Industry status on RBI technology and best practice implementation

A reliable Risk Based Inspection (RBI) technology is a fundamental necessity for a structured approach to economic, safe and effective management of static equipment assets of plant, as it will correctly assess the risk profiles of the Damage Mechanisms (DMs) for each item and it’s optimum inspection interval; the knowledge of ‘active’ and ‘potential’ DMs, related operating limits, critical maintenance activities and other risk mitigation measures being central to this. It is this knowledge supported by a reliable RBI methodology that gives the required confidence in the DMs risk-driven optimum inspection interval. The importance of all engineers involved in inspection, integrity, process and plant operation having a good understanding of corrosion and other DMs cannot be underestimated as each of these disciplines have an important inter-dependent role to play.

Clearly therefore, RBI implementation is a highly critical process.  It effectively manages eventually - through the assigned responsibilities of Plant Inspection, Operations and Process Engineers - the asset integrity safely, reliably and at the most optimum costs throughout a plant's life cycle.  In order to deliver this, the following aspects must not be compromised as these are the 'bottom line' for implementing RBI successfully.  At PP SIMTECH, we carefully adhere to all of these aspects, as a minimum, during RBI implementation at plant sites.

1.     RBI Technology is reliable, incorporates best practices and is user-friendly for Engineers at plant site.

2.     RBI Team Study of each item is thorough and comprehensive - there is no short cut to this task, the required study time must not be compromised.

3.     In addition to RBI Engineer and Corrosion Specialist, the RBI Study Team includes Inspection, Operations and Process engineers from plant site.

4.     RBI Team Study Output is reliable, comprehensive, embedded into site practices and matches plant site objectives and goals.

5.     RBI software system comprehensively supports 1-4, is fully transparent and auditable.

For example, compromising quality of the RBI Team Study by not providing sufficient study time, in order to reduce project timescales and costs adversely affects correct identification of 'active' and 'potential' DMs applicable to an item.  This has a detrimental effect on the confidence that can be placed on the RBI study output particularly on the risk profiles of DMs and the related inspection interval for an item. As such, the claimed outcomes in improvements in plant and equipment reliability, safety and financial benefits are questionable, as is the management decision to buy into RBI Study output and implement it in the hope of achieving the claimed benefits.

It is critical therefore, that senior management at plant site are committed to support the RBI best practices and provide the required resources from site, time allocation for RBI team study and implementation of the output.

Industry Status on RBI Technology:-   A word of 'caution', RBI is still a developing technology and as such various RBI methodologies are available, including API 581:2008.  All have merits and weaknesses.  Companies who have already implemented RBI have reported varying outcomes from implementation.  Consequently, UK Health & Safety Executive (HSE) and API 580 issued guidance to help minimise inconsistencies.

Original versions of API 580 and API 581 were published in May 2002 and May 2000.  Completely revamped versions were published in November 2009 and September 2008 respectively.

The API 580:2009 gives guidance for key aspects which should be considered for implementing RBI at plants, using either Qualitative (Level-1), Semi-Quantitative (Level-2) or Quantitative (Level-3) RBI methods.  The API 581:2008 was developed only to deal with Quantitative RBI method. 

API 581:2008 Concerns:- In theory, the accuracy, detailed nature of the assessment and confidence in results are supposed to increase with the increased Level of assessment. Unfortunately, this is not the case if API 581 methodology is used.  Noting that RBI is still a developing technology, the latest API 581 Quantitative RBI method has uncertainty in some of the technology used and is not end-user-friendly due to its technical complexity. Critical uncertainties include - validity of "failure frequency data" in relation to DMs and equipment types and the related "probability of failure" assessment method; assessment of "consequence of failure" with respect to each "DM" and its "failure mode"; "Management Factor" considerations.  Additionally, majority of the DMs listed in API 571 are not covered; in fact API 581 does not fully cover all the applicable DMs relevant to at least one of the industry sectors (refining, gas processing, petrochemical, chemical, fertilizer, power generation). This means that other methods of risk assessments need to be used within a plant site for DMs which are not covered.  Undoubtedly, all these aspects lead to uncertainty in the derived optimum inspection interval for each item.

As per API 580:2009, any of the three Assessment Levels is acceptable; but plant site must ensure the chosen RBI methodology and assessment Level (supplied by the service provider) is defendable and end-user-friendly, detailed, documented, transparent and auditable with the facility for future update of the initial implementation, whilst at the same time it is imperative to ensure that the methodology matches the output requirements of the end user.  Furthermore, end-user-friendliness is important, in order to ensure success after implementation, as the process is managed by engineers from plant site.

It is also emphasised that the selected RBI assessment Level must have the methodology to reliably assess the 'probability of failure' and 'risk profiles' of each of the DMs applicable to an item;  Noting that failure to satisfy these important criteria, the confidence in the optimum inspection interval derived for each item is fundamentally questionable. This is simply because the optimum inspection interval is derived from the risk profile of each of the applicable damage mechanisms. It must also be supported by a comprehensive team study method that ensures identification of all active & potential damage mechanisms as well as any integrity related operating limits and maintenance activities, together with any other risk mitigation measures.

Based on the foregoing, the vast industry experience clearly shows that a Semi-Quantitative (Level-2) RBI methodology, which satisfies criteria outlined above, plus API-580:2009 and the UK HSE guide, supported by a multi-discipline team study which includes plant inspection, operation and process engineers proves to deliver the required output and confidence in the results whilst meeting plant sites objectives and goals.  i.e. It delivers safe and reliable management of equipment integrity based on RBI, at optimum costs.  For user-friendliness, almost all global multi-national companies in the oil, gas and petrochemical industries prefer and use Level-2 RBI methodology.

Due to the fact that API is again considering to revamp the API 581 Quantitative (Level-3) RBI technology with an alternative methodology based on fitness-for-service/structural integrity models, it is recommended to avoid its use until such time this Level-3 RBI methodology is stabilised, reliable, end-user-friendly, better in key aspects compared to Level-2 methodology and fully approved by wider RBI experts in relevant industry sectors, whilst also ensuring all relevant DMs applicable to at least the refining, gas processing, petrochemical, chemical and fertilizer industries are included in it.  However, API-581 is useful for obtaining damage rate and other relevant information on certain DMs when using Level-2 (semi-quantitative) RBI methodology.  Importantly, there is no demand rush for level-3 technology; Level-2 RBI is proven, end-user-friendly and working fine.