HAZOP Basics
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Basic understanding of HAZOP it covers: -Basic understanding of HAZOP -HAZOP requirements -How it works -Case study -HAZOP team -Advantage & disadvantage
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HAZOP Basics
- 1. HAZOP Designed by Hossam A. Hassanein
- 2. Goals Basic understanding of HAZOP HAZOP requirements How it works Case study HAZOP team Advantage & disadvantage 2
- 3. You and your family are on a road trip by using a car in the middle of the night. You were driving at 100 km/h and, it was raining heavily. The car hits a deep hole and, one of your tire blows. You hit the brake, but due to slippery road and your car tire thread was thin, the car skidded and was thrown off the road. Scenario 3 What is the cause of the accident? What is 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? Points to Ponder
- 4. Definition HAZOP (Hazard & Operability) Study - Is structured technique, which may be applied typically to a chemical production process, identifying hazards resulting from potential malfunctions in the process 4
- 5. History 5 Initially prepared by Dr. H G Lawley and associates of ICI at Wilton in 1960’s . In 1977, Chemical Industries Association published the edited version. ICI expanded the procedure called HAZARD STUDY levels 1 to 6.
- 6. ICI Six Levels 6 Project exploration / preliminary project assessment Project definition Design and procurement During final stages of construction During plant commissioning During normal operation, some times after start-up
- 7. REMEBER 7 HAZOP is an identifying technique and not intended as a means of solving problems
- 8. Features of HAZOP Study 8 Subsystems of interest line and valve, etc Equipment, Vessels Modes of operation Normal operation Start -up mode Shutdown mode Maintenance /construction / inspection mode Trigger events Human failure Equipment /instrument/component failure Supply failure Emergency environment event
- 9. Features of HAZOP Study 9 Effects within plant Changes in chemical conditions Changes in inventory Change in chemical physical conditions Corrective actions Change of process design Change of operating limits Change of system reliability Improvement of material containment Change control system Add/remove materials
- 10. Features of HAZOP Study 10 How would hazardous conditions detected ? During normal operation Upon human failure Upon component failure In other circumstances Contingency actions Improve isolation Improve protection
- 11. Documents Needed for HAZOP Study 11 Preliminary HAZOP – Process Flow Sheet or digram ( PFS or PFD ) – Description of the Process Detailed HAZOP – Piping and Instrumentation Diagram (P & ID) – Process Calculations – Process Data Sheets – Instrument Data Sheets – Interlock Schedules – Layout Requirements – Hazardous Area Classification – Description of the Process
- 12. Process Flow Diagram (PFD) 12 Is a diagram commonly used in chemical and process engineering to indicate the general flow of plant processes and equipment. The PFD displays the relationship between major equipment of a plant facility and does not show minor details such as piping details and designations
- 13. Process Flow Diagram (PFD) Example 13
- 14. P&ID 14 A Piping and Instrumentation Diagram - P&ID, is a schematic illustration of functional relationship of piping, instrumentation and system equipment components. P&ID represents the last step in process design.
- 15. P&ID Example 15
- 16. HAZOP Procedure 16 Possible Causes Process Deviations Possible Consequences List of guide words for generation of process deviations
- 17. Definitions 17
- 18. Study Nodes The locations (on piping and instrumentation drawings and procedures) at which the process parameters are investigated for deviations. 18
- 19. Intention The intention defines how the plant is expected to operate in the absence of deviations at the study nodes. 19
- 20. Deviations Is a way in which the process conditions may depart from their design/process intent 20
- 21. Causes These are the reasons why deviations might occur 21
- 22. Consequences The results of the deviation, in case it occurs. 22
- 23. Safeguards Facilities that help to reduce the occurrence frequency of the deviation or to mitigate its consequences. 23
- 24. A short word to create the imagination of a deviation of the design/process intent. Guide Words 24
- 25. Guide Words Used (most 7 used) 25 Guide Words Meaning No Negation of the design intend Less Quantitative Decrease More Quantitative Increase Part of Qualitative Decrease As Well As Qualitative Increase Reverse Logical opposite of the intend Other Than Complete Substitution
- 26. HAZOP Deviation Guide 26 No, Not, None Less, Low, Short More, High, Long Part of As Well As, Also Other Than Reverse Flow No Flow Low Rate High Rate Missing Ingredient Misdirection, Impurities Wrong Material Backflow Pressure Open to Atmosphere Low Pressure High Pressure ___________ _ ___________ _ ___________ _ Vacuum Temperature Freezing Low Temperature High Temperature ___________ _ ___________ _ ___________ _ Auto refrigeration Level Empty Low Level High Level Low Interface High Interface ___________ _ ___________ _ Agitation No Mixing Poor Mixing Excessive Mixing Mixing Interruption Foaming, Extra Phase ___________ _ Phase Separation Reaction No Reaction Slow Reaction Runaway Reaction Partial Reaction Side Reaction Wrong Reaction Decompositio n Time Procedure Skipped or Missed Step To Short, To Little Too Long, Too Much Action Skipped Extra Action (Shortcuts) Wrong Action Out of Order, Opposite Speed Stopped Too Slow Too Fast Out of Synch ___________ _ Web or Belt Break Backward Special Utility Failure External Leak External Rupture Tube Leak Tube Rupture Startup, Shutdown, Maint ___________ _ Process Variable Guide Words
- 27. Process Parameters Physical parameters related to input medium properties Physical parameters related to input medium conditions Physical parameters related to system dynamics Non-physical tangible parameters related to batch type processes Parameters related to system operations 27 Process parameters may generally be classified into the following groups:
- 28. Examples of Process Parameters 28 Flow Pressure Composition Addition Separation Time pH Signal Start/stop Operate Maintain Services Communication Temperature Mixing Stirring Transfer Phase Speed Particle size Measure Control Level Viscosity Reaction Sequence
- 29. Simply How does it work? 29 NODE: Pipe after pump and splitter PARAMETER: Flow rate GUIDE WORD: Less (less than normal value) DEVIATION: less flow than normal CAUSE: of deviation, can be more than one CONSEQUENCE: of the deviation/cause ACTION: initial idea for correction/ prevention/mitigation A group members focus on the same issue
- 30. The HAZOP Process 30 Monitor Actions For Completion Agree Actions To Be Taken Apply Risk Ranking Associate Consequences Identify Causes Choose Deviation OR Parameters & Guide Words Select Equipment Node
- 31. 31 Case Study
- 32. Case Study 1: Preliminary HAZOP on Reactor 32 Cooling Water Refer to reactor system shown. The reaction is exothermic. 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 result could be a runaway reaction with pressures exceeding the bursting pressure of the reactor. The temperature within the reactor is measured and is used to control the cooling water flow rate by a valve. Perform HAZOP Study
- 33. Case Study 1: Preliminary HAZOP on Reactor 33 Guide Word Deviation Causes Consequences Action 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 valveMore 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 ineffective and effect on the reaction If less cooling, TAH will detect. If detected, isolate water source. Back up water source? Cooling Water
- 34. Case Study 2: Shell & Tube Heat Exchanger 34 Using relevant guide words, perform HAZOP study on shell & tube heat exchanger
- 35. Case Study 2: Shell & Tube Heat Exchanger (Answer 1) 35 Guide Word Deviation Causes Consequences Action 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 maintenance and operator alert Corrosion Corrosion of tube Hardness of cooling water Less cooling and crack of tube Proper maintainence
- 36. Case Study 2: Shell & Tube Heat Exchanger (Answer 2) 36 Guide 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 line Install 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 line Install 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 Contamination Process fluid contamination Contamination in cooling water Outlet temperature too low Proper maintenance and operator alert
- 37. HAZOP Team 5to7members Design Engineer Process Engineer Operations Supervisor Instrument Design Engineer Chemist Maintenance Supervisor Safety Engineer (team leader) 37
- 38. HAZOP Advantage Easy to learn Stimulates creativity and generates ideas Systematic and through procedure Participants gain valuable knowledge of process Readily acceptable to regulatory authorities 38
- 39. HAZOP Disadvantage Time consuming Focusing too much on solutions Team members allowed to divert into endless discussions of details HAZOP is poor where multiple-combination events can have severe effects. 39
- 40. Division Into Sections Guideline 40 Choices of lines–P&ID must be divided logically. Not too many sections. Each section should contain active components, which gives rise to deviations. e.g piping which contains control valves can give rise to flow deviations, heat exchangers can cause Temp. deviations. Materials in section – contain significant amount of hazardous materials. Section based on process and states of materials. Only 1 process operation per 1 section. Define each major process component as a section. Define one line section between each major process component. Define additional line sections for each branches off the main process flow. Define a process section at each connection to existing equipment. Define only one process section for equipment in identical service. Define only one line at the end of a series of components if there are no other flow paths. Define only one additional line section if there are alternative flow paths, regardless of how many branches there are.
- 41. 41
Editor's Notes
- A qualitative technique based on “guide-words” to help provoke thoughts about the way deviations from the intended operating conditions can lead to hazardous situations or operability problems HAZOP is basically for safety Since, Hazards are the main concern & Operability problems degrade plant performance (product quality, production rate, profit) - Considerable engineering insight is required
- Project exploration / preliminary project assessment – to identify inherent hazards of process chemicals, site suitability and probable environmental impact. Project definition – to identify and reduce significant hazards associated with items and areas, check conformity with relevant standards and codes of practices. Design and procurement – to examine the PID in detail for identification of deviations from design intent capable of causing operability problems or hazards. During final stages of construction – to check that all recommended and accepted actions recorded in steps i, ii and iii implemented. During plant commissioning – to check that all relevant statutory requirements have been acknowledges and all installed safety systems are reliably operable. During normal operation, some time after start-up – especially if any modification been made. To check if changes in operation has not invalidated the HAZOP report of step 3 (Design and procurement) by introducing new hazards.
- The development of the detailed P&I Diagram is the last stage of the process design. The development will follow a normal standard procedure and include the following considerations : – Basic process control system - this is a closed loop control to maintain process within an acceptable operating region. – Alarm system - this is to bring unusual situation to attention of a person monitoring the process in the plant – Safety interlock system - this is to stop operation or part of the process during emergencies. – Relief system - this is to divert material safely during emergencies.
- Typically, process flow diagrams of a single unit process will include the following: Process piping Major equipment items Control valves and other major valves Connections with other systems Major bypass and recirculation streams Operational data (temperature, pressure, mass flow rate, density, etc.), often by stream references to a mass balance. Process stream names Process flow diagrams generally do not include: Pipe classes or piping line numbers Process control instrumentation (sensors and final elements) Minor bypass lines Isolation and shutoff valves Maintenance vents and drains Relief and safety valves Flanges Process flow diagrams of multiple process units within a large industrial plant will usually contain less detail and may be called block flow diagrams or schematic flow diagrams.
- - P&ID shows all of piping including the physical sequence of branches, reducers, valves, equipment, instrumentation and control interlocks. - P&ID is normally developed from process flow diagram (PFD). - The P&ID are used to operate the process system. A process cannot be adequately designed without proper P&ID.
- The P&IDs are divided into nodes. Each node represents a line or process equipment which has the same design intentions such as pressure, temperature or flow. HAZOP is based on sets of key words which stimulate through. In HAZOP the thoughts are about deviations from the design intention. The set of key words contain two sub-sets, which are: property word. guide word.
- . Several causes may be identified for one deviation. It is often recommended to start with the causes that may result in the worst possible consequence. These causes can be hardware failure, human errors, an unanticipated process state (e.g. change of composition), external disruptions (e.g. loss of power), etc.
- . Consequences may both comprise process hazards and operability problems, like plant shut-down or reduced quality of the product. Several consequences may follow from one cause and, in turn, one consequence can have several causes
- There are, in principle, five types of safeguards that: 1. Identify the deviation (e.g., detectors and alarms, and human operator detection) Worksheet entries 2. Compensate for the deviation (e.g., an automatic control system that reduces the feed to a vessel in case of overfilling it. These are usually an integrated part of the process control) Process parameters Guidewords Procedure HAZOP Reporting Conclusions 3. Prevent the deviation from occurring (e.g., an inert gas blancket in storages of flammable substances) Worksheet entries - (4) 4. Prevent further escalation of the deviation (e.g., by (total) trip of the activity. These facilities are often interlocked with several units in the process, often controlled by computers) 5. Relieve the process from the hazardous deviation (e.g., pressure safety valves (PSV) and vent systems)
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