This is achieved by separating ferrous debris from lubricating oil by use of a magnetic field with an instrument called a ferrograph, the result is then examined with microscopy.
Ferrography was pioneered in the 1970s by the late Vernon C. Westcott,[1] sponsored by the Advance Research Projects Agency of the United States Department of Defense[2] At the time, the methods used to gauge wear; spectroscopic analysis and ferromagnetic chip detectors, could only provide warning of imminent failure, after the wear had already reached the severity, where preventative maintenance alone would not be an effective control to prevent catastrophic failure.
[1] In 2009 a new method of visual on-line ferrography was published by a group of researchers from Xi'an Jiaotong University, Theory of Lubrication and Bearing Institute.
Continuous monitoring of the lubricating oil allows a change from expensive and often unnecessary preplanned maintenance to more cost-effective failure prevention.
[5] Ferrography is unique because it can deliver information about enclosed parts as lubricating oil circulates through these areas and is still accessible.
Rinsing vital components with particle-free lubricant and analyzing the output can offer a detailed report of machine wear without disassembling anything.
These uses have been found in processing grease samples, gas emissions; and in examining wear on arthritic joints.
On-line visual ferrography (OLVF) allows for images of wear debris to be acquired during routine operation of machinery.
Additionally, for the qualitative approach which is analytical ferrography, experts are needed to make sense of the raw output.