The objectives of the thesis are to provide a methodology consideration for performance criteria (target SIL) and preparation for safety requirements specifications for SISs used in offshore facilities, as-sess methods for the verification of SIS design with their uncertainties. The requirements on the design of SISs (Safety Instrumented Systems) based on SIL (Safety Integrity Level) have been developed continuously in the offshore industry. IEC 61508 and IEC 61511 illustrate various methodologies to determine the target SIL for specified safety functions, such as risk graph, layer of protection analysis, etc. These methods could arrive at different target SILs for the same safety function, mainly due to uncertainty in the models. In addition, uncertainties in the input parameters contribute to uncertainty in the target SIL. In the offshore industry, engineers usually utilize two or more methods to assess target SILs for the same function and take the most conservative value as the target SIL. In this paper, we investigate on the uncertainty in determining target SILs evaluated by the risk graph method, Minimum SIL Table from OLF 070 and LOPA. A procedure of SIL determination accounting for uncertainties is proposed for the risk graph method, Minimum SIL Table from OLF 070 and LOPA by using a Fuzzy Set approach only and the combination of Monte Carlo simulation and Fuzzy Set approach. This thesis consists of following contents. Chapter 2 discuss (i) uncertainty sources in SIL determination methods, specifically risk graph method, minimum SIL Table from OLF 070 and LOPA, (ii) propose procedures for the uncertainty analysis in SIL determination by risk graph method, minimum SIL Table from OLF 070 and LOPA, using a Fuzzy Set approach (non-probabilistic method), Monte Carlo simulation (probabilistic method) and a combination of Monte Carlo simulation and the Fuzzy Set approach, iii) give a case study. Chapter 3 describes the characteristics of reliability calculation based on estimation of PFDavg of SISs. The uncertainty of PFDavg calculation is assessed with types of uncer-tainty, model uncertainty, completeness uncertainty, and parameter uncertainty. Especially, a determination procedure for most influence parameter, β-factor, on uncertainty of PFDavg estimation is suggested. The operation phase of the safety lifecycle procedures is out of scope of the thesis.
본 논문은 해양플랜트에 적용되는 안전제어시스템을 설계함에 있어 목표 성능 결정, 안전목표 사양 정립, 목표 성능 검증에 필요한 방법론을 불확실성 해석을 기반하여 제시하고 있다. 해양플랜트의 안전제어시스템 설계는 IEC 61508 및 IEC 61511 등에서 제시하는 안전 전과정 주기(Safety Lifecycle) 개념을 따르게 된다. 이들은 해양플랜트 안전제어시스템의 설계, 설치, 운전에 필요한 일반적인 기준과 절차를 제공함에도 불구하고 이를 실질적인 설계 단계에서 적용하기 위해서는 많은 어려움이 존재한다. 이런 어려움의 대표적인 사례는 방법론 또는 적용 사례에 따라 다른 결과가 나오거나 활용할 수 있는 자료의 부족이다. 본 연구에서는 기존 먼저 안전제어시스템의 목표 성능인 SIL을 결정하는데 활용되는 Risk graph 방법, Minimum SIL 방법, LOPA 방법을 Fuzzy Set approach 또는 Monte Carlo simulation와 결합을 통해 그 불확실성을 평가하고자 하였다. 마지막으로 안전제어시스템의 설계 검증인 SIL Verification에 대한 방법론과 적용 가능한 입력 자료 등을 제안하였다. 또한 SIL Verification에 적용되는 모델, 데이터 등의 불확실성이 함께 검토되었다.
