hazop methodology - eduwavepool.unizwa.edu.om

Short Course on HAZOP and Risk Assessment

UDPS 1

Hazard and Operability Hazard and Operability Study Study

(HAZOP)(HAZOP)

2

I suppose that I should have done that

HAZOP Study!


UDPS 2

3

A scenario…A scenario…

You and your family are on a road trip by using a car inthe middle of the night. You were replying a textmessage while driving at 100 km/h and it was rainingheavily. The car hits a deep hole and one of your tireblows.

You hit the brake, but due to slippery road and your cartire thread was thin, the car skidded and was thrown offthe road.

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Points to ponderPoints to ponder

What was the cause of the accident?

What was the consequence of the event?

What can we do to prevent all those things to happen in the first place?

What other possible accidents might happen on the road trip?

Can we be prepared before the accident occurs?


UDPS 3

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Can we make it more systematic?Can we make it more systematic?Parameter Guideword Possible

Causes

Consequences Action Safeguard

Car speed Too fast

Too slow

Rushing Skidded when emergency brake

- Slow down

- Speed up

-ABS brake system

-Safety belt

- Air bag

Tire No thread

Less thread

Tire too old, often speeding and emergency break

Car skidded - Check frequently

- Have spare tire

Window visibility

Low

Very low

Rain Cannot see the road

Car light Dim

No light

-Stop car

-Go to nearest garage

-Use emergency signal

Road With holes

Rocky

Breaks the car tire

- Put a signboard

-Street lights

Travel time Night

Foggy

No street light -Travel during daylight

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What is a HAZOP study?What is a HAZOP study?

Systematic technique to IDENTIFY potential HAZardand OPerating problems

Involves a multi-disciplinary team methodically“brainstorming” the plant design

A qualitative technique based on “guide-words” tohelp provoke thoughts about the way deviations fromthe intended operating conditions can lead tohazardous situations or operability problems


UDPS 4

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What is a HAZOP study?What is a HAZOP study?

A HAZOP study is an examination procedure.

Its purpose is to identify all possible deviation from theway in which a design is expected to work and to identifyall the hazards associated with these deviations.

When deviation arise that results in hazards, action aregenerated that require design engineers to review andsuggest solutions to remove the hazard or to reduce itsrisk to an acceptable level.

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Potential Hazard Potential Hazard ANDAND Operability Operability ProblemsProblems


UDPS 5

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ExampleExample

A study was commissioned for a new plant.

Some two years previously, and for the first time, asimilar study had been carried out on differentplant at the same site which was then in theprocess of being designed.

Before the latest review commenced, theProduction Manager expressed the hope that thesame benefits would accrue as before, stating that

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Definition of Hazard & OperabilityDefinition of Hazard & Operability

Hazard - any operation that could possibly causea catastrophic release of toxic, flammable orexplosive chemicals or any action that could resultin injury to personnel.

Operability - any operation inside the designenvelope that would cause a shutdown that couldpossibly lead to a violation of environmental, healthor safety regulations or negatively impactprofitability.


UDPS 6

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BenefitsBenefits

The circumstances when HAZOPs are likely to producebenefits are:– during the design or installation of any new plant or process, or

major modification to an existing one;– when there are unique hazards such as environmental hazards

and quality or cost issues associated with the operation;– following a major incident involving fire, explosion, toxic release

etc; and– to justify why a particular code of practice, guidance note or

industry code is not to be followed.

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When should a HAZOP be heldWhen should a HAZOP be held

During various stages of plant design – At the beginning of the project as a ‘safety and environmental

specification’– Towards the end of process definition, when the Process Flow

sheets are available as a Safety and Environmental Review– When P&IDs are at ‘Approved for Design’ stage (Final design

HAZOP) During construction site inspections ensure that

recommendations arising from the HAZOP or other safety and environmental reviews are being implemented.

A pre-commissioning study reviews plant procedures and perform a conventional safety audit

Once operational, an audit of plant and procedures at regular interval ensures ongoing safety awareness


UDPS 7

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HAZOP study of existing plantHAZOP study of existing plant

Can be done at any time Mainly used to improve operating procedures or when

modifying plant Sometimes used to identify possible improvements in

plants where accident or incident rate is abnormally high Can be used in conjunction with plant safety audits Needs exceptional care to fully define the scope and

aims of the study Despite detailed operation knowledge, much of the

original design intent is often unknown

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Simple Example of a HAZOP StudySimple Example of a HAZOP Study

Diammonium Phosphate (DAP) Production

Phosphoric acid and ammonia are mixed, and a non-hazardousproduct, diammonium phosphate (DAP), results if the reaction ofammonia is complete. If too little phosphoric acid is added, thereaction is incomplete, and ammonia is produced. Too littleammonia available to the reactor results in a safe but undesirableproduct.

Both chemicals will be used in large quantities and inconcentrated form. Due to the highly corrosive nature ofboth chemicals, the project team was assigned toinvestigate the hazards posed to staff from the reactionresulting from study line 1 (phosphoric acid delivery line).


UDPS 8

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Production of DAP (continuous process)Production of DAP (continuous process)

Ammonia

Valve B

Reactor

Diammonium Phosphate (DAP)

Valve C

Valve A

Phosphoric Acid

Study line 1Phosphoric acid delivery line

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HAZOP Study Report on line 1 of DAP HAZOP Study Report on line 1 of DAP


UDPS 9

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Preliminary HAZOP ExamplePreliminary HAZOP Example

TC

Cooling Coils

MonomerFeed

Cooling Water to Sewer

Cooling Water In

Thermocouple

Refer to reactor system shown.

The reaction is exothermic. A coolingsystem is provided to remove theexcess energy of reaction. In the eventof cooling function is lost, thetemperature of reactor would increase.This would lead to an increase inreaction rate leading to additionalenergy release.

The result could be a runaway reactionwith pressures exceeding the burstingpressure of the reactor. Thetemperature within the reactor ismeasured and is used to control thecooling water flow rate by a valve.

Perform HAZOP Study

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Preliminary HAZOP on Reactor Preliminary HAZOP on Reactor -- ExampleExample

Guide Word Deviation Causes Consequences Action

NO No cooling Temperature increase in reactor

REVERSE Reverse cooling flow

Failure of water source resulting in backward flow

MORE More cooling flow

Instruct operators on procedures

AS WELL AS Reactor product in coils

Check maintenance procedures and schedules

OTHER THAN Another material besides cooling water

Water source contaminated


UDPS 10

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Preliminary HAZOP on Reactor Preliminary HAZOP on Reactor –– AnswerAnswer


NO No cooling Cooling water valve malfunction

Temperature increase in reactor

Install high temperature alarm (TAH)

REVERSE Reverse cooling flow

Failure of water source resulting in backward flow

Less cooling, possible runaway reaction

Install check valve

MORE More cooling flow

Control valve failure, operator fails to take action on alarm

Too much cooling, reactor cool

Instruct operators on procedures

AS WELL AS Reactor product in coils

More pressure in reactor

Off-spec product Check maintenance procedures and schedules

OTHER THAN Another material besides cooling water

Water source contaminated

May be cooling inefffective and effect on the reaction

If less cooling, TAH will detect. If detected, isolate water source. Back up water source?

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Term Definition

Cause The reason(s) why the DEVIATION could occur. More CAUSES can be identified for one DEVIATION.

Comments Any remarks to be given to the RECOMMENDATIONS or which, in another way, showed up during the HAZOP sessions.

Consequence The results of the DEVIATION, in case it occurs. CONSEQUENCES may both comprise process hazards and operability problems, like plant shutdown. More CONSEQUENCES can follow from one cause and, in turn, one CONSEQUENCE can have several CAUSES.

HAZOP Terminology HAZOP Terminology -- 11


UDPS 11

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Term DefinitionDeviation A way in which the process conditions may depart from their

INTENTION.

Intention / Design intent

Description of how the process is expected to behave at the Study Line. This is qualitatively described as an activity (e.g., feed, reaction, sedimentation) and/or quantitatively in the process parameters, like temperature, flow rate, pressure, composition, etc.

Keyword/ Guideword

A short word to create the imagination of a DEVIATION of the INTENTION. The mostly used set of Guidewords is: NO, MORE, LESS, AS WELL AS, PART OF, OTHER THAN and REVERSE. The GUIDEWORDS are applied, in turn, to all the PARAMETERS, in order to identify unexpected and yet credible DEVIATIONS from the INTENTION.


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Term DefinitionParameter The relevant parameter for the condition(s) of the process,

e.g., pressure, temperature, composition, etc.

Study Line/ Node A specific location in the process in which (the deviations of)the process intention are evaluated. Examples might be:separators, heat exchangers, scrubbers, pumps, compressors,and interconnecting pipes with equipment

Recommendation Activities identified during a HAZOP study for follow-up. Thesemay comprise technical improvements in the design,modifications in the status of drawings and processdescriptions, procedural measures to be developed or furtherin-depth studies to be carried out.



UDPS 12

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Term Definition

Action – Where a credible cause results in a negative consequence, it mustbe decided whether some action should be taken. It is at this stagethat consequences and associated safeguards are considered. If it isdeemed that the protective measures are enough, then no actionneed be taken, and words to that effect are recorded in the Actioncolumn.

– Actions fall into two groups:• Actions that remove the cause.

• Actions that mitigate or eliminate the consequences.

– Whereas the former is to be preferred, it is not always possible,especially when dealing with equipment malfunction. However,always investigate removing the cause first, and only wherenecessary mitigate the consequences.

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HAZOP Planning and ExecutionHAZOP Planning and Execution

PLANSelect Team

Examine SystemKeywords

CLOSE OUTRecord/File Completed

ActionsTRACK

ACTIONSHAZOP Review Meeting

TEAMSystem

AssessmentTeam Activity

REPORTAction List

HAZOP Report


UDPS 13

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HAZOP leader - The leader should be independent (i.e. has no responsibility for the process and/or the performance of operations)•Plan sessions and timetable•Control discussion•Limit discussion•Encourage team to draw conclusion•Ensure secretary has time for taking note•Keep team in focus•Encourage imagination of team members•Motivate members•Discourage recriminations•Judge importance issues

Responsibility of HAZOP Team MembersResponsibility of HAZOP Team Members

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Checklist for HAZOP LeaderChecklist for HAZOP Leader

Always prepare study program in advance.

Agree on the format or form to be used.

Prepare follow up procedures.

Brief members about HAZOP during first meeting.

Stop the team trying to redesign the process.

HAZOP is a team exercise. Do not let anybody (including the leader himself to dominate).


UDPS 14

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Process Engineer

• Provide a simple description

• Provide design intention for each process unit

• Provide information on process conditions and design conditions

• Provide a simple description

• Provide design intention for each process unit

• Provide information on process conditions and design conditions


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Mechanical Design Engineer

• Provide specification details

• Provide vendor package details

• Provide equipment and piping layout information

Instrument Engineer

• Provide details of control philosophy

• Provide interlock and alarm details

• Provide info on shutdown, safety features



UDPS 15

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Plant Engineer or Manager• Provide information on compatibility with any existing adjacent plant• Provide details of site utilities and services• Provide (for study on existing plant) any update on maintenance access and

modifications

Shift Operating Engineer or Supervisor• Provide guidance on control instrumentation integrity from an operating

experience view point• Provide (for study on existing plant) information on plant stability at the

specified control parameters• Provide information on experienced operability deviations of hazard

potential


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Chemist

• Provide details of process chemistry

• Provide details of process hazards (polymerisations, byproducts, corrosion

etc)

Project Engineer

• Provide details of cost and time estimation and also budget constraints.

• Ensure rapid approval if required



UDPS 16

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Required informationRequired information

P & IDs

Process flow diagrams

Heat and Material Balances

Layouts

Logic Diagrams

Equipment Data Sheets

Material Hazard Data Sheets

Hazardous area Layouts

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Does any other guideword combine with this parameter to give a meaningful deviation?

Specify the section or stage to be examined

Describe & discuss the step/ operation; determine the design envelope.Develop & record the design intention

From the description and the design intention select a parameter

Combine this parameter with a guideword to develop a meaningful deviation

Seek a possible cause of the deviation and identify the consequences

Evaluate the safeguards and decide if they are adequate of if a changeor further study is needed.

Have all causes of this deviation been considered?

YES

Are there further parameters to consider?

Examination of the steps/ stage is complete

NO

NO

YES

YES

NO

PHASE 2: SELECT A LINE

Record

Divide section into Study linePHASE 1: DIVIDE SECTION

PHASE 3: ANALYSIS

PHASE 4: RECORDING

PHASE 5: REEVALUATE

Sequence for conducting a HAZOP StudySequence for conducting a HAZOP StudyFlow diagram for the HAZOP analysis Flow diagram for the HAZOP analysis –– The parameterThe parameter--first approachfirst approach


UDPS 17

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Process HAZOP worksheetProcess HAZOP worksheetHazards and Operability Review

Project Name: Date: Page of

Process :

Section: Ref. Drawing:

Item Study node

Process Parameter

Deviations (guide words)

Possible causes

Possible consequences

Action Required

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Guidewords/ KeywordsGuidewords/ KeywordsThe basic HAZOP guide-words are:

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 desired

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


UDPS 18

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Additional guidewordsAdditional guidewords

Guide-word Meaning

Early/ late The timing is different from the intention

Before/ after The step (or part of it) is effected out of sequence

Faster/ slower The step is done/not done with the right timing

Where else Applicable for flows, transfer, sources and destinations

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Process parameterProcess parameter

Process parameter may generally be classified into the following groups:– Physical parameters related to input medium properties– Physical parameters related to input medium conditions– Physical parameters related to system dynamics– Non-physical parameters related to batch type process– Parameters related to system operations

These parameters are not necessarily used in conjunction with guide-words• Instrumentation• Relief• Startup/ shutdown• Maintenance• Safety/ contingency• Sampling


UDPS 19

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Examples of process parameterExamples of process parameter

Flow Composition pH

Pressure Addition Sequence

Temperature Separation Signal

Mixing Time Start/stop

Stirring Phase Operate

Transfer Speed Maintain

Level Particle size Service

Viscosity Measure Communication

Reaction Control Absorb

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Guidewords + ParameterGuidewords + Parameter

Some examples of combinations of guide-words and parameters:

NO FLOW– Wrong flow path – blockage – incorrect slip plate – incorrectly fitted

return valve – burst pipe – large leak – equipment failure – incorrect pressure differential – isolation in error

MORE FLOW– Increase pumping capacity – increased suction pressure – reduced

delivery head – greater fluid density – exchanger tube leaks – cross connection of systems – control faults

MORE TEMPERATURE– Ambient conditions – failed exchanger tubes – fire situation – cooling

water failure – defective control – internal fires


UDPS 20

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HAZOP ExerciseHAZOP Exercise

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Case Study Case Study –– Shell & Tube Heat ExchangerShell & Tube Heat Exchanger

Using relevant guide works, perform HAZOP study on shell & tube heat exchanger

Processfluid

Cooling water


UDPS 21

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HAZOP on Heat Exchanger HAZOP on Heat Exchanger –– Answer 1Answer 1


Less Less flow of cooling water

Pipe blockage Temperature of process fluid remains constant

High Temperature Alarm

More More cooling flow

Failure of cooling water valve

Temperature of process fluid decrease

Low Temperature Alarm

More of More pressure on tube side

Failure of process fluid valve

Bursting of tube Install high pressure alarm

Contamination Contamination of process fluid line

Leakage of tube and cooling water goes in

Contamination of process fluid

Proper maintainanceand operator alert

Corrosion Corrosion of tube

Hardness of cooling water

Less cooling and crack of tube

Proper maintainence

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HAZOP on Heat Exchanger HAZOP on Heat Exchanger –– Answer 2Answer 2Guide Word Deviation Causes Consequences Action

NONE 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 lineInstall TAH

MORE More cooling water flow

Failure of inlet cooling water valve to close

Output of Process fluid temperature too low

Install Temperature indicator before and after process fluid lineInstall TAL

LESS Less cooling water

Pipe leakage Process fluid temperature too low

Installation of flow meter

REVERSE Reverse process fluid flow

Failure of process fluid inlet valve

Product off set Install check valve (whether it is crucial have to check?)

CONTAMINATION

Process fluid contamination

Contamination in cooling water

Outlet temperature too low

Proper maintenance and operator alert

hazop methodology - eduwavepool.unizwa.edu.om

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