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.

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.

Probability of Initial Failure for Spring Operated Relief Valves

2011 ◽  
Author(s):  
Julia V. Bukowski ◽  
Robert E. Gross ◽  
William M. Goble
Keyword(s):  
Failure Mode ◽  
Pressure Vessel ◽  
Convincing Evidence ◽  
Material Composition ◽  
Safety Standards ◽  
Initial Failure ◽  
Safety Integrity Level ◽  
Average Probability ◽  
Section Viii

We present clear and convincing evidence that, for new spring operated relief valves (SORV) that are not proof tested by the user shortly before installation, there is a non-trivial probability that the SORV will be installed in the fail-to-open (stuck shut) failure mode. Using the results of over 4800 new ASME Boiler and Pressure Vessel Code Section VIII SORV proof tests, we estimate the probability of initial failure (PIF) due to manufacturer/assembly anomalies, as well as PIF due to in-storage aging of SORV based on their material composition. We indicate how PIF can be reduced by various preinstallation activities that may be undertaken by the user. We show how to compute values of PIF to be used in calculating the average probability of fail danger (PFDavg) (as required by IEC61508 and similar safety standards in order to determine a safety integrity level (SIL)) which accounts for both the SORV material composition and the pre-installation activities undertaken. For four typical SORV of different material compositions we show how pre-installation activities influence the achievable SIL. We discuss the implication of these findings for estimating PIF for used (previously installed) SORV. We close with recommendations to further address PIF.

Engineering and design of fast reactors

1990 ◽  
Vol 331 (1619) ◽  
pp. 301-312 ◽  
Keyword(s):  
Fast Neutrons ◽  
Large Temperature ◽  
Steam Generators ◽  
The Core ◽  
Mode Of Operation ◽  
Protection Systems ◽  
Core Components ◽  
Main Components ◽  
System Layout ◽  
Coolant System

The paper deals with the basic engineering aspects specific to a fast breeder reactor. The characteristic design features are mainly determined by the coolant being sodium and the fast neutrons in the core. Some particular properties of sodium, the high temperature and the large temperature differences impose severe requirements on materials and structures. Also the mode of operation, the protection systems and the auxiliary systems are strongly influenced by these conditions. The resulting engineering implications will be illustrated by describing, firstly, the core layout and the core components, secondly, the main coolant system layout and its auxiliaries and, thirdly, the design aspects of main components such as pumps, heat exchangers and steam generators.

Uncertainty analysis of common cause failure in safety instrumented systems

2011 ◽  
Vol 225 (4) ◽  
pp. 450-460 ◽  
Author(s):  
W Mechri ◽  
C Simon ◽  
K Ben Othman
Keyword(s):  
Fuzzy Numbers ◽  
Epistemic Uncertainty ◽  
Monte Carlo Sampling ◽  
Fault Trees ◽  
Common Cause ◽  
Common Cause Failure ◽  
On Demand ◽  
Safety Integrity Level ◽  
Imperfect Knowledge ◽  
The Common

This paper analyses the problem of epistemic uncertainty in assessing the performance of safety instrumented systems (SIS) using fault trees. The imperfect knowledge concerns the common cause failure (CCF) involved in the SIS in low demand mode. The point-valued CCF factors are replaced by fuzzy numbers, allowing experts to express their uncertainty about the CCF values. This paper shows how these uncertainties propagate through the fault tree and how this induces an uncertainty to the values of the SIS failure probability on demand and to the safety integrity level of the SIS. For the sake of verification and comparison, and to show the exactness of the approach, a Monte Carlo sampling approach is proposed, where by a uniform or triangular second-order probability distribution of CCF factors is considered.

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.  

NEW RELIABILITY MEASURE FOR SAFETY INSTRUMENTED SYSTEMS

2013 ◽  
Vol 20 (01) ◽  
pp. 1350005 ◽  
Author(s):  
HUI JIN ◽  
MARY ANN LUNDTEIGEN ◽  
MARVIN RAUSAND
Keyword(s):  
Risk Reduction ◽  
Quantitative Measure ◽  
Functional Test ◽  
Test Interval ◽  
High Demand ◽  
On Demand ◽  
Demand Rate ◽  
Reduce Risk ◽  
Standard Probability

Safety instrumented systems (SISs) are installed to provide risk reduction and the performance of a SIS can be assessed by its ability to reduce risk. This article introduces a new quantitative measure for the risk reduction, denoted PFD*. Compared with the current reliability measures, the new measure takes into account the demand rate, and therefore can be used for SISs operating in both low-demand and high-demand mode. For a SIS operating in low-demand mode, the PFD* is approximately equal to the standard probability of failure on demand (PFD) used in IEC 61508 and related standards. PFD* can therefore be considered as an extension and improvement of the standard PFD. Successful handling of a demand verifies the functional status of a SIS in a way similar to a functional test, and the PFD* will therefore depend on the demand rate. The PFD* can be used to select the functional test interval according to the risk reduction allocated to the specific SIS. The properties of the new measure are analyzed through a case study of a 1-out-of-2 system of pressure transmitters.

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