Failure is unavoidable
for everything in the real world, and engineering systems/subsystem and
associated equipments are no exception. However failure and its impact can
definitely be minimized to the extent possible at optimal cost by adopting latest strategies/approaches.
Before going further
in details on new approaches to minimize the failure and safety incidents, we
should understand about the fundamentals of reliability engineering and safety
engineering.
Reliability engineering
deals with the failure concept to minimize the occurrence of failure whereas
the safety engineering deals with the consequences of the failure to minimize the impact on the surrounding environment. Inherent /inbuilt safety
systems/measures ensure that consequences of failures are minimal.
The impact of failures
may vary from minor inconvenience and costs to personal injury, significant
economic loss, environmental impact, and fatalities.
Examples of major accidents are Bhopal gas tragedy, Fukushima-Daiichi nuclear disaster, Deepwater Horizon oil spill, etc. Causes of failure may include bad engineering design, faulty manufacturing, inadequate testing, human error, poor maintenance, improper operation/use and lack of protection system against excessive stress/strain.
Original equipment
manufacturer (OEM), designers, and end users strive to minimize the occurrence
and recurrence of failures. In order to minimize failures and safety incidents in
engineering systems, it is essential to understand and implement FMECA (Failure
mode, effects and criticality analysis) recommendations.
Need for higher reliability and safety is further emphasized by the following factors in order to ensure consistently safe, reliable, profitable and compliant plant operation:
• Increased complexity
of products
• Accelerated growth
of technology
• Competitive market
• customer requirement
• Modern safety and regulatory
laws
• Lesson learnt from past
system failures
• Cost of failures,
damages and warranty
• Safety considerations
with unacceptable consequences
1.Vibration Analysis. When a motor bearing is properly lubricated, the vibration level is typically low. However, as the lubrication film becomes strained due to lack of grease, the bearing’s surface asperities begin to contact, which results in low amplitudes, but high-frequency physical displacement, or vibration, which alerts the lubrication technician that the bearing requires relubrication. The reestablishment of the lubrication film should reduce or eliminate the high-frequency vibrations. If the condition is not rectified, asperity contacts will become more severe and eventually produce impacts. When impacting occurs, damage to the rolling elements and or the raceways occurs, which is detectable as bearing fault defects, which normally are lower-frequency, higher-amplitude vibrations. Vibration analysis can supplement conventional calculation-based regrease interval estimates to refine motor lubrication practices.
2. Acoustic Emissions Analysis. As with vibration analysis, asperity contact caused by the initial stages of lubricant starvation also manifests in the form of acoustic emissions. Unlike vibration analysis, where the frequency of vibration produced is a function of running speed, ultrasonic acoustic emissions associated with the lack of lubrication always occur at approximately the 25 to 35 kHz frequency range. When a motor bearing requires grease, the
amplitude of the ultrasonic signal will increase, indicating a need to relubricate. When grease reaches the bearing, a reduction in the amplitude of acoustic emissions is detectable by listening with headphones. Like vibration analysis, ultrasonic analysis can be employed in conjunction with and to refine calculated relubrication intervals and to ensure that grease is reaching the bearings.
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