Methodology Step 11

Step 11 Review the Results – NID, MII, IS, Inspection Effectiveness:

Below the Step 11 Methodology is described. See also Software Step 11.

Understand Where Results Come From

For Age-Related DMs

• IMS uses a "half-life" (or "full-life") table to determine an IF from the Criticality (Step 9) and the Confidence (Step 10). See Risk Based Inspection (RBI) - Theory.
• The IF then determines the fraction of RL (Step 6) at which to inspect, i.e., the Maximum Inspection Interval (MII = IF x RL);
• Then IMS determines the NID, from the MII and Last Inspection Date (LID) (Step 5). NID = MII + LID. The NID indicates the ultimate date by which the inspection Schedules should be completed. Schedules not inspected before NID should be recorded in the IMS as overdue.
• Additionally, you must use the IF and RL to determine the required Inspection Effectiveness. See the table in Risk Based Inspection (RBI) - Theory.

For Non-Age-Related DMs

• IMS determines an IS (and in some cases a MII) from the Criticality and Confidence (see Risk Based Inspection (RBI) - Theory).
• The Guidance per Special Emphasis and Guidance per DM sections will help you with the interpretation of the results for the specific NAR DMs, e.g., SCC, HTHA, etc. (see the summary table below).

For more background, refer to Risk Based Inspection (RBI) - Theory.

Age-Related DMs – take note

Take note of the following:

• The AR DM Inspections should be aimed at quantifying the rate of degradation (e.g., CR).
• Legislation: A MII defined by local or national legislation may only be exceeded after approval by the regulatory body;
• Lining/Coating: It is possible to take credit for Lining/Coating - see Step 6. This will extend the RL and, in turn, the MII (and NID) will be extended;
• Unit Maximum RL: For each Unit, the Company can define a Maximum RL. If the calculated RL is greater than this value, the Company value will be used for determining the MII. See Configuring the Toplevel via Settings.
• Negligible Criticality: For items with Negligible Criticality, the IF results in an inspection close to the end of the (inherently long) RL. This inspection should review the need for end of life replacement; and
• Extreme Criticality: The IF table gives no IF for Extreme Criticality. In this case specific risk management is required; the risk cannot be managed to ALARP through inspection and IOW alone. For each individual case, specific actions, to reduce the risk to an acceptable level, should be identified. Process controls (e.g., down rating of pressure, temperatures), re-design (e.g., material upgrade) and dedicated specific inspection / proactive monitoring efforts are possible actions.

Non-Age-Related DMs – take note

In general, take note of the following:

• Here the effective strategy is to prevent (process) conditions under which the NAR DMs can initiate.
• It should be ensured that the Inspection Schedule (see Step 12) matches the recommendation/strategy (analysis result) of S-RBI.
• For low Confidence, the strategy aims at increasing Confidence and confirm the absence of damage. If that is not immediately possible, specific risk management should apply until integrity has been confirmed. Detailed analysis of the variables affecting the DM and their historical values should determine the scope and coverage of inspection. The IOW should be defined (see Step 2) and monitored (see Methodology Step 12 - proactive monitoring plan) to increase Confidence.
• Medium to high Confidence: In this case, a proactive monitoring plan should be followed (see Step 12).
• For lower Confidences and low Criticalities, improvement of the proactive monitoring plan should be considered (see Step 12).
• Negligible Criticalities, or low Criticalities (with high Confidences), require no additional action.
• Where applicable, Guidance per Special Emphasis Components and Guidance per DM should be followed (see se summary table below).

Required Inspection Effectiveness

The Required Inspection Effectiveness can be derived from the IF and RL. For pressure Equipment, the table given in Risk Based Inspection (RBI) - Theory should be used to determine the Required Inspection Effectiveness. The Required Inspection Effectiveness should then be used to determine specific inspection techniques and coverage. The table below gives an example for generalized corrosion morphology. For more guidance in this regard: refer to Guidance per Special Emphasis and Guidance per DM (see the summary table below).

The inspection technique and coverage, for General Thinning, to achieve a required Inspection Effectiveness:

Specific Guidance Summary

Specific guidance summary - Interpreting results (NID, IS, Inspection Effectiveness):