Fault Propagation Modeling

There are different methods that are currently used to model the fault propagation within plant processes such as sign directed graphs, or simply SDG, (Androw and Lees, 1975). One major limitation of sign directed graph is its limitations to represent the environment factors that affect physical equipments. 

One key issue to automate the hazard evaluation process is to find a systematic way to represent the fault propagation in the plant process. This section describes a new way of representing the fault propagation in process plant using examples from HDS reactor CGU. 

Reactor CGU of HDS is used as a case study to illustrate the fault propagation model. The simplified P ID of the reactor CGU is shown in figure 3-21. The equivalent object-oriented model representation of the 

The scenario shown in this table presents the initial event of failure in the temperature control valve TC-2-2, where the temperature is lower than expected. 

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The analysis of the chain of events that leads to an incident. By analyzing what events initiate that chain, which events contribute to it or allow the incident to propagate, and establishing how they are logically related, the event frequency can be determined. Fault propagation modeling techniques use the failure rates of individual components to determine the failure rate of the overall system. 

From a study of literature, it has been found that scientists from Okayama University, Japan developed a dynamic model to utilize FTA for batch process. According to the paper [6], batch processes are divided into several safety objects linked to operation level. Dynamic simulation and fault propagation models are generated to evaluate safety objects. With the help of this model, FTA method using house event-time, an event expected to happen, can be developed for calculating the probability of failures. The time-dependent failures can be considered as unavailability of safety objects that can lead to accidents in plants. The rank of safety object performance index (PI) can be estimated using importance measures. PI shows the prioritization of safety objects that should be investigated for safety improvement in the plants. 

Model is a formal description of a system or a process. Entity M is a model of a system S , if M can be used to answer questions related to characteristics of the system S (Woods, 1993). The model development is intended to represent one or more points of view for the underline system (or plant) (Gabbar, 2000g). This means developing a model to represent a system can t be achieved unless we specify which point of view(s) such model represent the system. Information model of a system represents the information organization point of view of a given system. Other examples of models are fault propagation model, data model, knowledge model, etc. 

Design of Practical Enterprise Safety Management System 3.5. Fault Propagation Modeling... 

The idea behind this analysis is to detect a certain pattern that can be used to automate the fault propagation modeling and analysis practices. It is obvious that for each fault description, there should be NAS , PEC , and POS . However, the NAS could be related to equipment i.e. Breakage, or related to fluid i.e. Big Amount of fluid, or related to operation i.e. fail to close valve. Figure 3-24 shows the possible fault propagation schemes, which shows that NAS can affect PEC, PV, or FED. And NAS affecting PV, FED, and PEC can propagate to each other. For example, failure in equipment can lead to abnormal situation in the fluid, internal, or external environment, while abnormal situation... 

The above analysis and model is useful to enable us to draw the structure of the database of the failure data group and to automate the hazard evaluation practice. But in order to do that it is essential to define the fault propagation model and its representation in the plant design model using the above analysis results. 

Fault propagation model elements (FPMEs) are as stated earlier PEC, PV, NAS, POS, FLD, and OPR. These elements can be mapped to the plant object oriented model (POOM) as per table 3-6. 

Table 3-6 Fault Propagation Model Mapping to POOM...

Fault Propagation Model Element (FPME) Representation in POOM... 

Figure 3-26 Fault Propagation Model for Control Valve Represented as SDG...

Failure Mode and Effect Analysis Failure Mode and Effect Criticality Analysis Fault Propagation Eayers Fault propagation model... 

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