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Risk Based Inspection RBI

RBI is most often used in engineering industries and in the oil and gas industry

Risk Based Inspection RBI

Risk Based Inspection (RBI) is an Optimal maintenance business process used to examine equipment such as pressure vessels, heat exchangers and piping in industrial plants.
RBI is a decision-making methodology for optimizing inspection plans.
RBI is most often used in engineering industries and in the oil and gas industry. 

The inspection of pressure plant, structures and machinery was once determined from custom industry practice based on prescriptive codes and health and safety legislation.
The inspection frequency, methods employed and locations examined were determined by the type of equipment with little consideration given to its age, specific duty or likely damage.
Increased operational experience and a greater appreciation of ageing and the hazards has led some parts of industry to adopt a more informed approach to inspection planning, specifying an inspection appropriate to manage the risk of failure within regulatory expectations.

The inspection of pressure plant, structures and machinery was once determined from custom industry practice based on prescriptive codes and health and safety legislation. The inspection frequency, methods employed and locations examined were determined by the type of equipment with little consideration given to its age, specific duty or likely damage. Increased operational experience and a greater appreciation of ageing and the hazards has led some parts of industry to adopt a more informed approach to inspection planning, specifying an inspection appropriate to manage the risk of failure within regulatory expectations.

Risk based inspection is the process of developing a scheme of inspection based on knowledge of the risk of failure. The essential process is a risk analysis. This is the combination of an assessment of the likelihood (probability) of failure due to flaws damage, deterioration or degradation with an assessment of the consequences of such failure.

The information gained from this process is used to identify:

  •  the type of damage that may potentially be present,
  • where such damage could occur, 
  • the rate at which such damage might evolve, 
  •  where failure would give rise to danger. 

Areas at high risk usually have credible damage mechanisms combined with high consequences from structural failure, the release of hazardous substances or stored energy. 
A suitable inspection scheme will deploy techniques at a frequency that provides adequate confidence about the condition, taking account of the damage mechanisms and the reliability of the inspection techniques used.
Industry sees RBI as a way to obtain economic benefits from extended run lengths and as means of using inspection resources more effectively from the use of automated NDT or non-invasive inspection schemes. 
Regulatory pressure will ensure that the process of RBI is carried out rigorously so that inspection decisions are based on adequate information and expertise. 
In some industry sectors (e.g. nuclear) where there very high consequences from failure, an approach to assuring safety based only on RBI may not be entirely tenable.


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 is a function of analysis methodology, data quality and consistency of execution.
Precision 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 (as in a qualitative analysis), because of uncertainty that is inherent with probabilities and consequences.

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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).