1. P&ID’s
PIPING & INSTRUMENTATION DIAGRAMS

2. Format & Layout
Title Block
Sheet Number
Revision Number
Date

3. Format & Layout Layout Rules of Thumb No Scale
Flow From Left to Right across page
Important Process Streams Heavy Dark
Less Important (utilities, instrumentation lines lightweight)
Horizontal Lines ‘break’ vertical Lines
Process Lines Break Instrumentation Lines
Pumps along bottom
Tanks above pumps

4. P&ID’s - Symbology Equipment Symbology Instrumentation Symbology
See the document “P&ID Symbols and Photos.DOC”

5. P&ID’s - Equipment
Keep in mind the development of the P&ID’s is really developing the process
The way it will start-up / shut-down and normally operate
Procedure
Start with the Simulation and Equipment List
Draw Equipment (including spares)
Draw the major process Lines, then Utilities

6. P&ID’s - Safety - ALWAYS!!!!!
ALWAYS Consider Safety!!
Think, what happens if the control valve doesn’t operate as intended?
What happens if the pump stops working?
How will the operators troubleshoot the problem?
What if the operators ignore an alarm
...
Consider the need for redundant controls and equipment, but only if deemed necessary.
Redundant things are twice as likely to fail!

7. P&ID’s - Simplicity Rules
The easiest process to operate and understand is the simplest one
K.I.S.S.
Add “indicators” (flow, pressure, temperature) for trouble shooting
Don’t add “controls” unless they are absolutely necessary
Only resort to complicated controls when you have to... Consider the consequences of operators not understanding them.

8. P&ID’s - Rookie Mistakes
Don’t put level control on Storage Tanks
They’re there to take up variations in flow, therefore the level is supposed to ‘float’
Let Pressures in the process ‘float’ as much as possible, try not to over control operating pressures.
Don’t try to control liquid flow at two points in a pipe - remember conservation of mass
Don’t look at one P&ID only - Look at the big picture then consider the details

9. P&ID’s - Rookie Mistakes
Draw the equipment the way it’s going to be built - don’t oversimplify it’s representation
more equipment/inst detail is better
Show Liquid levels / internals etc.
It helps you design the controls
It helps operators understand how it works FV FT
FIC FE
1200 kg/hr

10. Simplicity
Watch Out For Controls on Different Sheets L F A A

11. P&ID’s - Costs Are Important
Goal: Lowest Capital costs and Lowest Operating Costs.
Only build what’s required
The Cheapest Process that meets the need of all involved is the most profitable.
It’s got to work! After that, make it cheap as possible.

12. P&ID’s - Control
The Flow that occurs in a pipe is a function of the Pressure Drop.
Valves add or subtract from the natural pressure drop of the pipe.
Valves change the pressure drop to give us the flow rate we want

13. P&ID’s
Control (Globe) Valves can have just about any pressure drop and flow combination
On the other hand, pipes have very definite flow/pressure relationship
5 psi
50 gizillion psi
20 m3/hr
2” pipe, 20 m long, 20 m3/hr P = 5 kPa

14. P&ID’s Piping Pressure Drop “System Curve” for 4” pipe, length 100 ft
Resulting Flow Through Pipe
Pressure Differential

15. P&ID’s Piping Pressure Drop “System Curve” for 4” pipe, length 100 ft
Pressure Differential
Resulting Flow Through Pipe

16. P&ID’s Piping Pressure Drop “System Curve” for 4” pipe, length 100 ft
Pressure Differential
With a valve that’s
50% closed
Resulting Flow Through Pipe

17. P&ID’s
In a Liquid System (non compressible flow) two valves in series have the same flow rate through them
Press
7 bar(g)
DP = 3 bar
DP = 20 bar
Assume each segment of pipe has a DP of 1 bar

18. P&ID’s
Backing Up ?
Press
7 bar(g) ?

19. P&ID’s Pumps (Centrifugal) System Curve
Pressure Increase That Pump Is Able To Produce
Pump Curve
Flow Through Pump

20. P&ID’s - Control Systems
First ask what controls the production rate of the process?
How will we control this production rate
Flow control

21. P&ID’s - Control Systems
Mentally take note of other critical things that need to be controlled (flow, temperature, pressure, level)
Feed - do we need flow control ?
Multiple feeds - do we need to ratio one flow rate to another? A
Flow of B
depends on A B

22. Ratio Control FV FT
FIC FE
Primary
Rate
FRIC FT
Ratio To
Primary FV FE

23. Pressure To Decrease the Pressure of a Tank
allow material to be removed (at a faster rate)
condense vapour faster
PIC
PIC PT PT PV PV
Control Downstream Pressure
Control Upstream Pressure

24. Temperature
Usually you increase the flow or pressure of one stream. The effect of that change is to cause another streams temperature to change.

25. Level To Decrease the Level of a Tank
allow material to be removed (at a faster rate)
Tanks and Pumps
Always Provide a way of preventing your pumps from running dry
Always Provide a way of preventing your pumps from being “dead headed”
Recirc the pump discharge to the tank with a “minimum flow bypass”

26. Controls Failure Position of Valves
Most of the time it’s safer to bottle up the process and prevent failure from propagating downstream by making control valves “fail closed”
Occasionally it’s better to fail open
ie. Cooling water