Research Papers: Operations, Applications & Components

Evaluating Risk and Safety Integrity Levels for Pressure Relief Valves Through Probabilistic Modeling

[+] Author and Article Information
Emily M. Mitchell

Dept. of Biostatistics and Bioinformatics,
Emory University,
Atlanta, GA 30322

Robert E. Gross

Site Infrastructure Reliability Engineering,
Savannah River Nuclear Solutions,
Aiken, SC 29808

Stephen P. Harris

Computational Sciences,
Savannah River National Laboratory,
Aiken, SC 29808

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the Journal of Pressure Vessel Technology. Manuscript received April 9, 2012; final manuscript received October 10, 2012; published online March 18, 2013. Assoc. Editor: Allen C. Smith.

J. Pressure Vessel Technol 135(2), 021601 (Mar 18, 2013) (8 pages) Paper No: PVT-12-1040; doi: 10.1115/1.4007959 History: Received April 09, 2012; Revised October 10, 2012

The probability of failure on demand (PFD) for spring-operated pressure relief valves (SORVs) is estimated by applying the Fréchet and Weibull probability distributions using proof test data from the United States Department of Energy's Savannah River Site (SRS) in Aiken, South Carolina. The data can be accessed through the Center for Chemical Process Safety (CCPS) Process Equipment Reliability Database (PERD). The probability distributions enable the evaluation of risk, estimation of ANSI/ISA-84.00.01 Safety Integrity Levels (SILs), and the impact of potential modifications of the maintenance plan. Current SRS practices are reviewed, and recommendations are made for risk-based adjustments to the maintenance plan. Subsets of valves are identified in which maintenance times can be extended and in which increased safety margins may be needed.

Copyright © 2013 by ASME
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ASME PCC-3-2007, Inspection Planning Using Risk-Based Methods, June 30, 2008.
API RP 581 Risk-Based Inspection Technology, Section 7 Pressured Relief Devices, American Petroleum Institute (API) Recommended Practice 581, 2nd ed., September 2008.
Abernethy, R. B., 2004, The New Weibull Handbook, R. B.Abernethy, ed., North Palm Beach, FL.
Castillo, E., Hadi, A. S., Balakrishnan, N., and Sarabia, J. M., 2005, Extreme Value and Related Models With Applications in Engineering and Science, John Wiley & Sons, New York.
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Gross, R. E., and Harris, S. P., 2008, “Analysis of Safety Relief Valve Proof Test Data to Optimize Lifecycle Maintenance Costs,” Proceedings of the 2008 Annual Reliability and Maintainability Symposium (RAMS), Las Vegas, NV, Jan. 28–31.


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Fig. 1

(a) Conventional spring design steam service valve; cap and bonnet removed, (b) valve body and inlet nozzle; very few deposits on the seating surface and no cuts, (c) Inside the valve bonnet; corrosion evident but not much loose debris, and (d) Spring, spring washers, disc holder and disc, stem, sleeve guide, and stem retainer

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Fig. 2

Ratio versus date by working fluid

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Fig. 3

Ratio by working fluid

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Fig. 4

Maintenance time distribution (years) over all working fluids

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Fig. 5

Time (years) by working fluid

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Fig. 6

PFD for the Fréchet and Weibull distributions for air, gas, and steam services

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Fig. 7

PFD for the Fréchet and Weibull distributions for liquid services

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Fig. 8

Weibull fit for the probability of failure, air, gas, and steam services combined

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Fig. 9

Fréchet fit for the probability of failure for the liquid service group

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Fig. 10

Risk versus cost by maintenance time (years) for air, gas, and steam service combined

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Fig. 11

Risk versus cost by maintenance time (years) for liquid service

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Fig. 12

PFDavg and SIL by maintenance time based on bench proof tests

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Fig. 13

PFDavg and SIL by maintenance time based on forecasted field values



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