Associating Potential Degradation Mechanisms (PDMs)

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

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

Suppose your Corrosion Loop record represents the OVHD system. You may have determined that RBI Components in this Corrosion Loop can fail in the following ways:

• Exchanger Failure. For example, the tubes in the exchanger could foul and cause the exchanger to produce too much or too little cooling.
• Column Failure. For example, the column may be susceptible.

In this case, the Corrosion Loop record would be linked to two Potential Degradation Mechanisms records to represent each type of degradation mechanism in the preceding list. After the degradation mechanisms are associated with the Corrosion Loop as a whole and you have determined which RBI Components are involved in that Corrosion Loop, you will need to validate the degradation mechanisms for each RBI Component.

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

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

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

Criticality Calculator RBI Components Record	Potential Degradation Mechanisms Record
Column Top	Environmental Cracking
Outlet Nozzle	External Corrosion
Exchanger Shell	Environmental Cracking

So, while the Corrosion Loop record is linked to two Potential Degradation Mechanisms records, each Criticality Calculator RBI Components records is linked to only one Potential Degradation Mechanisms record.