The answer to this month’s trouble shooter is provided by MISTRAS Group Ltd. Question: How can I assess and monitor the condition of bearings that rotate at speeds of between 0.5 and 60 RPM?

Published:  05 April, 2016

Answer:

At lower bearing speeds (i.e. between 0.5 and 60 RPM) a number of proven inspection methodologies and advanced diagnostics are available to rapidly assess the condition of rotating or reciprocating bearings during normal operation. These techniques, which include the use of acoustic emissions technology, are particularly effective on high value capital plants and machinery, where the cost of any lost production or machine downtime due to bearing failures is high.

These techniques have been successfully used in thousands of field tests on a variety of machines, plants and structures, including pressure vessels, power transformers, bridges, process storage tanks, pipelines, valves, nuclear lift rigs, railroad tank cars, cranes, Basic Oxygen Steelmaking (BOS) vessels and compressed gas cylinders.

A variety of bearing defects can be monitored, including corrosion of tracks or balls (emission from corrosion product break-up), insufficient lubricant (emission from surface fretting), cracking or plastic deformation of bearing material (balls, track and cage), crushing and fracture of debris in the bearing. These techniques are even effective at assessing the condition of bearings that rotate at less than one revolution per minute.

Low-speed rotating or reciprocating bearing signatures can be produced after a few dozen assessment cycles. A more detailed analysis would involve the identification and elimination of extraneous noise, grading the severity of the bearing signature, and identifying any features that may indicate the root cause of the problem.

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