Best Practice for Risk Based Inspection

In quantitative analysis, risks are evaluated taking account of all the probabilities,
and are normally presented on logarithmic probability-consequence plots.
Whilst all these approaches to risk analysis are valid, it is important that there is a
high degree of transparency to the process and the data. This may restrict the use of
non-validated computer software. The risk analysis process must be capable of
being independently assessed.
6.2. IDENTIFICATION OF ACCIDENT SCENARIOS
An accident scenario within RBI is a set of circumstances that involves deterioration
of equipment, with the possibility of failure and subsequent events leading to wider
detrimental effects and consequences. For example:
• Circumstances could be the susceptibility of materials to corrosion, cyclic
loading causing fatigue, failure in water chemistry control, or the potential for
damage from impacts or poor maintenance.
• Subsequent events could include fire, explosion, or the release of steam or
dangerous gases.
• Detrimental effects and consequences could include effects on the Health and
Safety of employees and the public, the environment, and the economics of lost
production, equipment and company reputation.
There are many techniques available for Duty Holders to use to identify accident
scenarios (6.3). They differ in the degree of detail to which events leading up to and
after the failure are identified and quantified within a logical structure. The
following lists the main specialist techniques that may be used:
• Hazards and Operability Study (HAZOPS)
• Failure Modes and Effects Analysis (FMEA)
• Fault Tree Analysis (FTA)
• Event Tree Analysis (ETA)
• Human Reliability Analysis (HRA)
Appendix C gives a description of each of these techniques.
6.3. IDENTIFICATION OF DETERIORATION AND MODES OF FAILURE
The process used for identifying deterioration mechanisms for pressure systems and
other systems containing hazardous materials should be conducted in a wide
ranging and systematic manner. It is more effective if it involves experienced staff
from different disciplines rather than being the work of a single person. Acceptable
processes could include combinations of the following:
• Review of specific plant history and information from previous inspections
• Review of experience across similar industries or plants
• Expert elicitation of knowledge of structural integrity and materials
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