Problems with MTBF
As of 1995, the use of MTBF in the aeronautical industry (and others) has been called into question due to the inaccuracy of its application to real systems and the nature of the culture which it engenders. Many component MTBFs are given in databases, and often these values are very inaccurate. |
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Variations of MTBF
There are many variations of MTBF, such as mean time between system aborts (MTBSA) or mean time between critical failures (MTBCF) or mean time between unit replacement (MTBUR).
Such nomenclature is used when it is desirable to differentiate among types of failures, such as critical and non-critical failures. For example, in an automobile, the failure of the FM radio does not prevent the primary operation of vehicle.
Mean time to failure (MTTF) is sometimes used instead of MTBF in cases where a system is replaced after a failure, since MTBF denotes time between failures in a syste |
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TPM Goals
1) TPM aims to maximize equipment effectiveness.
2) TPM establishes a thorough system of Preventive Maintenance (PM) for the equipment�s entire life span.
3) TPM is cross-functional, implemented by various departments (engineering, operators, maintenance, and managers).
4) TPM involves every single employee.
5) TPM is based on the promotion of Preventive Maintenance through the motivation of management and autonomous Small Group Activity (SGA).
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Holistic Measurement & OEE
All losses that have an impact on equipment performance are measured e.g. machine not being available when needed; not running at an ideal rate, and not producing the right quality on the first pass. OEE %( Overall Equipment Effectiveness) is used to measure how productively a machine is being utilised. In principle, OEE is calculated as |
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TPM has 8 key strategies
1) Focused Improvements (Kaizen);
2) Autonomous Maintenance;
3) Planned Maintenance;
4) Technical Training;
5) Early Equipment Management;
6) Quality Maintenance;
7) Administrative and Support Functions Management;
8) Safety and Environmental Management.
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Failure Mode and Effects Analysis (FMEA / FMECA)
This method was developed in the 1950s by reliability engineers to determine problems that could arise from malfunctions of military system. Failure mode and effects analysis is a procedure by which each potential failure mode in a system is analyzed to determine its effect on the system and to classify it according to its severity.
When the FMEA is extended by a criticality analysis, the technique is then called failure mode and effects criticality analysis (FMECA). Failure mode and effects analysis has gained wide acceptance by the aerospace and the military industries. In fact, the te |
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Discussion and Conclusion
The tree-based methods are mainly used to find cut-sets leading to the undesired events. In fact, event tree and fault tree have been widely used to quantify the probabilities of occurrence of accidents and other undesired events leading to the loss of life or economic losses in probabilistic risk assessment. However, the usage of fault tree and event tree are confined to static, logic modeling of accident scenarios. In giving the same treatment to hardware failures and human errors in fault tree and event tree analysis, the conditions affecting human behavior can not be modeled explicitly. Th |
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Safety Management Organization Review Technique
Safety management organization review technique (SMORT) is a simplified modification of MORT developed in Scandinavia. This technique is structured by means of analysis levels with associated checklists, while MORT is based on a comprehensive tree structure. Owing to its structured analytical process, SMORT is classified as one of the tree based methodologies.
The SMORT analysis includes data collection based on the checklists and their associated questions, in addition to evaluation of results. The information can be collected from interviews, studies of documents and investigations. Th |
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Management Oversight Risk Tree (MORT)
Management oversight risk tree (MORT) was developed in the early 1970s, for the U.S. Energy Research and Development Administration as safety analysis method that would be compatible with complex, goal-oriented management systems. MORT is a diagram which arranges safety program elements in an orderly and logical manner. Its analysis is carried out by means of fault tree, where the top event is "Damage, destruction, other costs, lost production or reduced credibility of the enterprise in the eyes of society". The tree gives an overview of the causes of the top event from management oversights a |
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Cause-Consequence Analysis
Cause-consequence analysis (CCA) is a blend of fault tree and event tree analysis. This technique combines cause analysis (described by fault trees) and consequence analysis (described by event trees), and hence deductive and inductive analysis is used. The purpose of CCA is to identify chains of events that can result in undesirable consequences. With the probabilities of the various events in the CCA diagram, the probabilities of the various consequences can be calculated, thus establishing the risk level of the system.
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Event Tree Analysis
Event tree analysis - consists of an analysis of possible causes starting at a system level and working down through the system, sub-system, equipment and component, identifying all possible causes. (What faults might we expect? How may they be arrived at?)
Assessment methods which allow quantifying the probability of an accident and the risk associated with plant operation based on the graphic description of accident sequences employ the fault tree or event tree analysis (FTA or ETA) techniques
Event Tree Analysis is a logical method of analyzing how and why a disaster could occu |
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Methodologies for Analysis of Dynamic System
In this section, GO method, digraph / fault graph, event sequence diagrams, Markov modeling, dynamic event logic analytical methodology and dynamic event tree analysis method will be discussed |
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Tree Based Techniques
In this section, fault-tree analysis (FTA), event-tree analysis (ETA), cause - consequence analysis (CCA), management oversight risk tree (MORT) and safety management organization review technique (SMORT) will be discussed.
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Markov Modeling
Markov modeling is a classical modeling technique used for assessing the time-dependent behavior of many dynamic systems. In a ‘Markov chain’ processes, transitions between states are assumed to occur only at discrete points in time. On the other hand, in a ‘discrete Markov process’, transitions between states are allowed to occur at any point in time. For process system, the discrete system states can be defined in terms of ranges of process variables as well as component status.
This methodology also incorporates time explicitly, and can be extended to cover situations where problem pa |
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Hazard and Operability Studies (HAZOP)
The HAZOP technique was developed in the early 1970s by Imperial Chemical Industries Ltd. HAZOP can be defined as the application of a formal systematic critical examination of the process and engineering intentions of new or existing facilities. To assess the hazard potential that arises from deviation in design specifications and the consequential effects on the facilities as a whole.
This technique is usually performed using a set of guidewords: NO / NOT, MORE / LESS OF, AS WELL AS, PART OF REVERSE, AND OTHER THAN. From these guidewords, scenarios that may result in a hazard or an ope |
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Preliminary Risk Analysis
Preliminary Risk Analysis Preliminary risk analysis or hazard analysis is a qualitative technique which involves a disciplined analysis of the event sequences which could transform a potential hazard into an accident. In this technique, the possible undesirable events are identified first and then analyzed separately. For each undesirable events or hazards, possible improvements, or preventive measures are then formulated.
The result from this methodology provides a basis for determining which categories of hazard should be looked into more closely and which analysis methods are most sui |
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Qualitative Risk Analysis Methodologies
In the this section, we will deal with the qualitative methods used in risk analysis namely preliminary risk analysis (PHA), hazard and operability study (HAZOP), and failure mode and effects analysis
(FMEA / FMECA). |
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Fault Tree Analysis
The concept of fault tree analysis (FTA) was originated by "Bell Telephone Laboratories" in 1962 as a technique with which to perform a safety evaluation of the Minutemen Intercontinental Ballistic Missile Launch Control System. A fault tree is a logical diagram which shows the relation between system failure, i.e. a specific undesirable event in the system, and failures of the components of the system. It is a technique based on deductive logic. An undesirable event is first defined and causal relationships of the failures leading to that event are then identified
Fault tree can be use |
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FMECA Background
This paper presents a Failure Modes, Effects and Criticality Analysis of the ITIS Governance process. It is useful to set the stage by first showing the relationships of the various processes, including Governance, used to conduct the business of ITIS. A Functional Hierarchy Diagram is constructed in the next section to accomplish this. We will treat the collective set of processes as a system, with processes decomposing to sub-processes, etc. To track all of this activity, a model of the “Process” system was constructed in CORE. All of the rules of traceability to requirements, hierarchical |
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Performing the FMECA
Determination of the Causes of Failure : Causes of failure are listed in column 4 of the FMECA worksheet. In this study the failure causes are those that are specific to the Governance process. Failures in the Systems Engineering process become Governance failures only if Governance does not catch and correct them.
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TELL
FIRENDS
