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hazard & operability study

By: Eng. Mohamed SelimBy: Eng. Mohamed Selim

HAZOP

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Contents Introduction.Introduction. What is a HAZOP study.What is a HAZOP study. Why do a HAZOP study.Why do a HAZOP study. HAZOP requirements.HAZOP requirements. HAZOP Procedure.HAZOP Procedure. HAZOP worksheet.HAZOP worksheet. Case study.Case study. HAZOP Advantages.HAZOP Advantages.

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Introduction

There are many techniques to highlight how There are many techniques to highlight how hazards can occur in the process industries.hazards can occur in the process industries.

They also provide a clearer understanding They also provide a clearer understanding of hazards nature and possible of hazards nature and possible consequences, thereby improving the consequences, thereby improving the decision making process.decision making process.

These techniques assures more safe and These techniques assures more safe and operable design.operable design.

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Introduction

These techniques range from relatively These techniques range from relatively simple qualitative methods of hazard simple qualitative methods of hazard identification to advanced quantitative identification to advanced quantitative methods.methods.

The advanced quantitative methods of The advanced quantitative methods of hazard identification and risk assessment, in hazard identification and risk assessment, in which numerical values are derived for the which numerical values are derived for the judgement on the process design.judgement on the process design.

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Introduction

These techniques are most effectively These techniques are most effectively applied during planning, process design applied during planning, process design and design engineering stages.and design engineering stages.

where it is easily and cheaply to make where it is easily and cheaply to make changes, which are less expensive than changes, which are less expensive than when equipment/plants are operational.when equipment/plants are operational.

Hazard analysis is an essential part of the Hazard analysis is an essential part of the overall risk assessment procedure.overall risk assessment procedure.

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What is a HAZOP study

HAZOP is a systematically structured HAZOP is a systematically structured technique for identifying hazards, failures technique for identifying hazards, failures and operability problems resulting from and operability problems resulting from potential malfunctions in the process potential malfunctions in the process (process deviation). (process deviation).

It is a qualitative procedure in which a small It is a qualitative procedure in which a small team systematically examine the proposed team systematically examine the proposed process design issue.process design issue.

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Why do a HAZOP study

HAZOP study generates a list of identified HAZOP study generates a list of identified process and operability problems.process and operability problems.

In addition to suggestions for improvement In addition to suggestions for improvement of the system under study.of the system under study.

Alert operators from possible process Alert operators from possible process deviations and what to do in such cases. deviations and what to do in such cases.

HAZOP review is very cost effective, as it HAZOP review is very cost effective, as it appears from the following example.appears from the following example.

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Why do a HAZOP study

$$ %% Project total capital costProject total capital cost 38,00038,000 100100 Cost of HAZOP studyCost of HAZOP study6060 0.20.2 Cost of correctionsCost of corrections 647647 1.71.7 Cost of corrections if Cost of corrections if

no HAZOP doneno HAZOP done 1,4871,487 3.93.9 SavingsSavings 780780 2.12.1 Continuing cost savingContinuing cost saving 262/yr262/yr 0.70.7

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HAZOP requirements

HAZOP is carried out on the Piping & HAZOP is carried out on the Piping & Instrument Diagrams (P&IDs) in the detailed Instrument Diagrams (P&IDs) in the detailed design phase.design phase.

That means after issuance of the following That means after issuance of the following documents for internal discipline comments documents for internal discipline comments and client approval:and client approval: Process Flow Diagram (PFD) Process Flow Diagram (PFD) Piping & Instrument Diagrams (P&IDs).Piping & Instrument Diagrams (P&IDs).

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HAZOP requirements

HAZOP also may be carried out on an existing HAZOP also may be carried out on an existing plant to check the following:plant to check the following: Operability.Operability. Maintability.Maintability. Isolation.Isolation. Start-up and Shutdown.Start-up and Shutdown.

In this case, HAZOP is conducted on the In this case, HAZOP is conducted on the construction or as-built issue of the P&Ids.construction or as-built issue of the P&Ids.

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HAZOP Procedure

The P&IDs are divided into nodes.The P&IDs are divided into nodes. Each node represents a line or process Each node represents a line or process

equipment which has the same design equipment which has the same design intentions such as pressure, temperature or intentions such as pressure, temperature or flow.flow.

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HAZOP Procedure

HAZOP is based on sets of key words which HAZOP is based on sets of key words which stimulate through. stimulate through.

In HAZOP the thoughts are about deviations In HAZOP the thoughts are about deviations from the design intention.from the design intention.

The set of key words contain two sub-sets, The set of key words contain two sub-sets, which are:which are: property word.property word. guide word.guide word.

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HAZOP Procedure

Property word which focus attention on the Property word which focus attention on the design conditions and the design intention.design conditions and the design intention.

Property words such as:Property words such as: PressurePressure TemperatureTemperature FlowFlow Level, …etc.Level, …etc.

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HAZOP Procedure

Guide word which focus attention onto Guide word which focus attention onto possible deviations from the design possible deviations from the design intention.intention.

Seven Guide words are normally used such Seven Guide words are normally used such as: No, More, Less, As Well As, Part Of, as: No, More, Less, As Well As, Part Of, Reverse, Other Than.Reverse, Other Than.

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HAZOP Procedure Guide words are described in the following table.Guide words are described in the following table.

Guide WordGuide Word MeaningMeaning

No or NOTNo or NOT The complete negation of these intentionsThe complete negation of these intentions

MOREMORE Quantitative increase (e.g. high pressure)Quantitative increase (e.g. high pressure)

LESSLESS Quantitative decrease (e.g. low pressure)Quantitative decrease (e.g. low pressure)

AS WELL ASAS WELL AS Qualitative increase (e.g. impurity)Qualitative increase (e.g. impurity)

PART OFPART OF Qualitative decrease (e.g. only one of two components)Qualitative decrease (e.g. only one of two components)

REVERSEREVERSE The logical opposite of the intention (e.g. back flow)The logical opposite of the intention (e.g. back flow)

OTHER THAN OTHER THAN Complete substitution (e.g. flow of wrong material)Complete substitution (e.g. flow of wrong material)

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HAZOP Procedure

HAZOP review identify the following:HAZOP review identify the following: Process design intentions.Process design intentions. Process deviations or process equipment Process deviations or process equipment

failures. failures. operability problems resulting from operability problems resulting from

potential malfunctions in the process.potential malfunctions in the process. Direct causes for these deviations.Direct causes for these deviations.

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HAZOP Procedure

Possible consequences resulting from Possible consequences resulting from these deviations.these deviations.

The existing safeguards to prevent or The existing safeguards to prevent or protect the system from these deviations.protect the system from these deviations.

Judgement on the adequacy of the existing Judgement on the adequacy of the existing safeguards.safeguards.

Proposed recommendations or corrective Proposed recommendations or corrective actions to improve the system operability.actions to improve the system operability.

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HAZOP Procedure

Possible

Causes

Process

Deviations

Possible

Consequences

List of guide words for generation of

process deviations

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HAZOP Procedure

All these guide words are not mandatory.All these guide words are not mandatory. It may be more efficient to use only NO, It may be more efficient to use only NO,

MORE, and LESS with a larger set of MORE, and LESS with a larger set of property words. property words.

Accordingly, guide words should be chosen Accordingly, guide words should be chosen beforehand.beforehand.

HAZOP is generally carried out and directed HAZOP is generally carried out and directed by an experienced group leader.by an experienced group leader.

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HAZOP Procedure

The study is of the brain-storming type and The study is of the brain-storming type and could be very time consuming.could be very time consuming.

Therefor, only those deviations which Therefor, only those deviations which would lead to hazardous outcomes are to be would lead to hazardous outcomes are to be used and recorded for future actions.used and recorded for future actions.

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HAZOP WORK SHEETGW Divination Causes Consequence Safe Guard Recomm.

Guide Word

Possible divination from the design intention.

Possible causes of these divinations

The resulting consequence.

The existing Safeguard and protective systems.

Recommendations and corrective actions to improve the system safety and operability.

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Case study

PIPI

FICFIC

PICPIC

To FlareTo Flare

Relief ValveRelief Valve

NitrogenNitrogen

From TankFrom Tank

To ReactorTo Reactor

25 M3

1.1 BAR

20 C

Pump P-1Pump P-1

Line 1Line 1

Pump P-2Pump P-2 Line 2Line 2

CV-1CV-1CV-2CV-2

To AtmosphereTo Atmosphere

V-7V-7

V-6V-6

V-5V-5

V-1V-1

V-2V-2

V-3V-3

V-4V-4 CV-3CV-3

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Case study

Feed supply system to a process reactor. Feed supply system to a process reactor. A light study is to identify offsite hazards.A light study is to identify offsite hazards. HC reagent is pumped from a Nitrogen HC reagent is pumped from a Nitrogen

blanketed buffer tank (T-1), which supplies blanketed buffer tank (T-1), which supplies the process reactor.the process reactor.

A Piping and Instrument Diagram (P&ID) A Piping and Instrument Diagram (P&ID) is used for the HAZOP study.is used for the HAZOP study.

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Case study

The instruments include:The instruments include: Pressure indicator. (PI)Pressure indicator. (PI) Pressure indicator controller. (PIC)Pressure indicator controller. (PIC) Flow indicator controller. (FIC)Flow indicator controller. (FIC)

No alarms were included at this stage.No alarms were included at this stage. Starting with (T-1), and applying guide Starting with (T-1), and applying guide

words as shown in the following table.words as shown in the following table.

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Case studyGW Divination Causes Consequence Safe Guard Recomm.

More

Less

Level. 1. Pump P-1 fails to stop.2. Reverse from process.

3. Pump p-1 cavitates.4. Rupture in line 2.5. V-3 open.6. V-6 open.

1. Reagent released.2. Reagent released.

3. Damage to P-1.4. Reagent released.5. Same.6. Same.

None.

None.

1. Incorporate high level alarm and trip.2. Consider check valve in line 2.3. Can reagent explode If pump overheats ?4.Consider alarm and pump shut down.5. Consider alarm.

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Case studyGW Divination Causes Consequence Safe Guard Recomm.

Other than

Composition 1. Wrong reagent.

2. Impurity in reagent.

1. Possible reaction.

2. Possibleoverpressure.

1. None.

2. None.

1. Is reagent sampled before pumping ?

2. What are the possibleimpurities ?

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Case studyGW Divination Causes Consequence Safe Guard Recomm.

Less Pressure. 1. Break in flare or Nitrogen lines.

2. Loss of Nitrogen.

3. CV-2 fails closed.

4. PIC fails.

1. Reagent released.

2. Tank implodes.

3. Tank implodes.

4. Tank implodes.

1. None.

2. None.

3. None.

None.

1. Consider low pressure alarm.

2. What is the design vacuum of tank ?.

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Case studyGW Divination Causes Consequence Safe Guard Recomm.

More Pressure. 1. PIC fails.

2. CV-1 fails closed.

3. V-7 closed.

4. Overfill tank.

1. Reagent released via relief valve.

2. Reagent released via relief valve.

3. Same.

4. See (6).

1. relief valve.

2. relief valve.

3. relief valve.

4. relief valve.

1. What is capacity of CV-1 and relief valve ?

2. Is V-7 locked open ?

3. Is V-8 locked open ?

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Case study

Good estimation of event credibility comes Good estimation of event credibility comes only from experience in hazard analysis.only from experience in hazard analysis.

When members of HAZOP team have this When members of HAZOP team have this experience, they can generally eliminate experience, they can generally eliminate many more deviations and minimize record-many more deviations and minimize record-keeping.keeping.

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HAZOP Advantages

HAZOP review has the advantage of alerting HAZOP review has the advantage of alerting the operators and designers from the the operators and designers from the following:following: Possible process deviations.Possible process deviations. Possible process equipment failures. Possible process equipment failures. Operability problems.Operability problems. Different modes of operation.Different modes of operation. Potential malfunctions in the process.Potential malfunctions in the process.

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HAZOP Advantages

Deeper understanding of the system.Deeper understanding of the system. Direct causes for these deviations.Direct causes for these deviations. Possible consequences resulting from these Possible consequences resulting from these

deviations.deviations. Control and feedback systems.Control and feedback systems. Emergency and shutdown response.Emergency and shutdown response. The existing safeguards to prevent or protect The existing safeguards to prevent or protect

the system from these deviations.the system from these deviations.

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HAZOP Advantages

Judgement on the adequacy of the existing Judgement on the adequacy of the existing safeguards.safeguards.

Proposed corrective actions to improve Proposed corrective actions to improve system safety and operability.system safety and operability.

Define the responsibilities of the Define the responsibilities of the recommendations or corrective actions.recommendations or corrective actions.

Reporting and documentation of process Reporting and documentation of process design issue.design issue.

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Thank You

Eng. Mohamed SelimEng. Mohamed Selim

ENPPI ENPPI

HSE Department ManagerHSE Department Manager