Design failure

Fault Tree Analysis. Fault trees represent a deductive approach to determining the causes contributing to a designated failure. The approach begins with the definition of a top or undesired event, and branches backward through intermediate events until the top event is defined in terms of basic events. A basic event is an event for which further development would not be useful for the purpose at hand. For example, for a quantitative fault tree, if a frequency or probabiUty for a failure can be deterrnined without further development of the failure logic, then there is no point to further development, and the event is regarded as basic. 

Failure Mode and Effects Analysis. The system design activity usually emphasizes the attainment of performance objectives in a timely and cost-efficient fashion. The failure mode and effects analysis (FMEA) procedure considers the system from a failure point of view to determine how the product might fail. The terms design failure mode and effects analysis (DFMEA) and failure mode effects and criticaUty analysis (EMECA) also are used. This EMEA technique is used to identify and eliminate potential failure modes early in the design cycle, and its success is well documented (3,4). 

If the pump is put into service with a bent or unbalanced shaft assembly, its premature tailure can be traced to inadequate maintenance practices. The evidence does not lie. However, if the premature failure leaves evidence of a deflected shaft, this would be an operations or design failure. All too often, the mechanic is blamed. The two pictures above show how a deflected shaft appears when rotated 180 degrees (Figure 9-11 and Figure 9-12). 

It has always seemed strange to us that the mechanics, or the manufacturer, are blamed when a mechanical seal fails after 3 months of service. If the seal fails on start-up, maybe you could point to the mechanic or the seal, but not after 3 weeks or 4 months of operation. This would most likely be an operational failure (a failure in operations), or a design failure (a failure in the system s design). And what is really amazing is that this statement and these words have never been recognized or said before.)... 

Butikofer (1986) Accidents in petrochemical imlusir , equipment and design failures 41 - personnel and maimenance . ili. os >1 in.rdcquutc procedures 1 inadequate in.speciion other 2. ... 

The standard requires validation results to be recorded and design failures to be documented in the validation records. 

The standard requires the corrective and preventive action procedures to be followed in addressing design failures. 

Finally, failure analysis is the process of comparing actual performance with the desired performance. Thus, failure analysis is a nontrivial part of the structural design process. Facets of failure analysis including what failure means for a structure are addressed in Section 7.6 on Design Requirements and Design Failure Criteria. 

DESIGN REQUIREMENTS AND DESIGN FAILURE CRITERIA 7.6.1 Introduction... 

The area of design failure criteria impacts, and is a quantitative measure of, the success of a design. Fundamentally, design failure criteria are the statement of the design requirements. The manner in which individual laminae as well as laminates fail is but a part of design failure criteria. Failure of laminae and laminates, as in Chapters 2 and 4, is a fundamental portion of all strength-related failure criteria, but those failures are also determining factors in stiffness-related failure criteria. 

Butikofer (1986) Accidents in petrochemical and refinery units equipment and design failures 41% personnel and maintenance failures 41% inadequate procedures 11% inadequate inspection 5% other 2%... 

It should be noted that the data collection and conversion effort is not trivial, it is company and plant-specific and requires substantial effort and coordination between intracompany groups. No statistical treatment can make up for inaccurate or incomplete raw data. The keys to valid, high-quality data are thoroughness and quality of personnel training comprehensive procedures for data collection, reduction, handling and protection (from raw records to final failure rates) and the ability to audit and trace the origins of finished data. Finally, the system must be structured and the data must be coded so that they can be located within a well-designed failure rate taxonomy. When done properly, valuable and uniquely applicable failure rate data and equipment reliability information can be obtained. 

D. Mackenzie, "Design Failures tliat Caused Bhopal Disaster," New Sci., p. 

Preparing a complete list of design constraints is a crucial first step in the design failure to take this step can lead to costly errors. For example, a designer might have an... 

The scale models must be carefully designed. Failure to match the important dimensionless parameters will lead to erroneous simulation results. Modeling can be extended to particle convective heat transfer. Wear or erosion of in-bed surfaces can be qualitatively studied, although quantitative assessment requires the identification and simulation of additional wear-related parameters. 

Mechanical Design Failure Analysis With Failure Analysis System Software for the IBM PC, David G. Ullman... 

A survey of the load-deformation curves for linear polymers at different temperatures is given in Fig. 25.1A. Each mechanism is further illustrated by a schematic diagram (Figs. 25.1B-E). The mathematical equations for the different mechanisms were given in the Chaps. 13-15. Based on the respective equations Ahmad and Ashby designed Failure Mechanism Maps. The most important of these are reproduced here as Fig. 25.2A-D. 

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