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Optimization of periodic inspection time of sis subject to a regular proof testing
Published in Stein Haugen, Anne Barros, Coen van Gulijk, Trond Kongsvik, Jan Erik Vinnem, Safety and Reliability – Safe Societies in a Changing World, 2018
H. Srivastav, A.V. Guilherme, A. Barros, M.A. Lundteigen, F.B. Pedersen, A. Hafver, F.L. Oliveira
A Safety Instrumented System (SIS) is often used to detect hazardous events and to mitigate their consequences at facilities and plants that produce or handle hazardous substances, like e.g. hydrocarbon fluids and gases. Due to their criticality, they must obey to regulatory requirements and international standards on safety. IEC 61508 (1998) and related standards (such as IEC 61511 (2002) for the process industry sector) are key in framing the design and operation of SIS. One important requirement mandated by these standards is the need to verify, by quantitative analysis, that the safety performance is adequate in light of risk acceptance criteria. Most safety functions implemented by a SIS, the so-called Safety Instrumented Functions (SIFs), are seldom demanded as the normal operation is managed by a dedicated control system. According to the mentioned IEC standards, the SIFs are classified as operating in the low demand mode.
Safety and reliability analysis for butterfly valves in the offshore oil and gas industry
Published in Safety and Reliability, 2022
A risk mitigation rating informs us to what extent the instrumented function meets its requirements to mitigate risk. Once we have assigned an SIL value to each instrumented function within a safety instrumented system, the combination of these values will indicate the overall safety integrity of the safety instrumented system to which the instrumented functions belong. The three basic methods used to assess SIL are as follows:Risk matrix or graphs: You can utilise the standard GE Digital APM Risk Matrix interface to select the risk rank values for specific categories of risk in order to assess the SIL of an instrumented function.Layer of Protection Analysis (LOPA): A Layer of Protection Analysis (LOPA) is a risk assessment that determines the SIL associated with the protective instruments that reduce the risks that the instrumented function reduces.Hazards Analysis Risk Assessment: In case we have performed risk assessments for a Hazards Analysis via the Hazards Analysis module, we can utilise one of those risk assessments for determining the SIL for an instrumented function. In this paper, the method used to determine SIL is based on a hazard analysis and risk assessment, as follows:
Safety Criteria and Dependability Management Practices: A Case Study with I&C Systems of Prototype Fast Breeder Reactor
Published in Nuclear Technology, 2018
Srikantam Sravanthi, R. Dheenadhayalan, K. Madhusoodanan, K. Devan
The prototype fast breeder reactor (PFBR) is a [1250 MW(thermal) 500 MW(electric)] pool-type sodium-cooled fast reactor under commission in India. Instrumentation and control (I&C) is provided to facilitate controlled heat transfer from the core to the turbine and to ensure safety by timely shutdown (scram) in case of any anomaly and subsequent decay heat removal. The I&C systems of PFBR are classified as Safety Class-1 (SC-1), Safety Class-2 (SC-2), Safety Class-3 (SC-3), and Non-Nuclear Safety Systems. All systems that monitor scram parameters like core temperature, neutronic flux, primary sodium pump speed, and reactor inlet temperature are classified as SC-1. Additionally, I&C of Safety Grade Decay Heat Removal (SGDHR) system and reactor containment isolation logic are classified as SC-1. The I&C of SC-1 systems comes under the category of Safety Instrumented System (SIS) as defined in International Electrotechnical Commission (IEC) 61508 (Ref. 1). Each SIS loop is composed of sensor(s), logic solver(s), and final control element(s) for the purpose of taking the process to safe state. These systems deploy various techniques to achieve very high dependability. While the I&C design for PFBR has been already completed, this author and her team have undertaken a detailed study of dependability aspects of SISs aiming at improvements for future reactors. This technical note presents a review of the practices, assumptions, and techniques followed in PFBR I&C design to achieve high reliability in safety systems. Moreover, the research and development work done for improvements in the fail-safe behavior of such systems is highlighted.