The first four boxes are described by phases i and ii of the traditional RCM process (see Sections 2.1.1 and 2.1.2). These boxes provide already established methodologies to the frame- work, where a dashed line is drawn around the boxes to indicate the boundaries of the traditional process i and ii. A fifth box (no. 5) is then introduced, attached to the boxes 2 and 3, to integrate dedicated uncertainty assessments into the framework. These assessments are included as an integrated part of the PM task and interval assessments (i.e. these two boxes), and adds to the uncertainty assessments performed as integral parts of the traditional RCM methodology (steps nos. 1–4), for example assessments in FMECA, where uncertainties are partially covered through subjective (epistemic) probabilities for failure events and their consequences.
In the fifth box (see Fig. 3) we specifically address the uncertainty factors. Many of these factors are derived from the assumptions made in the established assessment tasks in boxes 2 and 3, as the uncertainty factors cannot be revealed and assessed before the traditional probability based analysis has been conducted. In line with Aven [19] and Flage and Aven [33], the uncertainty analyses cover the following main tasks:
1. Identification of uncertainty factors.
2. Assessment and categorization of the uncertainty factors with
respect to degree of uncertainty.
3. Assessment and categorization of the uncertainty factors with
respect to degree of sensitivity.
4. Summarization of the uncertainty factors’ importance.
Table 1 indicates a score system for tasks 2–4, inspired by Selvik
and Aven [34] and Flage and Aven [33]. All the tasks 1–4 are applied for both the PM task assessment and the PM interval assessment. When we apply this system for box 2, the judgement of the sensitivity score is linked to the extent that the factor is able to change the PM task. To integrate these scores into the PM task and interval assessments we expand the FMECA to include all the results from the assessments in steps (boxes) nos. 1–5. Such expansion will also benefit the later presentation of the results.
Steps 1–4 (see Fig. 3) together with 5 thus provide the input for the total uncertainty evaluation of the system studied; see box no. 6. An important part of the uncertainty evaluation is communication of the results to the management function. The value of the information should be considered, to not overload the management with information not relevant to the decision-making.
The RRCM framework also includes managerial review and judgement, as shown in the seventh box in Fig. 3, in line with the decision framework presented in Aven [19]. The inputs to management from the various assessments are placed into a broader context, where the boundaries and limitations of the various assessments are taken into account, and also additional aspects and inputs are taken into consideration, for example manufacturer recommendations and existing PM programmes. The managerial review and judgement may also request revisions or analytic changes results should appear unreasonable.
Section 3.1 presents the results from the uncertainty assess- ment for the flowline case.