Centrifugal compressor overhauling procedure
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Centrifugal Compressor Overhauling Procedure:
Overhauling a centrifugal compressor involves a detailed inspection, repair, and maintenance of its key components. This process is critical to ensure the efficient and reliable operation of the compressor, especially in industries like oil and gas, chemical processing, and HVAC systems. Below is a step-by-step guide to the overhauling procedure.
1. Preparation for Overhaul:
1.1. Shutdown Procedure:
- Isolate the Compressor: Follow proper lockout/tagout (LOTO) procedures to ensure that the machine is isolated from electrical power and steam or gas sources.
- Depressurization: Completely depressurize the compressor and its associated piping to eliminate any stored energy.
- Cool Down: Allow the compressor to cool down to a safe temperature if it was operating at elevated temperatures.
1.2. Documentation and Records:
- Gather Documentation: Review the compressor’s maintenance records, manufacturer’s manuals, and previous overhaul data.
- Inspection Checklist: Create a checklist of parts to be inspected, replaced, or cleaned. Record the initial conditions, such as vibration levels, temperature readings, and pressures.
1.3. Tool and Equipment Preparation:
- Ensure that all necessary tools and equipment, including specialized tools like dial indicators, torque wrenches, and balancing machines, are available and calibrated.
- Arrange for replacement parts such as bearings, seals, gaskets, and O-rings.
2. Dismantling the Compressor:
2.1. Removal of External Components:
- Remove Piping: Disconnect all suction and discharge piping from the compressor. Cap or seal the openings to prevent contamination.
- Disengage Couplings: Disconnect the compressor from the drive system (typically a motor or turbine). Properly label and store coupling parts.
- Remove Auxiliary Systems: Detach lubrication, sealing, and cooling systems as necessary.
2.2. Disassemble the Compressor Casing:
- Remove Casing Bolts: Carefully unbolt the compressor casing using the appropriate tools. Follow the recommended bolt loosening pattern to avoid stress on the casing.
- Lift the Casing: Use lifting equipment to remove the casing without damaging the internals. Ensure safety protocols are followed during lifting.
2.3. Rotor and Impeller Removal:
- Mark Component Positions: Use punch marks or labels to note the position of key components (rotor, impellers, diaphragms, etc.) to ensure correct reassembly.
- Remove Rotor Assembly: Carefully extract the rotor assembly, which includes the shaft, impellers, and bearings, from the casing.
- Remove Impellers and Diffusers: Disassemble the impellers, diffusers, and diaphragms for individual inspection.
2.4. Bearing and Seal Removal:
- Inspect Bearings and Seals: Remove the bearings and mechanical seals. Examine them for wear, scoring, and contamination.
- Thrust Bearings: Pay special attention to thrust bearings, as they manage the axial loads in the compressor.
3. Inspection of Components:
3.1. Rotor and Shaft Inspection:
- Visual Inspection: Inspect the rotor and shaft for signs of wear, pitting, corrosion, and cracks.
- Dimensional Check: Measure the rotor and shaft dimensions to ensure they are within acceptable tolerances as specified by the manufacturer.
- Runout Test: Conduct a runout test to check the shaft’s alignment and straightness using a dial indicator.
3.2. Impeller Inspection:
- Inspect Blades: Look for erosion, cracks, and deposits on the impeller blades. Corrosion or pitting may compromise performance.
- Balance Check: Perform a dynamic balance test on the impellers. Any imbalance can cause excessive vibration and damage to the compressor.
3.3. Bearing and Seal Inspection:
- Inspect Bearings: Check for signs of wear, overheating, and lubrication issues. Replace bearings if necessary.
- Seal Condition: Inspect mechanical seals for leakage, scoring, and wear. Replace if necessary to avoid future seal failures.
3.4. Casing and Diffuser Inspection:
- Visual Inspection: Examine the casing and diffusers for signs of corrosion, cracking, or erosion. Ensure that no foreign materials are present.
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- Dimensional Check: Measure key areas of the casing, such as the wear rings and seal areas, to ensure they are within tolerance.
4. Component Replacement and Repair:
4.1. Bearing and Seal Replacement:
- Install New Bearings: Replace worn bearings with new ones, ensuring that they are properly lubricated and correctly aligned.
- Install New Seals: Fit new mechanical seals and O-rings. Ensure proper seating of seals to avoid future leaks.
4.2. Balancing of Rotor Assembly:
- Dynamic Balancing: After repairs or replacements, balance the rotor assembly to ensure smooth operation and to minimize vibration during operation.
- Check Alignment: Ensure that the rotor and shaft are correctly aligned, both axially and radially.
4.3. Reconditioning of Components:
- Blade Reconditioning: If minor wear or erosion is found on impellers or diffuser blades, they can often be repaired by polishing or grinding.
- Casing Repair: If minor damage is found on the casing, it may be repaired using specialized techniques like welding or machining.
5. Reassembly of the Compressor:
5.1. Rotor and Impeller Installation:
- Position Rotor and Impellers: Install the rotor assembly, ensuring the correct positioning of the impellers and other internal components as marked during disassembly.
- Install Diffusers: Refit the diffusers and diaphragms according to the manufacturer’s guidelines.
5.2. Bearing and Seal Installation:
- Install Bearings: Fit the new or reconditioned bearings in place, ensuring proper lubrication and alignment.
- Seal Installation: Carefully install the new seals, making sure that they are seated correctly to prevent leaks.
5.3. Casing Assembly:
- Reinstall Casing: Refit the compressor casing over the rotor assembly. Ensure proper alignment of the casing halves.
- Bolt Tightening: Tighten the casing bolts according to the specified torque values using the correct bolt-tightening sequence.
5.4. Coupling and Alignment:
- Reattach Coupling: Reinstall the coupling between the compressor and the driver (motor/turbine). Ensure that the coupling is properly aligned to avoid vibration.
- Check Shaft Alignment: Perform a laser or dial indicator alignment to ensure the shafts of the compressor and the driver are perfectly aligned.
6. Final Checks and Testing:
6.1. Pre-Startup Checks:
- Lubrication System: Ensure that the lubrication system is operational, with oil levels at the correct level and the system free of contamination.
- Cooling System: Check the integrity and functionality of the cooling system.
- Seal Integrity: Ensure all mechanical seals are properly installed and leak-free.
6.2. Testing:
- Initial Run: Perform a test run without a load to verify that the compressor operates smoothly.
- Vibration Analysis: Monitor vibration levels during the test run. Any excessive vibration could indicate a misalignment or imbalance.
- Temperature Monitoring: Check bearing and casing temperatures to ensure they are within acceptable limits.
- Pressure Testing: Conduct a pressure test on the casing and seals to ensure that there are no leaks.
6.3. Load Test:
- Full Load Testing: After passing the initial checks, run the compressor under full load conditions. Monitor all key parameters (pressure, temperature, vibration, and flow) to ensure the compressor is functioning as per design specifications.
7. Post-Overhaul Documentation:
- Record Results: Document all test results, including vibration analysis, bearing temperatures, alignment readings, and pressure tests.
- Maintenance Log: Update the compressor's maintenance records with details of the overhaul, parts replaced, and any special observations during the process.
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