Best Practice for Risk Based Inspection

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TECHNIQUES FOR IDENTIFYING ACCIDENT SCENARIOS Hazard and Operability Studies (HAZOP) HAZOP is a structured brainstorming exercise by a team discussion designed to identify potential variations and deviations from the design or operating intent and their consequences. A list of guidewords is sometimes used to stimulate the discussions. Typically, these focus initially on credible variations of process parameters (flow, level, temperature) before branching out to consider human factors and less likely ‘what if’ scenarios. HAZOP is a procedural tool designed to highlight and identify hazards and operability problems in industrial plants that could reduce the plant’s ability to achieve productivity in a safe manner. Studies tend to be wide-ranging and threats to the integrity of pressure systems may only be considered briefly. This procedure is a powerful tool for hazard analysis and its methodical approach ensures that weaknesses in the design intent are detected and acted upon. Failure Modes and Effects Analysis (FMEA) FMEA is a qualitative structured method for identifying the immediate effects of failure at the component level. It is implemented by considering each item of equipment and associated systems in the plant, detailing the possible failure modes (e.g. leak or break in the case of pressure equipment), and determining their resulting effect on the rest of the system. The analysis is more concerned with the specifying the likely effects and criticality of different modes of failure rather than the mechanisms or events leading to the failure. It is a simple method that is easy to apply, yet it is a powerful tool that can be used to improve the quality of products and processes. It can lead to focussing on consequences and additional safeguards to mitigate the effects of the failure. It is common for individuals familiar with system functionality to perform FMEA, but teams of experts can produce greater insight into the mechanisms and wider range consequences. Fault Tree Analysis (FTA) Fault tress analysis (FTA) is a logic-based methodology that is used for identifying and analysing the events that could lead to an accident or other undesirable outcome. The technique is one of ‘reverse thinking’ where the analyst begins with the final undesirable event that is to be avoided and identifies the immediate causes of that event. The aim of the analysis is to determine the chains or combinations of preceding events and circumstances. Tracing the chain of events leading to the final outcome can indicate where extra monitoring, regular inspection and protective devices such as temperature and pressure sensors and alarms, could protect and forewarn impending failure. By analysing failure data and assigning probabilities to each preceding event, the probability of the final outcome occurring can be determined. C1
Fault tree analysis is a very useful tool for studying the routes by which an accident can occur, and is particularly effective at identifying accident scenarios due to secondary and tertiary causes. It requires a great deal of skill and effort to implement. For this reason it is expected to be used only by industries where the consequences of failure could be very severe. Event Tree Analysis (ETA) Like FTA, event tree analysis is also a logic based methodology for identifying accident scenarios, but unlike FTA it is forward thinking. The analysis begins with a given initiating failure event and develops the resulting sequence of events, normally over a short time interval, making assumptions about the availability or otherwise of safeguards and back-up systems such as protective devices. ETA is an extension of failure modes and effects analysis to cover the whole system. Event trees are valuable for examining the consequences of failure. They are less effective for the analysis of the causes of system failure. The short timescale over which events are considered may mask longer term consequences such as the gradual deterioration of equipment due to faults elsewhere. Human Reliability Analysis (HRA) HRA was introduced as a means of quantifying the interaction between human and engineering systems. It aims to improve the understanding of the contribution made by all people to engineering systems. It is a systematic evaluation of the factors that influence the performance of all personnel such as operators, maintenance engineers, technicians etc, and is normally undertaken as a group activity. C2
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HSE Health & Safety Executive Best
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© Crown copyright 2001 Application
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5.3. PUBLISHED DATA, EXPERIENCE AND
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Any feedback or comments on the con
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Duty Holders inspect plant to manag
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inspection planning processes are b
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when a root cause has led to deteri
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plant database containing an invent
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Fig. 1.1 Process diagram for plant
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using suitable techniques, includin
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With this information the manufactu
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isk assessment carried out under Re
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CEOC recognises that it would seem
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• The second details how to estim
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a) Amount of equipment within item.
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2.9 SAFed - Guidelines on Periodici
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3.2. CRITERIA FOR APPLICATION Good
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3.3. DRIVERS TOWARDS RBI The reason
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4. THE RBI TEAM 4.1. COMPOSITION AN
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assessment and inspection may affec
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5. PLANT DATA REQUIREMENTS 5.1. ESS
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If the need for repair or modificat
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5.2. FAILURE CONSEQUENCES ASSESSMEN
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• Accident Databases. Many user o
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detected by periodic examination. D
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• Use of check-lists and mechanis
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Step 1. Determine and score (on a s
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The main problem with this approach
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Methods used to assess the release
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6.8. SUMMARY OF MAIN POINTS a) Risk
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within a written scheme. It may be
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For equipment purchased second hand
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(b) Industry guidelines The Institu
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Conversely, it would be prudent to
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HSE commissioned research (7.9) to
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They provide a basic proof of leak
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uncertainty will exist. For equipme
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8. ACHIEVEMENT OF RELIABLE INSPECTI
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Relevant Personnel Certification:
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Relevant Standards: BS EN 1711: 200
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measurements will more than likely
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Probability of detection (POD) resu
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• D-scan presentation: the displa
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Table 1 Generally accepted methods
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Table 4 NDT method versus damage ty
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8.2. REMOTE SCREENING TECHNIQUES Re
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The technique is particularly appli
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AE can be a very sensitive test met
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Because of the interdependence of t
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8.3.3. Discussion of POD and Flaw M
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a) A Technical Justification, and b
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ecommended. In particularly difficu
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8.7 HSE Project: ‘Programme for t
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Fig. 8.2 Example of Receiver Operat
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9. FEEDBACK FROM RISK BASED INSPECT
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Page 117 and 118: It is considered best practice if t
Page 119 and 120: 9.6. A DYNAMIC PROCESS - THE NEED F
Page 121 and 122: 10. EVIDENCE OF EFFECTIVE MANAGEMEN
Page 123 and 124: Evidence of good co-operation can u
Page 125 and 126: • Fitness-for-service assessments
Page 127 and 128: 10.12. SUMMARY OF MAIN POINTS (a) D
Page 130 and 131: A1. INTRODUCTION This Authoritative
Page 132 and 133: fed via pressure system 0019 - S -
Page 134 and 135: Probability of Failure Internal Cor
Page 136 and 137: (a) Vessels B1, B2 and B3 : Jackete
Page 138 and 139: (b) Vessel B4: Catalyst Column Prob
Page 140 and 141: Examination Periodicity: The freque
Page 142 and 143: (d) Vessel B6 : Catchpot Probabilit
Page 144: APPENDIX B AUDIT TOOL FOR RISK BASE
Page 147 and 148: 1. Assess the requirements for inte
Page 149 and 150: B1.5. HOW DO INTEGRITY MANAGEMENT A
Page 151 and 152: B3. SPECIFYING THE RBI MANAGEMENT T
Page 153 and 154: B4. ASSEMBLY OF THE PLANT DATABASE
Page 155 and 156: B5.5. HOW HAS THE LIKELIHOOD OF FAI
Page 157 and 158: B6.5. WHAT METHODS AND FACTORS ARE
Page 159 and 160: B7.6. IS EVIDENCE OF NDT CAPABILITY
Page 161 and 162: B9. FEEDBACK FROM INSPECTION B9.1.
Page 164: APPENDIX C TECHNIQUES FOR IDENTIFYI
Page 170 and 171: TYPES OF DETERIORATION AND MODES OF
Page 172 and 173: Fig.D3 Creep fissure in pipework wa
Page 174 and 175: Fig.D6 Stress corrosion cracking in
Page 176 and 177: maximum permissible pressure must b
Page 178: APPENDIX E SOFTWARE PACKAGES SUPPOR
Page 181 and 182: These modification factors reflect
Page 184: APPENDIX F GLOSSARY OF TERMS
Page 187 and 188: Duty Holder Within this report, the
Page 189 and 190: Qualitative Risk Analysis Qualitati
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Best Practice for Risk Based Inspection

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