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PLAIN BEARING FAILURE
6.0 Chemical effects
- Chemical effects Index
6.6 Sulphur Attack of Copper-Based Bearing Alloy
| Click on photograph to enlarge | |
 | Sulphur attack of lead-bronze tilting-pad journal bearing |
| Main Characteristics | Black deposit in loaded area of pad, suggesting chemical attack. Diagnosis depends on chemical identification of the deposit. |
| Cause | Deposit was identified by x-ray diffraction as copper sulphide. Copper alloys are more prone to attack than tin-rich white metal. In this case the attack has come from the presence of the sulphur-containing load-carrying additive zinc dialkyl dithiophosphate commonly used in High Duty (HD) Hydraulic Oils. |
| Note | This example comes from a high speed centrifugal pump with an integral gear. An HD Hydraulic Oil was used to provide additional protection for the gears. These were turbine quality gears that can operate perfectly satisfactorily with oils without load-carrying additives. A change to a turbine oil solved the problem. Note this bearing had not actually failed. The machine was shut down because of failure of the thrust bearing (see Sulphur Attack of Silver Bearing). |
| Possible Confusion with Other Types of Damage | Other deposits described in this Section tend to look superficially the same. The final diagnosis requires chemical analysis |
| Comment | Extreme pressure (EP) and High Duty hydraulic oils that contain active sulphur additives should be avoided in systems where there are copper-based bearing alloys. |