RBI Risk Based Inspection

Chapter 3

Basic Concepts

What is Risk?

• Risk is something that we live with on a day-to-day basis
• What is a Risk Decision?
• Examples from every day life

An Example of a Risky Decision

Acceptance of Risk

• We accept risk because the probability of a serious catastrophe is sufficiently low to make it acceptable

Risk

• Risk is the combination of the probability of an event occurring during some time period and the consequence (generally negative) associated with the event

Risk = Probability x Consequence

Perception of Risk Versus Reality

Management      Perception

Engineers

Supervisors

Operators

Craftsman         Reality

A Perception of a Risky Decision

Risky Decision Event Tree

Risk Management and Risk Reduction

• Not really synonymous
• Risk reduction is a part of risk management

1. Act of mitigating a known risk to a lower level

• Risk Management is a process

1. To assess risk
2. To determine if risk reduction is required
3. To develop a plan to maintain risks at an acceptable level
4. Some risks may be identified as acceptable
5. Some risks may be inherent

Management of Risk Using RBI

Evolution of Inspection Intervals

• Inspection programs are established to detect and evaluate deterioration due to in-service operations
• Periodic verification of equipment integrity evolved as “calendar-based” intervals
• Effectiveness varied widely

Evolution of Inspection Approach

• Better understanding of type and rate of deterioration
• Intervals became more dependent on equipment condition
• Codes and standards evolved

1. Percentage of equipment life interval
2. On-stream in lieu of internal inspection
3. Process environment induced cracking
4. Consequence based inspection intervals

Traditional Equipment Inspection

RBI – The Next Generation

• Ultimate Goal of Inspection

1. Safety and Reliability of Operating Facilities

• RBI Approach

1. Focuses attention specifically on equipment and associated deterioration mechanisms representing the most risk to the facility

Inspection Optimization

• Optimization for planning and implementing a risk based inspection program needs information on:

1. Risk associated with equipment
2. Relative effectiveness of inspection techniques to reduce risk

• Not all inspection programs are equally effective in detecting in-service deterioration and reducing risks
• Various inspection techniques are usually available to detect any given deterioration mechanism
• Each method will have a different effectiveness.

Relative Risk vs. Absolute Risk

• Complexity of risk calculation is function of factors affecting risk

1. Absolute risk is virtually impossible to determine because of too many uncertainties

• RBI is focused on a systematic determination of relative risk
• Risk acceptance may be evaluated by sensitivity analysis