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PLAIN BEARING FAILURE
6.0 Chemical effects
6.8 Chemical Effects - Summary
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Characteristics
Chemical effects can result in changes to the profile of the bearing surface, either by corrosion of the bearing material or by the formation of deposits on the bearing surfaces. Attack may also occur on the journal or thrust collar and these should be examined when the damage to the bearing has been so severe that the evidence for the cause of the failure has been removed.
Possible Causes
Chemical attack can be caused by the use of unsuitable lubricants containing active chemical additives (e.g. anti-wear and extreme pressure load-carrying additives) or by contamination from external sources, most frequently the process material being handled.
Actions
Diagnosis of chemical effects depends on identification of the reactants or the deposits forming on the bearing surfaces. Where chemical effects are suspected or where there is no clear evidence for the cause of a failure, a careful examination should be made of the other bearing surfaces that have not failed.
Useful Analytical Techniques
X-ray diffraction analysis can be used for the specific identification of inorganic deposits, provided the deposit has a crystalline structure.
Where the deposit is non-crystalline, ESCA may provide useful evidence by identifying the chemical elements present. Identification of organic deposits is much more difficult. Infrared spectroscopy can be used to identify hydrocarbon mineral oil degradation deposits, which are also usually soluble in aromatic solvents, but the identification of other organic deposits require more sophisticated techniques such as mass spectroscopy or nuclear magnetic resonance (NMR) and the services of a skilled analyst. Again, where there is any suspicion of chemical effects, the lubricating oil should be analysed for contaminants.