Post on 04-Jun-2018
Prof. Enrico Zio
Hazard Operability Analysis
Prof. Enrico Zio
Politecnico di Milano
Dipartimento di Energia
Prof. Enrico Zio
HAZOP
• Qualitative
• Deductive (search for causes)
• Inductive (consequence analysis)
AIM:
Identification of possible process anomalies and
their associated causes and consequences
Prof. Enrico Zio
HAZOP
Initially developed to analyze chemical process
systems; later extended to complex operations and
other types of systems (e.g., software)
It is a qualitative, structured and systematic
examination of a planned or existing process or
operation in order to identify and evaluate problems
that may represent risks to personnel or equipment, or
prevent efficient operation
Deductive (search for causes)
Inductive (consequence analysis)
Prof. Enrico Zio
HAZOP: When?
Design
Phase
Completeness
of HAZOP
study
Impact of
results on
Design
HAZOP as a final check
upon detailed design
HAZOP study: better later than never. It may also be
performed on an existing facility (improvement of the
operability, risk reduction)
Prof. Enrico Zio
HAZOP: Who?
HAZOP team members (multidisciplinary):
Team Leader (HAZOP experienced)
Project engineers
Process engineers
Instrument/electrical engineers
Safety engineers
Maintenance Engineers
….
Prof. Enrico Zio
HAZOP: How?
1. Clearly identify the study nodes, i.e., the locations
(e.g., on piping) at which the process parameters are
investigated
2. Identify the functionally independent process units
(pumps, vessels, heat exchangers, etc.) that are
between the nodes (which cause changes in the
parameters between nodes)
3. For each node identify its operation modes (start-up,regime, shut-down, maintenance, etc.) and thecorresponding plant configurations (valves open orclosed, pumps on or off, etc.)
4. For each node in each of its operation modes,identify the possible deviations from nominalbehavior, by compiling an HAZOP table
Prof. Enrico Zio
HAZOP: Procedure steps
1. Decompose the system in functionally independent process units
2. For each process unit identify its operation modes (start-up, regime, shut-down, maintenance, etc.) and configurations (valves open or closed, pumps on or off, etc.)
3. For each process unit in each of its operation modes, identify the possible deviations from nominal behavior, by compiling an HAZOP table
Prof. Enrico Zio
HAZOP: Procedure steps
specify unit in/out fluxes (energy, mass, control signals, etc.) and process variables (temperature, flow rate, pressure, concentrations, etc.)
write down unit functions (heating, cooling, pumping, filtering, etc.)
apply keywords (low, high, no, reverse etc.) to the unit process variables and functions => process deviations
for each process deviation (qualitatively) identify its possible causes and consequences
Prof. Enrico Zio
HAZOP: A synoptic
Taken from Rausand, M. and Høyland, A.: "System Reliability Theory: Models,
Statistical methods, and Applications" (2nd ed.), Wiley, Hoboken, 2004
Prof. Enrico Zio
HAZOP: Details of procedure steps
Specify elements: in/out fluxes (e.g., energy, mass, controlsignals, etc.), process variables (e.g., temperature, flow rate,pressure, concentrations, etc.), etc.
Flow Composition pH
Pressure Addition Sequence
Temperature Separation Signal
Mixing Time Start/stop Stirring Phase
Operate Transfer Speed
Level Maintain Particle size
Services Viscosity Measure
Communication Reaction Control
Prof. Enrico Zio
HAZOP: Details of procedure steps
Specify elements: in/out fluxes (e.g., energy, mass, controlsignals, etc.), process variables (e.g., temperature, flow rate,pressure, concentrations, etc.), etc.
Apply Guide-Words to the unit process variables and in/outfluxes => process deviations
Guide-word Meaning Example
No (not, none) None of the design intent is achieved No flow when production is expected
More (more of, higher) Quantitative increase in a parameter Higher temperature than designed
Less (less of, lower) Quantitative decrease in a parameter Lower pressure than normal
As well as (more than) An additional activity occurs Other valves closed at the same time
(logic fault or human error)
Part of Only some of the design intention is
Achieved
Only part of the system is shut down
Reverse Logical opposite of the design intention
occurs
Back-flow when the system shuts
down
Other than
(other)
Complete substitution - another activity
takes place
Liquids in the gas piping
Early /late The timing is different from the intention
Prof. Enrico Zio
HAZOP: Details of procedure steps
Specify elements: in/out fluxes (e.g., energy, mass, controlsignals, etc.), process variables (e.g., temperature, flow rate,pressure, concentrations, etc.), etc.
Apply keywords (low, high, no, reverse etc.) to the unit processvariables and in/out fluxes => process deviations
For each process deviation (qualitatively) identify its possiblecauses and consequences
Prof. Enrico Zio
HAZOP TABLE
UNIT :
OPERATION MODE:
Keyword Deviation Cause Consequence Hazard Actions needed
More More Temperature
Additional Thermal Resistance
Higher pressurein tank
Release due to Overpressure
Install high temperature warning and pressurerelief valve
Prof. Enrico Zio
HAZOP TABLE
Keyword Deviation Cause Consequence Hazard Actions needed
More More Temperature
Additional Thermal Resistance
Higher pressurein tank
Release due to Overpressure
Install high temperature warning and pressurerelief valve
1. Identify the deviation (install an alarm)
2. Compensate for the deviation (automatic control system)
3. Prevent the deviation from occurring
4. Prevent further escalation of the deviation (plant shut-down)
5. Relieve the process from the hazardous deviation (pressure safety valve)
UNIT :
OPERATION MODE:
Prof. Enrico Zio
EXAMPLE: SMALL EXTERNAL POOL
The water of the pool is in re-circulation through pumps that aspire the water of the
compensation tank making it pass through the treatment organs before throw it
again in the pool.
SYSTEM TO
CORRECT WATER
PH
SYSTEM TO
DISINFECT THE WATER
SYSTEM TO
FILTER
THE WATER
Prof. Enrico Zio
HAZOP TABLEThe objective of the HAZOP analysis is to identify the possible deviations to the
normal operation that can contribute to the reduction of the quality of the water.
Prof. Enrico Zio
SYSTEM: shell & tube heat exchanger
Study Node: 1
Operational Mode: Nominal Conditions
Design Intent: P= 2bar, T=20°C, Flow=1l/sec
Process fluid
Cooling water
Hazop: example
12
3
4
Prof. Enrico Zio
Solution
Guide
WordElement Deviation Causes Consequences Action
LESS FLOW Less flow of cooling
water
Pipe blockage Temperature of
process fluid remains
constant
High Temperature
Alarm
NONE FLOW No cooling water flow Failure of inlet cooling
water valve to open
Process fluid
temperature is not
lowered accordingly
Install
Temperature
indicator before
and after the
process fluid line
Install TAH
MORE FLOW More cooling flow Failure of cooling water
valve
Temperature of
process fluid decrease
Low Temperature
Alarm
REVERSE FLOW Reverse s cooling fluid
flow
Not credible Not credible Not credible
MORE PRESSURE More pressure on tube
side
Failure of process fluid
valve
Bursting of tube Install high
pressure alarm
.... ... .... …. …. ....
Prof. Enrico Zio
HAZOP results
•Improvement of system or operations
– Reduced risk and better contingency
– More efficient operations
•Improvement of procedures
– Logical order
– Completeness
•General awareness among involved parties
Prof. Enrico Zio
HAZOP: Strength
1. Simple and systematic (computer tools available)
2. Include consequence effects also on other units: domino effects.
3. Covers human errors
4. Covers safety as well as operational aspects
5. It gives good identification of cause and excellent identification of critical deviations.
6. HAZOP is an excellent well-proven method for studying large plant in a specific manner.
Prof. Enrico Zio
HAZOP: weakness
1. Very time consuming and laborious (boredom for
analysts)
2. Tends to generate many failure events with
insignificance consequences and generate many
failure events which have the same consequences
3. Does not identify all causes of deviations (it may
omit some scenarios)
4. Does not allow to consider with multiple-combination
events
5. Gives little account to the probabilities of events or
consequences (meaningfulness of deviations are
expert judgment based)
Prof. Enrico Zio
HAZOP: comments
1. Include consequence effects also on other units: domino effects.
2. Simple and systematic (computer tools available)
3. Subjective (relies on analyst’s expertise)
4. Often used in support to the construction of FT and for RCM