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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


Some equipment are used to separate material

Horizontal Separator


Vertical Separator


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


Needle Valve


Ball Valve


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


Level Transmitter

LT


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


LLL=250 mm LC

LY LV

Steam

Condensate


PSV

D-101


253253

253

111

Drawing Ref.

Drawing Ref.

LG253

2”

2”

3”

3”

3/4”

3/4”

6” 6”

6”

6”


6”

Star

t

Step 2: Identify possible failures

The control loop can malfunction causing the valve LV253 to fail in the closed position

LT253


LLL=250 mm LC

LY LV

Steam

Condensate


PSV

D-101


253253

253

111

Drawing Ref.

Drawing Ref.

PG253

2”

2”

3”

3”

3/4”

3/4”

6” 6”

6”

6”


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


LLL=250 mm LC

LY LV

Steam

Condensate


PSV

D-101


253253

253

111

Drawing Ref.

Drawing Ref.

LG253

2”

2”

3”

3”

3/4”

3/4”

6” 6”

6”

6”


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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