Degradation Mechanisms

About Degradation Mechanisms (DMs)

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.

Example: Degradation Mechanisms

The following table provides a list of DMs that can be linked to each component type. This list is not comprehensive.


Component	Degradation Mechanism
Pump	Amine Cracking
	Blocked Discharge
	Brittle Fracture
Vessel	Carburization
	Caustic Cracking
	Chloride Stress Corrosion Cracking (CI SCC)
Heat Exchanger	Amine Cracking
	Caustic Cracking
	Criticality Calculator External Corrosion

When you associate degradation mechanisms with a Corrosion Loop, you have two options:

You can link only the DMs that are common across all underlying RBI Components. If you choose this option, you will need to link additional degradation mechanisms with each RBI Component as needed.

-or-
You can associate all possible DMs for all underlying RBI Components, even if those DMs apply only to one or a few of the components. If you choose this option, you will need to unlink DMs from each component as needed.

Unmitigated Risk for RBI Degradation Mechanisms

When you calculate an RBI Criticality Analysis, the unmitigated risk and unmitigated financial risk for each DM is calculated automatically and stored in the related RBI Degradation Mechanisms record. If you have created a custom calculator, unmitigated risk will be calculated by your custom calculator and displayed on the following datasheets:

Risk Matrix
Degradation Mechanism with Risk Mitigation
Degradation Mechanism without Risk Mitigation

After the unmitigated risk and unmitigated financial risk are calculated for the DMs, depending on how the administrative settings are configured, you can:

Accept the calculated unmitigated values.

-or-
Override the calculated unmitigated values.

About Associating Potential Degradation Mechanisms (PDMs)

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.

Note: PDMs can be standardized and inherited from RBI Corrosion Loops. When a new RBI Component is generated from and linked to a specific RBI Corrosion Loop, the PDMs associated with that RBI Corrosion Loop will be inherited by the new RBI Component.

Example: Overhead (OVHD) System

Suppose you have created an RBI Corrosion Loop to represent an OVHD system. You may have determined that components in this corrosion loop can fail in the following ways:

Exchanger Failure: The tubes in the exchanger could foul and cause the exchanger to produce too much or too little cooling.
Column Failure: The column may be susceptible.

In this case, the RBI Corrosion Loop would be linked to two PDMs to represent each type of degradation mechanism in the preceding list. After the PDMs are linked to the RBI Corrosion Loop as a whole, and you have determined the components in the corrosion loop, you will need to validate the degradation mechanisms for each component.

Assuming that the OVHD system contains the Exchanger and the Column, the RBI Corrosion Loop representing the OVHD system would be linked to the following RBI Component records:

Column Top (belongs to the Column)
Outlet Nozzle (belongs to the Column)
Exchanger Shell (belongs to the Water Heater)

Each of these RBI Components would be linked automatically to all the PDMs that are linked to the Corrosion Loop. You would need to determine, however, which degradation mechanisms make sense for each component. To do so, you might decide that the RBI Component should be linked to the PDMs as described in the following table.


RBI Component	PDM
Column Top	Environmental Cracking
Outlet Nozzle	External Corrosion
Exchanger Shell	Environmental Cracking

So, while the RBI Corrosion Loop is linked to two PDMs, each RBI Component is linked to only one PDM in this case.

About Degradation Mechanism Evaluations (DMEs)

For each Degradation Mechanism (DM) that belongs to an RBI Criticality Analysis, a corresponding Criticality Degradation Mech Evaluation record also belongs to that RBI Criticality Analysis. In each Criticality Degradation Mech 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 Criticality Analysis contains an Erosion DM, it will also contain a corresponding Erosion Criticality Degradation Mech 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 erosion.

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

Suppose a Degradation Mechanisms Evaluation Factors record contains the following values in the following fields:

Degradation Mechanism: Erosion
Ranking: 1
Ranking Description: Erosion - Impact Resistant Material. Good Inspection History with no evidence of Damage.

If an RBI Analysis is linked to an Erosion Criticality Degradation Mech Evaluation, and you select 1 in the Probability Category field, the value in the Probability Category Description field will be populated with the value in the Ranking Description field in the Degradation Mechanisms Evaluation Factors record containing the values Erosion and 1. In this example, the Probability Category Description field would be populated with the value Erosion - Impact Resistant Material. Good Inspection History with no evidence of Damage.

Add Degradation Mechanisms (DMs)

About This Task

For each Potential Degradation Mechanism (PDM) linked to the Component, a DM is added to the Analysis. You can, however, add additional DMs to the analysis.

Note: You cannot add a DM if the state of the analysis is Risk Completed.

Procedure

Access the analysis to which you want to add DMs.
In the Degradation Mechanisms section, select .
A window appears, displaying a list of the DMs that can be applied to the RBI Criticality Analysis, displaying the methodology type of each DM.

Tip: If you select the link that corresponds to a DM, the associated PDM record appears in Record Explorer on a new page.
In the row containing each DM that you want to add, select the check box, and then select Add.

The selected DMs are added to the RBI Criticality Analysis.

Results

A Consequence Evaluation is created and linked to the RBI Criticality Analysis.

What To Do Next

Evaluate a Degradation Mechanisms Record (DM).

Evaluate a Degradation Mechanism (DM)

Procedure

Access the analysis containing the DM that you want to evaluate.
In the Degradation Mechanisms section, in the row containing the DM that you want to modify, select the link.

A window appears, displaying a blank datasheet of the corresponding Degradation Mechanism Evaluation (DME).
Enter values in the available fields.
Select .

The DM is evaluated.

Assess the Unmitigated Risk of a Degradation Mechanism (DM)

Before You Begin

Procedure

Access the analysis containing the DM for which you want to assess the unmitigated risk.
In the Degradation Mechanisms section, select the row containing the DM that you want to assess, and then select .

The Risk Matrix window appears.
Select the cell that represents the risk rank for each category, and then select Done. These categories depend on the risk matrix that is defined by your organization. By default, these categories are Safety, Environment, Operations, and Financial.

The unmitigated risk and unmitigated financial risk values for the DM are saved.

Access the Inspection History of a Degradation Mechanism (DM)

Procedure

Access the analysis whose inspection history you want to access.
Below the graph, in the row containing the analysis whose Inspection History you want to access, select the link.
The Analysis workspace appears.
In the Degradation Mechanisms section, select the row containing the DM whose inspection history you want to view, and then select .

A window appears, displaying the inspection history for the selected DM.
Tip: If you want to access the Inspection in Inspection Management, select the link in the Inspection Report column. The Inspection Data section appears, displaying the Inspection datasheet.

Assign Inspections to a Degradation Mechanism Evaluation (DME)

Before You Begin

You can assign up to six Inspections.

Important: For RBI 580 Qualitative DMs, you can access the inspection history; however, you cannot take credit for an Inspection to calculate the Damage Factor.

Procedure

Access the inspection history for the analysis containing the DME to which you want to assign Inspections.

Note: The listed inspections fall within a specified 20-year window.
In the row containing each Inspection that you want to assign, select the check box, and then select OK.
The selected Inspections are assigned to the DME.
Tip: To view the Inspection in Inspection Management, select the link in the Inspection Reports column.

Link an Inspection Consequence Evaluation to an RBI Degradation Mechanism Evaluation (DME)

About This Task

Important: To link an Inspection Confidence Evaluation to an RBI DME, the Risk Based Inspection or the RBI 581 license must be active.

Procedure

Access the analysis containing the RBI DME to which you want to link an Inspection Confidence Evaluation.
Note: To link an Inspection Confidence Evaluation to an RBI DME, the associated RBI Analysis must be in the Active state. Only Active RBI Analyses will display current Inspection Reports in their corresponding Inspection History section.
In the Degradation Mechanism section, select the row containing the DME that you want to link to the Inspection Confidence Evaluation, and then select .

Note: The RBI DME that you select must also be the DME in the corresponding Inspection Confidence Evaluation.

A window appears, displaying a list of corresponding Inspection Reports.
Next to the Inspection Report containing the Inspection Confidence Evaluation that you want to link to the RBI DME, select the check box.
In the lower-right corner of the section, select OK.

The Inspection Confidence Evaluation is linked to the RBI DME.

Delete Degradation Mechanisms (DMs)

Before You Begin

When you delete a DM, the associated RBI Degradation Mechanism Evaluation (DME) and RBI Consequence Evaluation records are also deleted.
You cannot delete a DM if the associated analysis is in Risk Completed state.

Procedure

Access the analysis that contains the DMs that you want to delete.
In the Degradation Mechanisms section, select the row containing the DM that you want to delete, and then select .

A message appears, asking you to confirm that you want to delete the selected DM.
Select Yes.

The DMs, along with the associated DMEs and RBI Consequence Evaluations, are deleted.