Hazop basic concepts.pdf

8/9/2019 Hazop basic concepts.pdf

1/14

054402 DESIGN AND ANALYSISLECTURE TWELVE

Daniel R. Lewin, Technion1

12 - HAZOPDESIGN AND ANALYSIS - (c) Daniel R. Lewin1

054402 Design and Analysis

LECTURE 12: HAZARD AND OPERABILITY(HAZOP) STUDIES

Daniel R. Lewin

Department of Chemical EngineeringTechnion, Haifa, Israel


! Provide motivation for performing a HAZOP/HAZAN studyon a process

! This lecture provides instruction on how to carry out aHAZOP analysis" HAZOP is a technique for identifying hazards without waiting

for an accident to occur.! Next lecture, we will learn about the tools and methods

used in a HAZAN analysis" HAZAN is a technique for estimating the probability and

consequences of a hazard.

OUTLINE

Sources: T. Kletz, HAZOP and HAZAN , 3rd Ed., IChemE (1992) T. Kletz, Learning from Accidents in Industry ,

Butterworths (1988) T. Kletz, What Went Wrong? , 2nd Ed., Gulf Publishing Co. (1988)

This lecture, and next week’s lecture:


2/14




FEED SECTION OF PROPOSED OD PLANT

Restriction plateROPTemperature rec.TR

Relief flareRFPress. controllerPICFlow indicatorFI

Flow controllerFRCLevel controllerLICPressure guagePG

FI

#What can go wrong ?

$ What will be the consequences?

% How often will it occur ?

& How can it be prevented ?

' Is the cost of prevention justified ?


FROM “AN ATLAS OF SAFETY THINKING”

The first and most importantstage in any hazard study is to

identify the most importantthings that can go wrong andproduce accidents or operatingproblems.

1. Identify what can go wrong.

The ideas expressed in this section are best summarized in thefollowing frames.

A HAZOP is a systematic procedure to analyze the hazardsassociated with each process pipeline, applying the followingguide words: NONE, MORE OF, LESS OF, REVERSE, OTHERTHAN, PART OF, MORE THAN.


3/14





We need to know how often thehazard is likely to occur (HAZAN).

3. How often will it occur?

2. How big will the consequences be?

We need to know theconsequences to employees,members of the public, plant andprofits, now and in the long term.



We should compare the risk(that is, the probability timesthe consequence) with generallyaccepted codes and standards orwith the other risks around us.

5. What should we do?

4. Prevention.

How can we prevent the accidentoccurring, or make it lessprobable or protect people fromthe consequences?


4/14





Perhaps our method of

prevention has disadvantages,and better methods can besuggested. We should answerthis question before a table ismade and a glass ordered.

6. Is it worth the cost?

We should also compare the costof prevention with the cost ofthe accident to see if theremedy is ‘reasonably practical’or we should look for a cheapersolution.

7. Prevention 2.


DEVIATIONS GENERATED BY GUIDE WORDS

PART OF

OTHER THAN

MORE THAN

REVERSE

LESS OF

MORE OF

NONE

DeviationsGuide Word

No forward flow when there should be: i.e. no flow

More of any relevant physical property than thereshould be: e.g. higher F, higher T, higher P.

Less of any relevant physical property than thereshould be: e.g. lower F, lower T, lower P.

Composition of system different than it shouldbe: e.g. ratio different, or component missing.

More components present than there should be:e.g. extra phase present, or impurities.

What else can happen apart from NOC: e.g. start-up, shut-down, failure of services…

Flow in the reverse direction than that expected


5/14


6/14




HAZOP PROCEDURE

Note: In addition to identifying each hazard, it is importantto also estimate its severity, on a scale of 1 (high) to 4(low), and likelihood, on a scale of 1 (high) to 4 (low).


HAZOP PROCEDURE - SEVERITY

Medium HighMedium High – Injury hazard or hazard leading to loss of

1-6 months production or loss between $1-10M

2

LowLow – No injury hazard or hazard leading to loss of 6 months production or loss greater than $10M

1

SignificanceSeverity


7/14




HAZOP PROCEDURE - LIKELIHOOD

Medium HighMedium High – Hazard expected several times in theplant life.

2

LowLow – Hazard not expected at all in the plant life.4

Medium LowMedium Low – Hazard not expected more than once inthe plant life.

3

HighHigh – Hazard expected more than 1/year1

SignificanceLikelihood


HAZOP PROCEDURE – RISK RANKING

Almost acceptable risk levelAlmost acceptable risk level.. Acceptable if suitably controlledby management. Should check that suitable procedures and/orcontrol systems are in place.

B

Unacceptable risk level.Unacceptable risk level. Must be reduced to level B at themost by engineering or management control.

D

Undesirable risk levelUndesirable risk level.. Must be reduced to level B at the mostby engineering or management control.

C

Acceptable risk level.A

SignificanceRanking

AAAB4

AABC3

ABCD2

ACDD1

4321

Severity

Likelihood


8/14




DETAIL OF THE PROPOSED OD PLANT

FI


HAZOP STUDY ON PROPOSED OD PLANT

B

B

B

R

2

2

2

L

3

3

3

S

(c) Installkickback on J1pumps.(d) Check designon J1 pumpstrainers.

Covered by (b).

(a) Ensurecommunicationwith intermediatestorage operator.

(b) Install low

level alarm onsettling tank LIC.

Action Required

As for (1). J1pumpoverheats.

As for (1).

Loss of feedto reactor.Polymerformed inHEX with noflow.

Consequences

NoFlow

Dev’n

(3) Lineblockage,isolation valveclosed inerror, or LCVfails shut.

(2) J1 pumpfails.

(1) No HCavailable atintermediatestorage.

NONE

PossibleCauses

GuideWord


9/14





C

C

R

2

2

L

2

2

S

Moreflow

MOREOF

(f) Install highlevel alarm on LICand check sizing ofrelief oppositeliquid overfilling.

(g) Institutelocking offprocedure for LCVbypass if not in use.

Covered by (b).

(e) Instituteregular patrollingand inspection oftransfer line.

Action Required

Settling tankoverfills. Dangerof spillage ofHC. Fire hazard.

As for (1).HC dischargedinto areaadjacent topublic highway.

Consequences

Noflow

Dev’n

(5) LCVfails openor LCVbypassopen in

error.

(4) Linefracture.

NONE

PossibleCauses

GuideWord



D

B

R

1

2

L

2

3

S

Morepress-ure

(j) Covered by(c) except whenkickback blockedor isolated.Check line andFI. Install a PGupstream of LCVand anindependent PGon settling tank.

(h) Extend J2pump suction lineto 12” abovetank base.

Action Required

Transfer linesubject to fullpump deliveryor surgepressure.Possibility offracture andrelease of HC.

Incompleteseparation ofwater phase intank, leadingto problems inreactor

section.

Consequences

Moreflow

Dev’n

(6) Isolationvalve closedin error orLCV closeswith J1pumping.

(5) LCV failsopen or LCVbypass openin error.

MOREOF

PossibleCauses

GuideWord


10/14





C

C

R

2

2

L

2

2

S

Moretemp.

(l) Checkwhether thereis adequate

warning of hightemperature atintermediatestorage. If not,install.

(k) Installthermalexpansion reliefon valve section.

Action Required

High pressurein transferline and

settling tank.

Line fractureand possiblerelease of HC.

Consequences

Morepressure

Dev’n

(8) Highintermediatestorage

temperature.

(7) Thermalexpansion inisolatedvalve sectiondue to fireor strongsunlight.

MOREOF

PossibleCauses

GuideWord



Not applicable (n/a)REVERSE

A

C

R

1

2

L

4

2

S

Lesstemp.

(m) Lag watersump down todrain valve andsteam tracevalve and drainlinedownstream.

Covered by (e)and the checksin (j).

Action Required

Water sumpand drain linefreeze up.

Material lossadjacent topublic highway.

Consequences

Lessflow

Dev’n

(10) Winterconditions.

(9) Leakingflange ofvalved stubnot blankedand leaking.

LESS OF

PossibleCauses

GuideWord


11/14





4

4

S

1

1

L

A

A

R

High con-centration

of loweralkanes oralkenes instream.

(p) Check thatsettling tank

and piping,including reliefvalve, will copewith suddeninflow of morevolatile HCs.

(n) Arrangefor frequentdraining off ofwater fromintermediatestorage.Install highinterface levelalarm on sump.

ActionRequired

Higher systempressure.

Water sumpfills up morequickly. Morechance ofwater phasepassing toreactionsection.

Consequences

Highwaterconcent-ration instream.

Dev’n

(12) Disturb-ance on

distillationcolumnsimmediatelyupstream ofintermediatestorage tank.

(11) Highwater level inintermediatestorage tank.

PARTOF

PossibleCauses

GuideWord



A

A

R

1

1

L

4

4

S

OTHER Mainten-ance.

(r) Installlow-pointdrain and N2purge pointdownstreamof LCV. AlsoN2 vent onsettling tank.

(q) Checksuitability ofmaterials ofconstruction.

ActionRequired

Line cannot becompletelydrained orpurged.

Water sumpfills up morequickly. Morechance ofwater phasepassing to

reactionsection.

Consequences

Organicacidspresent

Dev’n

(14) Equip-mentfailure,flange leak,etc.

(13) As for(12).

MORETHAN

PossibleCauses

GuideWord


12/14




! PROJECT or DESIGN ENGINEER – Often a MechE. Responsiblefor keeping costs within target. He/she will want to minimizechanges, but at the same time wants to find out now rather thanlater if there are any unknown hazards or operating problems.

! PROCESS ENGINEER – Usually a ChemE. The person who drewdeveloped the flowsheet.

! COMMISSIONING MANAGER – Usually a ChemE. He/she willhave to start-up and operate the plant, and will be in favor of anychanges that will make life easier.

! INSTRUMENT DESIGN ENGINEER – A modern plant containssophisticated control and trip systems, and HAZOPs often result

in even more instrumentation.! RESEARCH CHEMIST – If new chemistry is involved.! INDEPENDENT CHAIRMAN – An expert in the HAZOP technique,

but not the plant. If he/she is not a represntative of the plantsafety department, one needs to be present.

WHO CARRIES OUT A HAZOP ? A HAZOP team for a new process consists of the following members:


TRACKING ACTION ON HAZOP

CMInstitute regular patrolling andinspection of transfer line.

e

IDEInstall high level alarm on LIC.More flowf

DECheck design on J1 pumpstrainers.

d

b

c

Follow-upreviewcomments

DE

IDE

CM

Actionby

No flow

OperatingDeviation

Install kickback on J1 pumps.

Install low level alarm onsettling tank.

Ensure communication withintermediate storage operator.

a

Action notes and queriesRef.No.


13/14




CHECK OUT THIS “BIT OF PLANT”


RLSAction RequiredConsequencesDev’n Possible CausesGuideWord

HAZOP STUDY ON “BIT OF PLANT”


14/14



CHECK OUT THIS “BIT OF PLANT”


" Applying the guide words systematically to identifythe most imporant hazards affecting each line in theprocess.

" Categorizing each hazard according to its severity,likelyhood and cost.

" Realizing that a HAZOP analysis is an ongoing processthat needs to be documented and followed up.

SUMMARY

On completing this week’s materials, you should be able tocarry out a HAZOP analysis:

Next lecture, we will learn about the tools and methods usedin a HAZAN analysis, which is a technique for estimating theprobability and consequences of a hazard.

Documents

Hazop basic concepts.pdf