Centrifugal Compressor: 5 Common Fault Solutions

2024-09-20

Centrifugal air compressor is a kind of high-speed rotating equipment commonly used in chemical production. Through high-speed rotation, centrifugal force is generated, so that the gas expands and flows in the impeller of the air compressor. The flow rate and pressure of the gas flowing out of the impeller are correspondingly increased, thereby realizing compressed air.

Sudden drop in oil pressure
The sudden drop in the oil pressure of the compressor is relatively complicated in cause and is closely related to the internal components of the unit. Dealing with this fault depends on the actual situation.
In general, the drop in oil pressure is related to the lubrication system oil pipes such as oil pumps and oil pipes. To deal with this fault, pressure testing and handling work need to be done.
For example, when the oil pump fails and the pressure is reduced, the oil pump should be inspected in time to find out the cause of the failure; when the fault is related to the oil pipe, the fault is caused by leakage due to pipe rupture. The specific measure is to replace the new oil pipe.
Decrease in gas outlet flow
The main reason for the decrease in gas outlet flow lies in filters and sealing devices. Improper control of these two components will reduce the gas flow and affect the normal function of the compressor equipment.
Troubleshooting methods:
First, the blockage of the gas filter resulting in a reduction in inhalation volume is the main cause of filter failure. The fault can be eliminated by cleaning the gas filter;
Second, the cause of the failure of the sealing device is that the sealing gap is too large, resulting in leakage. The best solution is to replace the seal or adjust it according to the regulations.
Excessive temperature at the outlet of the cooler
The temperature at the outlet position of the gas cooler is greater than 60°C. The occurrence of this fault is related to the cooling water volume of the cooler, its cooling tube, flow velocity, and the cooperation between the tube plate and the tube.
For example, when the cooperation between the tube plate and the tube is loose or the cooling tube is broken, the temperature at the outlet position of the gas cooler cannot be maintained, and it exceeds the allowable range; the high operating pressure of the compressor increases the wear of the components and causes a significant temperature rise.
Specific treatment measures are to tighten the loose tubes with a tube expander, or block the two ends of the damaged tubes, and clean the core of the cooler.
Excessive bearing temperature
The bearing is the core component of centrifugal compressor operation failure and determines the operation efficiency of the entire equipment. Excessive bearing temperature is a relatively common fault in compressor operation.
Temperature fault main manifestations: The orifice diameter of the throttle ring at the oil inlet of the bearing is too small and the oil inlet volume is insufficient; the oil pressure of the lubrication system drops or the oil filter is blocked, and the oil inlet volume is reduced; the cooling water volume of the oil cooler is insufficient and the oil inlet temperature is too high.
According to these fault phenomena, in the actual handling process, it is necessary to overhaul the lubrication system oil pump, oil pipe or clean the oil filter; adjust the inlet water volume of the cooling water of the oil cooler; the orifice diameter of the throttle ring at the oil inlet of the bearing is too small and the oil inlet volume is insufficient. Appropriately increase the orifice diameter of the throttle ring; overhaul the oil cooler, eliminate water leakage faults or replace with new oil.
Excessive bearing vibration
Vibration load increases the bearing capacity range of the bearing and causes the failure and loss of the structure of the centrifugal air compressor, which is very harmful to the damage of parts.
Fault manifestations of excessive bearing vibration load: The dynamic balance accuracy of the rotor or the pinion and bull gear of the speed increaser is destroyed; the interference between the bearing cap and the back of the bearing bush is too small; the gear meshing is poor, the gear is severely worn or damaged.
For this kind of fault handling, the main methods are to re-calibrate the dynamic balance; scrape the horizontal parting surface of the bearing cap or grind the adjusting gasket to ensure that the interference is 0.02-0.06mm; check the gear wear condition, and re-calibrate the non-parallelism, center distance and meshing area between the pinion and bull gear to meet the requirements.
Next, we list some faults that may occur during the operation of centrifugal compressors and solutions for your reference:
Abnormal vibration and noise
Q: Misalignment
A: Disconnect the coupling and let the prime mover rotate alone. If there is no abnormal vibration when the prime mover rotates, the fault may be caused by misalignment; check the alignment and refer to the installation manual.
Q: Unbalanced compressor rotor
A: Check the rotor to see if it is caused by dirt or damage. If necessary, rebalance the rotor.
Q: Damaged impeller
A: Check the impeller and repair or replace it if necessary.
Q: Abnormal cause of bearing
A: Check the bearing, adjust the clearance, and repair or replace it if necessary.
Q: Coupling failure or imbalance
A: Check the balance of the coupling and check the coupling bolts and nuts.
Q: Poor sealing ring
A: Check and measure the gap of the sealing ring and repair or replace it if necessary.
Q: Abnormal oil pressure and oil temperature
A: Check and measure the gap of the sealing ring. Check the oil pressure, oil temperature and working condition of the oil system at each oil filling point. If any abnormality is found, try to adjust it. Repair or replace it if necessary.
Q: There is dirt and uncleanness in the oil, which causes bearing wear.
A: Find out the source of dirt, check the oil quality, filter when adding oil, change the oil regularly, check the bearing and adjust the clearance.
Q: Surge
A: Check whether the compressor is operating far away from the surge point, whether the anti-surge margin is correct, and whether the anti-surge device is working normally.
Q: The stress of the gas pipeline is transmitted to the casing, resulting in misalignment.
A: The gas pipeline should be well fixed to prevent excessive stress from acting on the compressor cylinder; the pipeline should have sufficient elastic compensation to cope with the amount of thermal expansion.
Q: There are other equipment working near the compressor.
A: Separate the foundation of their pedestals from each other and increase the elasticity of the connecting pipe.
Thrust bearing failure
Q: Excessive axial thrust
A: Check the clearance of the thrust bearing, check the pressure difference between the gas inlet and outlet, and if necessary, check whether the gap data of the internal sealing ring is exceeded, and check whether the gap of the sealing ring of the balance disc between stages is exceeded.
Q: Abnormal lubrication
A: Check the oil pump, oil filter and oil cooler, check the oil temperature, oil pressure and oil volume, and check the quality of the oil.
Oil seal ring and sealing ring failure
Q: Misalignment and vibration
A: Refer to the vibration part.
Q: There is dirt in the oil.
A: Check the oil filter, replace the filter element with dirt; strengthen online filtration.
Q: There is a deviation in the gap of the sealing ring.
A: Check the gap and adjust or replace it if necessary.
Q: Insufficient oil pressure
A: Check the reference gas pressure and it must not be lower than the minimum limit value.
Q: Insufficient precision of the sealing ring.
A: Check the sealing ring and repair or replace it if necessary.
Q: The quality and temperature of the sealing oil do not meet the requirements.
A: Check the oil quality and oil temperature and solve it.
Unstable and abnormal operation of sealing system
Q: Insufficient precision of the sealing ring.
A: Check the oil quality and oil temperature and check the sealing ring. Repair or replace it if necessary and solve it.
Q: The quality or temperature of the sealing oil does not meet the requirements.
A: Check the quality of the sealing oil. If the index does not meet the requirements, replace it; check the sealing oil temperature and adjust it.
Q: The oil and gas pressure difference system is not working properly.
A: Check the reference gas pressure and circuit and adjust it to the specified value; check the working conditions of each component of the pressure difference system.
Q: The sealing part is worn or damaged.
A: Remove the seal and reassemble after adjusting the gap; repair or replace it as required.
Q: The contact wear of the floating ring seat is uneven.
A: Grind and correct the contact surface or replace with new spare parts.
Q: There are gaps or worn sealing surfaces on the end face of the floating ring seat.
A: Eliminate suction damage and reduce wear. Replace with new spare parts if necessary.
Q: The sealing ring is broken or damaged (damaged during assembly or thermal stress damage during idling).
A: Damage may be caused during assembly. Pay attention during assembly; minimize no-load operation; replace if it cannot be repaired.
Q: The sealing surface, sealing element and O-ring are corroded.
A: Analyze the gas properties and replace the material of the components or replace with new spare parts.
Q: The sealing part freezes due to low-temperature operation.
A: Eliminate freezing or purify the sealing atmosphere with dry nitrogen.
Q: Measurement instrument working error
A: Check the measuring instrument of the system. If it is found to be out of calibration, repair or replace it.
Performance does not meet requirements
Q: Design error
A: Review the original design and check whether the technical parameters meet the requirements; if problems are found, negotiate with the seller and the manufacturer.
Q: Manufacturing error
A: Check the original design and manufacturing process requirements; check the material quality and processing accuracy; if problems are found, negotiate with the seller and the manufacturer in time.
Q: Gas property differences
A: Check various property parameters of the gas. If the gas properties are very different from the original design, it will inevitably affect the performance indicators of the compressor; try to solve it according to actual needs and possibilities.
Q: Changed operating conditions
The actual operating conditions are very different from the design conditions, which will inevitably cause the compressor's operating performance to deviate from the design performance. If abnormalities are found, find out the reasons.
Q: The gap of the sealing ring is too large.
A: Check all gaps. If they do not meet the requirements, they must be adjusted or replaced.
Surge
Q: The operating point falls into the surge area or is too close to the surge boundary.
A: Check the position of the operating point on the compressor characteristic line. If it is too close to the surge boundary or falls into the surge area, the working condition should be adjusted in time and the surge should be eliminated.
Q: Insufficient anti-surge margin setting.
A: Determine the anti-surge margin under various working conditions in advance; the anti-surge margin line should be adjusted to the best.
Q: Insufficient suction flow.
A: Possible reasons include insufficient opening of the intake valve, too dirty or frozen valve core, blocked intake passage, reduced or cut off of the inlet gas source. Find out the cause and try to solve it.
Q: The blow-off valve or return valve is not opened in time when the working condition changes.
A: When the inlet flow rate decreases or the speed drops, or the speed rises rapidly, find out the reason and open the anti-surge blow-off or return valve in time.
Q: The pressure of the compressor outlet gas system is extremely high.
A: When the compressor decelerates or stops, the gas is not vented or returned; if the check valve at the outlet is malfunctioning or not tight and the gas is backfilled, find out the reason and take measures.
Q: The anti-surge device is not put into automatic.
A: The anti-surge device should be put into automatic during normal operation.
Q: The anti-surge device or mechanism is inaccurate or malfunctioning.
A: Regularly check the working condition of the anti-surge device. If it is found to be malfunctioning, inaccurate or stuck, and not working properly, it should be solved in time.
Q: The anti-surge setting value is inaccurate.
A: Strictly set the anti-surge value and test it regularly. If the value is found to be inaccurate, correct it in time.
Q: Accelerate and increase pressure too quickly.
A: When the working condition changes, the speed increase and pressure increase should not be too violent or too fast. They should be carried out alternately, slowly and evenly.
Q: Reduce speed without reducing pressure first.
A: Reduce pressure before reducing speed to avoid surge.
Q: The gas properties change or the state changes drastically, and the compressor components are damaged and fall off.
A: Before the gas properties or state change, the characteristic line should be converted. According to the changed characteristic line, set the anti-surge value. The damage and fall off of the interstage seal, balance disc seal and O-ring will induce surge. They should be checked frequently to keep them in good condition.
Q: The check valve on the compressor gas outlet pipeline is not working properly.
A: The check valve on the compressor outlet gas pipeline should be checked frequently to keep it flexible and reliable; to prevent gas backflow when the speed is reduced or the unit is shut down.
Impeller damage
Q: Unqualified material and insufficient strength.
A: Re-review the materials used in the original design and manufacturing. If the material is unqualified, replace the impeller.
Q: Poor working conditions (decreased strength).
A: The working conditions do not meet the requirements. Due to harsh conditions, the strength is reduced. The working conditions should be improved to meet the design.
Q: Excessive load and reduced strength.
A: Due to excessive speed or too large flow rate and pressure ratio, the strength of the impeller is reduced and damaged; severe overloading or overspeed operation is prohibited.
Q: Abnormal vibration, dynamic and static parts collide.
A: Excessive vibration causes the rotating part to contact and collide with the stationary part, resulting in damage. It is strictly prohibited to operate forcibly when the vibration value is too large.
Eliminate abnormal vibration.
Q: Foreign matter falls in.
A: Foreign matter entering the compressor will damage the impeller or other components. Foreign matter is strictly prohibited from entering the compressor. Check whether the inlet filter is damaged.
Air leakage
Q: Deposited impurities.
A: Keep the gas pure. When there are sediments in the flow passage and the cylinder, they should be removed as soon as possible.
Q: Stress corrosion and chemical corrosion, poor sealing system operation.
A: Prevent stress concentration, prevent harmful components from entering the compressor, and take anti-corrosion measures for the compressor. Check each element of the sealing system and find out the cause and solve it in time.
Q: Poor O-ring.
A: Check each O-ring. If it is found to be defective or aged, replace it.
Q: Air leakage at the cylinder or groove joint.
A: Check the gas joint surface and each flange joint. If air leakage is found, take measures in time.
Q: Sealant failure.
A: Check the sealing glue and packing at the middle parting surface of the cylinder and other parts. If it fails, replace it.
Q: Abnormal operation.
A: Check whether the operation indicators are correct and check the running status of the compressor. If any abnormality is found, solve it in time.
Q: The sealing ring is damaged, broken, eroded or worn.
A: Check each sealing ring. If breakage, damage, wear and corrosion are found, find out the cause and repair or replace it in time.
Insufficient flow and discharge pressure
Q: There is a problem with the flow rate.
A: Compare the discharge pressure and flow rate with the characteristic curve to see if the problem has been found.
Q: Compressor reversal.
A: Check the rotation direction. The rotation direction should be the same as the arrow direction on the compressor casing.
Q: Low suction pressure.
A: Check the inlet filter.
Q: Inconsistent molecular weight.
A: Check the actual molecular weight of the gas. Compare it with the specified value in the instruction manual. If the actual molecular weight is smaller than the specified value, the discharge pressure will be insufficient.
Q: The speed of the prime mover is lower than the designed speed.

A: Check the operating speed of the compressor and compare it with the instruction manual. If the speed is indeed low, increase the speed of the prime mover.
Q: The circulation volume from the exhaust side to the suction side increases.
A: Check the circulating gas volume and check the external piping; check the opening degree of the circulating gas valve. If the circulating volume is too large, it should be adjusted.
Q: Pressure gauge or flowmeter failure.
A: Check each measuring instrument. If a problem is found, it should be calibrated, repaired or replaced.
Overload of prime mover
Q: The molecular weight is larger than the specified value.
A: Check the actual molecular weight of the gas and compare it with the design specification.
Q: There is a problem with the prime motor in electrical aspects.
A: Check the thermal capacity coordination operation status of the circuit breaker; check whether the voltage is reduced; check whether the current difference between each phase is within 3%; find and solve the problem in time.
Q: The surface of the diffuser adjacent to the impeller is corroded and the diffusion degree is reduced.
A: Disassemble and check. Check each flow passage of the diffuser. If there is corrosion, improve the material quality or increase the surface hardness; clean the surface to make it smooth; if the impeller collides with the diffuser or the diffuser is deformed, replace it.
Q: The impeller or diffuser is deformed.
A: The impeller or diffuser should be repaired or replaced if deformed.
Q: The rotating part collides with the stationary part.
A: Disassemble the prime mover, compressor and gearbox, check the gaps of each part and compare with the instruction manual. If a problem is found, solve it in time.