Types of Failure

Corrosion fatigue is a type of failure (cracking) which occurs when a metal component is subjected to cyclic stress in a corrosive medium. In many cases, relatively mild environments (e.g., atmospheric moisture) can greatly enhance fatigue cracking without producing visible corrosion. 

Dielectric Strength. Dielectric failure may be thermal or dismptive. In thermal breakdown, appHed voltage heats the sample and thus lowers its electrical resistance. The lower resistance causes still greater heating and a vicious circle, leading to dielectric failure, occurs. However, if appHed voltage is below a critical value, a stabilized condition may exist where heat iaput rate equals heat loss rate. In dismptive dielectric failure, the sample temperature does not iacrease. This type of failure is usually associated with voids and defects ia the materials. 

In design against creep, we seek the material and the shape which will carry the design loads, without failure, for the design life at the design temperature. The meaning of failure depends on the application. We distinguish four types of failure, illustrated in Fig. 17.3. 

Problem evaluation in turbomachinery is complex, but with the aid of performance and mechanical signals, solutions can be found to diagnose various types of failures. This is done by using several inputs and a matrix. A sample of some of the problems are given in the next few sections. 

There are many types of failures assoeiated with a gas turbine, sinee these units are very eomplex in their overall makeup. The failures in the hot seetion far outnumber the problems in the eompressor due to the high temperatures assoeiated with the hot seetion. Hot-seetion failures are usually eonneeted to problems assoeiated with fuels. Turbine failures ean be very eostly, the average eost runs about 500,000 for units between 10 and 50 MW and about 700,000 for units above 50 MW. These average failures result in downtime of between 12 and 16 weeks. The type of operation the unit experienees is a major faetor in the problem. The unit has a more trouble-free operation if it is a baseload unit. 

The primary drawback to the application of XPS in adhesion science is associated with the limited spatial resolution of the technique. This can make it difficult to study processes that are highly localized, such as corrosion, or to accurately characterize certain types of failure surfaces where, for example, the locus of failure may pass back and forth between two phases. 

Safety analysis. A formal method of assessment should be used. Each component within the system should be considered in turn. The likely types of failure and their consequences for the system should be taken into account. This should include consideration of the reliability of operating procedures, where safety depends upon them, and should encompass both inadvertent and deliberate failure to follow procedures. 

It may be seen from Fig. 2.71 that in most cases where the failure is ductile the isometric curves are approximately parallel to the fracture curve, suggesting that this type of failure is primarily strain dominated. However, the brittle... 

Answer Review the plant s design to determine how radioactive water could get from the plant to the river. Some ways are i) through the heat exchanger and through the condenser, ii) from the closed circuit water into the service water, iii) from the spent fuel storage pool, and iv) from the sump. Prepare fault trees or adapt existing fault trees to determine the probability of each of these release paths. Obtain reliability data for the components that are involved and evaluate the fault trees to determine the probability of each type of failure. For those pathways with a probabilit >7/y,... 

Excessive temperature can lead to premature failure of an item of equipment at pressures below its design maximum working pressure. Such a failure can create a leak, potentially leading to fire or explosion if gas is leaked or to oil pollution if oil is leaked. This type of failure should be gradual, with warning as it develops, and thus does not require as higli a degree of protection as those previously mentioned. 

This type of failure underscores the earlier comment that individuals should, if possible, be actively involved in the development of procedures that they are required to use, so that they imderstand the underlying pmpose behind them. 

Both of the sources above contain tWo types of failure rate data used in CPQRAs time-related failure rates and demand-related failure rates. Time-related failure rates, presented as failures per 10 hours, are for equipment that is normally functioning, for example, a running pump, or a temperature transmitter. Data are collected to reflect the number of equipment failures per operating hour or per calendar hour. 

The failure description is the third part of the taxonomy structure and involves the modes, severities, and types of failures. These are based on models in the In-Plant Reliability Data Base for Nuclear Power Plant Components Data Collection and Methodology Report (IPRDS) and IEEE Std. 500-1984,2 which are discussed in Chapter 2. 

Engine failures over a five year span for 138 emergency generators are listed. Discussion of each type of failure is presented. Data listed includes percentage of failure over the population and time period. All failures were presumably insured by Hartford Steam Boiler and subject to functional inspections and audits. 

Three reports have been issued containing IPRDS failure data. Information on pumps, valves, and major components in NPP electrical distribution systems has been encoded and analyzed. All three reports provide introductions to the IPRDS, explain failure data collections, discuss the type of failure data in the data base, and summarize the findings. They all contain comprehensive breakdowns of failure rates by failure modes with the results compared with WASH-1400 and the corresponding LER summaries. Statistical tables and plant-specific data are found in the appendixes. Because the data base was developed from only four nuclear power stations, caution should be used for other than generic application. 

Where e.xperience indicates a reiisoiiable potential for equipment failure (such as a tank overflow, rupture, or leakage), the plan is to include a prediction of the direction, rate of flow, and total quantity of oil that could be discharged from the facility as a result of each major type of failure... 

Chloride salts (sodium chloride, potassium chloride) tend to interfere with the formation of a protective layer over metals. Chloride salts destroy the passivity of some stainless steels and cause them to fail by rapid cracking under tensile stress at temperatures higher than about 176°F (80°C). This type of failure is called chloride stress cracking (CSC) [186,194]. 

Most microprocessor-based analyzers permit direct comparison to two machine-trains or components. The form of direct comparison, called cross-machine comparison, can be used to identify some types of failure modes. 

The types of wear and failure that occur in metallic gears are distinctive and have been subjected to close analysis over many years. The more common types of failure are abrasion, scuffing, pitting, corrosion, plastic yielding and... 

Experience shows that some machines have more frequent failures than do others. Obviously, different failure modes have different frequencies of occurrence. This is usually described as mean-time-between-failure (MTBF) and expresses the probability of machinery failure and breakdown events as a function of time. This is of particular interest to the maintenance failure analyst and troubleshooter who have to grapple with the realization that some machinery failure modes appear slowly and predictably whilst others occur randomly and unpredictably. In most cases, both types of failures have been encountered. 

Atmospheric exposure trials, carried out in Cambridge, established the fact that when rusty specimens were painted in the summer, their condition, after some years exposure, was very much better than that of similar specimens painted in the winter It was found that steel weathered in Cambridge carried spots of ferrous sulphate, deeply imbedded in the rust, and that the quantity of ferrous sulphate/unit area was very much greater in the winter than in the summer this seasonal variation was attributed to the increased sulphur dioxide pollution of the atmosphere in the winter, caused by the combustion of coal in open grates. It was concluded that there was a causal relationship between the quantity of ferrous sulphate and the effective life of the paint. It was suggested that these soluble deposits of ferrous sulphate short-circuit the resistance of the paint film and, since paint films are very permeable to water and oxygen, the ferrous sulphate will become oxidised and hydrolysed with the production of voluminous rust, which will rupture the film at numerous points, thus giving rise to the characteristic type of failure seen on painted rusty surfaces. 

Lifting may also occur if a paint containing strong solvents (xylol or solvent naphtha, not to mention such active solvents as esters and ketones) is applied (not necessarily by brushing) over a paint which is not resistant to them. The older an oxidising paint film becomes, the more solvent-resistant it will be. Short-oil media and pigment-rich paints are not so prone to lifting. This type of failure is not restricted to oil-base materials it can, for example, also occur with chlorinated rubber paints. 

The term fracture implies fragmentation of a solid body into two or more bodies under the action of stress. Two main types of fracture mode are observed in solids. The first is ductile fracture which is the failure of a material after it has undergone a considerable amount of plastic deformation. The other is brittle fracture which is the failure of a material without undergoing practically any plastic deformation. The type of failure which occurs depends largely on the nature of the material and its condition however, failure is also affected by... 

When the mechanisms restricting bacterial colonization in the upper gut fail, due to disease or dysfunction, bacterial overgrowth develops. The segmental distribution may be gastric, intestinal or both depending on the type of failure. The consequences for the host vary from none to life-threatening complications, caused by severe water and electrolyte deficiencies and septic manifestations. 

A water spray protection system around vessels is recommended to prevent this type of failure. These water spray protection systems, commonly called deluge systems, are designed to keep the vessel cool, flush away potentially hazardous spills, and help to knock down gas clouds.13 Deluge systems can also provide enough time to transfer material out of a storage tank into another (safe) area. 

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