RBI for PRDs

Properly functioning PRDs are considered to be the critical “Layer of Protection” for pressurized systems; they are essential for avoiding unexpected overpressure events, equipment damage, loss of containment, and plant shutdowns.

Regular inspection, testing, and overhaul of PRDs are needed to ensure proper function upon demand. Most inspection programs adequately manage the unreliability of PRDs without much consideration to potential consequences of PRD failure to open or leakage.

Many plants inspect PRDs on preset intervals as recommended by inspection Codes such as NB-23 and API 510. These Codes allow for an increase in inspection intervals based on the historical performance of the PRD.

The use of an RBI methodology allows optimum intervals to be set immediately based on the probability and consequences associated with PRD failure. This enables you to plan maintenance programs based on risk and prioritizes resources in the following ways:

  • Targets the most critical PRDs
  • Allows deferral of lower-risk PRDs
  • Considers other “Layers of Protection”
  • Optimizes intervals based on plant risk targets

The API RBI PRD Difference

API PRD RBI methodology evaluates the criticality of PRDs and sets inspection/testing frequencies accordingly. This quantitative approach is consistent with API 510 Pressure Vessel Inspection Code and employs extensive computational analysis by considering the following:

  • PRD Reliability/Failure Rate Database – Considers the fluid service, duration in service, and type of device, and provides default PRD failure rates backed by an extensive database of bench tests
  • Criticality – Considers the overpressure scenarios (e.g., loss of cooling, fire, blocked discharge) applicable to each PRD
  • Integrated Consequence Analysis Package – Considers the fluid severity and hazard potential (flammable and toxic consequences) when evaluating the loss of containment as a result of PRD failure to open or the consequences of PRD leakage
  • Documented Inspection History – Updates the default Probability of Failure using the historical PRD inspection data

This is an optimized approach to PRD inspection as compared to the traditional condition-based PRD inspection program. It has the potential to significantly reduce maintenance costs without jeopardizing the safety of the plant.

PRD Expertise

E2G is uniquely qualified to implement the API PRD RBI technology because we are recognized industry leaders in risk-based inspection and pressure relieving systems.

Philip Henry, P.E., an expert in pressure relief systems, led the development of the API PRD RBI methodology as Chairman of the API RBI Technical Working Group. Phil is also the API Pressure Relieving Systems (PRS) Subcommittee chairman of TF520, which delineates standards associated with the sizing, selection, and installation of PRDs.

Download RBI Case Study: PRDs

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