Optimize PRS Inspection Intervals

Do you know if the pressure relief devices (PRDs) at your facility are working properly? Regular inspection, testing, and overhaul are necessary to ensure these critical devices will function upon demand to prevent unexpected overpressure events, equipment damage, loss of containment, and plant shutdowns.

Many plants inspect PRDs on preset intervals as recommended by inspection codes such as NB-23 and API 510 Pressure Vessel Inspection Code, which allow increased inspection intervals based on the historical performance of the PRD. However, most inspection programs only adequately manage the unreliability of PRDs without considering the consequences of a potential failure or loss of containment.

How to Calculate Risk

E2G will use risk-based inspection (RBI) to quantify risk and make informed decisions about how, when, and where to inspect PRDs. Accounting for both probability of failure (POF) and consequence of failure (COF) will remove uncertainty by evaluating your equipment and re-focusing inspection efforts onto the highest-risk items.

Effective PRD maintenance programs are prioritized based on risk. Relief system RBI allows you to plan maintenance programs and prioritize resources by:

  • Targeting the most critical PRSs and PRDs
  • Deferring lower-risk items
  • Considering other layers of protection
  • Optimizing inspection intervals, using facility risk targets

E2G's API PRD RBI Methodology

API PRD RBI methodology uses a quantitative approach to evaluate the criticality of PRDs and set the inspection and testing frequencies accordingly. Using API 510 as a foundation, our team uses the API RBI software to conduct extensive computational analysis.

This method uses:

  • PRD reliability/failure rate database – reviews fluid service, duration in service, and type of device to provide default PRD failure rates
  • Criticality – considers potential overpressure scenarios (e.g., loss of cooling, fire, blocked discharge) applicable to each PRD
  • Integrated consequence analysis package – examines fluid severity and hazard potential (flammable and toxic) when evaluating either the loss of containment if a PRD failed to open or the consequences of PRD leakage
  • Documented inspection history – updates default POF using historical PRD inspection data


This optimized approach to PRD inspection can significantly reduce maintenance costs without jeopardizing the safety of the plant. 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.

Recommended Reading

Pressure Relieving Systems & RBI Expertise

E2G’s risk-based inspection engineers have supported the implementation of RBI programs for many refining, energy, petrochemical, and chemical facilities across North America. Our team of internationally recognized experts in pressure relief system design, optimization, and installation will provide practical recommendations to increase safety and maximize reliability.

Our experts:

  • Have 350+ years of combined field experience
  • Have served as the API 520 task force chairman for more than 25 years
  • Are the lead investigators on API 581
  • Developed the only API-branded and fully compliant API 581 RBI software