HAZard Operability Analysis

Exercise lesson

Politecnico di Milano

Dipartimento di Energia

2HAZOP: Exercise 1 → Chemical Reactor

• A single monomer component is introduced in

the reactor and, with the help of a catalyst

already present in the reactor, the monomer

polymerizes into a more complex chemical.

• The reaction is an exothermic (produces heat)

polymerization.

• A cooling system is provided to remove the

excess energy of reaction.

• In the event of cooling function is lost, the

temperature of reactor would increase. This

would lead to an increase in reaction rate

leading to additional energy release.

• The temperature within the reactor is measured

and is used to control the cooling water flow

rate by a valve.

Stirrer

3

Node Parameter Guideword Causes Consequences Action

Cooling coil

Stirrer

HAZOP: Exercise 1 → Chemical Reactor

Stirrer

4HAZOP: Exercise 2

• The combustion air is filtered and, a part of it,

sent to heat exchanger

• In the heat exchanger, combustion air increases

its temperature thanks to the heat exchange

with hot fume coming from the furnace.

• The warm combustion air is sent to the

Furnace.

• The fume are sent to the chimney.

• In the fume side, the heat exchanger is

controlled by a pressure valve, which is

controlled by a pressure sensor.

• In the air side, the heat exchanger is controlled

by a temperature sensor.

5

Fume

side

Air

side

HAZOP: Exercise 2

6

Node Parameter Guideword Causes Consequences Action

Air side

Air side

Air side

Air side

HAZOP: Exercise 2

7

Node Parameter Guideword Causes Consequences Action

Fume

side

Fume

side

Fume

side

Fume

side

HAZOP: Exercise 2

Failure Mode and Effects Analysis

Exercise lesson

Politecnico di Milano

Dipartimento di Energia

Content 9

1. A simple exercise to warm up

2. Two real exercises

• Complete and submit by group!

Exercise 1: Domestic Hot Water System

In the domestic hot water system in

the Figure 1, the control of the

temperature is achieved by the

controller opening and closing the

main gas valve when the water

temperature goes outside the preset

limits min max140F, 180F.T T= =

1. Formulate a list of undesired safety

and reliability events

2. Perform FMECA (V03, V04, TSC01)

Exercise 1: Domestic Hot Water System

FMECA Sheet:

Component Failure modeEffect on whole

systemCritically class

Failure

frequency

Detection

methodsProtections and mitigation

Pressure relief

valve (V04)

Gas valve (V03)

Temperature

measuring and

comparing

device (Tsc01)

Exercise 2: Storage Tank System

The system consists of a water tank,

with a water supply on the right hand

side on the top and a water outlet at

the bottom. The tank is normally full

with both inlet and outlet closed (i.e.,

the valves are normally closed – NC).

Water is released manually, by pushing the pushbutton. This opens the valve on

the outlet line and water flows out. When the water level reaches the low level

controller (LC2), the outlet valve is closed. The inlet valve is also opened when the

water level reaches the low level controller (LC2). This valve remains open until

the water level again reaches the high level (at LC1) when the valve closes.

• Perform FMEA (inlet valve, LC1)

Exercise 2: Storage Tank System

FMECA Sheet:

Component Ops mode Failure mode

Failure

mechanism

（Possible）

Local effect Effect on whole

systemDetection

Inlet valve

Closed

open

LC1

Measuring

water level

Sending signal

to valve

Exercise 3: Storage Tank System

The tank acts as buffer storage for

transport of liquid from a source to

a consumer. The consumption is

not constant and the liquid level

therefore varies and is controlled

automatically.

Valves V1 and V2 are open and when the tank fills up, the level switch LSH

will send a signal to valve V1 to close. Filling then stops. If this fails and the

level continues to rise, there is an emergency high level switch, LSHH, which

sends a signal to valve V2 to close and valve V3 to open. The drain pipe (V3)

has a higher capacity than the source pipe (V1 and V2)

Exercise 3: Storage Tank System

FMECA Sheet:

Component Failure mode Probability Severity Detection

methods

Effect on whole

system

Protections and mitigation

v1

v2

v3

LSH

LSHH

TANK