A process flow diagram (PFD) is a diagram commonly used in chemical and process engineering to indicate the general flow of plant processes and equipment. The PFD displays the relationship between major equipment of a plant facility and does not show minor details such as piping details and designations.  Typically, process flow diagrams of a single unit process will include the following:

• Process piping
• Major equipment items
• Control valves and other major valves
• Connections with other systems
• Major bypass and recirculation streams
• Operational data (temperature, pressure, mass flow rate, density, etc.).
• Process stream names

Process flow diagrams generally do not include:

• Pipe classes or piping line numbers
• Process control instrumentation (sensors and final elements)
• Minor bypass lines
• Isolation and shutoff valves
• Maintenance vents and drains
• Relief and safety valves
• Flanges

Process flow diagrams are high levels drawings usually of multiple process systems within a large industrial plant and may be called block flow diagrams or schematic flow diagrams.  Figure 1 illustrates a typical PFD for an evaporator
system.
Figure 1 – PFD of Typical Evaporator system

1.2    Process and Instrumentation Drawing (P&ID)

The P&ID shows the interconnection of process equipment and the instrumentation used to control the process.  In the process industry, a standard set of symbols is used to prepare P&ID drawings of processes as can be seen in Figure 2 below.  For processing facilities, a P&ID is a pictorial representation of the following:

• Key piping and instrument details
• Relationship between control instruments and process equipment
• Control and shutdown schemes
• Safety and regulatory requirements
• Basic start up and operational information

Figure 2 – P&ID of Typical compressed air system
As a rule P&IDs do not have a drawing scale and present only the relationship or sequence between components. Just because two pieces of equipment are drawn next to each other does not indicate that in the plant the equipment is even in the same building; it is just the next part or piece of the system. These drawings only present information on how a system functions, not the actual physical relationships.  Because P&IDs provide the most concise format for how a system should function, they are used extensively in the operation, repair, and modification of the plant.

2.0  Drawing Practical

 
Practical Task
This is a practical task. Please refer to relevant sections of the course notes and your instructor for additional information and instruction.

2.1    Exercise No. 2.5.4a

 

2.2    Exercise No. 2.5.4b

 

 

Figure 3 – Common Isometric Pipe symbols

2.3    Exercise No. 2.5.4c

 

 

Figure 4- Common GA Pipe symbols

Exercises

• Identify and draw Piping and Instrument Diagram (P&ID) symbols frequently used for valves instruments and equipment as per Exercise No. 2.5.4a
• Identify and draw isometric symbols used for piping systems i.e. screwed, butt welded as per Exercise No. 2.5.4b
• Identify and draw pipe General Arrangement (GA) symbols that are used for piping general arrangement drawings as per Exercise No. 2.5.4c
• Sketch single line piping isometric for 2 of the piping assembly spools from Phase 2, Module 4, Unit 6.
• Dimension and label these single line piping isometric drawings
• Sketch correct piping GA views for 2 of the piping assembly spools from Phase 2, Module 4, Unit 6.

Additional Resources

 

Title	Author	Ref. Code
The Induction Book, “Code of Behaviour & Health & Safety Guidelines”	SOLAS
Basic Welding and Fabrication	W Kenyon	ISBN 0-582-00536-L
Fundamentals of Fabrication and Welding Engineering	FJM Smith	ISBN 0-582-09799-1
Workshop processes, practices and materials, 3rd edition, Elsevier Science & Technology	Black, Bruce J 2004	ISBN-13: 9780750660730
New Engineering Technology	Lawrence Smyth & Liam Hennessy	ISBN 086 1674480