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The methodology of Risk-Based Inspection ranges from qualitative to quantitative and everything in between.

In the era of digitalization, there exist numerous RBI (risk-based inspection) methodologies and software. Companies are trying to comprehend the distinctions between Qualitative and Quantitative risk assessments to ascertain the appropriate approach for their organization. Generally, risk assessment methods are categorized as follows:

  • Qualitative (Expert Judgment)

  • Semi-quantitative (Rule-Based Analysis)

  • Quantitative (Probabilistic, Statistical, Mathematical Modeling)

Risk Assessment Standards

Numerous international engineering standards and recommended practices have been established to outline the necessities, approaches, and execution of RBI. These include ASME PCC-3, remap, API 580, API 581, API 571, and others. These standards are generally applied to particular sectors of the industry. For instance, ASME is an American standard that caters to fixed pressure-containing equipment, while API is also an American standard that is specifically intended for the oil and gas sector. On the other hand, remap is a European standard that is more relevant to power plants.

Sometimes, people find it difficult to differentiate between the various recommended practices. For instance, API 580 specifies the requirements for an RBI assessment, including conceptual approaches and necessary elements, while API 581 offers a methodology that aligns with the requirements of API 580. It's possible for RBI software packages to adhere to the best practices outlined in API 580 without implementing the associated methodology in API 581. The standards typically don't prescribe a single approach, such as a strictly quantitative one. API 580, for example, provides guidance for RBI implementations using level 1 (qualitative), level 2 (semi-quantitative), or level 3 (quantitative) methods, with API 581 falling under level 3 RBI methods.

It is important that the RBI methodology and RBI team study method are reliable, transparent, auditable, detailed, user-friendly, and well-documented. To ensure alignment with API 580, the software must implement an easy-to-understand RBI methodology that is familiar to plant inspection engineers and operations engineers. Failure to do so could result in an increased equipment risk instead of a risk reduction. Additionally, the RBI technology method (level 1, level 2, or level 3) must be robust and able to assess the probability of failure and the risk profiles of all applicable degradation methods and failure modes. This is necessary for confidence in the optimum inspection interval. The team study method must also identify all FMS, operating limits, maintenance activities, and other risk mitigation actions.


Let's explore the differences between qualitative, semi-quantitative, and quantitative risk assessment software. All three types can meet industry standards, but what sets them apart? First, let's define each type. Quantitative data is focused on collecting hard, numerical facts and statistics. Qualitative data, on the other hand, aims to describe a topic using impressions, opinions, and views. Semi-quantitative data falls somewhere in between, containing both qualitative and quantitative elements.

Quantitative risk assessment produces numerical estimates of risk based on defined parameters, while qualitative assessment evaluates risk based on verbal qualifiers such as high or low likelihood. In theory, reliable quantitative data should provide the most precise and accurate results, but obtaining this type of data can be difficult and time-consuming. As a result, less reliable data may be used, leading to less accurate results.

When it comes to risk assessments, accuracy is dependent on the analysis methodology, data quality, and consistency of execution, while precision is determined by the selected metrics and computational methods. It is important to exercise caution because a result may be very precise, but if there is a significant amount of uncertainty in the probabilities and consequences, the result can still be inaccurate.

Can you tell me about the advantages and disadvantages of Qualitative and Quantitative RBI Software? It's hard to say which one is superior because qualitative, semi-quantitative, and quantitative risk assessments can all yield positive results. Let's begin by examining the differences between standard qualitative and quantitative risk assessments:

One of the greatest benefits of using qualitative methods is their user-friendliness. They are generally less complex, making it easier to create a user-friendly experience.

When it comes to fully understanding, a qualitative methodology is generally more transparent. Quantitative methods, on the other hand, due to their complex calculations, are often implemented as black boxes.

When it comes to obtaining good data, quantitative methodologies can excel in terms of precision and accuracy. These methods involve rigorous quantitative assessments of the probability of failure (POF) and the consequence of failure (COF) associated with each equipment item. However, it's important to keep in mind that accuracy is influenced by the inherent uncertainty in the probabilities and consequences.

When it comes to data, qualitative analysis can be done with a smaller amount compared to other methods.

When it comes to conducting an RBI analysis, a qualitative approach is faster than a quantitative one. Gathering all the data required for a quantitative analysis can be time-consuming and demanding.

The accuracy of a qualitative RBI analysis depends largely on the skill and knowledge of the team conducting the analysis, making it more subjective. On the other hand, quantitative analysis is considered more objective. Nevertheless, it's important to note that a quantitative approach is not necessarily infallible. To achieve reliable results, it's crucial to have experienced RBI and inspection professionals involved in the process.

The process of automation is simpler with quantitative methods as they require less team involvement.

Both qualitative and quantitative methodologies have their limitations and strengths. Combining these two methods can enhance the benefits and minimize the drawbacks.

Therefore, utilizing a semi-quantitative risk assessment methodology can prove to be advantageous as it is simple to comprehend, user-friendly, and more precise. However, it is imperative to have the backing of a proficient multi-disciplinary team's study to ensure trust in the outcomes. To ensure accuracy in specific areas of the risk assessment, a qualitative analysis would be conducted, while in other sections (chosen based on a confidence/sensitivity analysis), a quantitative risk assessment would be performed. Another approach to get the best of both would be first to do a (faster) high-level qualitative RBI analysis to select the high-risk facilities in one's plant. Then one can do quantitative RBI analyses only on these high-risk facilities. Remember, good data and an experienced multi-disciplinary team study remain a requirement for accurate results.
We are frequently asked about the RBI methodology used by AsInt.

AsInt software offers a range of methodologies, including qualitative, semi-quantitative, and quantitative approaches. Our qualitative approach is fully compliant with the damage mechanisms of API 580, API 581, and API 571. For semi-quantitative and quantitative methodologies, we have developed specific calculators, such as Liquid release, CUI, SSC, and other corrosion prediction models. Additionally, we use detailed questionnaires to calculate POF and COF based on the most relevant failure modes. With AsInt, all critical planning and risk management information is easily accessible and not duplicated within the core Enterprise Asset Management solution. We have created a highly configurable, templatized solution that can implement any methodology based on industry standards or internal corporate approaches. AsInt offers the European PED model and our own semi-quantitative model called RBI Plus. Our innovative approach allows users to interact and persist with the SAP Master Data. All data, including algorithms, are exposed for the risk analyst to understand and make recommendations.

Please note that AsInt is not a standalone RBI tool. It is designed to merge the RBI results with inspection outcomes, wall thickness measurements, and schedules. This integration enables the RBI outcomes to determine the next inspection dates that are then fed into the IDMS component of the tool. The IDMS component can further interface with the site's CMMS (computerized maintenance management software) software, such as SAP.

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At AsInt, we aim to revolutionize software development, delivery, and accessibility in cross-industry. Our objective is to offer a comprehensive range of applications that cater to various asset integrity requirements across platforms. Our software is user-friendly and readily available in app stores, ensuring seamless functioning.
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Founder & CEO at AsInt, Inc.
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