Fault qualitative

MORT (see Johnson. 1980) Model of components or systems Qualitative used to syrtliesize fault trees compleisiiy increases rapidly... 

MOCUS implemented the Fussell algorithm (Fussell, 1974) for top-down solutions of the fault tree. This algorithm was used in ALLCUT and was modified to be bottom-up in WAMCE T. While cutsets are valuable for qualitative and quantitative purposes, they are not compact. They are thousands of trains (AND sequences) connected to one OR gate. 

A flooding analysis for major plant systems uses a qualitative fault tree that takes into account the elevation of system components. This procedure, illustrated in Figure 5.3-1, uses a fault tree captioned for the top event, "core melt due to internal flood." The fault tree is developed under the assumption that a flood causes a transient, small, or large LOCA, or causes the failure of... 

If the results of the qualitative analysis are to be used as a starting-point for quantification, they need to be represented in an appropriate form. The form of representation can be a fault tree, as shown in Figure 5.2, or an event tree (see Bellamy et al., 1986). The event tree has traditionally been used to model simple tasks at the level of individual task steps, for example in the THERP (Technique for Human Error Rate Prediction) method for human reliability... 

EGSG Idaho s Idaho National Engineering Laboratory reviewed Licensee Event Reports (LERs), both qualitatively and quantitatively, to extract reliability information in support of the USNRC s effort to gather and analyze component failure data for U.S. commercial nuclear power plants. LERs describing failures or command faults (failure due to lack of needed input) for selected components have been analyzed in this program. Separate reports have been issued for batteries and battery chargers, control rods and drive mechanisms, diesel generators, ISC, Inverters, primary containment penetrations, protective relays and circuit breakers, pumps, and valves. 

A large number of model-based systems use either qualitative or quantitative simulation, such as FAULTFINDER (Kelly and Lees, 1986) or EA-GOL (Roth, Woods, and Pople, 1992). These systems simulate normal behavior and compare the simulation results with observations, they simulate faults and compare simulation results with detected symptoms, or they interleave simulation with observation comparing the two to dynamically track normal and abnormal states. It is computationally very expensive to... 

A fault tree is, itself, a Boolean equation relating basic events to the top event. The equation can be analyzed quantitatively or qualitatively by hand or by using computer code(s). If it is analyzed quantitatively, the probabilities or frequencies of the intermediate events and the top event are calculated. If it is analyzed qualitatively, a list of the failure combinations that can cause the top event is generated. These combinations are known as cut sets. A minimal cut set (MCS) is the smallest combination of basic events that, if they occur or exist simultaneously, cause the top event. These combinations are termed "minimal" because all of the basic events in a MCS must occur if the top event is to occur. Thus, a list of MCSs represents the known ways the top event can occur, stated in terms of equipment failures, human errors, and associated circumstances. 

Identification and quantitative estimation of common-cause failures are general problems in fault tree analysis. Boolean approaches are generally better suited to mathematically handle common-cause failures. The basic assumption is that failures are completely independent events, but in reality dependencies will exist and these are categorized as common cause failures (CCFs). Both qualitative and quantitative techniques can be applied to identify and assess CCFs. An excellent overview of CCF is available (AIChE-CCPS, 2000). 

Several qualitative approaches can be used to identify hazardous reaction scenarios, including process hazard analysis, checklists, chemical interaction matrices, and an experience-based review. CCPS (1995a p. 176) describes nine hazard evaluation procedures that can be used to identify hazardous reaction scenarios-checklists, Dow fire and explosion indices, preliminary hazard analysis, what-if analysis, failure modes and effects analysis (FMEA), HAZOP study, fault tree analysis, human error analysis, and quantitative risk analysis. 

An additional feature of chemometrics that is appealing to process analytical applications is the use of qualitative models to detect and characterize faults in the analyzer system (calibration, instrument, sampling interface, and sampling systems), sample chemistry, and process dynamics. Such faults can be used to trigger preventive maintenance, and to troubleshoot- thus supporting the long-term reliability of the analyzer system. Specihc examples of such fault detection are given in references [15-16]. 

The term fault tree means different things to different people. Some people use the term to describe trees that have frequency terms included. These quantitative trees can be solved mathematically to provide a frequency of the incident. However, for incident investigation, the term commonly refers to a qualitative tree. 

These complications show wli we emphasize simple and qualitative problems in this course. In reactor engineering the third decimal place is almost always meaningless, and even the second decimal place is fiequently suspect. Our answers may be in error by several orders of magnitude through no fault of our own, as in our example of the temperature dependence of reaction rates. We must be suspicious of our calculations and make estimates with several approximations to place bounds on what may happen. Whenever a chemical process goes badly wrong, we are blamed. This is why chemical reaction engineers must be clever people. The chemical reactor is the least understood and the most complex unif of any chemical process, and its operation usually dominates the overall operation and controls the economics of most chemical processes. 

J. R. Whiteley and J. F. Davis, "Qualitative Interpretation of Sensor Patterns using a Similarity-Based Approach," paper presented at the IFAC Symposium on On-Une Fault Detection and Supervision in the Chemical Process Industries, Newark, Del., Apr. 1992. 

Model-based approaches to fault diagnosis can be divided into qualitative methods [51] and quantitative methods [35, 36],... 

Since perfect knowledge of the model is rarely a reasonable assumption, soft computing methods, integrating quantitative and qualitative modeling information, have been developed to improve the performance of observer-based schemes for uncertain systems [36], Major contributions to observer-based approaches can be found in [39, 56] as well, where fault isolation is achieved via a bank of observers, while identification is based on the adoption of online universal interpolators (e.g., ANNs whose weights are updated on line). As for the use of observers in the presence of advanced control techniques, such as MPC or FLC, in [44] an unknown input observer is adopted in conjunction with an MPC scheme. 

RM. Frank. Analytical and qualitative model-based fault diagnosis—a survey and some new results. European Journal of Control, 2 6-28, 1996. 

V. Venkatasubramanian, R. Rengaswamy, and S.N. Kavuri. A review of process fault detection and diagnosis part II Qualitative models and search strategies quantitative model-based methods. Computers and Chemical Engineering, 27 313-326, 2003. 

The estimated impact is then compared to hazard acceptance criteria to determine whether the consequences are tolerable without additional loss prevention and mitigation measures. If the identified consequences are not tolerable, the next step is to estimate the ffequency/probability of occurrence of the identified failure modes leading to loss of containment. For simple cases, frequency estimates are combined with consequences to yield a qualitative estimate of risk. For complex cases, fault tree analysis is used to estimate the frequency of the event leading to the hazard. These estimates are then combined with the consequences to yield a measure of risk. The calculated risk level is compared to a risk acceptance criterion to determine if mitigation is required for further risk reduction. 

Module 3 (Description) a dozen employees already have been trained in qualitative fault tree analysis by an external training institute. 

Description of the selected event, by means of qualitative fault tree techniques ... 

HAZOP and What-If reviews are two of the most common petrochemical industry qualitative methods used to conduct process hazard analyses. Up to 80% of a company s process hazard analyses may consist of HAZOP and What-If reviews with the remainder 20% from Checklist, Fault Tree Analysis, Event Tree, Failure Mode and Effects Analysis, etc. An experienced review team can use the analysis to generate possible deviations from design, construction, modification, and operating intent that define potential consequences. These consequences can then be prevented or mitigated by the application of the appropriate safeguards. 

In the imaging modes used most commonly for imaging crystal defects (such as dislocations and stacking faults), the image is formed using only the transmitted beam or a single diffracted beam. The way in which defects are revealed in these images is discussed qualitatively in the first part of Chapter 5. This is followed by an explanation of how the mathematical description of the distortion around a defect in a crystal is incorporated... 

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