PRD Analyses

Details

A PRD Analysis for a pressure relief device can be created once you have identified at least one piece of an asset or RBI Component that it protects. PRD Analyses function the same way as RBI Analyses.

However, the following features that are available for RBI Analyses are not available for RBI PRD Analyses:

• Creating What If Analyses from RBI PRD Analyses
• Specifying that TM Analysis values at the TML Group level be used to calculate RBI corrosion rate values

When you create a Criticality Calculator PRD Component:

• When prompted to select an Asset, you should select the Asset that represents the pressure relief device itself.
• When prompted for the Component family, you should select one of the following options:

  • Criticality Calculator PRD Component - Relief Valve

  • Criticality Calculator PRD Component - Rupture Disk

• When prompted for the Component Type, you should select one of the following options:

  • Balanced Bellows PRD

  • Conventional PRD

  • Pilot-Operated PRD

  • PRD with Rupture Disk

  • Rupture Disk Only

• An Asset that represents a Pressure Relief Device cannot be linked to both RBI Components and PRD Components.

Details

As part of each analysis, you can choose the inspection for each DME. This selection assists in reducing uncertainty posed by the particular Degradation Mechanism (DM) and in determining its rate of deterioration. Each Inspection is quantitatively assessed to determine its effectiveness in achieving this goal.

The resulting quantitative value, or Inspection History, indicates how effective prior inspections were at identifying the DM and the rate of degradation.

Assigning Inspections to DMEs in RBI

If an RBI Component represents parts of a piece of an asset that you have inspected in the past, and have recorded results in Inspection records, you can assign those inspections to the appropriate DMEs for that component. By doing so, you identify the inspections that were used to detect DMs for that component.

The type of analysis used will determine what happens when you assign an inspection to a DM. For any RBI 580 DME, the listed inspections fall within a specified 20-year window. When you are working with an RBI Analysis, APM uses the values in the Inspection Confidence field of the Inspection records to automatically populate the following fields in the Criticality Degradation Mech Evaluation representing that degradation mechanism:

• Inspection Confidence: Indicates how effective the last inspection was at detecting the DM and identifying the rate of degradation.
• Equivalent Number of Inspections: Indicates the number of inspections that will be used when calculating the analysis.

Assigning PRD Inspections to DMEs

You can also assign inspections that are associated with pressure relief devices (PRDs) when you are working with an RBI PRD Criticality Analysis. When you do so, the Inspection records that you select will belong to the PRD Pop Test Checklist family, and values that are stored in the PRD Pop Test Checklist records that you select will be used as inputs to RBI PRD Criticality Analysis calculations. Specifically, values in the following fields in the PRD Pop Test Checklist records are used in RBI PRD Criticality Analysis calculations:

• Completion Date
• Inspection Confidence
• Leak Test Results
• Over Pressure Test Results

For any PRD DME, the listed inspections fall within a specified 20-year window. The Date in Service field must contain a date prior to the date in the Completion Date field. The Completion Date and Inspection Confidence fields in the PRD Pop Test Checklist must contain values in order to assign a PRD Pop Test Checklist to a DM that is associated with an RBI PRD Criticality Analysis.

The Leak Test Results and Over Pressure Test Results fields, however, do not have to contain values in order to assign an Inspection record of this type to a DME. Instead, in this case, the following default values will be used in the RBI PRD criticality Analysis calculations:

• Leak: This value is used as an input by default when the Leak Test Results field does not contain a value in the PRD Pop Test Checklist that you assign to a DME.
• Fail: This value is used as an input by default when the Over Pressure Test Results field does not a value in the PRD Pop Test Checklist that you assign to a DME.

When you are working with an RBI 581 Risk Analysis or an RBI Criticality Analysis, (i.e., not an RBI PRD Criticality Analysis), if you want to specify manual values, you can choose to override the automatic Inspection Confidence and Equivalent Number of Inspections. In most cases; however, you will want APM to populate the fields automatically to avoid subjective interpretations of the values.

Inspection Priority for Current Interval

When you calculate an RBI PRD Criticality Analysis, in each RBI Degradation Mechanism Evaluation linked to the RBI Analysis a probability of failure and consequence of failure are calculated for the current interval. The current interval is defined as the difference of the calculation date and the value of the Next Inspection Date field stored on the RBI PRD Criticality Analysis. Together, the values are used to determine an Inspection Priority. The fields used to determine the inspection priority are:

• Leak Degradation Mechanism Evaluations
  • Probability of Leak – Current Interval
  • Leak Consequence Category
    Note: This field is stored on the related PRD Consequence Evaluation.
• Over Pressure Degradation Mechanism Evaluation
  • Probability of Loss of Containment – Current Interval
  • Consequence of Failure at Over Pressure

The Degradation Mechanism Evaluation on a PRD Criticality Analysis with the most conservative inspection priority for the current interval becomes the driving risk for the current interval. The driving risk values are stored on the PRD Criticality Analysis under the Analysis Outputs Current Interval column.

Inspection Priority and Risk Matrices

Specifically, to determine the Inspection Priority, the Probably of Failure and Combined Consequence are plotted on a matrix available by selecting the area in the page header that contains Inspection Priority, Risk Category, and APM Risk data.