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1

An extended risk based inspection methodology

Selvik J. T., Scarf P., Aven T.

Journal of Polish Safety and Reliability Association

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2010

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Vol. 1, No. 1

221--230

EN

Risk based inspection (RBI) is a methodology commonly used in planning of inspections for static mechanical equipment, in particular piping networks. The inspections are prioritized based on risk, expressed as expected values, integrating the likelihood and consequences of failures. In this paper we suggest an extension of the RBI methodology which reflects risk and uncertainties beyond expected values. We argue that such an extension is essential for adequately supporting the inspection planning. A pipeline example from the Norwegian oil and gas industry is presented to illustrate and discuss the suggested approach.

2

A holistic framework for conceptualising and describing risk

Aven T.

Journal of Polish Safety and Reliability Association

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2010

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Vol. 1, No. 1

7--14

EN

A number of definitions and interpretations of the risk concept exist. Many of these are probability-based. In this paper we present and discuss a structure for characterising the definitions, which is founded on a clear distinction between (a) risk as a concept based on events, consequences and uncertainties; (b) risk as a modelled, quantitative concept; and (c) risk descriptions. The discussion leads to a holistic framework for conceptualising and assessing risk, which is based on risk defined by (a), and the probability-based definitions of risk can be viewed as related model parameters and/or risk descriptions. Two ways of detailing the framework are outlined: the relative frequency-based approach and the Bayesian approach. The Framework provides clear guidance on how to think when conceptualising and assessing risk in practice. Such guidance is strongly needed for the risk analysis discipline which is young and characterised by many different risk perspectives and approaches.

3

A conceptual framework for risk assessment and risk management

Aven T.

Journal of Polish Safety and Reliability Association

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2010

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Vol. 1, No. 1

15--26

EN

This paper presents and discusses a conceptual framework for risk assessment and risk management where risk is based on the triplet events, consequences and uncertainties. In addition to risk, the framework highlights the concepts of vulnerability and resilience. An example of the analysis of an LNG (Liquefied Natural Gas) plant is included to demonstrate the applicability of the framework. The proposed framework is more general than existing frameworks, for example the traditional Kaplan & Garrick approach, and provides also New perspectives on how to understand and describe uncertainties in a risk assessment and risk management context.

4

Safety oriented bubble diagrams in project risk management

Abrahamsen E. B., Aven T.

Journal of Polish Safety and Reliability Association

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2008

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Vol. 1

1--5

EN

In project risk management many firms use bubble diagrams to get a graphical presentation of a project’s most uncertain attributes. The bubble diagrams and procedures used to put attributes into these diagrams are seen to provide a rational framework for managing risks. In this paper we review and discuss the use of these diagrams and procedures. Special attention is given to the way safety is treated. We show that the standard use of bubble diagrams is not adequate for identification and follow up critical activities that affect safety. The main problem is that the present structure means that the uncertainty is not properly taken into account. In this paper a reformulated bubble diagram is suggested that better reflects safety related uncertainties. The offshore oil and gas industry is the starting point, but the discussion is to large extent general.

5

Expressing and communicating uncertainty in relation to quantitative risk analysis (QRA)

Flage R., Aven T.

Journal of Polish Safety and Reliability Association

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2008

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Vol. 1

109--115

EN

A quantitative risk analysis (QRA) should provide a comprehensive, informative and balanced picture of risk, in order to support decisions. To achieve this, a proper treatment of uncertainty is a prerequisite. Most approaches to treatment of uncertainty in QRA seem to be based on the thinking that uncertainty relates to the calculated probabilities and expected values. This causes difficulties when it comes to communicating what the analysis results mean, and could easily lead to weakened conclusions if large uncertainties are involved. An alternative approach is to hold uncertainty as a main component of risk, and regard probabilities as epistemic-based expressions of uncertainty. In the paper the latter view is taken, and we describe what should be the main pillars of a risk description following this approach. We also indicate how this approach should relate to decision-making. An important issue addressed is how to communicate the shortcomings and limitations of probabilities and expected values. Sensitivity analysis plays a key role in this regard. An example is included to illustrate ideas and findings.

6

On how to use expert judgements in regularity analyses to obtain good predictions.

Hjorteland A., Aven T.

Zagadnienia Eksploatacji Maszyn

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2007

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Vol. 42, nr 3

157-169

EN

The purpose of regularity analysis is to assess future deliveries of production and transportation systems, such as oil and gas installations. When conducting such analysis, models are developed reflecting the performance of various equipment, for example compressors and pumps. To assess the equipment performance there is a need for relevant konwledge, including observed data and expert judgements. One of the challenges in regularity analyses is to assess uncertainties for the large number of quantities in the models being used. These quantities are either, observable quantities such as lifetimes or repair times, or statistical expected values or probabilities, such as MTTF or MTTR. The purpose of this paper is to present and discuss a practical approach for such assessments using the combination of expert judgements and hard data. The approach is based on a Bayesian framework, with focus on prediction and uncertainty assessments of observable quantities.

PL

Celem analiz regularności jest oszacowanie wielkości przyszłych dostaw surowców za pomocą systemów produkcyjnych i transportowych, takich jak instalacje naftowe i gazowe. Przeprowadzając taką analizę buduje się modele opisujące działanie różnorodnego wyposażenia, np. sprężarek lub pomp. Aby ocenić pewność działania wyposażenia technicznego niezbędna jest odpowiednia wiedza, obejmująca zaobserwowane wielkości i opinie ekspertów. Jednym z wyzwań w analizach regularności jest oszacowanie niepewności w warunkach dużej liczby elementów składowych w zastosowanych modelach. Te elementy składowe mogą być wielkościami obserwowalnymi, takimi jak czas do uszkodzenia lub czas naprawy, mogą być też wielkościami statystycznymi, wyrażonymi jako wartości oczekiwane, bądź prawdopodobieństwa, na przykład MTTF (średni czas do uszkodzenia) lub MTTR (średni czas naprawy). Celem niniejszego artykułu jest przedstawienie i przedyskutowanie praktycznych sposobów dokonywania takich analiz w oparciu o kombinację opinii eksperckich i twardych danych. Proponowane podejście oparte jest na modelu Bayesowskim, przy czym skupiono się na predykcji i ocenie niepewności dla wielkości obserwowalnych.