Step 8 Do Confidence Assessment & determine Interval Factor (AR) (Civil)

For Age-Related DMs, you first need an Interval Factor, before the Next Inspection Date can be calculated.

Methodology 

Common industry practice is to conduct inspection at regular, time-based, intervals. The intervals chosen are based on the importance of the asset, industry and site experience. Furthermore, statutory or other mandatory requirements (e.g. turnaround frequency) may determine the inspection interval. These intervals generally include a ‘safety margin’ to ensure that there is enough time to arrange and conduct maintenance if the inspection results indicate that this is necessary.

When inspection of an asset requires major effort and significant cost, then the Risk-Based Inspection (RBI) functionality within Civil can be used to optimize the inspection date. This is typically relevant if inspection resources or access is an issue, e.g. underground, high elevations, confined spaces, hazardous areas. In these situations, one would only want to inspect when it is necessary, from a risk perspective. Note that this functionality is only applicable for AR DMs as they allow (to some degree) prediction when failure might occur.

The w-IMS Civil methodology results in an inspection interval that depends on the condition status of the asset and the Remaining functional Life (RL). This yields a maximum Next Inspection Date (NID) that is well before the time that failure is expected, as is shown below. Local legal requirements may override the optimized inspection date, i.e. inspection has to be done earlier than determined with w-IMS Civil methodology.

The inspection interval (Safety Margin) depends on the condition status of the asset and the RL. This yields a NID.After preparing the basis for the plan, the optimization of an inspection date and frequency as part of a risk-based inspection plan is based on the inspection Interval Factor (IF) that is governed by the Criticality and Confidence in the estimate for the Remaining Functional Life (RL). The IF is calculated as a value between 0.1and 0.8. See the table below. The default Confidence is marked.

The Interval Factor (IF) is based on Criticality and Confidence. An asset with a low criticality and an intermediate confidence rating, yields an Interval Factor of 0.5. In other words, the Component (or asset) should be inspected at the latest when half of the estimated Remnant Life (RL) has passed since the last inspection date. For assets with an extremely high criticality, or high criticality combined with a very low confidence rating, it is advised to redesign (parts of) the asset, which is reflected in the matrix by the empty cells.

Software

Confidence Assessment (AR)

To do a Confidence Assessment:

• Select the Confidence tab.
• Click Edit.
• Fill out the Confidence questionnaire.

Fill in the Confidence questionnaire.

Inspection Interval Factor (AR)

The inspection interval factor (IF) is calculated based on Confidence Rating and Criticality. The resulting value is shown in the Analysis Window under the column IF as well as in the header.

The IF value is shown in the Analysis Window.