Risk Based Inspection (RBI) is an
Optimal maintenance Optimal maintenance is the discipline within operations research concerned with maintaining a system in a manner that maximizes profit or minimizes cost. Cost functions depending on the reliability, availability and maintainability characteristics o ...
business process used to examine equipment such as pressure vessels, (QOC) quick opening closure - doors, heat exchangers, and piping in industrial plants. RBI is a decision-making methodology for optimizing inspection plans. The RBI concept lies in that the risk of failure can be assessed in relation to a level that is acceptable, and inspection and repair used to ensure that the level of risk is below that acceptance limit. It examines the
Health, Safety and Environment (HSE) and business risk of ‘active’ and ‘potential’ Damage Mechanisms (DMs) to assess and rank failure probability and consequence. This ranking is used to optimize inspection intervals based on site-acceptable risk levels and operating limits, while mitigating risks as appropriate. RBI analysis can be qualitative, quantitative or semi-quantitative in nature.
Probability of Failure (PoF) is estimated on the basis of the types of degradation mechanisms operating in the component. It is calculated as the area of overlap between the distributions of the degradation rate for each degradation mechanism (based on uncertainties in rate) with the distribution of the resistance of the component to failure.
Consequence of Failure (CoF) is defined for all consequences that are of importance , such as safety, economy and environment. Consequence of failure is evaluated as the outcome of a failure based on the assumption that such a failure will occur.
Accuracy
Accuracy and precision are two measures of ''observational error''.
''Accuracy'' is how close a given set of measurements ( observations or readings) are to their ''true value'', while ''precision'' is how close the measurements are to each oth ...
is a function of analysis methodology, data quality and consistency of execution.
Precision
Precision, precise or precisely may refer to:
Science, and technology, and mathematics Mathematics and computing (general)
* Accuracy and precision, measurement deviation from true value and its scatter
* Significant figures, the number of digit ...
is a function of the selected metrics and computational methods. Risk presented as a single numeric value (as in a quantitative analysis) does not guarantee greater accuracy compared to a
risk matrix A risk matrix is a matrix that is used during risk assessment to define the level of risk by considering the category of probability or likelihood against the category of consequence severity. This is a simple mechanism to increase visibility of ri ...
(as in a qualitative analysis), because of uncertainty that is inherent with probabilities and consequences.
RBI is most often used in
engineering
Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range of more speciali ...
industries and is predominant in the process industry (oil&gas, petrochemical, pharmaceutical, power generation). Assessed risk levels are used to develop a prioritized inspection plan. It is related to (or sometimes a part of) Risk Based Asset Management (RBAM), Risk Based Integrity Management (RBIM) and Risk Based Management (RBM). Generally, RBI is part of Risk and Reliability Management (RRM). The basis of most RBI programs is the Corrosion
Circuit, in which each circuit can be compared for relative risk levels to aid in inspection and maintenance planning.
Inspections typically employ
non-destructive testing (NDT).
Prioritization
Items with high probability and high consequence (i.e. high risk) are given a higher priority for inspection than items that are high probability but for which failure has low consequences. This strategy allows for a rational investment of inspection resources.
Objectives
RBI assists a company to select cost effective and appropriate maintenance and inspection tasks and techniques, to minimize efforts and cost, to shift from a reactive to a proactive maintenance regime, to produce an
auditable system, to give an agreed “operating window”, and to implement a
risk management tool.
The purposes of RBI include:
# To improve risk management results
# To provide a holistic, interdependent approach for managing risks
# To apply a strategy of doing what is needed for safeguarding integrity and improving reliability and availability of the asset by planning and executing those inspections that are needed
# To reduce inspections and shutdowns and provide longer run length without compromising safety or reliability
# To safeguard integrity
# To reduce the risk of failures
# To increase plant availability and reduce unplanned outages
# To provide a flexible technique able to continuously improve and adopt to changing risks
# To ensure inspection techniques and methods consider potential failure modes
Standards
International engineering standards and recommended practices outline requirements, methodologies and the implementation of RBI.
* EN 16991: Risk-based inspection framework
* API 580: Risk-Based Inspection - Recommended Practice (Third edition, February 2016)
* API 581: Risk Based Inspection Methodology - Recommended Practice (Third edition, April 2016)
* ASME PCC-3: Inspection Planning Using Risk-Based Methods
* DNV-RP G101: Risk Based Inspection Of Offshore Topsides Static Mechanical Equipment
* EEMUA 159: Chapter 17 - RBI methodology for aboveground storage tanks
* EPRI TR-112657: Revised Risk-Informed Inservice Inspection Evaluation
* NCHRP Report 782: Proposed Guideline for Reliability-Based Bridge Inspection Practices
See also
*
Reliability engineering
*
Piping corrosion circuit
Piping corrosion circuit or Corrosion loop
/ Piping Circuitization and Corrosion Modelling, is carried out as part of either a Risk Based Inspection analysis (RBI) or Materials Operating Envelope analysis (MOE). It is the systematization of the ...
References
* (1) Chapter 008, Risk-Based Inspection Technique by Mohamed El-Reedy (Author) Publisher: Gulf Professional Publishing (17 July 2012) ASIN: B00DGSWO4S
* (2) A. Martínez, G. Lara*, R. Pascual, E. Lopez, Optimal failure-finding intervals for heat shields in a gas turbine combustion chamber using a multi-criteria approach, Journal of Engineering for Gas Turbines and Power, 137(7), 2015.
Risk management