Critical failure

Figure 1.11 The potential cost of safety critical failures...

We have already seen elements of the CA approach when considering the costs due to safety critical failures. A further insight into the way that failure costs can be estimated for non-safety critical failures is also used to support the CA methodology. Estimates for the costs of failure in this category are based on the experiences of a sample of industrial businesses and published material as follows. 

From an FMEA of the system design, a Severity Rating S) = 1 was allocated, relating to a safety critical failure in service. It is required to find the optimum unequal angle section size from the standard sizes available. It is assumed that the load is carried at the section s centre of gravity, G, and only stresses due to bending of the section are considered, that is, the torsional effects are minimal. The combined weight of the beam and tie rod are not to be taken into account. 

Cases (a) and (b) are the critical failure modes for protecting the equipment, and the reliability of the disc in these modes is referred to as the primary reliability. Case (c) is inconvenient and sometimes costly, but it is not usually dangerous unless the containment or disposal system for the discharge is inadequate. Cases (d) and (e) are comparatively rare. 

Proper lubrication is essential for all jackshafts and spindles. A critical failure point for spindles (see... 

Critical currents, 23 821-823 in superconducting, 23 819-825 Critical event (CE), 15 462 Critical failure, 26 982 Critical features, in separating nonideal liquid mixtures, 22 307 Critical fields, thermodynamic, 23 809-811 Critical flocculation concentration, 11 631 Critical item evaluation, for reliability, 26 991... 

Specify the number of years of life which need to be predicted and the acceptable uncertainty. In all probability the uncertainty can only be stated in general terms commensurate with how critical failure in service would be. 

Knowing the heat flux from a fire and temperatures, the time to structural failure can be estimated. A somewhat more detailed approach is to evaluate the heat transfer to the structural element and compare the resulting temperature to critical failure temperatures. Failure of a structural metal element occurs... 

Note that two of the four possible critical failures are human. The operator fails to check the level indicator before unloading, or the purchasing department orders a new supply before the reorder level is reached, reached. 

The CII and its context are dynamic. Being robust and reliable today doesn t preclude that new conditions tomorrow will not prove that the same architecture and policy are susceptible to critical failures. 

A diagram that one might use to illustrate a possible set of experimental data to represent all failure modes of an adhesive joint is presented in Fig. 15.1. When the data are closely analyzed and the extent of ultimate service life and proper safety margins are specified, the critical failure mode and time can be defined by identifying the weakest link — in this case the corrosion mechanism. If this predicted life is longer than the expected service life of the product, then the material specified for the adhesive joint can be qualified for use. 

Mixed poisons are counted as multiple doses, always using the highest DC, adding +1 for the second poison and each additional dose for Fortitude and Crafting Checks. If there are symptoms common to each individual poison, the GM may decide to increase the severity, or simply apply the symptom as normal. In some cases, the cheniistiy of two or more poisons is incompatible, and will actually render both poisons harmless. If a Critical Failure is rolled when making a Craft Skill check, the poisons have become inert and harmless. The GM should make a note that those poisons are not compatible and can never be mixed successfully. 

Incoordination Uncoordinated creatures lack normal control of muscular movement. -5 penalty on any attempts to Attack, Defend, or perform Skills or Feats that require coordination, -2 Effective Dexterity. Critical Failures require the creature to make a Reflex Save or suffer an immediate attack of opportunity from all opponents currently engaged. 

Vessel Damage The Blood Vessels of the creature have become damaged and cannot efficiently deliver blood. Any Critical Failures require the creature to make a Fortitude Save or immediately "black-out".The creature is then treated as Unconsciousness for D4 Rounds. 

Knowledge of the equipment system s critical failure modes is essential to cost-effective oil and machinery monitoring [13]. No equipment-monitoring programme should be established without clear knowledge of the critical failure modes including the ... 

In general, all fluid measurement technologies must utilize effective analysis methods, performed at appropriate intervals whether sampled or online. However, what is effective There are many different equipment-monitoring techniques and most can be justified on the basis of one technical reason or another. It is not always clear which technique is the most effective or economical. Nor do all the available techniques provide reliable or early indications of relevant critical failure modes. To be effective, the monitoring instruments or sensors must indicate the critical failure modes. Finally, the cost of using a particular technique must be considered. If the relevant critical failure mode symptoms are not properly measured and trended, the (lower) cost of the instrument or method becomes questionable. 

In conclusion, oil data interpretation is mathematically feasible for equipment fleets where there is sufficient history of all critical failure modes and respective maintenance responses. Most operators of large equipment fleets or equipment that has been in use for long periods of time have sufficient historical data to determine data interpretation criteria and the impact of operations on oil data reliability and to map the specific events that affect data integrity. Lubricant analysis expert systems are in daily operation confirming the stability and reliability of the procedures used. 

Fracture Energy. The fracture energy of cured phthalonitrile samples was measured by using standard compact tension specimens (8). A precrack was always introduced at the end of the saw-cut with a razor blade. Specimens were fractured in an INSTRON at a crosshead speed of 0.125 cm/min. The critical failure load was... 

The calculated control parameters are transmitted via an interface to the control units, such as the charger and the load. The task with the highest priority is safety management. Any critical failure must be detected by this task and substitute... 

A detonation refers to a shock wave in an energetic material that runs at a steady velocity driven by chemical reactions initiated at the shock front [38,39]. Due to damping at edges and surfaces, the detonation state can occur only if the sample is larger than the critical failure diameter [3]. With a few exceptions, the critical diameter is typically in the nun to cm range, so detonations are associated with macroscopic loads of energetic materials and are extremely powerful. For HMX, the detonation velocity is 9.1 km/s, the pressure is 39 GPa,... 

R. M. Matveevsky [56] discussed the influence of temperature on lubricant additive action in terms of whether the additive functions by an adsorption/desorption mechanism or by a chemical reaction mechanism. If the additive is a blend of two components, one of which acts via adsorption and the other by reaction, and if the critical temperature of desorption is lower than the temperature at which the rate of chemical reaction of the other additive will contribute substantially to the lubrication process, then the critical desorption temperature will control lubricant failure. Thus, if the load induces frictional heating at the rubbing interface so that the conjunction temperature exceeds the critical desorption temperature, this will be the critical failure load. But if the surface exposed by desorption of the first additive reacts with the second additive at the temperature prevailing there, the failure load will be raised. Cameron and his co-workers [48, 57] used these concepts, although not as explicitly proposed by Matveevsky, to explain the behavior of multicomponent compounded lubricants containing dibenzyl disulfide and a commercial calcium petroleum sulfonate as the additives. The failure temperature characteristic of the calcium sulfonate as the sole additive was 468 K (195 C), whereas failure with dibenzyl disulfide was observed at 543 K (270 C). With the two-component additive, incipient failure began at ca. 473-493 K, which seems to mark a balance between desorption of the sulfonate and chemical reaction of the disulfide. As the temperature increased above 493 K, the reactivity of the disulfide became more apparent and the coefficient of friction decreased, until at 543 K, the temperature observed for the failure of the disulfide alone, the rubbing pieces scuffed. 

The most important consideration in the evaluation of corrosion-related failure is safety, that is, whether the failure causes a loss of life or of function or secondary damage that could have adverse effect on operating safety. A critical failure is any failure that could affect adversely the safety of operation of both the equipment and the operating personnel. The term, direct effect, implies certain limitations. The impact of the failure must be immediate if it is to be considered direct. Further, the consequences must result from a single failure and not from a combination of the failure with another that is yet to occur. If a failure has no resultant effect on the system, it cannot by definition have a direct effect on safety. 

It is to be noted that not every critical failure results in an accident. However, the question is not whether such consequences are inevitable, but whether they are possible. Safety considerations are conservative and rigid and they are assessed at the most conservative level. In the absence of proof that a failure cannot affect safety, it is considered by default as a critical issue that requires immediate consideration. 

When possible critical failure is envisaged, it is imperative that all possible effort must be made to prevent its occurrence. Quite often, redesigning of one or more vulnerable items is all that is required to avoid potential failure. However, the design and manufacture of new parts and their subsequent use in service equipment can take a long time, of the order of a few months, and sometimes as much as years. Thus temporary measures to rectify the problem are often required. 

Once the safety consequences are ruled out, attention turns toward the next set of consequences such as the effect of the failure on the operational capability of the system without any difficulty. A failure has operational consequences whenever a need to correct the failure disrupts the planned operations. The operational consequences consist of the need to abort an operation after a failure occurs, the delay or cancellation of other usual operations to make unanticipated repairs, or the need for operational limitations until the necessary repairs are made. A critical failure may be viewed as a special case of a failure with operational consequences. 

In theory, finite element strength reduction factor method can be expressed as in the finite element static steady-state calculation, if the system is unstable, finite element calculations will not converge. Based on this principle, in the nonlinear finite element slope stability analysis, we obtain formula (1), using equation (1) to adjust the surface of the structure strength (cohesion c and friction angle reduction factor CO, so that the system reaches a critical failure state... 

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