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Hazard Evaluation, HE, HE, Techniques The following are types of HE, HE, techniques:
What if
Check Lists
HAZOP
FMEA
FTA
CPQRA
Quantitative
Quantitative
FMEA, Failure Mode Effects Analysis is a preliminary qualitative technique that may require preliminary quantitative analysis (Mini-QRA) This presentation only considers the HAZOP HAZOP technique. technique.
Press Page Down for 9 pages of further information on HAZOPS HAZOPS.. (Best viewed viewed with with 24 lines per screen - adjust your Zoom% to suit) continue to page 2
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Hazards and Operability Analysis
HAZOP
HAZOP was developed by Lawley (1974) of ICI. Based on early a ccount by Elliott & Owen (1968) Hazop studies are carried out by an experienced, multidisciplanary team, who review all physical aspects of a process (lines, equipment, instrumentation) to discover potential hazards and operability problems using a check list approach. The basis for a HAZOP is a critical examination of information found in a word model, a process flowsheet, a plant layout, equipment specification or a P&ID, (Piping and Instrument Drawing). The principals of examination include: 1 2 3 4
Intention Deviation Causes Consequences (a) hazards (b) operating difficulties 5 Safeguards 6 Recommendations / Actions continue to page 3
See tabs D1 to D3 for examples of computer forms.
3
Early HAZOP studies used the following set of Guide Words to systematically review the process:
NO or NOT
Negation of intention
No Flow of A
MORE
Quantitative increase
Flow of A greater than design flow
LESS
Quantitative decrease
Flow of A less than design flow
AS WELL AS Quantitative increase
Transfer of some component additional to A
PART OF
Quantitative decrease
Failure to transfer all components of A
REVERSE
Logical opposite of intention
Flow of A in direction opposite to design direction
OTHER THAN Complete substitution
Transfer of some material other than A
More recent computerization techniques use a Standard Set Of Generic Deviations For Specific Section Types. See Dev'ns tab for examples. continue to page 4
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Some Common HAZOP Analysis Process Parameters
Flow
Time
Frequency
Mixing
Pressure
Composition
Viscosity
Addition
Temperature
pH
Voltage
Separation
Level
Speed
Toxicity
Reaction
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Prepare for the review
Attitude Preparation
Meeting Leadership HAZOP Review By Team
Knowledge Experience
Teams HAZOP Experience
Documentation
Follow-up
Info for study P&Ids, Layout
Table
Deviation
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Causes
Consequences
Safeguards
Action
6
HAZOP analysis method flow diagram Select a process section or operating step Explain design intention
Repeat for all process sections
Select a process variable or task
Repeat for all process variables
Apply guide word to process variable
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Repeat for all guide words
Examine Consequences associated with deviation
Develop action items
List possible causes of deviation
Assess acceptability of risk based on consequences
6 con't
Identify existing safeguards to prevent deviation
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Potential HAZOP Pitfalls 1
Poor understanding by management of the HAZOP procedure An Ethylene plant has 100 P&IDs, 625 equip't items. Consider 5 variables, Pressure, Temperature, Flow Composition and Function. Consider 6 Guidewords, None, More of, Less of Part of, More than and Other than. Questions to be answered = Consider 5 minutes per question = Time for ethylene plant HAZOP study = 4 hour, 240 minutes sessions per day = No. working of days = Days per week = No. of weeks to complete HAZOP for plant =
2
Inexperienced HAZOP team
3
Inadequately trained or in-experienced leader
continue to page 8
625 5 6 18750 5 93750 250 375 5 75
items
a
variables
b
guide words questions min./question minutes minutes/day days days/week weeks
c d = axbxc e f = dxe g h=f/g I j=h/I
8
Common Mistakes 1 Failing to establish a "safe" environment for team members 2 Consequences of events not carried to conclusion. 3 Taking unwarranted credit for safeguards
See example on page 9 - one page down
4 Too little credit given for safeguards 5 Maing recommendations as specific as possible 6 Poor recording of HAZOPS 7 Failure to HAZOP start-up and shut-down procedures 8 Poorly up-dated P&IDs 9 A HAZOP is performed in lieu of properly executed design reviews 10 Wrong technique for system being reviewed (See spreadsheet titled Fig 5.3) continue to page 9
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HAZOP Example
See page 8 - item No. 3
To Compressor Inlet LAH
Teams tend to quickly identify alarms, shut-downs and controls, and claim them for safeguards.
FV 1
An alarm not tested may not work when called upon to do so.
Inlet Line LIC
Nuisance alarms are frequently bypassed and are not effective as safeguards. Often operators are not monitoring control panel. Valve in manual
end
Automatic control routines are often set in manual mode.
See tab D1 for computer documentation example
Dev'ns
Table 1 Source
ID No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Example Standard Set Of Generic Deviations For Process Section Types Lessons Learned From HAZOPS Reviews of FCCUs by P.E. McCluer et al, Hydrocarbon Processing, Aug 1992, p-140-C
Deviation High Flow High Level High Interface High Pressure High Temperature High Concentration Low / No Flow Low Level Low Interface Low Pressure Low Temperature Low Concentration Reverse / Misdirected Flow Tube Leak Tube Rupture Leak Rupture
Column X X X X X X X X
X X
Some other typical HAZOP deviations
Tank or Vessel X X X X X X X X X X
X X
Line X
Heat Exchanger
Pump
X X X X
X X X
X X X X
X X
X X X X X X X
Press Page Down
More Flow Less Flow More Pressure Less Pressure More Level Less Level Part of, wrong concentration As well as, contaminants other than, wrong material More Reaction Less Reaction No Reaction More Mixing Less Mixing More Corrosion More Erosion Sampling
Page 10
Compressor
X X
X X
D1
Company Nova Location Corunna Leader RAH Scribe GFR Prod'n PM Node No.
1
Revision Dwg No. Proc Des Instr'ts Mech Describe
JB GH FD
0 Cor -123-4567 Research Electrical HH Safety MN
Date Page Op Tech Other Other
2-Jun-97 1
Transfer Ethane from Deethanizer to C2 KO Pot
Intention The intent is to transfer 150,000 lb/hr of C2/C2= mix at 300 psig and at -30 °F for the startup period.
Guide Wrd
High
Param
Flow
Dev'n High Flow
Possible Causes 1 FV-1 Wide open 2 3 Consequences 1 High level in KO pot with liquid carry-over to compressor with serious damage to rotor. Potential hydrocarbons release. 2 3 Safeguards 1 High level alarm LAH-1 2 3 Recommendation / Actions Respib By Date 1 Consider limiting flow orifice, auto SD trip on High-High level, smart check valve. 1 JB 1-Jan-99 2 2 3 3
Page 11
D2
Company Location Leader Scribe Prod'n
Nova Corunna RAH GFR PM
Node No. Intention
Revision Dwg No. Proc Des JB Instr'ts GH Mech FD
0 Cor -123-4567 Research Electrical HH Safety MN
0
Date Page Op Tech Other Other
2-Jun-97 2 0 0 0
1 Describe Transfer Ethane from Deethanizer to C2 KO Pot The intent is to transfer 150,000 lb/hr of C2/C2= mix at 300 psig and at -30 °F for the startup period.
0 0 Guide Wrd
Low
Param Flow
Dev'n Low Flow
Possible Causes 1 2 3 Consequences 1 2 3 Safeguards 1 2 3 Rec / Actions 1 2 3
Respib 1 2 3
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By
Date
D3
Company Location Leader Scribe Prod'n Node No.
Revision Dwg No. Proc Des Instr'ts Mech
Date Page Op Tech Other Other
Research Electrical Safety
Describe
Intention
Guide Wrd
Param
Dev'n
Possible Causes 1 2 3 Consequences 1 2 3 Safeguards 1 2 3 Rec / Actions 1 2 3
Respib 1 2 3
Page 13
By
Date
Chk List
Hazard & Operability Studies Check List Example 1 Changes In Quantity
2 Changes in physical condition
a
High Flow
b
Low Flow
c
No Flow
d
Reverse Flow
a
High or Low pressure
b
High or Low Temperature Static buildup
c
1 Pump racing, delivery vessel pressure lost, suction pressurized, scale dislodged, leak in heat exchanger 2 Pump failure, scaling of delivery, presence of foreign body, poor suction condition, cavitation, leak in heat exchanger, drain leak, valve jammed 3 Pump failure, delivery vessel overpressurized, gas blockage, presence of foreign body, scale, sediment, suction vessel empty. 4 Pump failure, pump reversed, delivery vessel over pressurized, poor isolation, gas locking, surging, back siphoning. 1 Boiling, cavitation, freezing, chemical breakdown, flashing, condensation, sedimentation, scaling, foaming, gas release, priming, exploding, imploding. Changes in viscosity, density. External Fire, Weather conditions, Hammer. 2 same as 1 3 Source of Ignition, Personnel shock.
3 Changes in chemical a condition b
High or Low Conentration Contaminants
1 Changes in proportion of mixture, in water or solvent content. 2 Ingress of air, water, steam, fuel, lubricant, corrosion products, other process materials from high pressure system, leakage through heat exchangers. gas entrainment, spray, mist.
4 Startup and Shutdown Condiotion.
a
Testing
1 Vacuum, pressure testing with with harmless material.
b
Commissioning
2 Concentration of reactants, intermediates
c
Maintenance
3 Purging, venting, sweetening, drying, warming. Access, spares.
a
Pipeline registration
1 Should this pipe be considered for registration?
5 Hazardous Pipelines
Page 14
Loss of automatic control Operator error
Failure of joint, pipe, valve, trap, bursting disc, relief valve.
