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How to Read a P&ID ForRiskAnalysis
P&ID is a Piping and Instrumentation Diagram
To identify risk from a set of P&ID you must have clear understanding of three things…
#1
Understand the process
#2 Understand the failures
#3
Understand the consequence
Lines are used for showing piping, equipment and instrumentation connections…
…so people can communicate the process sequence and the relationship of different equipment
Equipment and instrumentation are connected by lines
Here are some common connections
Pipe
Common Failure Modes:- Collapse- Burst/Rupture- Erosion- Corrosion
Electrical Signal
Common Failure Modes:- Open connection- Electrical shorting- Electromagnetic interference
Pneumatic Signal
Common Failure Modes:- Leakage of internal fluid- High components friction level- Loss of pressure
Data Signal
Common Failure Modes:- Radio interference - Signal filtering- Packets Loss- Loss of signal
Flexible Pipe
Common Failure Modes:- Compressive failure- Tensile failure- Over bending - Rupture
Symbols are used to simplify drawings
From this To this
>>>>>>
>>>
Some equipment are used to add or reduce energy in the material
Blower
Common Failure Modes:- Fail to operate on demand- Loss of pressure
Furnace
Common Failure Modes:- Flame out
Pump
Common Failure Modes:- Fail to operate on demand- Loss of pressure- Over pressure
Compressor
Common Failure Modes:- Fail to start- Damage due to liquid- Over pressure- Excessive vibration
Heat exchanger
Common Failure Modes:- Leakage- Corrosion- Plugged
Plate Heat Exchanger
Common Failure Modes:- Leakage- Corrosion- Plugged
Aerial Fan
Common Failure Modes:- Loss of air circulation
Some equipment are used for material storage
Floating Storage Tank
Common Failure Modes:- Overflow- Leakage
Sphere Tank
Common Failure Modes:- Overpressure
Pressurized Vessel
Common Failure Modes:- Overpressure
Some equipment are used to separate material
Horizontal Separator
Common Failure Modes:- Overpressure
Vertical Separator
Common Failure Modes:- Overpressure
Fluid Contacting Column
Common Failure Modes:- Overpressure- Corrosion- Plugged
Tray Column
Common Failure Modes:- Overpressure- Contamination
Valves are used to control the flow of material
Manual Valve
Common Failure Modes:- External leakage- Internal leakage- Inadvertent position
Control Valve
Common Failure Modes:- Fail to close on demand- Fail to open on demand- Spurious operation- Leakage
Solenoid Valve
S
Common Failure Modes:- Structural failure- Seat Leakage- Seal Leakage- Loss of actuator
Motor-operated Valve
M
Common Failure Modes:- Motor failure- Fail to stroke
Butterfly Valve
Common Failure Modes:- Fail to close on demand- Fail to open on demand- Spurious operation
Globe Valve
Common Failure Modes:- Fail to close on demand- Fail to open on demand- Spurious operation- Leakage
Needle Valve
Common Failure Modes:- Fail to close on demand- Fail to open on demand- Spurious operation- Leakage
Ball Valve
Common Failure Modes:- Fail to close on demand- Fail to open on demand- Spurious operation- Leakage
Check valve
Common Failure Modes:- Leakage- Stuck at open position
Some equipment are used to relief pressure in the process
Relief Valve
Common Failure Modes:- Fail to open
Curved Gas Vent
Common Failure Modes:- Plugged
Rupture Disk
Common Failure Modes:- Corrosion
Control system are used to manage the behaviour of the process
Programmable Logic Control
Common Failure Modes:- Software error- Execution error
Shared display, shared Control
Common Failure Modes:- Software error- Execution error
Sensors are used to measure the physical properties of the process and convert it into a signal
Flow Transmitter
FT
Common Failure Modes:- Spurious measurement- Loss of measurement
Pressure Transmitter
PT
Common Failure Modes:- Spurious measurement- Loss of measurement
Level Transmitter
LT
Common Failure Modes:- Spurious measurement- Loss of measurement
Now lets identify the risk of this process…
LT253
HLL=2550 mmNLL=1650 mm
LLL=250 mm LC
LY LV
Steam
Condensate
To atmosphere at safe location
PSV
D-101
D-101 Re-boiler Condensate Pot
253253
253
111
Drawing Ref.
Drawing Ref.
LG253
2”
2”
3”
3”
3/4”
3/4”
6” 6”
6”
6”
Size ½SET @ 700kPag
6”
Step 1: Understand the process
• There is low pressure steam flowing into the vessel
• The steam cools and forms condensate in the condensate pot
• The level of the condensate liquid is controlled by a level control loop
• Condensate is drained out the bottom of the vessel
LT253
HLL=2550 mmNLL=1650 mm
LLL=250 mm LC
LY LV
Steam
Condensate
To atmosphere at safe location
PSV
D-101
D-101 Re-boiler Condensate Pot
253253
253
111
Drawing Ref.
Drawing Ref.
LG253
2”
2”
3”
3”
3/4”
3/4”
6” 6”
6”
6”
Size ½SET @ 700kPag
6”
Star
t
Step 2: Identify possible failures
The control loop can malfunction causing the valve LV253 to fail in the closed position
LT253
HLL=2550 mmNLL=1650 mm
LLL=250 mm LC
LY LV
Steam
Condensate
To atmosphere at safe location
PSV
D-101
D-101 Re-boiler Condensate Pot
253253
253
111
Drawing Ref.
Drawing Ref.
PG253
2”
2”
3”
3”
3/4”
3/4”
6” 6”
6”
6”
Size ½SET @ 700kPag
6”
Step 3: Assess the consequence
• The level control valve fails in the closed position blocking the drain line
• Hazard is high level and high pressure in the tank
• Potential consequence of loss of containment and equipment damage with $$$$ losses
Now you have identified the cause of the overpressure hazard, can you identify the safeguard?
The pressure relief with a set point of 700 kPa will open and reduce but not eliminate the risk of rupture
LT253
HLL=2550 mmNLL=1650 mm
LLL=250 mm LC
LY LV
Steam
Condensate
To atmosphere at safe location
PSV
D-101
D-101 Re-boiler Condensate Pot
253253
253
111
Drawing Ref.
Drawing Ref.
LG253
2”
2”
3”
3”
3/4”
3/4”
6” 6”
6”
6”
Size ½SET @ 700kPag
6”
By understanding the P&ID you can clearly assess risk in your operation and make good decisions
Any Questions?
Risk. Inspired.
For more lessons go to www.icarus-orm.com
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