Degradation Mechanisms

A Degradation Mechanism is a defined method that affects failure as explained in an RBI Analysis. When an RBI Analysis is performed, DMs are assigned to capture the failure that should apply to an RBI Analysis to calculate its risk.

For each Degradation Mechanism (DM) that belongs to an RBI 581 Risk Analysis, a corresponding RBI 581 Damage Mechanism Evaluation record also belongs to that RBI 581 Risk Analysis. In each RBI 581 Damage Mechanism Evaluation that is associated with a qualitative degradation mechanism (i.e., the corresponding RBI Degradation Mechanisms record was created from a Potential Degradation Mechanism with the value Qualitative in the Methodology Type field), you can specify the probability that the corresponding component will fail due to that degradation mechanism.

For example, if an RBI 581 Risk Analysis contains a 581-Amine Cracking DM, it will also contain a corresponding RBI 581 Cracking Damage Evaluation. In this DME, you can specify a value in the Probability Category field to indicate the probability that the RBI Component will fail due to amine cracking.

After you select a value in the Probability Category field and calculate the RBI 581 Risk Analysis, the Probability Category Description field will be populated automatically based on the values in an existing Degradation Mechanisms Evaluation Factors record.

Integration between the RBI and Inspection Management modules allows you to take credit for inspection history when you calculate the damage factor of a Damage Mechanism (DM). You can, however, take credit for inspection history only for DMs that belong to the following Damage Mechanism Evaluations (DMEs):

In RBI 581:

• RBI 581 Cracking Damage Evaluation
• RBI 581 External Damage Evaluation
• RBI 581 Thinning and Lining Evaluation

In RBI 580:

• Criticality Env. Crack. Deg. Mech. Eval.
• Criticality Ext. Corr. Deg. Mech. Eval.
• Criticality Int. Corr. Deg. Mech. Eval.

To take credit for inspection history, you must:

• Enable the Inspection Auto-Selection feature. If you enable this feature, APM automatically assigns Inspections to a DM.

  -or-

• Assign Inspections to a DME manually.

To assign Inspections to a DME manually:

1. Create an Inspection in Inspection Management.
2. Specify the DM that you have inspected.
3. Create an RBI Analysis on the component that you have inspected.

4. Add the DM that you have selected in step 2.

5. Access the Inspection History of the DM.

   The Inspection that you have created in step 1 appears in the grid only if:

   • The date entered in the Date in Service field in the DME is earlier than the date entered in the Inspection Completion Date field in the Inspection.
   • The Inspection Confidence field in the Inspection is not blank.

   Additionally, if you have created an Inspection for a DM that belongs to the same or a related DME, it appears in the list as well.

6. Assign the Inspection to the DME. You can assign any inspection that appears in the list.

When you assign an Inspection to a DM, you can select Inspections performed on a DM that belong to the same DME or a related DME.

The following table provides a list of DMEs in RBI 580 that are related to DMEs in RBI 581. You cannot modify this mapping.

When you select an Inspection on a related DME, the values in the Inspection Confidence and Inspection Effectiveness fields are mapped as follows:

You can use Inspection Management to record inspection results for a piece of asset. In each Inspection, you can specify the DM for which you were looking during the inspection.

In RBI, you use RBI Components to divide a piece of asset into parts. You then define DMs for those components, and then conduct analyses for each RBI Component.

Each RBI Corrosion Loop contains multiple RBI Components. Each of these components can fail in multiple ways. To indicate the ways in which components can fail, you can link Potential Degradation Mechanisms (PDMs) to the RBI Corrosion Loops.

Each PDM that is linked to the RBI Corrosion Loop represents a degradation mechanism (a way in which the components in that Corrosion Loop might fail). Once the RBI Corrosion Loop has been associated with a PDM, all components added to that RBI Corrosion Loop will inherit the PDM.

For each component, you can define the specific ways in which the RBI Component that it represents can fail.

When you calculate an RBI 581 Risk Analysis, Degradation Mechanism Evaluations (DMEs) are used as an input to calculate the Probability of Failure. A key factor in calculating the Probability of Failure for the analysis is the assessment of previous inspections, which are contained in the Inspection History.