Failure rate comparison

The failure rates of a floating ball valve have been estimated for different application conditions based on a detailed FMEDA of a ball valve. 

Clean service, close to trip. Class IV leakage allowed 0 400 

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Following the lEC 61650 we choose the accurate calculation of two constant failure rates comparison using F - distribution. We calculate f using the equation (3). 

WASH-1400 is a fundamental document for PRA methodology. The data appendixes contain a great deal of useful information on methods of data assessment. A large number of sources for data are considered, and very general failure rate estimates will produce only gross approximations. Since the advent of data collection schemes across and within plants, the WASH-1400 data are solely useful as a constituent to a data aggregation process or as widely bounded figures that provide a basis for comparison. 

Marti, H. F. and R. A. Waller. An Exploratory Comparison of Methods for Combining Failure Rate Data from Different Data Sources. Report No. LA-7556-MS, Los Alamos Scientific Laboratory, 1987. 

Comparison of failure rate for various administered over approximately a 3-week period inhibits ovulation,... 

Intramuscular administration of nitrofurantoin sodium may also be successful in metastatic seminoma, the drug apparently decreases the size of lung metastases thus improving the patient s condition . Owing to the low blood levels which are achieved with nitrofurantoin, all indications for its use aside from urinary tract infections have meanwhile been abandoned hence nitrofurantoin is used orally as well as parenterally for the treatment of urinary tract infections only. Intravenous use of nitrofurantoin does not produce higher urine levels than oral administration or intramuscular injection does . A comparison of all three modes of application has proved that orally-administered nitrofurantoin is absorbed completely and metabolized rapidly since maximum drug levels appear in the urine within thirty to sixty minutes after administration. To reduce the rate of side effects, enteric coated tablets may be administered. Numerous reports especially from Japan have led to the conclusion that such tablets are absorbed at a slower rate and are, therefore, probably better tolerated. On the other hand, it seems likely that adequate bacteriostatic levels cannot be achieved and hence a higher failure rate will ensue with this method. 

Out of more than forty different porphyrinic and non-porphyrinic organic and inorganic electrocatalysts tested for these properties, only three show the desired characteristics tetrakis (3-methoxy-4-hydroxyphenyl)porphyrin, me50-tri(V-methyl-4-pyridinium)-p-phenylene-5 -0-2, 3 -0-isopropylideneuridine (PUP), and NA -bis[5-p-phenylene-10,15,20-tris(3-methoxy-4-hydroxyphenyl)-porphyrin]-l,10-phenanthroline-4,7-diamide( 1,10-phen)(TMHPP)2." Detection limit for NO depends on film quality and varies between 10 and 10 M. The best sensitivity is usually obtained using a PUP and (l,10-phen)(TMHPP)2 films with Ni(II) as the central metal. If a reproducibility of preparation procedure is considered (l,10-phen)(TMHPP)2 Ni(II) is much superior (failure rate 1 10) in comparison to two other porphyrins. 

Many companies have an internal expert who has studied these sources, as well as their own internal failure records, and maintains the company failure rate database. Some use failure data compilations found on the Internet. While the data in industry databases is not product specific or application specific, it does provide useful failure rate information for specific industries (nuclear, offshore, etc.) and a comparison of the data provides information about failure rates versus stress factors. 

Table 8-1 shows a comparison of data for a pressure transmitter. The failure rate numbers from the industry database sources are significantly higher than the FMEDA reports. 

For comparison purposes a single board PEC with 8 inputs and 4 outputs win be used in a series of examples. Assume that the failure rates are determined by a FMEDA of each circuit. The results of the input circuit analysis indicate the following failure rate categories ... 

Some major differences can straightforwardly observed between these results. Indeed, the elasticity concept for the maintenance impact allows to modeling preventive interventions delaying the start of aging, in comparison with the other models. As the maintenance efficiency has been chosen to tend to 0 with time, it is not surprising to observe that, no matter the value of the maintenance period, all resulting conditional failure rates become asymptotically parallel to the intrinsic (initial) failure rate evolution. 

Figure 5. Comparison of failure rate functions for a superposed process consisting of 500 source processes with weibull distributed interarrival times.

In this part of the paper the evaluated application of reliability data analysis techniques - procedure for comparison of two constant failure rates is perceived of an item produced for systems specific use/ utilization. 

Kapur, K. C. Lamberson, L. R. 1977. Reliability in Engineering Design. N.Y. John Wiley Sons. lEC 61650 Reliability data analysis techniques - Procedures for comparison of two constant failure rates and two constant failure (event) intensities. 

ABSTRACT This paper is focused on the safety analysis of an analogue transceiver located in the BTM, a subsystem of the European Railway Traffic Management System (ERTMS). Balise detection is the transceiver safety related function and the ERTMS specifications define it as a SIL2, setting a maximiun tolerable hazard rate of 10 failures per hour. By means of FTA and FMEA analyses, and failure rate calculation, this paper demonstrates that a bIsT topology is suitable to accomplish safety requirements. The description of the topology and the diagrams of both analyses are also exposed. To conclude, the comparison between the values obtained for both architectures are shown and the safety improvement is e)q)lained. 

Vaurio, J.K. and K.E. Jankala (2006). Evaluation and comparison for estimation methods of failure rates and probabilities. Reliability Engineering and System Stfety 91, 209-221. 

Suitable mathematical expressions representing the fault tree entries may be developed using Boolean algebra. When more than one event on a chart can contribute to the same effect, the chart and the Boolean expression indicate whether the input events must all act in combination (and relationship) to produce the effect, or whether they may act singly or relationship). The probability of failure of each component or of the occurrence of each condition or listed event is then determined. These probabilities may be from actual failure rates vendors test data comparison with similar equipment, events, or conditions or experimental data obtained specifically for the system. Hie probabilities are then entered into the simplified Boolean expressions. The probability of occurrence of the undesirable event being investigated may then be determined by calculation. When an FTA is used for qualitative analysis, care is required in the description of each event to be sure it can be fitted with a suitable probability. 

Comparison of observed failure rates, from user proof test and performance data, versus assumed dangerous failure rates - 5.2.5.3... 

This equation will formally have the form of a life function with constant failure rate. A5 can be viewed as the system failure rate in the case of a preset inspection interval. Such a view will of course make sense only when inspection intervals are small in comparison to the entire operation period to be considered. For the OR linkage, the following emerges from Equation (4-56) ... 

The following tabulation (Table 5.4) compares observed and—with the help of values obtained from the literature [5-26]—computed failure rates of electronic boards. The observed failure rates for the first four board types are greater than the computed ones since these boards are being used by first item lists at the input and monitoring levels and are subject to the aforementioned deterioration through external influence factors. However, this comparison of the failure rates still contains an uncertainty factor of... 

Table 5.4 Comparison of observed and computed failure rates in electronic boards...

In a prospective comparison of aprotinin (n = 1507) and aminocaproic add (n = 1830) in patients undergoing surgery, postoperative renal failure was significantly more common in the former (6.2% versus 2.7%) and at median 5.4-year follow-up (up to 12 years) mortality was higher (Kaplan-Meier failure rates 44% versus 24% at 8 years), with a stepwise relation between weight-based aprotinin dose and mortality [197 ]. 

Quantitative assessment of the random hardware failure functions (e.g., dangerous failure rate, probability of failure on d mand, spurious safety action rate). The figures obtained cou ld be compared with targets in the criteria, or as a basis for comparison with comparable situations (PES replacing a non-PES safety function, PES design alternatives). 

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