Journal of the Korean Society of Safety (한국안전학회지)

The Korean Society of Safety (한국안전학회)
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A Reliability Model of Process Systems with Multiple Dependent Failure States

다중 종속 고장상태를 갖는 공정시스템의 신뢰성 모델

  • Choi, Soo Hyoung (Division of Chemical Engineering, Chonbuk National University)
  • 최수형 (전북대학교 화학공학부)
  • Received : 2018.10.08
  • Accepted : 2018.11.12
  • Published : 2018.12.31
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Abstract

Process safety technology has developed from qualitative methods such as HAZOP (hazard and operability study) to semi-quantitative methods such as LOPA (layer of protection analysis), and quantitative methods are actively studied these days. Quantitative risk assessment (QRA) is often based on fault tree analysis (FTA). FTA is efficient, but difficult to apply when failure events are not independent of each other. This problem can be avoided using a Markov process (MP). MP requires definition of all possible states, and thus, generally, is more complicated than FTA. A method is proposed in this work that uses an MP model and a Weibull distribution model in order to construct a reliability model for multiple dependent failures. As a case study, a pressure safety valve (PSV) is considered, for which there are three kinds of failure, i.e. open failure, close failure, and gas tight failure. According to recently reported inspection results, open failure and close failure are dependent on each other. A reliability model for a PSV group is proposed in this work that is to reproduce these results. It is expected that the application of the proposed method can be expanded to QRA of various systems that have partially dependent multiple failure states.

Keywords

HOJHB0_2018_v33n6_37_f0001.png 이미지

Fig. 1. Markov state diagram for the proposed method.

HOJHB0_2018_v33n6_37_f0002.png 이미지

Fig. 2. Markov state diagram for the case study (A: open failure, B: close failure, C: gas tight failure).

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Fig. 3. Individual failure data.

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Fig. 4. Multiple failure data.

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Fig. 5. Probabilities of Markov process states.

Table 1. PSV inspection results7)

HOJHB0_2018_v33n6_37_t0001.png 이미지

Table 2. Errors of models in -ln[1 -F (t )]

HOJHB0_2018_v33n6_37_t0002.png 이미지

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