Cause Analysis and Treatment of Centrifugal Compressor Failure

Cause Analysis and Treatment of Centrifugal Compressor Failure? Centrifugal compressor is widely used in many fields such as petrochemical industry natural gas transportation and air separation etc. Its operation state is directly related to the reliability and economy of the whole process system. However, in high-speed, high-voltage, and continuous operation conditions, once a failure occurs, it will not only cause shutdown, but also cause reliable accidents. Therefore, in-depth analysis of the causes of common centrifugal compressor failure, and the establishment of targeted treatment and prevention measures, to ensure the long-term reliable and stable operation of the device is of great significance.
Turbo-Tech Introduction, Centrifugal Compressor Fault Analysis and Treatment
Ⅰ. Common failure types and cause analysis
1. Surge failure
Surge is a typical fault phenomenon of centrifugal compressors, which is manifested as the fluctuation of outlet pressure and flow rate, the low “wheeze” sound of the unit, and the strong vibration of the pipeline.
Reason analysis:
-The actual operating flow rate is lower than the surge flow rate, and the working point falls into the surge area;
-The inlet filter is blocked and the opening of the inlet valve is insufficient, resulting in a decrease in the inlet air volume;
-The pressure of the outlet pipe network suddenly rises, and the back pressure exceeds the exhaust capacity of the compressor;
Unreasonable set values of the anti-surge system or faulty or malfunctioning of the anti-surge valve;
-Rotational speed fluctuation is too large, and the operating point passes through the surge boundary on the characteristic curve.
2. Excessive vibration
Vibration is a more intuitive index reflecting the operating state of the unit. Excessive vibration often indicates unbalanced rotor, poor alignment or bumping of dynamic and static components.
Reason analysis:
-Insufficient dynamic balance accuracy of the rotor, or eccentricity caused by scaling and wear of the impeller;
-Poor alignment of couplings, loose anchor bolts, uneven foundation settlement;
-The increase of bearing wear clearance and oil film instability cause oil film oscillation;
-The sealing gap is too small, resulting in dynamic and static bumping;
Vibration caused by airflow pulsation under surge conditions;
-The critical speed is close to the working speed, causing resonance.
3. Bearing temperature is too high or shingles are burned
If the temperature of radial bearings and thrust bearings is too high, it will trigger interlock shutdown, or cause tile burning and shaft holding accidents.
Reason analysis:
-Insufficient lubricating oil supply pressure, insufficient oil supply or blockage of oil lines;
-Improper selection of lubricating oil grades, deteriorated oil quality, excessive water content or impurities;
-The clearance between the bearing Bush and the journal is too small or bad;
-Bearing installation errors, uneven load distribution;
-The heat exchange effect of the cooler is poor, and the inlet oil temperature is on the high side;
-Abnormal increase in axial thrust exceeding the bearing capacity of thrust bearings.
4. Leakage of shaft seal
The failure of dry gas seal or labyrinth seal will lead to process media leakage, which not only causes material loss, but also brings reliability and environmental protection hidden dangers.
Reason analysis:
-The sealing surface is worn, scratched or scaled, and the sealing gap exceeds the standard;
-The pressure and flow of the sealing gas are improperly adjusted, and the sealing gas carries liquid and dust;
-The vibration of the unit is too large, and the rotor causes the dynamic clearance of the seal to be unstable;
-Failure of sealing auxiliary system (filtration, heating, pressure regulating unit);
-Insufficient cleanliness of the seal assembly during installation or maintenance, and the seal is damaged by foreign objects.
5. High exhaust temperature and reduced efficiency
Abnormal increase in exhaust temperature and specific power of compressor is often the signal of deterioration of internal aerodynamic performance.
Reason analysis:
-Interstage cooler scaling, insufficient cooling water volume or high water temperature, poor cooling effect;
The impeller and the flow channel are scaled or corroded, which reduces the flow area and the aerodynamic efficiency;
-Inlet air temperature is too high or molecular weight deviates from design value;
-The sealing between stages is worn, and the leakage between stages is increased, resulting in the redistribution of stage work;
-The speed does not reach the rated value or the opening of the guide vane is improperly adjusted.
6. Damage of rotor and impeller
Mechanical damage such as impeller crack, block drop, wear and so on are serious equipment faults, which are mostly caused by fatigue or foreign body entry.
Reason analysis:
The impeller operates under alternating stress, producing fatigue cracks and gradually propagating;
-Foreign objects such as welding slag and rust in the inlet pipeline enter the high-speed rotating impeller;
-The medium contains droplets or solid particles, resulting in erosive wear;
-Overspeed or surging, exposing the impeller to abnormal stress;
-Defective materials or poor manufacturing techniques, with inherent weaknesses.
2. Fault handling measures
1. Treatment of surge fault
-When surge occurs, the inlet flow should be increased immediately or the vent valve and bypass valve should be opened to make the working point quickly leave the surge area;
-Check and clean the inlet filter to ensure that the inlet air is unobstructed;
-Verify the anti-surge control system, check the set value of the surge line, and recalibrate if necessary;
-Check the action flexibility and opening feedback of the anti-surge valve to remove jamming and hysteretic problems;
-Optimize process use, avoid large fluctuations in outlet pressure, and have sufficient surge margin in operating conditions.
2. Treatment of vibration fault
-Carry out dynamic balance verification of the rotor, remove the scaling of the impeller, and repair the worn parts;
-Re-align the unit, fasten the anchor bolts, and check whether the foundation has settlement and cracking;
-Check the bearing clearance and shoe surface, and replace the bearing shoe with severe wear;
-Measure parallel dynamic and static clearances to remove bumps;
-Determine the main frequency of vibration through spectrum analysis and other means, distinguish different vibration sources such as unbalance, misalignment, and oil film oscillation, and deal with symptoms;
-Appropriate working speed or support stiffness, avoiding resonance areas.
3. Handling of bearing faults
-Check the pressure of the lubricating oil system, oil temperature and flow rate, clean the oil circuit, and replace the filter element;
-Regular sampling and testing of lubricating oil, timely oil change or regeneration treatment, strict control of moisture content and particle size indicators in the oil;
-Scraping the bearing bush to ensure that the spots and gaps meet the technical requirements;
-Check the load status of the thrust bearing and the axial displacement indication, and check the cause of the abnormal increase in thrust;
-Clean the oil cooler to ensure cooling effectiveness, and replace the heat exchange tube bundle if necessary.
4. Treatment of shaft seal leakage
-Check the sealing surface and replace worn or damaged sealing rings or sealing assemblies;
-Sealing gas pressure and flow, ensure that the sealing gas is clean and dry, and set up reasonable pressure difference monitoring;
-Strengthen the maintenance of sealing gas filtration and heating units, and set up liquid and dust;
-Control the vibration and axial channeling of the unit within the allowable range, and improve the sealing operation;
-Strictly implement cleanliness management during maintenance to prevent foreign objects from entering the sealed cavity.
5. Treatment of exhaust temperature and efficiency
-Cleaning the interstage cooler bundle and checking the amount of water, water pressure and water quality of the cooling water system;
-Regular inspection and cleaning of impellers and flow channels to restore flow capacity;
-Check the process parameters to ensure that the intake air temperature, pressure and medium composition meet the design conditions;
-Replacement of worn inter-stage seals with internal leaks;
-Check the speed regulation system and guide vane actuator to ensure that the adjustment is accurate and in place.
6. Treatment of rotor impeller damage
-Perform penetration or ultrasonic testing of impellers suspected of having cracks, and replace impellers after confirming defects;
-Install filters and filters in the inlet pipes, and thoroughly clean up foreign objects in the pipes after maintenance;
-Surface strengthening or coating protection of vulnerable areas;
-Strictly control the speed not to exceed the rated value to prevent the unit from operating at the surge boundary;
-Establish a rotor service life file, and arrange regular inspection and replacement according to the number of operating hours.
Ⅲ. Preventive maintenance recommendations
1. Improve the condition monitoring system: implement online monitoring and trend analysis of key parameters such as vibration, temperature, pressure, and displacement, so as to achieve early detection and early treatment of faults.
2. Adhere to preventive maintenance: Reasonably arrange minor repairs and major repairs according to the operation cycle, and check vulnerable components such as impellers, bearings, and seals.
3. Strengthen lubrication and oil management: implement a regular lubricating oil testing system, and use oil monitoring data to guide oil change and maintenance.
4. Standardize process use: avoid load fluctuations and start-up and stop, and ensure that the unit is always operating in a stable working condition area.
5. Strengthen maintenance control: Strictly implement the acceptance standards for key processes such as rotor dynamic balancing, centering and alignment, and gap measurement.
6. Do a good job in the management of spare parts: rationally stock key spare parts such as bearings, seals, and impellers to shorten the repair time of faults.
The above is the introduction of “Centrifugal Compressor Fault Cause Analysis and Treatment”. The centrifugal compressor fault cause is complex and often presents the characteristics of multi-factor coupling. In practical work, the principle of “prevention first and prevention combined” should be adhered to, the health status of equipment should be grasped through state monitoring, the root cause should be identified through failure analysis, and targeted treatment and improvement measures should be taken to effectively prevent the failure rate, prolong the service life of the unit, and provide a reliable guarantee for the reliable production and economic benefits of the enterprise.