RBI Degradation Mechanism Evaluation records are used to determine degradation mechanisms that affect Equipment and Functional Locations. This topic provides an alphabetical list and description of the fields that exist for the RBI Degradation Mechanism Evaluation (DME) family. The information in the table reflects the baseline state and behavior of these fields. The Criticality Degradation Mech, Evaluation table lists common fields shared across several DMEs. Fields that are unique to a specific component type can be viewed by expanding the appropriate drop-down heading.
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Criticality Degradation Mech Evaluation
Field |
Data Type |
Description |
Behavior and Usage |
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Main |
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Custom Calculation Policies Used | Character | A list of custom policies that are used to calculate the DME. | The value in this field must be 500 characters or less. |
Custom Calculations Used | Logical | Indicates whether or not the Degradation Mechanism Evaluation was calculated using the method specified in the Custom DME Configuration. | |
Damage Mechanism |
Character |
A process that induces deleterious micro and/or macro material changes over time that are harmful to the material condition or mechanical properties. |
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Probability Category |
Character |
Extent to which an event is likely to occur within the time frame under consideration. The mathematical definition of probability is a real number in the scale of 0 to 1 and is attached to a random event. |
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Probability Category Description |
Character |
Category to which an event is likely to occur within the time frame under consideration. The mathematical definition of probability is a real number in the scale 0 to 1 and is attached to a random event. |
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Input Fields |
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Date in Service |
Date |
Indicates the date that the asset became exposed to the environment that makes it susceptible to this Degradation Mechanism. |
This date will be used as the basis of all the calculations for each Degradation Mechanism. |
Equivalent Number of Inspections |
Numeric |
A value that represents the summation of averaging a group of inspections over a period of time. |
This approach is used only with the semi-quantitative risk model in Meridium Enterprise APM. |
Estimated Rate |
Numeric |
The corrosion rate given by the subject matter expert for the asset. |
Should be used in the absence of quality ultrasonic thickness (UT) data. |
Inspection Confidence |
Character |
Describes how effective the prior inspections were at correctly identifying the presence and extent of internal corrosion. |
An input from the following categories:
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Selected Corrosion Rate |
Numeric |
Indicates which corrosion rate the risk analyst has chosen as the basis of the analysis. |
Used for all remaining life calculations in RBI. |
Use Combined Confidence |
Logical |
Indicates whether or not the risk analyst has chosen to use the Rule of Threes. |
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Wall Thickness Loss |
Numeric |
Indicates how much of the original wall thickness has been lost at the time of analysis. |
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Intermediate Output |
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DF |
Numeric |
Damage Factor (DF) is a calculated value that quantifies the extent of damage from this Degradation Mechanism at the time of the analysis. |
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Estimated Half Life |
Numeric |
Half of the calculated remaining life. |
The value in this field is the result of the following calculation: ((Initial Wall Thickness) – (Ext. Est. Wall Loss) – (Ext. Est. Min. Thickness)) / (2 * (Ext Corr. Rate)) This value will be used to cap the inspection interval. |
Estimated Wall Loss |
Numeric |
Estimates how much of the original wall thickness has been lost at the time of analysis. |
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Failure Frequency |
Numeric |
A Probability of Failure (PoF) developed for specific component types based on a large population of component data that does not include the effects of specific damage mechanisms. |
This data is one of the factors used to determine the PoF. |
Fractional Wall Loss |
Numeric |
The Fractional Wall Loss is calculated by dividing the estimated internal wall loss by the original wall thickness. |
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Wall Ratio |
Numeric |
The estimated remaining wall divided by the required minimum wall thickness. |
Used as a tool to validate the data used in the assessment. |
Years in Service |
Numeric |
The number of years an equipment item has been in service. This time frame is measured from the initial date in its current service to the time the Probability of Failure Analysis is performed. |
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