The objective of risk based inspection is to move from reactive to proactive maintenance that delivers an auditable, appropriate and cost-effective inspection and maintenance regime that operates within an agreed time frame.
RBI, which is often undertaken with the use of a risk management tool, takes account of two critical factors; the probability of failure (POF) and the consequence of failure (COF):
- Probability of Failure (POF): The POF is the chance that an asset will fail during a set time-frame. This involves an assessment of every area where damage could occur for individual items of equipment
- Consequence of Failure (COF): COF assesses the impact of mechanisms of parts failing. These consequences are split into three areas; health and safety impacts, environmental impacts, and business impacts
Risk based inspection begins with the collection of data about an organisation’s equipment and machinery, focusing on matters including potential damage, error frequency rates and where malfunctions may occur. This data collection can be broken down into three approaches:
- Qualitative: This covers descriptive data based on the experience and judgment of inspectors
- Quantitative: Based upon statistics and probability
- Semi-Quantitative: Combining both qualitative and quantitative data
Once the data has been collected, the risk analysis can begin. This uses the probability of failure (POF) and consequence of failure (COF), as highlighted above. This allows for the highest financial and safety risks to be determined so that the related assets can be assigned inspection and maintenance plans.
The risk is determined as follows:
POF x COF = Risk
The aim is to optimise the maintenance activities for those high risk assets most likely to suffer critical failures and to save resources on lower risk assets.
Proactive risk based inspections offer a number of benefits when compared to more reactive approaches, these include:
- Improved, proactive risk management through risk analysis and mitigation
- Reduced downtimes through the prevention of critical failure
- Cost-saving through inspection planning to reduce unplanned outages
- Workforce optimisation and time and cost-saving through the elimination of unnecessary inspections
- Economical use of inspection resources
- Overview of critical asset health
- Reduced failures
- Improved equipment efficiency and reliability
- Operational risk identification based on equipment degradation
- Avoidance of unnecessary delays and shutdowns through maintenance planning
- Equipment compliance with safety and environmental regulations
- Fewer technical malfunctions through regular asset monitoring
For all of the benefits, there are some challenges associated with a risk based inspection programme, including:
1. Commitment:
Managers and other staff need to commit to risk based inspection. This means committing to the results of RBI and planning future inspections, following procedures and processes as well as allocating resources and communicating the findings of the RBI.
2. Defining Processes:
Buying RBI software and assembling an RBI team does not equal an RBI programme, the RBI programs and processes need to be integrated and findings implemented for them to be effective.
3. Change Management:
There will often be a need to introduce people to new ways of working and new technologies. This can require support for staff to learn new skills as well.
The definition of RBI methodology was introduced by the American Petroleum Institute (API) in a base resource document called API PUBL 580 in 2000. This set out basic guidelines for the development and implementation of an RBI programme.
Outside of the United States, the European Commission also published a report on risk based inspection and maintenance principles (RIMAP) for use across Europe while, in the UK, the Health and Safety Executive (HSE) published their own recommendations and best practice for RBI.
The international engineering standards and practices are covered by the following codes:
- API RP 580 – Risk Based Inspection
- API RP 581 – Risk Based Inspection Technology
- ASME PCC-3 – Inspection Planning Using Risk-Based Methods
- RIMAP – Risk Based Inspection and Maintenance Approach
The API updated their RBI technology documentation in 2008 and 2016, with the latest version, API RP 581, containing over 1,000 technical changes from the previous version. API RP 581 sets out quantitative procedures for fixed equipment used in chemical process plants, oil and gas production facilities, refining, and petrochemical plants. This includes pressurised fixed equipment, pressure vessels, piping tanks, pressure relief devices and tube bundles for heat exchangers.
The documentation includes three primary goals:
- Define the quantity and rank the risk of process equipment failure so as to target the most essential process plant components
- Review environmental, safety, operator, equipment and business-related risks in a cost-effective manner
- Reduce the likelihood and consequences of any failure through the allocation of inspection resources for high risk equipment
Risk based inspection and condition based inspection are two different processes. While RBI involves developing a programme of inspection based on the risk of failure, condition based inspection (also known as condition based monitoring or CBM) involves monitoring the condition of equipment and systems with sensors and measurements. This data is then used to schedule maintenance actions based on the condition or pre-set thresholds.
Risk based inspection is a process used to examine a range of assets in order to optimise inspection plans. This includes assuring the mechanical integrity by assessing the risk and consequence of failure to set acceptable limits.
Combining active and potential damage mechanisms, RBI can be qualitative, quantitative or semi-quantitative in nature, covering aspects such as safety, economy and environment.
The purpose of RBI is to improve risk management results, provide an approach for managing risk, apply strategies to safeguard integrity and improve the reliability and availability of assets. In addition, RBI can reduce incidents of unforeseen shutdowns or outages and ensure inspections are carried out as required. RBI will not only reduce the risk of failure but, when used flexibly, it will constantly improve processes to adapt to changing risks.