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Impact of partial and imperfect testing on reliability assessment of safety instrumented systems - Possible approaches for inclusion of its effects in reliability assessments

机译：部分和不完善测试对安全仪表系统可靠性评估的影响-将其影响纳入可靠性评估的可能方法

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摘要

Testing of safety instrumented systems is vital to ensure they are able to perform the required safety function when the need arises. These tests are carried out at specified time intervals. The verification of the ability of the safety systems to perform as required is carried out by reliability assessment. This is the calculation of how likely it is that the safety instrumented system will function when needed.In carrying out reliability assessment, proof testing of safety systems is assumed to be perfect which is not always the case in reality. This thesis is important because it looks at how to evaluate this assumption to achieve a realistic estimate since testing is a key factor in reliability calculation. This study identifies the main causes of imperfectness which are classified with the five M-factors namely: Method, Machine, Manpower, Milieu and Material. Based on these, the situations where perfect test may not be realistic with examples are reviewed and documented.I have studied and compared different ways that the effects of tests can be treated. Three approaches to consider imperfectness of test were identified: the IEC 61508 approach where we consider the proportion (fraction) of dangerous undetected failures that are revealed by the proof test, the probability of detecting a dangerous undetected failure during a given proof test and the PDS method of adding a constant probability of test independent failures. The analysis carried out compared the first and second approach. Based on the analysis, the second approach was proposed to be the most suitable of the first two approaches.Furthermore, we present different reliability assessment methods for estimating the probabilityof failure on demand of a safety system. The methods used are: analytical formulas, multi-phase Markov, fault tree approach and Petri net. The principles of application and limitation with each of these approaches are presented in this thesis. In the course of this work, we discovered that some complicated cases and systems can only be analyzed by simulation. Finally, a chemical reactor protection system is used as a case study to demonstrate the principles and methods discussed in this thesis.
机译：安全仪表系统的测试对于确保在需要时能够执行所需的安全功能至关重要。这些测试以指定的时间间隔进行。通过可靠性评估对安全系统按要求执行的能力进行验证。这是对安全仪表系统在需要时起作用的可能性的计算。在进行可靠性评估时，假定对安全系统的证明测试是完美的，但实际情况并非总是如此。由于测试是可靠性计算中的关键因素，因此本论文很重要，因为它着眼于如何评估此假设以实现实际估计。这项研究确定了不完美的主要原因，这些不完美的原因分为五个M因子：方法，机器，人力，Milieu和材料。在此基础上，回顾并记录了可能无法通过示例进行完美测试的情况。我研究并比较了可以处理测试效果的不同方法。确定了三种考虑测试不完善性的方法：IEC 61508方法，其中我们考虑了由证明测试揭示的危险未检测到的故障的比例（分数），在给定的证明测试期间检测到危险未检测到的故障的概率以及PDS一种增加独立于测试失败概率的方法。进行的分析比较了第一种方法和第二种方法。在分析的基础上，第二种方法被认为是前两种方法中最合适的。此外，我们提出了不同的可靠性评估方法来估计安全系统需求时的失效概率。所使用的方法是：解析公式，多相马尔可夫，故障树方法和Petri网。本文介绍了每种方法的应用原理和局限性。在这项工作的过程中，我们发现某些复杂的案例和系统只能通过仿真来分析。最后，以化学反应器保护系统为例，论证了本文讨论的原理和方法。

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    Ocheni Eleojo Samuel;

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  • 年度 2015
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  • 原文格式 PDF
  • 正文语种 eng
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  • 入库时间 2022-08-20 20:14:36

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