The Effects of Maintenance Actions on the Average Probability of Failure on Demand of Spring Operated Pressure Relief Valves

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Julia V. Bukowski ◽  
William M. Goble ◽  
Robert E. Gross ◽  
Stephen P. Harris
Keyword(s):  
Probability Of Failure ◽  
Pressure Relief ◽  
Periodic Inspection ◽  
On Demand ◽  
Plant Safety ◽  
Safety Integrity Level ◽  
Proof Testing ◽  
Average Probability ◽  
Pressure Relief Valves ◽  
Inspection And Maintenance

The safety integrity level (SIL) of equipment used in safety instrumented functions is determined by the average probability of failure on demand (PFDavg) computed at the time of periodic inspection and maintenance, i.e., the time of proof testing. The computation of PFDavg is generally based solely on predictions or estimates of the assumed constant failure rate of the equipment. However, PFDavg is also affected by maintenance actions (or lack thereof) taken by the end user. This paper shows how maintenance actions can affect the PFDavg of spring operated pressure relief valves (SOPRV) and how these maintenance actions may be accounted for in the computation of the PFDavg metric. The method provides a means for quantifying the effects of changes in maintenance practices and shows how these changes impact plant safety.

scholarly journals The Effects of Maintenance Actions on the PFDavg of Spring Operated Pressure Relief Valves

2014 ◽  
Author(s):  
Julia V. Bukowski ◽  
William M. Goble ◽  
Robert E. Gross ◽  
Stephen P. Harris
Keyword(s):  
End User ◽  
Pressure Relief ◽  
Periodic Inspection ◽  
On Demand ◽  
Plant Safety ◽  
Safety Integrity Level ◽  
Proof Testing ◽  
Average Probability ◽  
Pressure Relief Valves ◽  
Inspection And Maintenance

The safety integrity level (SIL) of equipment used in safety instrumented functions is determined by the average probability of failure on demand (PFDavg) computed at the time of periodic inspection and maintenance, i.e., the time of proof testing. The computation of PFDavg is generally based solely on predictions or estimates of the assumed constant failure rate of the equipment. However, PFDavg is also affected by maintenance actions (or lack thereof) taken by the end user. This paper shows how maintenance actions can affect the PFDavg of spring operated pressure relief valves (SOPRV) and how these maintenance actions may be accounted for in the computation of the PFDavg metric. The method provides a means for quantifying the effects of changes in maintenance practices and shows how these changes impact plant safety.

Statistical Performance Evaluation of Soft (Elastomer) Seat Pressure Relief Valves

2013 ◽  
Author(s):  
Robert E. Gross ◽  
Stephen P. Harris
Keyword(s):  
South Carolina ◽  
Performance Evaluation ◽  
The United States ◽  
Probability Of Failure ◽  
United States Department ◽  
Relief Valve ◽  
Pressure Relief ◽  
On Demand ◽  
Pressure Relief Valves ◽  
Statistical Performance Evaluation

Risk-based inspection methods enable estimation of the probability of failure on demand for spring-operated pressure relief valves at the United States Department of Energy’s Savannah River Site in Aiken, South Carolina. This paper presents a statistical performance evaluation of soft seat spring operated pressure relief valves. These pressure relief valves are typically smaller and of lower cost than hard seat (metal to metal) pressure relief valves and can provide substantial cost savings in fluid service applications (air, gas, liquid, and steam) providing that probability of failure on demand (the probability that the pressure relief valve fails to perform its intended safety function during a potentially dangerous over pressurization) is at least as good as that for hard seat valves. The research in this paper shows that the proportion of soft seat spring operated pressure relief valves failing is the same or less than that of hard seat valves, and that for failed valves, soft seat valves typically have failure ratios of proof test pressure to set pressure less than that of hard seat valves.

scholarly journals The Operation Modes of E/E/PE System and Their Influence on Determining and Verifying the Safety Integrity Level

2010 ◽  
Vol 13 (1) ◽  
pp. 289-298
Author(s):  
Tomasz Barnert ◽  
Kazimierz Kosmowski ◽  
Marcin Śliwiński
Keyword(s):  
High Demand ◽  
Related Function ◽  
On Demand ◽  
Safety Integrity Level ◽  
Operation Modes ◽  
Mode Of Operation ◽  
Protection Systems ◽  
Average Probability ◽  
Quantitative Verification ◽  
Probabilistic Criteria

The Operation Modes of E/E/PE System and Their Influence on Determining and Verifying the Safety Integrity Level The standard PN-EN 61508 introduces some probabilistic criteria for the E/E/PE systems that can operate in different modes of operation, which are related to the safety integrity level (SIL). For the control and protection systems, operating in a low demand mode, the criterion is the average probability of dangerous failure on demand PFDavg. In case of systems working in a continuous mode of operation or high demand, the criterion is probability of dangerous failure per hour PFH. In practice, the E/E/PE systems implement many safety-related functions (SRFs), which have different requirements for high and low demands. Thus, there is the problem with choosing proper probabilistic criterion for determining required SIL for a safety-related function to be implemented by these systems as well as in the process of quantitative verification of SIL for considered architectures.

scholarly journals Unavailability of K-out-of-N: G Systems with non-identical Components Based on Markov Model

2019 ◽  
Vol 2 (1) ◽  
pp. 25-35
Author(s):  
Ayodeji Akinsoji Okubanjo ◽  
Olasunkami oriola Akinyemi ◽  
Oluwadamilola Kehinde Oyetola ◽  
Olawale omopariola Olaluwoye ◽  
Olufemi Peter Alao
Keyword(s):  
Markov Model ◽  
Probability Of Failure ◽  
Process Industry ◽  
Redundant System ◽  
System Architectures ◽  
On Demand ◽  
Proposed Model ◽  
Challenging Tasks ◽  
Average Probability ◽  
Analytical Formulas

The process industry has always been faced with the challenging tasks of determining the overall unavailability of safety instrumented systems (SISs). The unavailability of the safety instrumented system is quantified by considering the average probability of failure on demand. To mitigate these challenges, the IEC 61508 has established analytical formulas for estimating the average probability of failure on demand for K-out-of-N (KooN) architectures. However, these formulas are limited to the system with identical components and this limitation has not been addressed in many researches. Hence, this paper proposes an unavailability model based on Markov Model for different redundant system architectures with non-identical components and generalised formulas are established for non-identical k-out-of-n and n-out-of-n configurations. Furthermore, the proposed model incorporates undetected failure rate and evaluates its impact on the unavailability quantification of SIS. The accuracy of the proposed model is verified with the existing unavailability methods and it is shown that the proposed approach provides a sufficiently robust result for all system architectures.  

The Adhesion Failure Mode in Stainless Steel Trim Spring Operated Pressure Relief Valves

2012 ◽  
Author(s):  
Julia V. Bukowski ◽  
Robert E. Gross ◽  
William M. Goble
Keyword(s):  
Stainless Steel ◽  
Failure Mode ◽  
Failure Rate ◽  
Failure Modes ◽  
Service Failure ◽  
Failure Rates ◽  
Pressure Relief ◽  
Safety Integrity Level ◽  
Adhesion Failure ◽  
Pressure Relief Valves

This paper addresses dangerous failures of stainless steel (SS) trim spring operated pressure relief valves (SOPRV) due to a particular failure mode (SS-to-SS adhesion) which is not currently being included in SOPRV failure rates. As a result, current methods for estimating or predicting failure rates for SS trim SOPRV significantly underestimate these failure rates and, consequently, overestimate the safety provided by the SOPRV as measured by its average probability of failure on demand (PFDavg) or its corresponding safety integrity level (SIL). The paper also illustrates the critical importance of root cause analysis (RCA) of dangerous SOPRV failures in understanding the impacts of various failure modes. Over 1300 proof test results for both new and used SS trim SOPRV from the Savannah River Site (SRS) were identified. RCA was used on the failed valves to classify those failed due to SS-to-SS adhesions. Statistical analysis of the data convincingly demonstrates adhesions, previously assumed to be only an in-storage failure phenomenon, are also an in-service failure mode which needs to be included in SOPRV failure rates. The paper discusses the factors which potentially influence the adhesion failure mode and suggests a possible approach to including this mode in failure rate predictions. An example illustrates how current failure rate models overestimate SS trim SOPRV safety by one or two orders of magnitude.

The Adhesion Failure Mode in Stainless Steel Trim Spring-Operated Pressure Relief Valves

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Julia V. Bukowski ◽  
Robert E. Gross ◽  
William M. Goble
Keyword(s):  
Stainless Steel ◽  
Failure Mode ◽  
Failure Rate ◽  
Failure Modes ◽  
Service Failure ◽  
Failure Rates ◽  
Pressure Relief ◽  
Safety Integrity Level ◽  
Adhesion Failure ◽  
Pressure Relief Valves

This paper addresses dangerous failures of stainless steel (SS) trim spring-operated pressure relief valves (SOPRV) due to a particular failure mode (SS-to-SS adhesion), which is not currently being included in SOPRV failure rates. As a result, current methods for estimating or predicting failure rates for SS trim SOPRV significantly underestimate these failure rates and, consequently, overestimate the safety provided by the SOPRV as measured by its average probability of failure on demand (PFDavg) or its corresponding safety integrity level (SIL). The paper also illustrates the critical importance of root cause analysis (RCA) of dangerous SOPRV failures in understanding the impacts of various failure modes. Over 1300 proof test results for both new and used SS trim SOPRV from the Savannah River Site (SRS) were identified. RCA was used on the failed valves to classify those failed due to SS-to-SS adhesions. Statistical analysis of the data convincingly demonstrates adhesions, previously assumed to be only an in-storage failure phenomenon, are also an in-service failure mode, which needs to be included in SOPRV failure rates. The paper discusses the factors which potentially influence the adhesion failure mode, and suggests a possible approach to including this mode in failure rate predictions. An example illustrates how current failure rate models overestimate SS trim SOPRV safety by 1 or 2 orders of magnitude.

scholarly journals Evaluation Of The Safety Integrity Level (SIL) Due To The Guidelines Of EN 61508 And With The Use Of Markov Processes

2015 ◽  
Vol 35 (1) ◽  
pp. 73-84 ◽  
Author(s):  
Stanisław Młynarski ◽  
Robert Pilch ◽  
Maksymilian Smolnik ◽  
Maciej Szkoda ◽  
Jan Szybka
Keyword(s):  
Markov Process ◽  
Markov Processes ◽  
Renewal Process ◽  
Probability Of Failure ◽  
On Demand ◽  
Safety Integrity Level ◽  
Methods Of Evaluation ◽  
Safety Systems

Abstract The methods of evaluation of the Probability of Failure on Demand (PFD) of safety systems were presented in the paper, assuming that the safety systems may be represented by the k out of n reliability structures. The results of the calculations obtained according to EN 61508 were compared with another results, this time obtained from the calculations done for these systems assuming that their failure-and-renewal process is a Markov process.

Effect of Truncated Demand and Capacity Distributions on Reliability of Pipelines

2003 ◽  
Author(s):  
Ziad Nakat ◽  
Robert Bea
Keyword(s):  
Pressure Relief ◽  
Physical Constraints ◽  
Demand Distribution ◽  
On Demand ◽  
Truncated Distributions ◽  
Pressure Relief Valves ◽  
Analysis Of Results ◽  
Management Policies ◽  
Comparison And Analysis ◽  
Demand And Capacity

Reliability of pipelines has been considered assuming different probability continuous distributions of demand and capacities. These distributions in reality can be truncated at the tails by physical constraints such as pressure relief valves (demand truncation), and hydro-testing (capacity truncation). This paper describes the effect of truncations on the reliability of pipelines. The effect of truncation by relief valves on the demand distribution is studied first; the effect of truncation by hydro-testing on the capacity distribution is studied second; and last, the combined effect of truncation on demand and capacity is studied. A comparison and analysis of results is presented to assess the importance of truncated distributions of demand and capacity on the reliability of pipelines. The results show that truncated distributions can have large effects on the reliability and should be accounted for, since they can alter significantly inspection and management policies.

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