Causes and Countermeasures of Centrifugal Pump Bearing Overheating

In industrial production processes, centrifugal pumps are core equipment for fluid transportation, and their stable operation is directly related to production efficiency and operational safety. Bearings, as key transmission components of centrifugal pumps, bear the important functions of supporting the rotor and transmitting torque. Overheating is one of their most common failures. If not discovered and properly addressed promptly, it can lead to premature bearing damage and equipment downtime, or even serious accidents such as shaft seizure, seal failure, and even pump failure. This article analyzes the main causes of centrifugal pump bearing overheating and proposes some treatment strategies to provide some superficial reference for equipment operation and maintenance.

 

 

• Core Causes of Centrifugal Pump Bearing Overheating

Centrifugal pump bearing overheating is not caused by a single factor but rather by the combined effects of multiple issues, including lubrication, installation, load, component wear, and heat dissipation. These issues can be categorized into the following five categories.

 

(1) Overheating Caused by Lubrication

Related Standards for Lubricant Selection:

1. Grease Lubrication

Applicable to rolling bearings in small and medium-sized, low-speed (≤3000 rpm) centrifugal pumps. According to GB/T 3215-2007, the grease filling volume should be 1/2-2/3 of the bearing's internal space. Use a lithium-based grease or other grease that meets the temperature and water resistance requirements specified in the equipment manual. Verification and replacement should be performed according to GB/T 29711-2013 after 3000-5000 hours of operation.

2. Thin Oil Lubrication

Applicable to sliding or rolling bearings in large, high-speed (>3000 rpm) centrifugal pumps. According to GB/T 443-2016, use L-AN series total-loss system oil (of course, many also use 32# or 46# turbine oil). Supply oil through an oil bath or forced circulation method. Maintain the oil level within the specified range of the equipment oil gauge. Check the oil quality every 6-12 months. Replace immediately if oxidation or contamination is detected.

3. Key Notes

1. Clean the oil filler port and container before adding lubricant. Mixing different types and brands of lubricants is strictly prohibited to prevent chemical reactions that degrade performance.

2. Monitor bearing temperature during operation (should not exceed 80°C). If abnormalities are detected, shut down the machine for inspection. This complies with the troubleshooting requirements of GB/T 3215-2007.

2) Lubrication System Abnormality

Lubrication is essential for maintaining normal bearing operation. Lubrication failure is the primary cause of bearing overheating. The first is improper lubrication supply. Insufficient oil can prevent a complete oil film from forming on the friction surfaces, leading to intense friction and heat generation from direct metal-to-metal contact. Excessive oil increases internal stirring resistance, causing the oil to heat up and transfer heat to the bearings. The second is lubrication quality. Lubricating oil or grease can deteriorate due to oxidation, emulsification, or contamination after long-term use. Alternatively, the selected oil type may not match the bearing operating conditions (e.g., inconsistent viscosity grade). These factors can reduce lubrication performance and exacerbate bearing wear and heat generation.

 

(2) Overheating Caused by Installation and Alignment Misalignment

1. The Correlation Mechanism and Causes of Bearing Overheating with Misalignment

Misalignment between the motor shaft and the pump shaft of a centrifugal pump is primarily categorized as radial misalignment (non-concentricity) and angular misalignment (non-parallelism). When misalignment exists, the bearings are subjected to additional radial or axial loads, which damages the lubricating film and increases frictional heat generation, ultimately leading to abnormally high bearing temperatures (typically exceeding 70-80°C). Long-term operation can also accelerate bearing wear, shorten service life, and even cause serious failures such as shaft seizure.

Bearing installation accuracy directly affects its load-bearing state. Improper installation can easily cause additional loads and overheating. On the one hand, improper bearing assembly clearances can lead to a loss of radial or axial clearance, resulting in extrusion friction during operation; on the other hand, excessive looseness can cause unstable rotor operation and subject the bearings to impact loads. Both of these factors can lead to rapid temperature increases. On the other hand, excessive concentricity between the pump shaft and the motor shaft can subject the bearings to additional radial forces. Over-long operation can lead to uneven wear of the bearing raceways and rolling elements, accompanied by abnormal heating and vibration.

2. Relevant National Standards

GB/T 3215-2007 "Centrifugal Pumps for the Petroleum, Petrochemical, and Natural Gas Industries" specifies that the shaft alignment deviation between the centrifugal pump and the prime mover (e.g., motor) must comply with the equipment's technical documentation. Unless otherwise specified, the radial runout must meet accuracy requirements of ≤0.10mm and the end runout must meet accuracy requirements of ≤0.05mm.

 

(3) Abnormal Operating Load

When a centrifugal pump's actual operating load exceeds its design range, the bearings will overheat due to overload. Common causes include: the impeller becoming stuck in debris, causing friction between the impeller and the pump casing, resulting in a sudden increase in rotor resistance; the viscosity and density of the pumped medium far exceeding the design values, significantly increasing the pump's shaft power; the outlet valve suddenly opening fully or the pipe resistance being too low, causing the pump to operate at high flow rates, causing the bearings to be overloaded for a long time, and frictional heat generation exceeding the heat dissipation rate.

 

(4) Component Wear and Damage

Natural wear and tear or accidental damage to bearings and associated components is a direct cause of overheating. Bearing aging, such as ball/roller wear, cage deformation and fracture, and inner and outer ring raceway spalling, can disrupt smooth operation and generate abnormal friction and heat. Wear on the journal or bearing seat increases the clearance, shifting the rotor center and causing uneven bearing loads. Failure of seals can lead to fluid leakage into the bearing housing, contaminating the lubricant and corroding bearing components, further exacerbating overheating.

 

(5) Deterioration of heat dissipation conditions

If the heat generated during bearing operation cannot be dissipated promptly, the temperature will continue to accumulate and rise. The main causes include: Dust and oil clog the bearing housing's heat dissipation holes and heat sinks (most pumps I've seen are not addressed, and are almost always clogged. The structure of the breather cap varies, but the principle is generally the same; see the illustration below for an example), resulting in reduced ventilation and heat dissipation; excessively high operating temperatures, exceeding the normal operating temperature range of the bearings; and centrifugal pumps with cooling systems experiencing scaling of the cooling jacket, insufficient coolant, or clogged cooling lines, leading to ineffective cooling and ineffective removal of bearing heat.

 

• Countermeasures for Centrifugal Pump Bearing Overheating

For the above causes, it is necessary to follow the principle of "precise diagnosis and targeted treatment" and take targeted measures to eliminate the fault and restore normal bearing operation.

 

(1) Optimizing Lubrication Management

First, strictly follow the equipment manual and select the appropriate lubricant or grease. Avoid mixing lubricants of different brands and specifications. Secondly, standardize lubrication procedures. Use an oil level gauge or oil level indicator to control the oil level, ensuring it remains between 1/2 and 2/3 of the bearing's internal space. The grease fill should not exceed 1/2 to 2/3 of the bearing's internal space. If deterioration of the lubricant is detected, thoroughly clean the bearing housing and any remaining oil contaminants inside the bearing, replace the lubricant, and establish a regular lubrication inspection system, setting lubrication intervals based on operating conditions.

 

(2) Correcting Installation and Alignment Accuracy

For installation misalignment, disassemble the bearing assembly and readjust the bearing clearance. Use a feeler gauge or specialized instrument to ensure the clearance meets design standards. If the bearing seat is worn, repair it with spraying, inserting sleeves, or simply replace it with a new one. For shaft misalignment, use a dial indicator or other tool to perform alignment. Adjust the position of the motor or pump body to keep the radial runout and end-face runout of the pump and motor shafts within the allowable tolerances and reduce additional radial forces.

 

(3) Adjust the operating load to a reasonable range

If abnormal loads occur, immediately shut down the pump for inspection. Clean debris from the impeller and flow path, and repair any worn impellers or pump casings. If the pumping medium's characteristics are incompatible with the pump type, replace the pump with a suitable centrifugal pump or pre-treat the medium (e.g., heating to reduce viscosity). Also, adjust the outlet valve opening appropriately. Use flow and pressure monitoring instruments to control the pump's operating parameters within the design range to avoid prolonged overload.

 

(4) Replace Worn and Damaged Components

Regularly disassemble and inspect bearings. If wear, cracks, or flaking are observed on components such as the ball bearings, cage, inner and outer rings, replace them promptly. Ensure the bearings are of the same model and use specialized tools to assemble them to avoid damage from rough handling. For worn components such as the journal and bearing seat, repair or replace them based on the severity of the damage, ensuring the required fit. Also, inspect the integrity of seals and replace any failed seals to prevent leakage and contamination of the lubrication system.

 

(5) Improve heat dissipation

Regularly clean dust and oil from the bearing housing vents and heat sinks, and maintain adequate ventilation (this is often overlooked). If the equipment's operating temperature is too high, cooling measures such as installing fans and awnings can be implemented. For centrifugal pumps with cooling systems, regularly clean scale from the cooling jacket, replenish or replace the coolant, check the cooling lines for unobstructed flow, and repair any blockages or leaks to ensure proper operation of the cooling system and effectively dissipate heat generated by the bearings.

 

Centrifugal pump bearing overheating involves multiple aspects of equipment design, installation, operation, and maintenance, necessitating an operational and maintenance philosophy that prioritizes prevention, combining prevention with treatment. Strengthening routine inspections and monitoring (such as regularly monitoring bearing temperatures with infrared thermometers), standardizing lubrication and installation procedures, and regularly replacing vulnerable parts can effectively reduce the incidence of bearing overheating failures. Once overheating occurs, the cause must be quickly identified and scientific countermeasures implemented to minimize equipment downtime, ensure stable and efficient operation of the centrifugal pump, and provide reliable support for industrial production.