Conversion: CL300 ≈ PN50 (depending on the medium and temperature).

Q5. What if there is no standard definition of a symbol on a P&ID?

A5：

• Check the project specifications: Some companies have custom notation (e.g., Shell, BASF’s internal standards).
• Add legend description: Annotate the definition of the symbol in the blank space of the drawing.
• Avoid innovation: Try to use the closest standard symbol to reduce ambiguity.

As a professional service provider with decades of experience in process industry technology, JH-Valve has always taken ISO 14617 and ISA 5.1 international standards as its cornerstone. From petrochemical to P&ID design optimization in the new energy field, each drawing has passed the strict review of ISO 9001 quality management system and GB/T 6567 standard. With core technologies such as Class 150-2500 full pressure level coverage and PID intelligent calibration system, we provide global customers with professional P&ID solutions that comply with ANSI/ISA-5.1, DIN 19227 and other multinational standards, while meeting the customized drawing needs of small and medium-sized projects.

Whether it is the complex P&ID design of API 6D piping system or the logic diagram optimization of IEC 61511 safety instrumented system, Jiangheng, with 200+ international project experience and intelligent CAD collaborative platform, will become your full-cycle P&ID partner from process design to construction implementation – contact Jiangheng technical team immediately to obtain free P&ID standard interpretation and drawing compliance review services, so that precise engineering language can empower every process detail!