Bearings are one of the most common components used in industry. The following post details some of the main causes of bearing failure. I’ve come across some catastrophic bearing failures in my time. The following pictures detail what was left of a David Brown (DB37) pump NDE (NON DRIVE END) bearings after a catastrophic failure:

Please click on images to view.

Of course, a good condition monitoring system should hopefully pinpoint bearing wear through oil and vibration analysis, however, as we all know even with the best detection and preventative maintenance programmes – failure can still occur. One of the things we always try and do is to attempt to pinpoint the root cause of our bearing failure.

• Foreign Matter: When abrasive particles get into the oil and start to circulate around the bearing housing.
• Bearing Misalignment: An all too common problem that can often be spotted by examining the bearing raceways, the ball bearing track will display signs of the balls oscillating from side to side. The shaft should be checked by lasers or clock gauges to make sure it isn’t bent. The shaft should be true, as should any shaft shoulders, spacers and locking nuts.
• Machine Train Misalignment: Machine train misalignment is indeed a whole subject in its own right. Simply put, if your pump and motor train are misaligned, then you will experience increased temperatures and vibrations and your bearing life will plummet dramatically.
• Bearing Lubrication: Getting the bearing lubrication wrong can lead to overheating, subsequently leading to excessive wear. So selecting the wrong lubrication can be detrimental, also when the correct lubrication is selected the oil level must be correct. Oil level should be addressed by the implementation of constant oil levellers, that when correctly set up will keep the oil and the right level, especially at times when oil is lost through leakage. The oil should be visually checked by competent plant operators to ensure that lubricants have not been contaminated or broken down due to oxidisation or exposure to atmospheric conditions.
• Bearing Fatigue: Fatigue develops due to the magnitude of force exerted on the bearings and the frequency that the forces are repeated. The bearing’s rolling elements spread the metal in front of them as they roll, putting the metal components in compression and tension with this repeated action resulting in the flaking of the metal.
• High Temperatures: Bearing lubrication can be greatly affected by high temperatures. The formation of carbon can occur and lubricating elements are lost. The carbon formed can cause increased friction and has a tendency to jam the bearing. Also, the bearing metals are affected by the high temperatures. A change in the molecular structure of the metal can alter the metal’s strength and hardness characteristics substantially. A final point to note is that high temperatures have a tendency to expand the bearing metals leading to a reduction in bearing clearances resulting in increased preloading within the bearing. Note that this can also occur at low temperatures when dealing with cryogenic pumps.
• Bearing Corrosion:Ball and roller bearing surfaces are finished to a high standard in order to meet the tolerances required to perform with high efficiency. The bearing high quality surface finishes are subjected to corrosion by a whole range of different mediums; water, acid, broken down oils and greases, condensation from excessive temperature reversals. Corrosion causes abrasion and can account for excessive wear within bearings.