What are the common bearing failure modes of horizontal centrifugal pumps

Horizontal centrifugal pumps are one of the core equipment for conveying liquids in modern industry. Their stable operation depends largely on the support and lubrication of the bearing system. As the key transmission component between the pump shaft and the motor rotor, once the bearing fails, it will directly lead to increased vibration, poor rotation, and even sudden shutdown of the pump unit.

Fatigue spalling
During the high-speed operation of rolling bearings, their inner rings, outer rings and rolling elements continue to bear alternating loads, causing the microcracks on the surface of the material to gradually expand, and eventually metal particles to fall off, that is, the "fatigue spalling" phenomenon. This spalling will form pits and pits on the bearing raceway, resulting in increased vibration, increased noise, and unstable operation. Fatigue spalling is usually caused by long-term operation, insufficient material hardness, poor lubricant quality, or excessive bearing load.

Lubrication failure
Poor lubrication is one of the main causes of early damage to horizontal centrifugal pump bearings. When the amount of lubricating oil (or grease) is insufficient, the viscosity is not matched, the lubrication cycle is too long, or water and impurities are mixed in, the lubricating film will be broken, and dry friction will occur on the metal surface. In severe cases, it will cause bearing ablation, surface strain, and severe temperature rise. Lubrication failure directly affects the life and operating efficiency of bearings, and is also a key factor affecting the energy efficiency of the overall pump unit.

Cracks and fractures
Under harsh working conditions such as high temperature, high speed or uneven load, microcracks are prone to occur in bearing rolling elements or cages. These cracks expand under repeated stress and may eventually cause rolling element fragmentation or cage fracture. Especially in the case of long-term untreated centering errors or vibrations, the impact stress on the bearing structure will aggravate the development of cracks, causing sudden fractures, and then causing the entire pump unit to jam or be damaged.

Pitting corrosion
Pitting corrosion usually occurs in areas where the lubricant fails to effectively isolate the metal contact surface. Local high pressure causes the oil film to rupture, and trace metals directly contact and undergo electrochemical reactions or micro-welding, forming local melting spots. Pitting corrosion not only reduces the quality of the bearing contact surface, but also easily becomes the source of crack initiation under fatigue load, and is one of the potential early failure inducements. Pitting corrosion is closely related to bearing material selection, lubricant quality and impurity contamination.

Electrolytic erosion damage
In some motor drive systems, if no effective electrical isolation device is installed, the stray current between the pump shaft and the motor shaft may form a path through the bearing. When the current passes through the rolling contact surface of the bearing, it will cause a tiny arc discharge, causing surface ablation, melting, pitting or groove formation, which is called electrolytic erosion. Electrolytic erosion damage usually manifests as abnormal noise and gray-black spots on the surface at the beginning of bearing operation, which seriously affects the accuracy and life.

Cage damage
The cage is used to maintain the spacing and movement trajectory of the rolling elements, but under conditions such as poor lubrication, rolling element imbalance, and sudden load changes, the cage may deform, fatigue fracture or get stuck. Cage damage will cause the rolling elements to deflect or slip, aggravate bearing friction and heat, and is an important cause of pump shaft runout and increased system vibration.

Bearing overheating
Bearing overheating is a common failure manifestation, usually caused by insufficient lubrication, excessive preload, centering error, high ambient temperature or improper bearing clearance selection. Overheating of bearings will not only accelerate the oxidation and deterioration of lubricating oil, but also cause metal annealing, hardness reduction, expansion and deformation of parts, and eventually cause bearing jamming or even bursting, seriously affecting the safe operation of the pump.

Vibration-induced damage
Due to factors such as weak foundation, eccentric coupling, pipeline stress or unbalanced force, the pump body and its bearing seat may produce continuous or periodic vibration. High-frequency vibration will cause the rolling element of the bearing to jump, uneven contact, increased friction, induce raceway fatigue, pitting or loose cage problems, forming a vicious cycle of vibration-damage-failure.

Pollution damage
When dust, water vapor, metal debris or other foreign matter enters the inner cavity of the bearing, it will directly contaminate the lubricating oil, increase the friction coefficient, and damage the raceway surface. Bearing contamination not only comes from the external environment, but may also be caused by aging of the seal, improper assembly or excessive maintenance cycle. Pollution damage often appears as particle scratches or local erosion spots, which are difficult to repair and have a greater impact on the overall structure.

Failure caused by installation deviation
During the installation process of bearings, if the force is improperly applied, the installation position is offset, and the bearing preload force is inaccurately controlled, it is very easy to cause uneven force on the inner and outer rings, raceway deformation, and cage extrusion. Installation deviation can also induce abnormal noise, vibration and overheating in the initial operation, shortening the service life of the bearing. High-precision installation is an important prerequisite for ensuring the life of the bearing.