Failure modes/mechanisms

This report provides an aging assessment of electric motors and was conducted under the auspices of the USNRC NPAR. Pertinent failure-related information was derived from LERs, IPRDS, NPRDS, and NPE including failure modes, mechanisms, and causes for motor problems. In addition, motor design and materials of construction were reviewed to identify age-sensitive components. The study included consideration of the seismic susceptibility of age-degraded motor components to externally-induced vibrational effects. 

Nonelectronic Parts Reliability Data 1991 (NPRD-91) and Failure Mode/Mechanism Distributions 199V (FMD-91) provide failure rate data for a wide variety of component (part) types, including mechanical, electromechanical, and discrete electronic parts and assemblies. They provide summary failure rates for numerous part categories by quality level and environment. 

Failure Mode/Mechanism Distributions 1991, Reliability Analysis Center, P.O. Box 4700, Rome, NY, 1991. 

Bellows are the most fragile component in a spring-operated SRV and also the most expensive to replace. Usually, we can see one of the three different failure modes mechanical, fatigue or corrosion. 

FMD-97 Failure Mode /Mechanism Distributions. Reliability Analysis Center, 1997 (Ref. 5)... 

Failure Mode/Mechanism Distributions. Reliability Analysis Center, 1997. 

Definition of Failure Modes Mechanisms of Bond Failure... 

A spool valve in an aviation hydraulic actuator is chosen as a case study to demonstrate the proposed PoF-based component failure behavior modeling approach. As discussed in Example 1, the performance parameter of the spool is its clearance. According to the result of failure mode, mechanism, effect analysis (Liao, 2013), the spool is subjected to two failure mechanisms, i.e., adhesive wear and abrasive wear. 

The ultimate goal for reliability studies is to optimize the total reliability of the product. This involves reliability of the various elements of the system (electronic/electrical components, mechanical components, PWB, and solder joints), through different failure modes (mechanical, electrical, electrochemical, etc.), under the actual use conditions (which often involves complex loading conditions with multiple loadings simultaneously imposed, such as cyclic temperatures, humidity, atmospheric chemical exposure, electrical field, vibration, mechanical shock, etc.) (Ref 26). The interactions between... 

FMD-97 Failure Mode/Mechanism Distributions (RAC) Electronic, electrical, mechanical and electro-mechanical components... 

Introduction to Failure Modes Involving Mechanical Damage... 

Surface defects, if sufficiently severe, may result in failure by themselves. More commonly, they act as triggering mechanisms for other failure modes. For example, open laps or seams may lead to crevice corrosion or to concentration sites for ions that may induce stress-corrosion cracking. 

All areas of the cooling water system where a specific form of damage is likely to be found are described. The corrosion or failure causes and mechanisms are also described. Especially important factors influencing the corrosion process are listed. Detailed descriptions of each failure mode are given, along with many common, and some not-so-common, case histories. Descriptions of closely related and similarly appearing damage mechanisms allow discrimination between failure modes and avoidance of common mistakes and misconceptions. 

Remember that the failure position of a valve refers to its failure mode if there is a utility failure. A valve can mechanically fail in any position it is possible for a fail closed valve to get stuck in the open position. When doing a process hazard analysis it is important to consider all possible failure positions of a valve, and not only the failure position resulting from utility failure. 

This study is a good reference for the construction of fault/event trees of systems that are affected by valve performance. The valve failure modes are identified, the associated mechanisms are described in detail, and preventive measures are offered. 

Appendix III contains failure rate estimates for various genetic types of mechanical and electrical equipment. Included ate listings of failure rates with range estimates for specified component failure modes, demand probabilities, and times to maintain repair. It also contains some discussion on such special topics as human errors, aircraft crash probabilities, loss of electric power, and pipe breaks. Appendix III contains a great deal of general information of use to analysts on the methodology of data assessment for PRA. 

The sections to follow describe the most common machine-train failure modes critical speeds, imbalance, mechanical looseness, misalignment, modulations, process instability, and resonance. 

An imbalance profile can be excited due to the combined factors of mechanical imbalance, lift/gravity differential effects, aerodynamic and hydraulic instabilities, process loading, and, in fact, all failure modes. 

There are defect limits that are associated with random failure modes. For example, if there is a leak from a mechanical seal on a pump, where do we decide that the leakage is excessive and requires immediate maintenance Vibration analysis severity levels are also typical examples of when do we have severe enough conditions to warrant equipment shutdown and overhaul. In such circumstances, the defect limit is dependent upon individual subjective judgment. 

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... 

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