Risk Based Inspection

Definition of RBI

RBI is a risk assessment and management process that is focused on failure modes initiated by material deterioration, and controlled primarily through equipment and structure inspection. RBI combines risk assessment and risk management techniques with all inspection activities, such as planning, inspecting, documentation and data analysis, to develop inspection plans that direct inspections towards the areas of highest risk. RBI can be applied to all types of material deterioration processes that may cause loss of integrity for pressure retaining equipment and structures.

Risk Assessment and Inspection

Risk is defined as the product of the frequency with which an event is anticipated to occur and the consequence of the event’s outcome. In mathematical terms, risk is calculated by:

Risk = Frequency × Consequence

Risk assessment is the process of identifying the sources of hazards, estimating the risk and evaluating the results. The risk assessment process answers the following three questions to determine the risk:

• What can go wrong?
• How likely is it?
• What are the consequences?

Risk can be expressed quantitatively as a measure of loss per unit of time or presented qualitatively. Presenting risk qualitatively is an effective means of illustrating risk.

Figure 1 below illustrates how risk is related to the likelihood and consequence. This matrix is simply a plot with likelihood on one axis and consequence on the other. The matrix shows the basic principles behind all evaluations of risk.

Figure 1: Risk matrix

The challenge lies in addressing risks in the central area of the matrix between “Low” and “High”. In this “Medium Risk” range, the question arises as to how much risk is acceptable. An important concept to understand is that high consequence may not mean high risk, and similarly, high likelihood may not mean high risk. The level of risk can only be determined once both of these variables are known or estimated.

As previously defined, RBI is an inspection planning process using risk assessment and risk management. The setting of inspection frequency within RBI is not a rigid process with fixed, predetermined inspection intervals. Inspection intervals for any given component may change throughout the life of the asset as risk increases or decreases. The frequencies that RBI derives are aligned to the needs of the component or situation and the risks associated. There is, nonetheless, a general logic to the inspections and frequency of the inspections, namely:

• Higher risk systems/components generally have the shorter frequencies of inspection and have potentially larger inspection population requirements.
• Lower risk systems/components often have extended inspection frequency (or even no inspection) and have reduced inspection population requirements. 

Risk for RBI is considered to be the product of the factors of consequence and likelihood: 

• Consequence (i.e., the outcomes that would  ensue should a catastrophic failure of the component occur); and,
• Likelihood (i.e., the probability that a catastrophic failure for the component will occur).

In general, unless there is a major change in the use, service duty or service parameters for a given piece of equipment or structure, the consequence of failure from each type of degradation is likely to remain fixed for its service life. Given this fact, it is correct to assume that the type and frequency of inspection activity will have no impact in modifying the consequence factor values.

The RBI Process

Typical standard inspection programs base the inspection techniques and frequencies mainly on manufacturer’s recommendations, industry standards, classification society or regulatory requirements. The general belief is that a decrease in the level of inspection activities would bring an associated increase in failures and hence a risk increase. Conversely, an increase in inspection activities is thought to result in a safer installation, amid an increase in cost. This belief, though accurate in general, has exceptions: 

• If failure of a component does not result in significant risk exposure, then any inspection activity for that component will result in additional costs without any risk reduction and further inspection may not be necessary.
• Excessive inspection activities (i.e., too frequent) may not bring any additional risk decrease. The extra inspection could even cause a risk increase due to issues such as human error during inspection and damage to protective coatings.
• Inspection activities that do not focus on the detection of the specific degradation mechanisms to which the component is subjected to will result in cost without benefit.

The conclusion is that not all inspection programs are equally effective in detecting degradation mechanisms and reducing risks, and they all have different costs. RBI provides the tools and processes to determine the optimum combination of inspection methods and frequencies.

The basic elements in the development of an RBI program are the following:

• The determination of the risk introduced by the potential failures of each component.
• The identification of the degradation mechanisms that can lead to component failures.
• The selection of effective inspection techniques that can detect the progression of degradation mechanisms.
• The development of an optimized inspection plan using the knowledge gained in the three previous items.
• The analysis of the data obtained from the inspections and any changes to the installation in order to feed back into the RBI plan.

RBI Benefits

RBI programs address risks due to structural or equipment deterioration from a safety, environment and economic perspective. Implementation of RBI plans can provide and document the overall reduction in risk for the facilities assessed. RBI programs mayidentify risks of such low level that require little or no inspection as a means of mitigation, and consequently, improving management of inspection activities by directing resources to higher risk areas.  RBI ensures that maximum effectiveness and improved efficiency for inspection are gained by:

• Prioritizing the components based on risk to differentiate criticality.
• Ensuring that the correct items within the system are selected for inspection (the “at risk” components).
• Ensuring that the optimal inspection frequency is determined and met.
• Ensuring that the correct inspection resources are selected for the job (skills set, competence).
• Selecting the correct inspection methods, since there is a thorough understanding of the potential failure modes.
• Planning inspections to minimize business interruptions.
• Providing greater focus for future inspection programs as inspection results are used to update the RBI program.

Where RBI is implemented, it is common to observe improvement in both the technical and economic performance of the equipment and installation. This improved performance is delivered through:

• Reduced installation outages due to unexpected failure of systems or components (reduction in the number of reactive repairs).
• Safer operation due to higher level of integrity and reduction in failures.
• Greater focus to planned maintenance activities through providing predictive replacement times from derived inspection data for critical components or structures.
• Improved budgetary control and forecasting forward inspection planning and inspection survey execution.
• Reallocated inspection effort and resources to the items that would provide for the biggest impact on risk reduction.

It is important to recognize that seeking ways to relax inspection practices is not the goal of establishing an RBI program. Modifications to inspection plans are not achievable in all circumstances. Only when a relaxation of an inspection plan will not result in an unacceptable increase in risk can such a relaxation be made. This ensures that compromise to the integrity of the asset or component does not occur. The process of developing an RBI plan may uncover the fact that the operator of the asset has actually been operating, maintaining and inspecting some components in a manner which did not provide the most efficient use of inspection resources. RBI is specifically useful at matching the correct inspection frequency and methods to the level of risk posed by the inspectable item.

RBI Limitations

As with all inspection programs, RBI is subject to uncertainty in dealing with damage mechanisms, their progression rates and the response of equipment and structures to the damage. Some inspection specifications have developed over time in response to observed damage or failure, and these events tend to govern inspection plans for all such equipment or structures. While it is possible to improve inspection specifications (e.g., using more sophisticated predictive methods for measuring damage rates), it is unwise, without installation-specific or other pertinent data, to assume that inspections are excessive just because failures are rare. 

Data used to support the RBI plan must be well characterized and include a clear understanding as to the uncertainties associated with such factors as corrosion rates, fatigue crack growth, material strength and toughness and stresses. Many RBI programs start with a period of data gathering and analyses, allowing the inspection plan to be fine-tuned over a period of time as confidence in the data grow. It should be recognized that RBI does not eliminate risk. The likelihood and consequence of an event or failure is always present, RBI serves to help manage and control the risk to tolerable and sustainable levels by focusing the resources available towards the components that are recognizable as producing the highest risk to the asset. Within RBI, this consists of (1) ranking the components to be inspected according to risk and (2) devising a plan to proactively inspect these components at an appropriate level and frequency that provides the Owner confidence that such components’ integrity remains acceptable. It follows that high-risk contributors deserve stricter management than the low risk contributors. It is this prioritization that allows for an efficient allocation of inspection resources.

Main Steps in the Development of an RBI Program

This section will describe a typical methodology used  to develop an RBI program, but a variety of methodologies are accepted by ABS, provided that the steps in the development process as described in this section are included. If any of these steps are missing or they are considered in a substantially different way than common industry practice and standards, a suitable technical explanation on the adequacy of the methodology should be included with the submittal for ABS consideration and approval. 

The typical procedural steps for the development on an RBI program

• RBI Team Setup.  The first step consists of the setup of an RBI team who will establish (or be given) the goals of the RBI program, and will carry out the RBI methodology to arrive at an inspection plan that achieves those goals. 
• Component Grouping and Baselining.   The program development begins with the identification and grouping of the components that are subject to the RBI program, and includes service, design and applicable inspection history data collection for those items. If new construction, then comparable service degradation data or reference material may need to be gathered to establish degradation concerns. 
• Risk-Based Prioritization.   Perform a risk-based prioritization screening so that the components most critical to the safety of the installation can be identified. This requires a risk assessment to be initially performed that  considers consequences of failure from the anticipated failure modes and degradation  mechanisms and frequency based on expected degradation rates. If necessary, additional inspection data is specified if more data is needed to complete the risk assessment. The risk prioritization of the components occurs after the risk assessment is completed. 
• Inspection Plan Development.   An inspection plan is developed based on the risk prioritization information so that the risk of failure is at or below acceptable levels. 
• Inspection Execution and Analysis of Inspection Results.  As the RBI program is executed and each inspection conducted, the results should be analyzed. This analysis should evaluate whether the assumptions made and data used to develop the RBI plan are valid and if the observed state of the component is acceptable for continuing operation until the next inspection. 
• RBI Program Updating.  Finally, the observed degradation mechanisms and rates are used to update the RBI inspection plan. 

Each step in this process will be described in more detail in the remainder of this Section.  

RBI Team Setup

An RBI program is best performed by a multi-disciplinary team that synergistically brings together different perspectives and technical strengths. A team approach ensures that all required information that is available within the facility and/or organization is considered in the RBI program, as well as providing a wider perception of the risks of failure.

The specific composition of an RBI team varies depending on the complexity of the facility, scope of the RBI program and any applicable regulatory requirements. Some of the disciplines will be called in as advisors, but  a core team is essential for continuity. RBI aims to prevent failures that lead to safety, environmental or economic concerns by planning inspections on the basis of information obtained from a risk analysis. The risk analysis for components needs to identify potential causes of failure, likelihood of failure, as well as determine the consequences arising from the failure. The RBI team should contain the expertise to identify and analyze all of the above factors and their implications to personnel safety, environment, property and production. If during the RBI risk prioritization, failure scenarios are inaccurately determined to have low risk, the RBI program could potentially reduce inspection efforts to related components, thus resulting in a hazardous situation. Personnel with technical and risk analysis knowledge are essential for the program to function effectively. The RBI team will typically consist of individuals with experience and technical knowledge in the following disciplines:

• Maintenance and inspection
• Degradation and failure mechanisms
• Reliability 
• Operations
• Structural integrity
• Risk analysis
• Production process hazards
• Safety and health
• Materials of construction

Participation in the team of a representative with knowledge of RBI efforts in other similar facilities will ensure consistency throughout the organization and/or industry, as well as provide wider experience of risks and practices.

Risk-Based Prioritization

Prioritization of the components subject to inspection is a critical step in the development of an RBI program. Through prioritization, the most effective and efficient use of resources to execute the inspections is achieved. The prioritization process within RBI is largely governed by the derived risk rankings for systems and components. In the case of a mature RBI program, prioritization may also be influenced by additional factors such as anomalies, repairs or scheduled shutdown programs.

In general, the RBI prioritization is performed using risk as the ranking parameter, which gives an equal weight to the likelihood and consequence components in the risk equation. Using consequence or likelihood alone for prioritization purposes can prove problematic and may not accurately reflect the worst potential scenario, resulting in dissimilarities for priority of inspection. Using overall risk rank assures that the most critical components (higher consequence, higher likelihood) are easily distinguishable and, as such, are prioritized accordingly. For high and medium consequence scenarios, special attention should be paid when assigning the likelihood values so as not to inaccurately underestimate the overall risk. The use of conservative likelihood values is recommended so as not to screen out potentially high-risk scenarios.

There are many types of risk assessment methodologies that might be applied to evaluating risk for RBI component prioritization. It is important to re-emphasize that the primary objective of RBI is to determine what undesirable incidents could result from degradation of components, the severity in terms of consequence that may ensue and how likely those events would be. For RBI to have a positive impact on these factors, these events must be detectable by one or more inspection techniques. 

Risk assessments for RBI may be conducted at various levels ranging from fairly simple to highly complex, but essentially they seek to answer the same basic question set. 

The Risk Assessment Methodology

The choice of risk assessment methodology is highly dependent on several factors such as: 

• Whether the installation is a new build or existing asset
• Number of facilities/components/structure items to study
• Available resources
• Complexity of facilities and processes
• Nature and quality of available data
• Purpose of analysis (e.g., to support company policy, to satisfy a regulatory, legal or stakeholder requirement)

Once the above items have been evaluated, the method best suited to  the particular scenario may be selected and applied. There are three basic groups of methodologies:

• Fully qualitative
• Fully quantitative
• Semi-quantitative

In the fully qualitative approach, competent personnel may make expert judgments or subjective review within a formal evaluation process for assessment of the severity and likelihood of failure of each component under review. This process is usually facilitated by an individual experienced in risk assessment evaluation, thus focusing the study outcomes. Both factors of likelihood and consequence are assessed. A final value for risk is derived through placing the components’ derived likelihood and consequence assessments within a risk matrix, thus delivering a final component risk score or rank. Qualitative analyzes normally use descriptive ranges for inputs and outputs that are intended to be broad enough to cover the ranges of uncertainty involved. The most typical use of this technique is for the purpose of “screening” out low risk items for which the time and cost of a quantitative study cannot be justified. As an aid to solicitation of input, it is common to establish predefined categories or ranges for likelihood and consequences.