Spontaneous failure

A technical system normally has a number of standby components (components which become active only after demand). Components of the monitoring and safety systems belong to this category. These systems are devised to cope with accident initiating events. They form the barriers between the initiating and the undesired event. The latter only occurs if all barriers fad. The situation is shown schematically in Fig. 9.10. Obviously in the same system initiating events can occur for whose control various barriers may become effective, and initiating events which directly lead to the undesired event, for example the spontaneous failure of a chlorine pipe. 

The treatment of secondary failures, also called consequential failures is illustrated by an example. The fault tree of Fig. 9.34 models the failure of two pipes geometrically arranged in parallel. Apart from a spontaneous failure of pipe 1 (primary event Xi) pipe 2 may fail spontaneously (primary event X2) and as a consequence damage pipe 1 (primary event X3) by pipe whip or impinging steam jets. 

In addition there is the possibility of so called spontaneous failures (failure without an obvious reason from the Latin word sponte of one s free will, voluntarily) they might be caused, for example, by hidden flaws in structural materials. 

Depending on whether we deal with a risk-based or a detailed risk study the scope of the failure mechanisms represented by the failure rates must differ. For risk-based analyses the failure rates should represent besides spontaneous failure failures caused by impermissible loads on structural materials following malfunctions or operator errors. Since the latter are explicitly modelled in a detailed risk analysis the failure rates for passive components used there should only represent the spontaneous part. The scope of the failure mechanisms covered is usually not described in suflhcient detail and can practically not be determined a posteriori [5]. 

A reverse t m transformation and related volume increase during the course of cooling the zirconia parts from the processing temperature, which exceeds the reported temperature for unconstrained transformation of 1174 6 °C [177], results in significant strains, which can be only accommodated by the formation of cracks. Thus, the fabrication of large parts of pure zirconia is not possible due to spontaneous failure on cooling. 

Field failures typically represent unprovoked battery explosions and according to industry experts such events are rare and is estimated that one in 10 million Li-ion batteries fails that way [10]. Field failures are more challenging to reproduce and study in a lab because they happen so infrequently. Moreover, these incidents stand in contrast to failures of abuse-tolerance tests, in which batteries are methodically subjected to extreme conditions such as uncontrolled heating, overcharging, crushing or puncturing to assess the battery s response. Another difficulty in analyzing the causes of spontaneous failures is that batteries that fail in the field come from lots that have already passed abuse and reliability tests, and they appear to have worked normally. 

The question of safety is a complex issue and depends very much upon the battery application. ViTe may distinguish between the consequences of spontaneous cell failure, caused by electrolyte fracture, internal short circuiting etc, and externally imposed cell failure as a result of impact damage. For spontaneous cell failure, the principle being adopted in the U.K. is that a burn-out in one cell shall not propagate to adjacent cells. There is good evidence that this can be achieved the features of cell design which minimise the effec l of spontaneous failure have been discussed in a recent paper ... 

The rapid growth and expansion of the chemical industry has been accompanied by a spontaneous rise in human, material, and property losses because of fires, explosions, hazardous and toxic spills, equipment failures, other accidents, and business interruptions. Concern over the potential consequences of catastrophic accidents, particularly at chemical and petrochemical plants, has sparked interest at both the industrial and regulatory levels in obtaining a better understanding of the subject of this book Health, Safety, and Accident Management (HS AM). The writing of this book was undertaken, in part, as a result of this growing concern. 

Between these two extremes of spontaneous rearrangement and total failure to rearrange, Braverman and Stabinsky36-38 have observed intermediate behavior. The reaction of crotyl alcohol with C13CSC1 afforded an equilibrium mixture of both crotyl trichlormethanesulfenate (13) and a-methylallyl trichloromethyl sulfoxide (14, equation 9). 

Santantonio T, Fasano M, Sinisi E, Guastadisegni A, Casalino C, Mazzola M, FrancavUla R, Pastore G (2005) Efficacy of a 24-week course of PEG-interferon alpha-2b monotherapy in patients with acute hepatitis C after failure of spontaneous clearance. J Hepatol 42 329-333... 

In these 500 cases, there were 26 culture failures, an Incidence of about 5% Nine women of this group underwent a second aminocentesls, and successful cultures were obtained The other 17, or 3 4% of the total, did not obtain any results, either because of spontaneous abortions prior to the time a second amniocentesis could be performed (In four) or because the family elected not to proceed There were no Instances of severe or significant fetal Injury, although small linear "scars" were noted on four fetuses Three fetuses had abnormalities which were not related to the procedure Itself, Including spina bifida, osteogenesis Imperfecta, and congenital heart disease ... 

Environmental Cracking The problem of environmental cracking of metals and their alloys is very important. Of all the failure mechanism tests, the test for stress corrosion cracking (SCC) is the most illusive. Stress corrosion is the acceleration of the rate of corrosion damage by static stress. SCC, the limiting case, is the spontaneous cracking that may result from combined effects of stress and corrosion. It is important to differentiate clearly between stress corrosion cracking and stress accelerated corrosion. Stress corro-... 

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