Early failure

Early failures may occur almost immediately, and the failure rate is determined by manufacturing faults or poor repairs. Random failures are due to mechanical or human failure, while wear failure occurs mainly due to mechanical faults as the equipment becomes old. One of the techniques used by maintenance engineers is to record the mean time to failure (MTF) of equipment items to find out in which period a piece of equipment is likely to fail. This provides some of the information required to determine an appropriate maintenance strategy tor each equipment item. 

The large temperature difference of the remarkable borehole, opposite other boreholes and their environment is significant. This high temperature difference is a typical feature for a small wall thickness between borehole and blade surface. For technical reasons, precise eroding of the boreholes is difficult. Due to this, the remaining wallthickness between the boreholes and the blade surface has to be determined, in order to prevent an early failure, Siemens/Kwu developed a new method to determine the wallthickness with Impulse-Video-Thermography [5],... 

The failure rate changes over the lifetime of a population of devices. An example of a failure-rate vs product-life curve is shown in Figure 9 where only three basic causes of failure are present. The quaUty-, stress-, and wearout-related failure rates sum to produce the overall failure rate over product life. The initial decreasing failure rate is termed infant mortaUty and is due to the early failure of substandard products. Latent material defects, poor assembly methods, and poor quaUty control can contribute to an initial high failure rate. A short period of in-plant product testing, termed bum-in, is used by manufacturers to eliminate these early failures from the consumer market. 

The ha2ard function is a constant which means that this model would be appHcable during the midlife of the product when the failure rate is relatively stable. It would not be appHcable during the wearout phase or during the infant mortaHty (early failure) period. 

Eor steel and other ferromagnetic materials, property deterrnination is more difficult. Other tests are made to measure the continuity of protective metallic coatings. Residual stresses induced in welded stmctures and in components in service owing to chemical attack may contribute to early failure. 

In some appHcations, eg, CVJ boots, stabili2ers are extracted from the part by grease or oil, leading to early failure. 

For compressors in general and for some types in particular, the cleanliness of the gas stream is the key factor in a reliable operation. Moisture or liquids in various forms may be the cause of an early failure or in some-cases a catastrophic failure. Corrosive gases require material considerations and yet even this may not entirely solve the loss of material issue that can certainly cause early shutdowns or failures and high maintenance cost. Fouling due to contaminants or reactions taking place internal to the ( i-pressor can cause capacity loss and the need for frequent shutdowns. 

Minlicr fL-i.iiive contrifai im to early release frequency for PWRs than BWRs because of low early failure frequct.ry Irom other... 

PWRs indicate that most of the containments have relatively low conditional probabilities of early failure, although a large variability exists in the contributions of the different failure mod< "or both large dry and ice condenser containments. 

Partial waterlogging of heater batteries can lead to early failure due to differential thermal expansion. Steam trap selection should take account of this. 

If a section has broken due to fatigue, it is highly probable that other sections will have suffered similar fatigue and could be subject to early failure. 

The second limitation is the life dispersion of machinery components. It is difficult to predict time-dependent failure modes because even they do not occur at the exact same operating intervals. Consider the life dispersion of mechanical gear couplings on process compressors. Both components are clearly subject to wear. If we conclude that their MTBF (mean-time between failure), or mean-time-between-reaching-of-detect-limit is 7.5 years, it is possible to have an early failure after 3 years and another... 

Perhaps the closest approach to pure oxidation in everyday conditions arises in domestic electric heating appliances where the elements are exposed to the air. At some points the elements are necessarily in contact with supporting refractories, and if these are not of adequate purity, accelerated corrosion leading to early failure can occur. In a similar way the sheathed radiant-type elements of electric cookers usually fail owing to the corrosive effects of contaminants such as animal fats or salts from spilled liquids. 

Faulty geometrical design is a major factor in the corrosion of ferrous metals. A design may be sound from the structural and aesthetic points of view, but if it incorporates features that tend to promote corrosion, then unnecessary maintenance costs will have to be met throughout the life of the article, or early failure may occur. 

Early failures of platinised titanium anodes have been found to occur for reasons other than increased consumption of platinum or attack on the titanium substrate caused by voltages incompatible with a particular electrolyte. The following are examples ... 

It is necessary to ensure the integrity of anode cable connections and to give consideration to the number of such connections related to longitudinal resistance of the anode and current attenuation, if early failure is to be avoided. 

Failures due to delamination of the gunite coating have been reported in the USA, but have not been observed to any significant extent in F.urope although some early failures of the anode system have been associated with high local current densities in areas of low concrete cover and high moisture or salt contentThe major application of this anode system is therefore on structures that are relatively dry with a uniform current requirement. 

The standard of cleanliness which must be achieved has been stated to be that which will allow the subsequent process to be carried out satisfactorily . As an example, the degree of cleanliness required to satisfactorily zinc plate from an acid solution is somewhat higher than that required prior to zinc plate from a high-cyanide alkali zinc solution. This should never be taken as a licence to skimp on surface preparation. However, the arguments over surface-tolerant paint coatings abound and will probably continue. It is to a very large extent true that problems of early failure in metal finishing are traceable to incorrect or insufficient surface preparation. 

Maximum productivity is given by the shortest possible time of cure, provided the selected time and temperature do not produce an unacceptable level of defects or early failures in service. Sufficient cure must be given to prevent porosity, since badly undercured rubber will sponge at pressure release. It is better to risk a slight overcure rather than an undercure, since if the curatives are correctly chosen (in type and quantity) the compound should show a plateau effect, which means that a reasonable overcure will not have any marked effect on the physical properties of the product. 

Examination of reinforced structures has so far shown the creep strain to be less than predicted, generally because the soil carries more load than is allowed for in design. Tests on materials buried and then exhumed after 10-20 years have so far shown little significant evidence of degradation, although little would be expected in the relatively benign soil conditions experienced. In common with industrial products, early failures have been shown to be due to errors in design or construction any failures due to poor durability will occur later, hopefully very much later. 

Since no difference was found between FR and non-FR formulations in device aging studies, some other cause must account for the relatively early failures observed for devices molded in the electrical grade epoxy material and aged under bias at 200°C. These failures are attributed to chloride contamination present in the non-semiconductor grade epoxy resin. The extractable Cl concentration is a factor of four higher than Br, and this is correlated with a much higher concentration of CHoCl than CH Br in the EGA data below 200°C. The high Br concentration is also attributed to the... 

In his letter of July 10, 1808, Davy acknowledged his indebtedness to Berzelius and Dr. Pontin. After describing his early failures he said ... 

Persistence is an absolute requirement for the hybridoma producer fusions can fail for many reasons, and it is essential not to give up because of early failures. The methods described in this chapter include techniques for ... 

The obvious method for the preparation of this naphthyridine is the Skraup reaction applied to 4-aminopyridine after early failures,0, 80 the authors of this chapter81 utilized the sulfo-mix described by Utermohlen,82 to obtain 1,6-naphthyridine (2) in 40% yield. 

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