Reliability block diagram technique

IEC 61078 and Annex B of IEC 61508-6 illustrate the reliability block diagram technique for calculating the probabilities of failure for safety instrumented functions designed in accordance with IEC 61511-4-ANSI/ISA-84.00.01-2004 Parti (IEC 61511-1 Modi and this standard. 

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Having analysed the likely disaster causes, the next step is to evaluate the reliability of the whole system by applying the Reliability Block Diagram technique to an investigation of the possible design modifications that could enhance reliability. 

Fault Trees and Reliability Block Diagrams are both methods of showing probability combinations. There have been a number of solution techniques developed to solve probability combinations. These include Cut Sets, Tie sets. Event Space, Decomposition Method, Gate Solution Method, and many others. In this appendix three examples will be shown - the Event Space method and the Cut Set method, and the Gate Solution Method. Details and full development of the methods can be found in (Ref. 1) Chapter 5. 

The causes of hazards and functional failures are broken down, e.g. via Fault Tree Analysis (FTA). Other typical techniques are the Failure Modes, Effects and Criticality Analysis (FMECA) and the production of a Reliability Availability Maintainability Modelling and Prediction Report (RAM MPR), containing reliability block diagrams of the system. 

There are a number of techniques to analyze the safety integrity of an E/E/PE safety-related systems. The two most used techniques are reliability block diagrams and Markov models. Both methods, if properly applied, give similar results however, for complex programmable electronic sub-systems (e g. when a logic... 

This involves assessing the design, by means of reliability analysis techniques, to determine whether the targets can be met. Techniques include fault tree and logic block diagram and FMEA analysis, redundancy modeling, assessments of common cause failure, human error modeling, and the choice of appropriate component failure rate data. Reliability assessment may also be used to evaluate potential financial loss. The process is described in Work Instruc-tion/001 (Random hardware failures). 

You can quickly identify these plant sections by reviewing process flow diagrams and valving arrangements. Isolation points are defined by control valves or powered block valves that can be remotely activated. Process hazard analysis techniques help you identify the maximum credible accident scenarios. (Note that manual valves should not be considered reliable isolation points unless they are located to be accessible following a major accident. However, remotely-activated valves can only be considered reliable isolation points if there are adequate reliability engineering and maintenance programs in place.)... 

Figure 5.3 Diagram depicts the further-designed studies to test our hypothesis with respect to standardization of immunohistochemistry based on the antigen retrieval technique exemplified in a multiple direction to draw a conclusion, (a) Periods of formalin fixation, (b) Variable delay of fixation, (c) Storage of FFPE tissue blocks or sections, (d) Variable thickness of FFPE tissue sections, (e) Other variable conditions of processing FFPE tissue blocks. The stereoscopic frame of a cube represents the reliable limitation of quantitative IFIC demonstrated by serial studies as recommended in the text. Reproduced with permission from Shi et al., J. Histochem. Cytochem. 2007 55 105-109.

A similar technique, more common with air systems, is to automate the familiar double-block-and-bleed arrangement. The first step in this design might be to replace a simple check valve with a differential-pressure control valve that shuts when the pressure differential reverses. This affords two levels of protection, unless one assumes that the check valve is fundamentally untrustworthy and always allows somebackleakage. Check valves can, of course, be made more reliable by proper installation and by extra measures such as force loading. An elaboration on the diagram above is to add a second valve in the line that closes when the differential pressure is too low or even negative. Finally, the space between the two in-line check valves can be vented for more positive protection. 

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